JPH09191559A - Digital protective relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a digital protective relay which is not actuated by an exciting inrush current but actuated by a failure such as one inside a transformer, even in a transformer of electric power system which contains harmonic current near the second harmonic in a current on an internal failure. SOLUTION: As an amount which represent a dispersion (flatness) of N instantaneous values im to im-( N-1) in a fixed section of a cycle of differential current calculated by placing elements with terminals to be protected in between and using each phase's alternating current, a deviation value is obtained by dividing by N the total value of the Nth power (x=1, 2,..., x) of the difference between each instantaneous value and the average value of N instantaneous values. Provided are a second examining means 21, 22, which examines whether or not the deviation value so obtained is equal to a fixed value or less to produce an output when it is equal to a fixed value or less, and an excited inrush current dealing element 23, which has a reset delaying means to delay the reset of the output of the second examining means 21, 22 for a given period of time. The output of the excited inrush current dealing element 23 prevents the output of a differential protective element 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital protective relay used for protecting a power system, for example, a transformer,
In particular, the present invention relates to a digital protective relay that is surely inoperative under a transformer exciting inrush current and is surely operable against an internal transformer accident.

[0002]

2. Description of the Related Art FIG. 21 is a circuit diagram showing an example of a configuration in which a digital differential relay for protecting a transformer of this type (hereinafter referred to as a differential relay) is applied to a power transformer.

In FIG. 21, a power transformer (hereinafter, simply referred to as a transformer) Tr to be protected is connected to a power system power source G via a circuit breaker CB.

Further, main transformers CT1 and CT2 for extracting an alternating current for each phase are provided with the transformer Tr interposed therebetween.

Further, the alternating currents I ₁ and I ₂ extracted by the main current transformers CT1 and CT2 are introduced into the differential relay 1,
The transformer Tr is protected by operating during an internal accident of the transformer Tr and breaking the circuit breaker CB.

FIG. 22 is a functional block diagram showing an internal configuration example of the conventional differential relay 1. Note that here, the arithmetic processing executed in the central arithmetic processing unit (CPU) of the digital relay is shown as a functional block diagram.

In FIG. 22, a differential relay 1 comprises an input transformer 2, an analog / digital converter (hereinafter referred to as A / D converter) 3, a central processing unit (hereinafter referred to as CPU) 4 It consists of

The input transformer 2 is composed of main current transformers CT1 and CT2.
The alternating currents I ₁ and I ₂ extracted by the above are converted into appropriate magnitudes.

The A / D converter 3 samples the alternating currents I ₁ and I ₂ converted by the input transformer ₂ at regular time intervals (generally, 4.8 at a rated frequency of 50 kHz).
High-speed sampling of kHz) is performed and converted into a digital amount.

Further, the CPU 4 carries out digital arithmetic processing using the digital amount converted by the A / D converter 3, and outputs a protection command for the transformer Tr to the circuit breaker CB.

That is, the CPU 4 performs the following digital arithmetic processing using the electric quantities I ₁ and I ₂ converted into digital quantities.

Reference numeral 5 is a differential protection element (hereinafter simply referred to as a differential element) that is digitally processed by the CPU 4, and 6 is a CP.
It is a second harmonic detection element (hereinafter simply referred to as a 2f element) that is digitally processed in U4.

First, in the differential element 5, the amplitude value calculators 11 and 12 calculate the fundamental wave component 1f from the electric quantities I ₁ and I _2, respectively.
Is extracted, and the amplitude values | I ₁ | and | I ₂ | are obtained.

Further, the scalar sum (hereinafter referred to as suppression current) computing unit 13 obtains the scalar sum (suppression current = suppression amount) Σ | I | of the amplitude values | I ₁ | and | I ₂ |.

On the other hand, the vector sum (hereinafter referred to as differential current) computing unit 14 obtains the vector sum (differential current = operation amount) Id of the electric quantities I ₁ and I ₂ .

Further, the amplitude value calculator 15 is configured to detect the differential current Id.
The fundamental wave current 1f is extracted from this to obtain the amplitude value | Id _1f |.

Further, when the relationship between the suppression current Σ | I | and the differential current │Id _1f │ exceeds a predetermined value, the differential judgment calculation unit 16 judges that it is an internal accident and produces an output.

On the other hand, in the 2f element 6, the amplitude value calculator 17 extracts the second harmonic current 2f from the differential current Id to obtain the amplitude value | Id _2f |.

In addition, the 2f determination calculation unit 18 uses the differential current I
When the relationship between the fundamental wave current 1f contained in d and the second harmonic current 2f exceeds a predetermined value, it is determined as an exciting inrush current and an output is generated.

On the other hand, the logical product (AN) of the output of the 2f determination calculation unit 18 of the 2f element 6 and the output of the NOT calculation circuit 19 inverted and the output of the differential determination calculation unit 16 of the differential element 5
D) The AND operation circuit 20 performs the operation, and the output of the AND operation circuit 20 is sent as the output of the differential relay 1.

In the differential relay 1 having such a configuration, the AC currents I ₁ and I ₂ are introduced into the differential element 5 after being converted into digital quantities by the A / D converter 3 through the input transformer 2. .

Electric quantities I ₁ , I ₂ introduced into the differential element 5
Through the amplitude value calculation units 11 and 12, the suppression current calculation unit 13 derives the suppression current Σ | I | and the differential current calculation unit 14 derives the differential current Id = I ₁ + I ₂ .

This differential current Id is introduced into the amplitude value calculator 15 and the 2f element 6 as 1f.

In this case, the differential current Id due to the load current and the passing current at the time of an external accident becomes zero, and the power transformer T
At the time of the internal accident of r, a differential current Id corresponding to the accident current is generated.

The amplitude value | Id _1f | of 1f of the differential current Id output from the amplitude value calculator 15 and the suppression current Σ | I |
Are respectively introduced into the differential judgment calculation unit 16, and | Id _1f | −
When AΣ | I | ≧ B (A and B are constants),
It is determined that the transformer has an internal accident, and the differential element 5 produces an output.

On the other hand, the differential current I introduced to the 2f element 6
d is introduced into the amplitude value calculation unit 17, extracts the second harmonic current 2f from the differential current Id, outputs the 2f amplitude value | Id _2f |, and is introduced into the 2f determination calculation unit 18. In addition, this 2
The f determination calculation unit 18 has 1f calculated by the differential element 5.
An amplitude value | Id _1f | is also introduced, and the degree of the second harmonic current 2f to the fundamental wave current 1f contained in the differential current Id (|
When Id _2f | / | Id _1f |) exceeds a predetermined value, it is determined that the current is an inrush current and the 2f element 6 produces an output. When the 2f element 6 operates, its output blocks (locks) the output of the differential element 5 through the NOT operation circuit 19.
Therefore, the operation as the differential relay 1 can be prevented.

Next, the necessity of countermeasures for transformer exciting inrush current will be briefly described.

Now, by closing the circuit breaker CB in FIG. 21, a voltage is applied to the transformer Tr and an exciting inrush current based on the magnetization characteristics of the transformer core flows. This magnetizing inrush current apparently flows in from the power system power source G side like an internal accident of the transformer Tr, and becomes the operation amount of the differential relay 1 (differential current Id). It may cause malfunction (works even though it is not an accident).

Therefore, it is necessary to distinguish between the exciting inrush current and the current caused by the actual accident. As a method for this, the exciting inrush current contains a large amount of the second harmonic current 2f, so that it is included in the differential current Id. When the ratio of the second harmonic current 2f to the fundamental wave current 1f is equal to or more than a predetermined value (generally, about 15% is often used), the 2f element 6 which determines that the current is an exciting inrush current and outputs the current is detected. The output is locked to prevent the differential relay 1 from malfunctioning.

As described above, in the conventional transformer protection, the differential relay for detecting the fault of the transformer by the differential current is used, so that the differential relay 1 does not malfunction due to the transformer inrush current. In addition, the second harmonic current included in the exciting inrush current is detected, and the 2f element 6 that prevents the relay operation when the content rate exceeds a predetermined value is adopted.

However, in recent years, the introduction plan of 1000 kV power transmission and 500 kV long distance underground cable is progressing. Therefore, the capacitance of the electric power system becomes large, the resonance frequency is lowered, and it is included in the fault current. It is expected that the harmonic current near the second harmonic will increase.

As a result, in the conventional differential relay 1 adopting the second harmonic current detection system, the 2f element 6 operates even in the case of an internal failure of the transformer, and the differential relay 1 malfunctions (excessively operates). There is an accident due to the lock but cannot operate).

[0033]

As described above, in the conventional differential relay, the internal fault current is higher than that of the transformer of the power system in which the internal fault current includes the harmonic current in the vicinity of the second harmonic. There was a problem that it might not be able to operate reliably in an accident.

It is an object of the present invention to provide a digital protective relay which can surely become inoperative with a transformer exciting inrush current and can surely operate with respect to a transformer internal accident.

[0035]

In order to achieve the above-mentioned object, an alternating current for each phase is introduced across a protected object having a plurality of terminals, and the introduced alternating current is supplied at fixed time intervals. Sampling and converting into a digital amount, calculating the differential current for each phase using the converted digital amount, and when the electric amount based on the calculated differential current is equal to or greater than a predetermined value, the internal In a digital protective relay provided with a differential protection element having a first determination means for determining an accident and producing an output, first, in the invention corresponding to claim 1,
As a quantity representing the variation of the calculated N number of instantaneous value i _m of a predetermined section in one cycle of the differential current ~i _{m- (N-1) (flatness),} N pieces of the instantaneous value and the instantaneous value X is the difference from the average value of
The deviation value is calculated by dividing the sum of the squared values (x = 1, 2, ..., X) by N, and it is determined whether the calculated deviation value is less than or equal to a certain value. And an excitation inrush current countermeasure element having a return delay means for delaying the output of the second determination means by a predetermined time, and the output of the excitation inrush current countermeasure element causes the differential protection element to The output is blocked.

[0036] In the invention corresponding to claim 2, variations of the N instantaneous values i _m through i of a certain section in the one cycle of the calculated differential current _m-(N-1) (flatness) Is calculated as a quantity that represents the difference between each instantaneous value and the average value of N instantaneous values, and a deviation value obtained by dividing the sum of the values obtained by raising the power of x (x = 1, 2, ..., X) by N and Ratio (D / D) of the calculated deviation value and the maximum value deviation value D _{max in the} past one cycle including the section in which the deviation value is calculated or in another fixed section within one cycle
_max. ) is less than or equal to a certain value, and an exciting inrush current having a second determining means for producing an output when the value is less than or equal to a certain value and a return delay means for delaying the output of the second determining means by a predetermined time. A countermeasure element is provided and the output of the excitation inrush current countermeasure element prevents the output of the differential protection element.

Furthermore, in the invention corresponding to claim 3, the variation of the N instantaneous values i _m through i of a certain section in the one cycle of the calculated differential current _m-(N-1) (flatness) Is calculated as a quantity that represents the difference between each instantaneous value and the average value of N instantaneous values, and a deviation value obtained by dividing the sum of the values obtained by raising the power of x (x = 1, 2, ..., X) by N and Second determination that determines whether the ratio (D / I) of the obtained deviation value to the calculated amount I of the differential current (D / I) is less than or equal to a certain value and produces an output when the value is less than or equal to the certain value Means and an exciting inrush current countermeasure element having a return delay means for delaying the output of the second judging means by a predetermined time, and the output of the exciting inrush current countermeasure element blocks the output of the differential protection element. ing.

On the other hand, in the invention corresponding to claim 4, the variation of the N instantaneous values i _m through i of a certain section in the one cycle of the calculated differential current _m-(N-1) (flatness) And a second determination means for producing an output when the standard deviation σ is calculated as a quantity that represents, and whether or not the value of the obtained standard deviation σ is less than or equal to a certain value. Is provided with an exciting inrush current countermeasure element having a first return delay means for delaying the output of the judging means of 1. for a predetermined time, and the output of the differential protection element is blocked by the output of the exciting inrush current countermeasure element.

[0039] In the invention corresponding to claim 5, the variation of the N instantaneous values i _m through i of a certain section in the one cycle of the calculated differential current _m-(N-1) (flatness) , The maximum deviation value σ in the past one cycle or in another fixed section within one cycle including the section in which the standard deviation σ obtained and the standard deviation σ are obtained.
second determination means the ratio of the _{max (σ} / _{σ max)} is determined whether a predetermined value or less produces an output when the predetermined value or less, and a predetermined time return delay the output of the second determining means An exciting inrush current countermeasure element having a return delay means is provided, and the output of the exciting inrush current countermeasure element blocks the output of the differential protection element.

[0040] Further, in the invention corresponding to claim 6, variation of the N instantaneous values i _m through i of a certain section in the one cycle of the calculated differential current _m-(N-1) (flatness) Is calculated, and it is determined whether the ratio (σ / I) between the calculated standard deviation σ and the calculated amount I of the differential current (σ / I) is less than a certain value. And an exciting inrush current countermeasure element having a second determining means for producing an output when the value is equal to or less than a predetermined value and a return delay means for delaying the output of the second determining means by a predetermined time. The output blocks the output of the differential protection element.

On the other hand, in the invention corresponding to claim 7, in the digital protective relay of the invention corresponding to any one of claims 1 to 6, the first condition is that the output of the differential protection element is sent. The exciting inrush current countermeasure element is configured to activate the operation of the second judging means and to stop the operation of the second judging means on condition that the output of the differential protecting element is restored, and An operation delay means for delaying the operation of the output for a predetermined time is added, and the output of the operation delay means is blocked by the output of the excitation inrush current countermeasure element.

Further, in the invention corresponding to claim 8, in the digital protective relay of the invention according to any one of claims 1 to 6, the output of the differential protection element is delayed for a predetermined time. The operation delay means and the first AND operation means for calculating the AND of the output of the differential protection element and the output of the excitation inrush current countermeasure element are added, and the operation is performed by the output of the first AND operation means. The output of the delay means is blocked.

On the other hand, in the invention according to claim 9, in the digital protective relay of the invention according to any one of claims 1 to 6, the magnitude of the calculated differential current is a constant value. A current change width detection element having a third determination means that produces an output when the above change occurs and a second return delay means that delays the output of the third determination means by a predetermined time is provided. The operation of the second determining means of the exciting inrush current countermeasure element is started on the condition that the output is sent, and the operation of the second determining means of the exciting inrush current countermeasure element is performed on the condition that the output of the current change width detecting element is restored. I'm trying to stop.

Further, in the invention corresponding to claim 10, in the digital protective relay of the invention according to any one of claims 1 to 6, the quantity of electricity introduced to each terminal is converted into a digital quantity. A third judging means for producing an output when the magnitude of any one of the terminal currents or all the terminal currents changes by a predetermined value or more, and a second judging means for delaying the output of the third judging means by a predetermined time. A plurality of current change width detection elements having a return delay means, and a second excitation inrush current countermeasure element provided that the output of at least one or more current change width detection elements among the respective current change width detection elements is sent. The operation of the second determining means of the excitation inrush current countermeasure element is stopped on condition that all the outputs of the respective current change width detecting elements are restored.

Furthermore, in the invention corresponding to claim 11,
In the digital protective relay of the invention according to claim 9 or 10, the second operation for calculating a logical product of the output of the current change width detection element and the output of the excitation inrush current countermeasure element
The logical product calculating means is added, and the output of the second logical product calculating means blocks the output of the differential protection element.

On the other hand, in the invention corresponding to claim 12, in the digital protective relay of the invention corresponding to any one of claims 1 to 6, the current output of the second judging means and the current A third logical product calculating means for calculating a logical product with the output of the second judging means of one cycle or a plurality of cycles before is added, and the output of the third logical product calculating means is used as the input of the return delay means. I have to.

Further, in the invention corresponding to claim 13, an alternating current for each phase is introduced with the object to be protected having a plurality of terminals being sandwiched, and the introduced alternating current is sampled at constant time intervals. It is converted into a digital amount, the differential current for each phase is calculated using the converted digital amount, and when the electric amount based on the calculated differential current is equal to or more than a predetermined value, it is determined as an internal accident. In a digital protective relay provided with a differential protection element having a first determination means for producing an output, each electric quantity (average deviation or ratio of average deviations, or standard deviation or The current value of (standard deviation ratio) is compared with the value of one cycle or a plurality of cycles before to obtain the larger value, and it is determined whether the larger value is a certain value or less. Constant An exciting inrush current countermeasure element having a second determining means that produces an output at the following time and a return delay means for delaying the output of the second determining means by a predetermined time is provided, and a difference is generated by the output of the exciting inrush current countermeasure element. The output of the dynamic protection element is blocked.

The exciting inrush current always includes a section in which current flows due to magnetic flux saturation of the transformer core during one cycle and a section in which no current flows due to the saturation of the transformer core to be protected (no-current period). On the other hand, the fault current does not have a no-current period due to the superposition of the fundamental current or the unspecified harmonic current. Note that the current-less period that exists in one cycle of the exciting inrush current is essentially zero, but due to the loss of the direct current component due to the current transformer, the absence of the exciting inrush current (= differential current) seen by the protective relay is always present. It can be said that the period is not simply the current zero but a flat current period in which the change in the instantaneous value current is small. For this reason, it is possible to prevent an erroneous operation of the protective relay by determining that there is little variation in the instantaneous value current in a certain section in one cycle, that is, by looking at the flatness, as an exciting inrush current.

[0049] Therefore, first, in the digital protective relay invention corresponding to claim 1, of N instantaneous value i _m through i of a certain section in one cycle of the differential current _m-(N-1) A deviation value obtained by dividing the sum of the values obtained by multiplying the difference between each instantaneous value and the average value of N instantaneous values by the power of x (x = 1, 2, ..., X) by N, as a quantity representing variation (flatness). Then, it is determined whether or not this deviation value is less than or equal to a certain value, and a second determining means for producing an output when the deviation value is less than or equal to the certain value, and a return delay means for delaying the return of the output for a predetermined time are provided. In addition, by blocking the output of the differential protection element with the output of this exciting inrush current countermeasure element, it is possible to detect the inrush current and the fault current reliably by detecting the flatness of the differential current. Become.

As a result, even in the case of a transformer of a power system in which an internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, the magnetizing inrush current is surely inoperative. , It can operate reliably in case of internal accident of transformer.

[0051] The variation of the digital protective relay invention corresponding to claim 2, N pieces of the instantaneous value i _m through i of a certain section in one cycle of the differential current _{m- (N-1) (} As a quantity expressing the flatness), a deviation value obtained by dividing the sum of the values obtained by multiplying the difference between each instantaneous value and the average value of N instantaneous values by the power of x (x = 1, 2, ..., X) by N is obtained. And the ratio (D) of this deviation value and the maximum deviation value D _{max in the} past one cycle including the section where the deviation value was obtained or in another fixed section within one cycle.
/ D _max ) is less than or equal to a certain value, and an exciting inrush current countermeasure element having a second determining means for producing an output when the value is less than or equal to a certain value, and a return delay means for delaying this output for a predetermined time. By blocking the output of the differential protection element with the output of this excitation inrush current countermeasure element, it is possible to detect the inrush current and the fault current more reliably by detecting the flatness of the differential current. Become.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

[0053] In addition, variation of the digital protective relay invention corresponding to claim 3, N pieces of the instantaneous value i _m through i of a certain section in one cycle of the differential current _{m- (N-1) (} As a quantity expressing the flatness), a deviation value obtained by dividing the sum of the values obtained by multiplying the difference between each instantaneous value and the average value of N instantaneous values by the power of x (x = 1, 2, ..., X) by N is obtained. Second determining means for generating an output when the ratio (D / I) of the deviation value to the calculated amount I of the differential current (D / I) is less than a certain value and is less than the certain value. , And an exciting inrush current countermeasure element having a return delay means for delaying this output for a predetermined time, and by blocking the output of the differential protection element with the output of this exciting inrush current countermeasure element, the flattening of the differential current is achieved. It is possible to more surely distinguish the inrush current and the fault current by detecting the property.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

On the other hand, the variation of the digital protective relay invention corresponding to claim 4, N pieces of the instantaneous value i _m through i of a certain section in one cycle of the differential current _{m- (N-1) (} Flatness), a standard deviation σ as a quantity, and whether or not the value of the standard deviation σ is less than or equal to a certain value is determined. An exciting inrush current countermeasure element having a return delay means for delaying the return time is provided, and the output of this exciting inrush current countermeasure element is blocked to prevent the output of the differential protection element. It is possible to more surely distinguish the inrush current and the fault current.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

[0057] The variation of the digital protective relay invention corresponding to claim 5, N pieces of the instantaneous value i _m through i of a certain section in one cycle of the differential current _{m- (N-1) (} The standard deviation σ as a quantity representing the flatness) is calculated, and the standard deviation σ and the maximum deviation value σ _{max in the} past one cycle including the section in which the standard deviation σ is calculated or in another fixed section within one cycle Second determining means for determining whether or not the ratio (σ / σ _max ) is less than or equal to a certain value and producing an output when the ratio (σ / σ _max ) is less than or equal to the certain value;
And the flatness of the differential current by providing an exciting inrush current countermeasure element having a return delay means for delaying the return of this output for a predetermined time, and blocking the output of the differential protection element by the output of this exciting inrush current countermeasure element. It becomes possible to more reliably distinguish the exciting current and the fault current by detecting

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

[0059] In addition, variation of the digital protective relay invention corresponding to claim 6, N pieces of the instantaneous value i _m through i of a certain section in one cycle of the differential current _{m- (N-1) (} The standard deviation σ as an amount representing the flatness) is obtained, and it is determined whether or not the ratio (σ / I) of the standard deviation σ to the calculated amount I of the differential current is equal to or less than a certain value. And an exciting inrush current countermeasure element having a return delay means for delaying this output for a predetermined time, and differential protection is provided by the output of this exciting inrush current countermeasure element. By blocking the output of the element, it becomes possible to detect the flatness of the differential current and more reliably distinguish the magnetizing inrush current and the fault current.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

On the other hand, in the digital protective relay of the invention according to claim 7, in the digital protective relay of the invention according to any one of claims 1 to 6, the output of the differential protection element is The inrush current countermeasure element is configured so as to activate the operation of the second determining means on the condition that the output of the differential protection element is output, and stop the operation of the second determining means on the condition that the output of the differential protection element is restored. The output of the differential protection element that operates by the excitation inrush current is provided by providing the operation delay means for delaying the output of the dynamic protection element for a predetermined time, and by blocking the output of the operation delay means by the output of this excitation inrush current countermeasure element. It is possible to prevent the malfunction of the protective relay, and in the case of a fault current that does not have a flat section, the output of the differential protection element becomes the protective relay output as it is through the operation delay means, and the normal operation is performed. Can be performed, it is possible to distinguish detected and magnetizing inrush current and fault current flatness of differential current more reliably.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

Further, in the digital protective relay of the invention according to claim 8, in the digital protective relay of the invention according to any one of claims 1 to 6, the output of the differential protection element is And a first AND operation means for calculating the AND of the output of the differential protection element and the output of the exciting inrush current countermeasure element, and a first AND operation. By blocking the output of the operation delaying means with the output of the means, it is possible to prevent malfunction as a protective relay, and in the case of a fault current without a flat section, the output of the differential protection element is directly protected through the operation delaying means. It becomes a relay output and can perform a normal operation, and it becomes possible to more reliably distinguish the inrush current and the fault current by detecting the flatness of the differential current.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

On the other hand, in the digital protective relay of the invention according to claim 9, in the digital protective relay of the invention according to any one of claims 1 to 6, the magnitude of the differential current is increased. Is provided with a third determination means that produces an output when the value changes by a certain value or more, and a current change width detection element having a second return delay means that delays the return of this output for a predetermined time, and the output of this current change width detection element Of the excitation inrush current countermeasure element is started, and the operation of the second determination means of the excitation inrush current countermeasure element is stopped on condition that the output of the current change width detection element is restored. As a result, the operation output of the exciting inrush current countermeasure element activated by the current change width detection element that operates when the exciting inrush current flows prevents the output of the differential protection element and malfunctions as a protective relay. In the case of a fault current that can be prevented and does not have a flat section, the output of the differential protection element becomes the protective relay output as it is, and normal operation can be performed. It becomes possible to more reliably distinguish between the fault current and the fault current.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

Further, in the digital type protective relay of the invention corresponding to claim 10, the above-mentioned claim 1 to claim 6 are provided.
In the digital protective relay of the invention corresponding to any one of the above items, an output is produced when the magnitude of any terminal current or all terminal currents of the introduced electricity quantity of each terminal changes by a certain value or more. And a plurality of current change width detecting elements each having a second return delay means for delaying the return of the output for a predetermined time, and the magnetic field inrush is performed on condition that all outputs of the current change width detecting elements are sent out. The operation of the second determining means of the current countermeasure element is activated, and the second of the excitation inrush current countermeasure elements is conditioned on the condition that the output of at least one of the current variation width detecting elements is restored.
By stopping the operation of the determination means, the operation output of the exciting inrush current countermeasure element activated by each current change width detection element that operates when the exciting inrush current flows, blocks the output of the differential protection element. It is possible to prevent malfunction as a protective relay, and in the case of fault current that does not have a flat section, the output of the differential protection element becomes the protective relay output as it is, and normal operation can be performed, and the flatness of the differential current is improved. It becomes possible to more reliably distinguish the exciting current and the fault current by detecting

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

Further, in the digital protective relay of the invention according to claim 11, in the digital protective relay of the invention according to claim 9 or 10, the output of the current change width detection element and the exciting inrush current are added. An exciting inrush current flows by providing a second logical product calculating means for calculating a logical product with the output of the countermeasure element, and by blocking the output of the differential protection element with the output of the second logical product calculating means. The output of the differential protection element can be blocked by the output of the logical product operation of the current change width detection element and the excitation inrush current countermeasure element that operate when it is possible to prevent the malfunction of the protective relay due to the excitation inrush current. In the case of a fault current that does not have a flat section, the output of the differential protection element will be the output of the protective relay as it is, and normal operation can be performed. It is possible to distinguish the current more reliably.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

On the other hand, in the digital protective relay of the invention corresponding to claim 12, the above claims 1 to 6 are provided.
In the digital protective relay of the invention corresponding to any one of the above items, a third operation for calculating a logical product of the current output of the second determination means and the output of one cycle or a plurality of cycles before
By providing the logical product calculating means and the output of the third logical product calculating means as the input of the return delay means, the exciting inrush current countermeasure element operates reliably against the exciting inrush current and the protective relay is provided. It is possible to prevent erroneous operation of the protection relay, and even if there is a fault current that causes a transient flat portion, the protective relay can operate normally without the unnecessary output of the magnetizing inrush current countermeasure element and the periodicity of the differential current. It becomes possible to more reliably distinguish the exciting current and the fault current by detecting

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

Further, in the digital protective relay of the invention corresponding to claim 13, the respective electric quantities (average deviation or ratio of average deviations, or standard deviations or ratios of standard deviations) representing variations for judging the inrush current of excitation. ) The current value of 1) and the value of one cycle or a plurality of cycles before are compared to obtain the larger value, and a second determination means for producing an output when the larger value is equal to or less than a certain value, and By providing an exciting inrush current countermeasure element having a return delay means for delaying this output for a predetermined time, and blocking the output of the differential protection element by the output of this exciting inrush current countermeasure element, the average deviation or the ratio of average deviations Or, the periodicity of the differential current can be confirmed by comparing the current value of the standard deviation or the ratio of the standard deviation with the value of one cycle or multiple cycles before. Detecting the periodicity of the differential current becomes possible to distinguish the magnetizing inrush current and fault current more reliably.

As a result, regardless of the magnitude of the inrush current of the power system, the internal fault current, which has been difficult to apply in the past, includes a harmonic current in the vicinity of the second harmonic, regardless of the magnitude of the inrush current. , It surely becomes inoperative with the excitation inrush current, and can reliably operate in the case of an internal transformer failure.

[0075]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital protective relay according to the present embodiment. The same reference numerals are given and the description thereof is omitted, and only different portions will be described here.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 1, the excitation inrush current countermeasure element 6 in FIG. 22 is omitted, and in place of this, a new excitation inrush current countermeasure element 61 is provided.

The excitation inrush current countermeasure element 61 is composed of a flatness calculation section 21, a flatness determination calculation section 22, and a return delay timer 23.

Here, the flatness calculation unit 21 calculates the differential current I calculated by the differential current calculation unit 14 of the differential element 5.
The flatness of a certain section of the waveform of d is obtained.

[0080] That is, in this example, as the amount representing the variation (flatness) of the N instantaneous values i _m through i of a certain section in one cycle of the differential current Id _m-(N-1), each instantaneous The difference between the value and the average of N instantaneous values is the power of x (x = 1, 2, ..., x)
The deviation value is obtained by dividing the total sum of the above values by N.

Further, the flatness determination calculation unit 22 determines whether or not the flatness calculated by the flatness calculation unit 21 is less than or equal to a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and an output is output. It happens.

That is, in this example, it is determined whether or not the deviation value obtained by the flatness computing unit 21 is less than a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and an output is generated. is there.

Furthermore, the return delay timer 23 has a delay time of one cycle or more, and is used to make the output of the flatness determination calculation section 22 continuous.

As a result, the output of the return delay timer 23 blocks the output of the differential element 5.

Next, the operation of the differential relay 1 of the present embodiment configured as described above will be described.

Since the operation of the differential element 5 is the same as that in the case of FIG. 22, the description thereof will be omitted here.

In FIG. 1, the differential current Id derived by the differential current calculation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 61, and the flatness calculation unit 21 detects the flatness. Is calculated, and the average deviation D is calculated.
Then, when the average deviation D is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 outputs an output.

Since the output of the flatness determination calculation unit 22 is a continuous output once in one cycle, the recovery delay timer 23 having a time of one cycle or more is used for continuity, and the output of the recovery delay timer 23. Is sent as the output of the excitation inrush current countermeasure element 61.

On the other hand, the output of the return delay timer 23 is set to NO.
It is inverted in the T arithmetic circuit 19 and further the logical product arithmetic circuit 2
By performing a logical product operation with the output of the differential element 5 at 0, it is possible to prevent the output of the differential element 5 operating by the inrush current of the excitation and prevent the malfunction of the differential relay 1.

The above point will be described more specifically below.

First, the difference in the characteristics of the current waveforms of the fault current and the magnetizing inrush current due to an actual internal fault will be described.

FIG. 2 is a waveform diagram showing the difference in the current waveform characteristics of the fault current (a) and the exciting inrush current (b). The exciting inrush current is a current due to the flux saturation of the transformer core during one cycle. While there is always a section in which current flows and a section in which current does not flow due to saturation of the transformer core (no-current period), the fault current is a no-current due to superposition of fundamental current or unspecified harmonic current. No period will occur. In addition,
The current-less period existing in one cycle of the exciting inrush current is essentially zero, but the exciting inrush current (= differential current Id) seen by the differential relay 1 is not always due to the loss of the direct current component due to the current transformer CT. It can be said that the no-current period is not simply zero current but a flat current period in which the change in the instantaneous value current is small.

Therefore, it is possible to judge that the current is an exciting inrush current by observing that the variation of the instantaneous value current in a certain section in one cycle is small (= flatness). In this embodiment, this differential current is determined. By detecting the flatness of Id, it is determined as an exciting inrush current, and the malfunction of the differential relay 1 is prevented.

That is, the flatness calculating section 21 of the excitation inrush current countermeasure element 61 performs the following calculation for detecting the flatness.

FIG. 3A shows a value when the exciting inrush current is converted into a digital value (= instantaneous value). In FIG. 3A, the current instantaneous value is i _m , the instantaneous value before 1 sampling (hereinafter referred to as sp) is i _m-1 , the instantaneous value before 2 sp is i _m-2 , and so on. , (N-1) sp
The previous instantaneous value is i _{m- (N-1)} , and the previous instantaneous value (N) sp is i.
The instantaneous value before _{m- (N)} , (N + 1) sp is _{im- (N + 1)} ....
Similarly, the instantaneous value before (N + k) sp is set as _{im- (N + k)} .

[0096] Figure 3 when explaining the flatness detection operation at the instantaneous values of (a), sp instantaneous value of a constant interval in one cycle _{(e.g., i m ~i m- (N-} 1 sections _a)) And the total number of the instantaneous values is divided by the total number N, the arithmetic mean Im is calculated by the following equation (1).

The constant section is not limited to a specific period (time) as long as it is a period shorter than the no-current period at the maximum excitation inrush current.

[0098]

[Equation 1]

Furthermore, each instantaneous value in a certain section and the arithmetic mean I
The absolute value of the difference from m is taken, and the sum D of the differences is divided by the total number N to obtain a value D by the following formula (2).

[0100]

[Equation 2]

As a result, the equation (2) can be expressed by the following equation (3).

[0102]

(Equation 3)

This value of D is called the average deviation, and the differential current I
It represents the degree of variation (flatness) of the instantaneous value of d in a certain section, and D = 0 only when the change in current is zero.

Similar to the average deviation D of the section a, calculation is performed by using the past N number of sp for each sp (section b,
c)), it is possible to always see the flatness of a certain section, and the values of the individual average deviations Da, Db, Dc ... As shown in the calculation result of the flatness calculation unit 21 in FIG. 3B. Becomes

The value of the average deviation D in the differential current Id due to the magnetizing inrush current having the flat section as shown in FIG. 3B is the value of the average deviation D as the calculation section includes many flat sections. When it becomes smaller and the calculation section includes the entire flat part (Fig. 3
The value becomes the minimum in the section a) of (a).

Further, when the average deviation D takes a value smaller than the constant value k, the flatness determination calculation unit 22 produces an output as shown by the calculation result of the flatness determination calculation unit 22 in FIG. 3C.

The constant value k is a value for distinguishing between the fault current and the flat portion of the exciting inrush current, and does not cause erroneous determination due to loss of DC component due to the current transformer CT or calculation error of the relay. It is a value.

Next, an example of flatness detection between the fault current and the exciting inrush current will be described with reference to FIG.

First, the excitation inrush current (b) will be described.

As described above, the flatness computing unit 21 of the differential relay constantly computes the average deviation D of a certain section (here, it has a computation section of t1) for each sp, and has the flat section. The value of the average deviation D in the differential current Id due to the excitation inrush current becomes smaller as the calculation section (t1) includes many flat portions, and when the value is equal to or less than the constant value k, the flatness determination calculation unit 22 produces an output. .

[0111] t1 in Fig. 4 shows the calculation section when all the flat parts are included. After that, as the current rises, the flatness in the calculation section disappears until the average deviation D becomes a constant value k or more. During time t2, the flatness determination calculation unit 2
2 produces an output. Further, since the same detection is performed in the next cycle, the flatness determination calculation unit 22 always produces an output once in one cycle.

Therefore, the output of the flatness determination calculation section 22 is
Since the output is intermittent once in one cycle, the recovery delay timer 23 having a time of one cycle or more is used for continuity, and the output of the recovery delay timer 23 is used as the output of the excitation inrush current countermeasure element 61.

Then, the output of the return delay timer 23 is inverted by the NOT operation circuit 19 and the logical product operation with the output of the differential element 5 is performed by the logical product operation circuit 20. The output of the differential element 5 that operates in this way can be blocked, and malfunction of the differential relay 1 can be prevented.

On the other hand, the fault current (a) may include a large amount of harmonic current in addition to the fundamental wave current, and especially in the vicinity of the second harmonic where the conventional differential relay malfunctions. Since there is no flat section for t1 time even with respect to harmonics, there is no output from the flatness determination calculation unit 22, and the output from the differential determination calculation unit 16 passes through the logical product calculation circuit 20 as it is to the differential relay 1. It becomes an output and normal operation can be performed.

In the above description, the average deviation D is used as the value representing the flatness, but the value representing the flatness is represented by the following general formula (equation (0)). It may be a value.

That is, the instantaneous values i _{m to} i of N values in a certain section in one cycle of the calculated differential current Id.
_{As a} quantity (indicating flatness ₎ representing the variation of _{m- (N-1),} the difference between each instantaneous value and N average values of the instantaneous values is raised to the power x (x
= 1, 2, ..., X) The sum of the values obtained is divided by N to obtain the deviation value. That is, the deviation value a represented by the equation (0) is calculated as the flatness calculation.

[0117]

(Equation 4)

An exciting inrush current countermeasure element 61 provided with a flatness determination calculation section 22 that produces an output when the obtained deviation value a is less than a certain value is provided, and the output of the differential element 5 is provided by the output. By blocking, the same effect as the above-mentioned case can be exhibited.

As described above, in this embodiment,
Waveform difference between transformer inrush current and transformer internal fault current, that is, inrush current does not flow due to the saturation of transformer core due to flux saturation of transformer core during one cycle. While there is always a certain flat portion, the fault current does not have a flat portion in a certain section due to superposition of the fundamental wave current or a large number of unspecified harmonic currents, and during one cycle of the differential current Id. a certain section of the N instantaneous values i _m through i of _m-(N-1) dispersion of (flatness)
As a quantity that expresses, the deviation value obtained by dividing the sum of the values obtained by multiplying the difference between each instantaneous value and the N average values of the instantaneous values by the power of x (x = 1, 2, ..., X) by N is obtained. The flatness of the differential current Id is detected by providing an exciting inrush current countermeasure element 61 that produces an output when the value is equal to or less than a certain value, and the difference is detected by the output of the exciting inrush current countermeasure element 61. Since the output of the moving element 5 is blocked, it is possible to reliably distinguish the exciting inrush current and the fault current, and it is difficult to apply the above-mentioned conventional technique to the internal fault current, which is a harmonic near the second harmonic. It is possible to obtain a digital protective relay that can reliably operate even for a transformer Tr of a power system that includes a wave current due to the transformer inrush current and can reliably operate during an internal transformer failure. it can.

(Second Embodiment) FIG. 5 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer according to the present embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
Therefore, a part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 5, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 62 is provided.

The excitation inrush current countermeasure element 62 comprises a flatness calculating section 21, a flatness determining calculating section 24, and a return delay timer 23.

Here, the flatness calculation unit 21 calculates the differential current I calculated by the differential current calculation unit 14 of the differential element 5.
The flatness of a certain section of the waveform of d is obtained.

[0125] That is, in this example, as the amount representing the variation (flatness) of the N instantaneous values i _m through i of a certain section in one cycle of the differential current Id _m-(N-1), each instantaneous The difference between the value and the average of N instantaneous values is the power of x (x = 1, 2, ..., x)
The deviation value is obtained by dividing the total sum of the above values by N.

Further, the flatness determination calculation unit 24 determines whether or not the flatness calculated by the flatness calculation unit 21 is less than or equal to a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and is output. Is caused.

That is, in this example, the maximum value deviation value D _{max in the} past one cycle including the deviation value obtained by the flatness computing unit 21 and the section in which the deviation value is obtained or in another fixed section within one cycle. It is determined whether or not the ratio (D / D _max ) is less than or equal to a fixed value, and an output is generated when the ratio is less than or equal to the fixed value.

Further, the return delay timer 23 has a delay time of one cycle or more, and is for making the output of the flatness determination calculation section 24 continuous.

As a result, the output of the return delay timer 23 blocks the output of the differential element 5.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

Since the operation of the differential element 5 is the same as that in the case of FIG. 22, the description thereof will be omitted here.

In FIG. 5, the differential current Id derived by the differential current calculation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 62, and the flatness calculation unit 21 described above (3). The calculation based on the equation is performed, and each sp
The average deviation D of a fixed section in each case is calculated.

[0133] In the flat determination computing unit 24, a mean deviation D ₀ of current, each of the mean deviation D ₁ of the past one cycle comprising _{D 0, D 2, ...,} 96 pieces of D ₉₅ (where the rated Frequency 50 Hz, sp frequency 4.8 kHz,
The maximum average deviation D _max out of 96 sp numbers per cycle) is calculated, and the ratio of the current average deviation D ₀ to this maximum average deviation D _max (D ₀ / D _max ) is calculated to _obtain the average. When the deviation ratio (D ₀ / D _max ) is less than or equal to a predetermined value k1, it is determined that the current is an inrush current and an output is generated.

This relationship can be expressed by the following equation (4).

D ₀ / D _max ≦ k1 or D ₀ ≦ D _max · k1 Formula (4) That is to say, referring to FIG. 3 described above, the average deviation Da in the section a is the current average deviation D ₀ , D
b represents D ₁ , Dc represents D ₂ , and D ₉₅ represents Da to 96.
This is the average deviation of the previous one. Then, the maximum value of the 96 average deviations is taken out as D _max (D _max = Dy in FIG. 3).

As a result, the average deviation ratio (D
₀ / D _max ) becomes | Da / Dy |, and if this value is less than or equal to the predetermined value k1, the flatness determination calculation unit 24 outputs the output.

Since the output of the flatness determination calculation unit 24 due to the inrush current is an intermittent output that is output once or more per cycle, it is converted to a continuous output by the return delay timer 23, and then the difference is output through the NOT calculation circuit 19. The output of the moving element 5 is blocked.

As described above, the magnitude of the exciting inrush current takes various values depending on the voltage inrush phase, the difference in the transformer core, etc., but the larger the exciting inrush current due to the loss of the direct current component of the current transformer, the greater The flatness of the current period deteriorates, and the error of the average deviation may increase.

On the other hand, the maximum average deviation D in the past 1 cycle
_{Since the value of max} also increases as the exciting inrush current increases, the maximum average deviation D _max also increases as the exciting inrush current increases. _Therefore , the ratio of the maximum average deviation D _max to the current average deviation D ₀ ( By always looking at (D ₀ / D _max ), it is possible to more reliably determine the exciting inrush current regardless of the magnitude of the exciting inrush current.

Further, the fault current may include a large amount of harmonic current in addition to the fundamental wave current. In particular, the harmonic current in the vicinity of the second harmonic may cause malfunction of the conventional differential relay. On the other hand, since the flat section does not occur, the flatness determination calculation unit 24
Output does not occur, and the output of the differential judgment calculation unit 16 becomes the output of the differential relay 1 as it is through the logical product calculation circuit 20, and normal operation can be performed.

The maximum average deviation D _max is the past 1
Not only the maximum average deviation during the cycle but also the maximum average deviation within the last one cycle, for example, half cycle may be used, and there is a clear difference in the average deviation value between the flat part and the part where current is flowing. If so, the same effect as described above can be obtained.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
= 1, 2, ..., x) The deviation value obtained by dividing the total sum of the values divided by N is obtained, and the deviation value and the section in which the deviation value is obtained are included in the past one cycle or in another fixed section within one cycle. The flatness of the differential current Id is detected by providing an exciting inrush current countermeasure element 62 that produces an output when the ratio (D / D _max ) with respect to the maximum value deviation value D _max is a certain value or less, and this exciting inrush current countermeasure element is provided. Since the output of the differential element 5 is blocked by the output of 62, the magnetizing inrush current and the fault current can be more surely distinguished regardless of the magnitude of the magnetizing inrush current. Even for the transformer Tr of the electric power system, which was difficult to apply and the internal fault current includes harmonic currents near the second harmonic, the transformer inrush current certainly fails to operate, and A digital device that can operate reliably in the event of an accident It can be obtained form the protective relay.

(Third Embodiment) FIG. 6 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer according to the present embodiment, and the same portions as those in FIG. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
Therefore, a part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 6, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 63 is provided.

The excitation inrush current countermeasure element 63 comprises a flatness calculating section 21, a flatness determining calculating section 25, and a return delay timer 23.

Here, the flatness calculation unit 21 calculates the differential current I calculated by the differential current calculation unit 14 of the differential element 5.
The flatness of a certain section of the waveform of d is obtained.

[0148] That is, in this example, as the amount representing the variation (flatness) of the N instantaneous values i _m through i of a certain section in one cycle of the differential current Id _m-(N-1), each instantaneous The difference between the value and the average of N instantaneous values is the power of x (x = 1, 2, ..., x)
The deviation value is obtained by dividing the total sum of the above values by N.

Further, the flatness determination calculation unit 25 determines whether or not the flatness calculated by the flatness calculation unit 21 is less than or equal to a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and is output. Is caused.

That is, in this example, it is determined whether the ratio (D / I) between the deviation value obtained by the flatness calculating section 21 and the calculated amount I of the differential current is equal to or less than a certain value. Judgment is made and an output is produced when the value is below a certain value.

Further, the return delay timer 23 has a delay time of one cycle or more, and is used to make the output of the flatness determination calculation section 25 continuous.

As a result, the output of the return delay timer 23 blocks the output of the differential element 5.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

The operation of the differential element 5 is the same as that in the case of FIG. 22, so the description thereof is omitted here.

In FIG. 6, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 63, and the flatness operation unit 21 described above (3). The calculation based on the equation is performed, and each sp
The average deviation D of a fixed section in each case is calculated.

Further, in the flatness determination calculation section 25, the ratio ((D ₀ / | Id _1f | of the current average deviation D ₀ and the output | Id _1f | of the amplitude value calculation 15 of the differential current Id of the differential element 5 is calculated. |), And the average deviation ratio (D ₀ / | Id _1f |) is a predetermined value k.
When it becomes 2 or less, it is judged as an exciting inrush current and an output is generated.

Since the output of the flatness determination calculation unit 25 due to the inrush current is an intermittent output that is output once or more per cycle, it is converted to a continuous output by the return delay timer 23, and then the difference is output through the NOT calculation circuit 19. The output of the moving element 5 is blocked.

As described above, since the magnitude of the exciting inrush current has various values depending on the voltage application phase, the difference in the transformer iron core, etc., the larger the exciting inrush current is, the more the exciting inrush current becomes large due to the loss of the direct current component of the current transformer. The flatness of the current period deteriorates, and the error of the average deviation may increase. Therefore, the ratio (D ₀ / | Id _1f |) between the amplitude value | Id _1f | of the fundamental wave current included in the differential current Id proportional to the magnitude of the exciting inrush current and the current average deviation D ₀ is always By looking at it, the exciting inrush current can be more reliably determined regardless of the magnitude of the exciting inrush current.

On the other hand, the fault current may include a large amount of harmonic current in addition to the fundamental wave current. In particular, the harmonic current in the vicinity of the second harmonic may malfunction the conventional differential relay. On the other hand, since the flat section does not occur, the flatness determination calculation unit 25
Output does not occur, and the output of the differential judgment calculation unit 16 becomes the output of the differential relay 1 as it is through the logical product calculation circuit 20, and normal operation can be performed.

The amount representing the magnitude of the exciting inrush current is the 1f amplitude value | Id _1f of the differential current Id of the differential element 5.
Not limited to |, for example, the maximum value (peak value) of the instantaneous value of the differential current Id in one cycle including the section in which the current average deviation D ₀ is calculated may be used, and the magnitude of the differential current Id may be used. The same effect as described above can be obtained as long as the amount indicates the index.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
, 1, 2, ..., X), the deviation value is obtained by dividing the total sum of the values by N, and the ratio (D / I) of this deviation value and the amount I indicating the magnitude of the calculated differential current is constant. The flatness of the differential current Id is detected by providing the exciting inrush current countermeasure element 63 that produces an output when the value is less than the value, and the output of the differential element 5 is blocked by the output of the exciting inrush current countermeasure element 63. So
The excitation inrush current and the fault current can be more reliably distinguished regardless of the magnitude of the excitation inrush current, and it is difficult to apply the above-described conventional method to the internal fault current, and harmonics in the vicinity of the second harmonic. Even for a transformer Tr of a power system that includes a current, the transformer inrush current surely becomes inoperative,
It is possible to obtain a digital protective relay that can reliably operate in the event of an internal transformer failure.

(Fourth Embodiment) FIG. 7 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer according to the present embodiment. The same parts as those in FIG. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
7 is omitted, so that part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 7, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 64 is provided.

The excitation inrush current countermeasure element 64 is composed of a flatness calculation section 26, a flatness determination calculation section 27, and a return delay timer 23.

Here, the flatness calculation unit 26 calculates the differential current I calculated by the differential current calculation unit 14 of the differential element 5.
The flatness of a certain section of the waveform of d is obtained.

[0167] That is, in this example, the standard deviation of a quantity representing the variation (flatness) of the N instantaneous values i _m through i of a certain section in one cycle of the differential current Id _m-(N-1) This is to obtain σ.

Further, the flatness determination calculation unit 27 determines whether or not the flatness calculated by the flatness calculation unit 26 is less than or equal to a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and is output. Is caused.

That is, in this example, it is determined whether or not the value of the standard deviation σ obtained by the flatness computing section 26 is below a certain value, and when the value is below the certain value, an output is generated.

Furthermore, the return delay timer 23 has a delay time of one cycle or more, and is for making the output of the flatness determination calculation section 27 continuous.

As a result, the output of the return delay timer 23 blocks the output of the differential element 5.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

The operation of the differential element 5 is the same as that in the case of FIG. 22, so the description thereof will be omitted here.

In FIG. 7, the differential current Id derived by the differential current calculating section 14 of the differential element 5 is introduced into the exciting inrush current countermeasure element 64, and the flatness calculating section 26 detects the flatness. The following operation for performing the operation is performed.

FIG. 8A shows a value when the exciting inrush current is converted into a digital value (= instantaneous value), and the flatness detection calculation will be described with this instantaneous value.

Now, the current instantaneous value is i _m , the instantaneous value before ₁ sp is i _m-1 , the instantaneous value before ₂ sp is i _m-2 , ...
Similarly, the instantaneous value before (N-1) sp is _{im- (N-1)} ,
The instantaneous value before (N) sp is _{im- (N)} , and the instantaneous value before (N + 1) sp is _{im- (N + 1)} .... Similarly, (N + k) sp
_{Let the} previous instantaneous value be i _{m- (N + k)} .

In FIG. 8 (a), s of instantaneous values (for example, i _{m to} i _{m- (N-1) in the} section a) in a certain section in one cycle.
The total number of p is N, and the total of N instantaneous values is the total number N.
The arithmetic average Im divided by is calculated by the equation (1) described in the first embodiment. The fixed section may be a period shorter than the currentless period at the maximum excitation inrush current, and is not a particularly limited period (time).

Furthermore, each instantaneous value in a certain section and the arithmetic mean I
The square of the difference from m is taken, and the residual sum of squares Sx, which is the sum of the squares of the difference, is obtained by the following equation (5).

[0179]

(Equation 5)

This equation (5) can be converted into the following equation (6).

[0181]

(Equation 6)

Next, this residual sum of squares Sx is divided by the total number N of instantaneous values, and the square root is obtained by the following equation (7).

[0183]

(Equation 7)

This value of σ is called the standard deviation, and the differential current I
It represents the degree of variation (flatness) of the instantaneous value of d in a certain section, and σ = 0 only when the current change is zero.

Similarly to the standard deviation σ of the section a, sp
By performing the calculation using the past N number of sps for each time (sections b, c ... In FIG. 8A), it is possible to always see the flatness of a certain section, and the flatness calculation of FIG. 8B is performed. The values are the individual standard deviations σa, σb, σc ... As shown in the calculation result of the unit 26.

The value of the standard deviation σ in the differential current Id due to the excitation inrush current having the flat section as shown in FIG. 8A becomes smaller as the calculation section includes many flat portions. , When the calculation section includes all flat parts (Fig. 8
The value becomes the minimum in the section a) of (a).

Further, when the standard deviation σ takes a value smaller than the constant value k3, the flatness determination calculation unit 27 produces an output as in the flatness determination calculation result of FIG. 8C.

The constant value k3 is a value for distinguishing between the fault current and the flat portion of the exciting inrush current, and is a value that does not cause an erroneous determination due to a loss of a direct current component due to the current transformer CT or a calculation error of a relay. Is.

As described above, the flatness computing unit 26 of the differential relay 1 constantly computes the standard deviation σ in a constant section for each sp, and the differential current Id due to the exciting inrush current having a flat section is obtained. The value of the standard deviation σ decreases as the calculation section includes many flat portions, and when the value is equal to or less than the constant value k3, the flatness determination calculation unit 27 produces an output.

For this reason, the output of the flatness determination calculation unit 27 at the excitation inrush current is an intermittent output once in one cycle, so the return delay timer 2 having a time of one cycle or more.
3, the output of the return delay timer 23 is sent as the output of the excitation inrush current countermeasure element 64.

Then, the output of the return delay timer 23 is set to N.
The output of the differential element 5 operating by the inrush current of the excitation is blocked by inverting it by the OT operation circuit 19 and performing a logical product operation with the output of the differential element 5 by the logical product operation circuit 20. It is possible to prevent malfunction of the dynamic relay 1.

On the other hand, the fault current may include a large amount of harmonic current in addition to the fundamental wave current. In particular, the harmonic current in the vicinity of the second harmonic may malfunction the conventional differential relay. On the other hand, since the flat section does not occur, the flatness determination calculation unit 27
Output does not occur, and the output of the differential judgment calculation unit 16 becomes the output of the differential relay 1 as it is through the logical product calculation circuit 20, and normal operation can be performed.

As described above, in this embodiment,
Variation standard deviation σ of an amount representing a (flatness) determined for a predetermined section of the N instantaneous values _{i m ~i m- (N-1} ) in one cycle of the differential current Id, the standard deviation σ The flatness of the differential current Id is detected by providing an exciting inrush current countermeasure element 64 that produces an output when the value is a certain value or less, and the output of the differential element 5 is blocked by the output of this exciting inrush current countermeasure element 64. Therefore, it is possible to more reliably distinguish the exciting inrush current and the fault current regardless of the magnitude of the exciting inrush current. A digital protective relay that can reliably operate even for a transformer Tr of a power system that contains harmonic currents near the wave when the transformer inrush current is present, and can reliably operate when an internal fault occurs in the transformer. Can be obtained.

(Fifth Embodiment) FIG. 9 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer according to the present embodiment, and the same portions as those in FIG. 1 are designated by the same reference numerals. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
9 is omitted, so that part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 9, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 65 is provided.

The excitation inrush current countermeasure element 65 includes a flatness calculating section 26, a flatness determining calculating section 28, and a return delay timer 23.

Here, the flatness calculating section 26 calculates the differential current I calculated by the differential current calculating section 14 of the differential element 5.
The flatness of a certain section of the waveform of d is obtained.

[0199] That is, in this example, the standard deviation of a quantity representing the variation (flatness) of the N instantaneous values i _m through i of a certain section in one cycle of the differential current Id _m-(N-1) This is to obtain σ.

Further, the flatness determination calculation unit 28 determines whether or not the flatness calculated by the flatness calculation unit 26 is less than or equal to a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and is output. Is caused.

That is, in this example, the standard deviation σ obtained by the flatness computing unit 26 and the maximum deviation value σ in the past one cycle including the section in which the standard deviation σ was obtained or in another fixed section within one cycle. _It is determined whether or not the ratio (σ / σ _max ) to _max is a fixed value or less, and an output is generated when the ratio is a fixed value or less.

Further, the return delay timer 23 has a delay time of one cycle or more, and is used to make the output of the flatness determination calculation section 28 continuous.

As a result, the output of the return delay timer 23 blocks the output of the differential element 5.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

Since the operation of the differential element 5 is the same as that in the case of FIG. 22, the description thereof will be omitted here.

In FIG. 9, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 65, and the flatness operation unit 26 causes the differential current Id
The calculation based on the equation (7) described in the embodiment of
Standard deviation σ of a constant section in each sp of the differential current Id
Is calculated.

That is, in the flatness determination calculation unit 26, 96 standard deviations σ ₁ , σ ₂ , ..., σ ₉₅ of the current standard deviation σ ₀ and each standard cycle including the standard deviation σ ₀ in the past one cycle (however, , Rated frequency 50Hz, sp frequency 4.8kHz
In this case, the maximum standard deviation σ _max out of 96 sp numbers per cycle) is calculated, and the ratio of the current standard deviation σ ₀ to the maximum standard deviation σ _max (σ ₀ / σ
_max ), and when the ratio of standard deviations (σ ₀ / σ _max ) becomes equal to or smaller than a predetermined value k4, it is determined as an exciting inrush current and an output is generated.

This relationship can be expressed by the following equation (8).

Σ ₀ / σ _max ≦ k4 or σ ₀ ≦ σ _max · k4 (8) That is, referring to FIG. 8, the standard deviation σa in the section a is the current standard deviation σ ₀ , and σb is σ ₁
, Σc represents σ ₂ , and σ ₉₅ is 96 from σa.
This is the standard deviation of the previous one. Then, the maximum value of the 96 standard deviations is taken out as σ _max (σ _max = σ y in FIG. 8). As a result, the average deviation ratio (σ ₀
/ Σ _max ) becomes | Da / Dy |, and this value is a predetermined value k
If it is 4 or less, the flatness determination calculation unit 28 produces an output.

Since the output of the flatness determination calculation unit 28 due to the inrush current is an intermittent output that is output once or more per cycle, it is converted to a continuous output by the return delay timer 23, and then the difference is output through the NOT calculation circuit 19. The output of the moving element 5 is blocked.

As described above, the magnitude of the exciting inrush current takes various values depending on the voltage inrush phase, the difference in the transformer iron core, etc., but the larger the exciting inrush current due to the loss of the direct current component of the current transformer, etc. There is a possibility that the flatness in the no-current period deteriorates and the standard deviation error increases. On the other hand, the maximum standard deviation σ _max in the past 1 cycle also increases as the exciting inrush current increases, so the ratio (σ ₀ / σ _max ) between the maximum standard deviation σ _max and the current standard deviation σ ₀ is calculated. By always looking at it, the exciting inrush current can be more reliably determined regardless of the magnitude of the exciting inrush current.

On the other hand, the fault current may include a large amount of harmonic current in addition to the fundamental wave current. Especially, the harmonic current in the vicinity of the second harmonic that malfunctions the conventional differential relay may occur. On the other hand, since the flat section does not occur, the flatness determination calculation unit 28
Output does not occur, and the output of the differential judgment calculation unit 16 becomes the output of the differential relay 1 as it is through the logical product calculation circuit 20, and normal operation can be performed.

As the maximum standard deviation σ _max , not only the maximum standard deviation in the past 1 cycle but also the maximum standard deviation in the past 1 cycle, for example, in the half cycle may be used. If there is a clear difference in the value of the standard deviation of the part that has a mark, the same effect as the above case can be obtained.

As described above, in this embodiment,
The standard deviation σ of an amount representing the variation of the N predetermined section of the instantaneous value _{i m ~i m- (N-1} ) in one cycle of the differential current Id (the flatness), the standard deviation σ this was And the maximum deviation value σ _{max in the} past 1 cycle including the section where the standard deviation σ is obtained or in another fixed section within 1 cycle (σ
/ Σ _max ) is less than or equal to a certain value, and an exciting inrush current countermeasure element 65 that produces an output when the value is less than or equal to a certain value is provided to detect the flatness of the differential current Id. Since the output of the differential element 5 is blocked by the output of, the exciting inrush current and the fault current can be more reliably distinguished regardless of the magnitude of the exciting inrush current. It was difficult to ensure that even if the internal fault current was a transformer Tr of a power system in which the harmonic current near the second harmonic was included, the transformer inrush current would definitely cause a malfunction, resulting in a transformer internal fault. Sometimes it is possible to obtain a digital protective relay that can operate reliably.

(Sixth Embodiment) FIG. 10 is a functional block diagram showing a structural example of a differential relay for protecting a transformer according to the present embodiment, and the same parts as those in FIG. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
Therefore, a part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 10, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 66 is provided.

The excitation inrush current countermeasure element 66 is composed of a flatness calculation section 26, a flatness determination calculation section 29, and a return delay timer 23.

Here, the flatness calculation unit 26 calculates the differential current I calculated by the differential current calculation unit 14 of the differential element 5.
The flatness of a certain section of the waveform of d is obtained.

[0220] That is, in this example, the standard deviation of a quantity representing the variation (flatness) of the N instantaneous values i _m through i of a certain section in one cycle of the differential current Id _m-(N-1) This is to obtain σ.

Further, the flatness determination calculation unit 29 determines whether or not the flatness calculated by the flatness calculation unit 26 is less than or equal to a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and is output. Is caused.

That is, in this example, it is determined whether or not the ratio (σ / I) between the standard deviation σ obtained by the flatness calculation unit 26 and the amount I indicating the magnitude of the differential current Id is a fixed value or less. Then
Output is generated when the value is below a certain value.

Further, the return delay timer 23 has a delay time of one cycle or more, and is for making the output of the flatness determination calculation section 28 continuous.

As a result, the output of the return delay timer 23 blocks the output of the differential element 5.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

The operation of the differential element 5 is the same as that in the case of FIG. 22, so the description thereof is omitted here.

In FIG. 10, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 66, and the flatness operation unit 26 causes the fourth and The calculation based on the equation (7) described in each of the fifth embodiments is performed, and the standard deviation σ of the constant section in each sp of the differential current Id is calculated.

In the flatness determination calculation unit 29, the current standard deviation σ ₀ and the output of the amplitude value calculation unit 15 of the differential element 5 |
Id _1f | ratio of _{(σ 0 / | Id 1f |} ) to calculate the ratio of the standard deviation _{(σ 0 / | Id 1f |} ) when is equal to or less than a predetermined value k5, magnetizing inrush current and determination and output Cause

Since the output of the flatness determination calculation unit 29 due to the inrush current is an intermittent output that is output once or more per cycle, it is converted to a continuous output by the return delay timer 23, and then the difference is output through the NOT calculation circuit 19. The output of the moving element 5 is blocked.

As described above, the magnitude of the exciting inrush current takes various values depending on the voltage inrush phase, the difference in the transformer core, and the like. Therefore, the larger the exciting inrush current due to the loss of the direct current component of the current transformer, the greater the value. The flatness of the current period deteriorates, and the standard deviation error may increase.

Therefore, the amplitude value | Id _1f of the fundamental wave current included in the differential current Id proportional to the magnitude of the exciting inrush current.
Ratio of | and standard deviation σ ₀ at present (σ ₀ / | Id _1f |)
By always seeing, the exciting inrush current can be more surely determined regardless of the magnitude of the exciting inrush current.

On the other hand, the fault current may include a large amount of harmonic current in addition to the fundamental wave current. In particular, the harmonic current in the vicinity of the second harmonic may cause malfunction of the conventional differential relay. On the contrary, since the flat section does not occur, the flatness determination calculation unit 29
Output does not occur, and the output of the differential judgment calculation unit 16 becomes the output of the differential relay 1 as it is through the logical product calculation circuit 20, and normal operation can be performed.

The amount representing the magnitude of the exciting inrush current is determined by the 1f amplitude value | Id _1f | of the differential current Id of the differential element 5.
However, the maximum value (peak value) of the instantaneous value of the differential current Id in one cycle including the section in which the standard deviation σ ₀ at the present time is calculated may be used, and the maximum value of the magnitude of the differential current Id may be used. If the amount is an index, the same effect as the above case can be obtained.

As described above, in this embodiment,
The standard deviation σ of an amount representing a variation in the differential current the N instantaneous values of certain intervals during one cycle of _{Id i m ~i m- (N-} 1) ( flatness), and the standard deviation σ Differential current Id
It is determined whether the ratio (σ / I) with the amount I indicating the magnitude of is equal to or less than a certain value, and an exciting inrush current countermeasure element 66 that produces an output when the value is less than the certain value is provided. Is detected and the output of the differential element 5 is blocked by the output of the exciting inrush current countermeasure element 66, so that the exciting inrush current and the fault current can be more reliably irrespective of the magnitude of the exciting inrush current. The transformer Tr of the electric power system, which can be distinguished and which has been difficult to apply in the above-described conventional case and which includes the harmonic current in the vicinity of the second harmonic in the internal fault current,
It is possible to obtain a digital type protective relay that surely becomes inoperable when the transformer inrush current flows and that can reliably operate when an internal transformer accident occurs.

(Seventh Embodiment) FIG. 11 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer according to the present embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
Therefore, a part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 11, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 67 is provided, and the differential element 5 and the AND operation circuit 2 are provided.
An operation delay timer 30 for delaying the output of the differential element 5 for a time of one cycle or more is provided between the operation delay timer 30 and 0.

The excitation inrush current countermeasure element 67 is composed of a flatness calculation section 21, a flatness determination calculation section 31, and a return delay timer 23, and outputs the output of the differential determination calculation section 16 of the differential element 5. The flatness of the excitation inrush current countermeasure element 67 is activated on condition that the flatness determination operation unit 31 of the excitation inrush current countermeasure element 67 starts the determination operation, and the output of the differential determination arithmetic unit 16 of the differential element 5 is restored. The determination operation of the determination calculation unit 31 is stopped.

Here, the flatness calculating section 21 has the same function as in the case of the first embodiment.

Further, the flatness determination calculation unit 31 determines whether or not the flatness calculated by the flatness calculation unit 21 is equal to or less than a fixed value, and when the flatness is equal to or less than the fixed value, it is determined as an exciting inrush current and an output is output. The differential determination calculation unit 16 of the differential element 5
The determination operation is activated on the condition that the output of the output of 1 is output, and the determination operation is stopped on the condition that the output of the differential determination calculation unit 16 of the differential element 5 is restored.

Further, the return delay timer 23 has a delay time of one cycle or more, and is for making the output of the flatness determination calculation section 31 continuous.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

The operation of the differential element 5 is the same as that in the case of FIG. 22, so the description thereof will be omitted here.

In FIG. 11, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 67, and the flatness operation unit 21 causes the first current to flow. The calculation based on the equation (3) described in the embodiment is performed to calculate the average deviation D of the differential current Id for each sp in a certain section.

On the other hand, the flatness determination calculation unit 22 of the first embodiment always makes a determination calculation of the average deviation D in a constant section for each sp, and the average deviation D is calculated as the calculation section includes many flat portions. The value becomes smaller, and when the value is equal to or less than the constant value k, the flatness determination calculation unit 22 outputs. Therefore, the output of the flatness determination calculation unit 22 at the excitation inrush current becomes an intermittent output once in one cycle, and is made continuous by the return delay timer 23 having a time of one cycle or more. Is used as the output of the excitation inrush current countermeasure element.

However, since the differential current Id is zero when the load current is flowing or the passing current is flowing due to an external accident, the flatness determination calculation unit 22 always determines the operation output state. Therefore, the output of the differential element 5 is always blocked. When an internal accident occurs at this time, the differential element 5 operates and the output of the flatness determination calculation unit 22 returns, but the operation time of the differential relay 1 is the delay of the return of the excitation inrush current element. Timer 23
There will be a delay corresponding to the time required to restore the output of the.

In this respect, in the present embodiment, the flatness determination calculation unit 31 of the exciting inrush current element 67 is activated by the operation output of the differential determination calculation unit 16 of the differential element 5, and the output of the differential determination calculation unit 16 is started. By stopping with the recovery of the differential current Id, there is no unnecessary output blocking by the magnetizing inrush current countermeasure element 67 in a steady state where there is no differential current Id, and even if an internal accident occurs from this state, the differential relay 1 It is possible to reduce the operation time delay of.

The operation delay timer 30 for delaying the output of the differential judgment calculation unit 16 is for time coordination with the excitation inrush current countermeasure element 67 activated by the output of the differential judgment calculation unit 16, During the exciting inrush current, the output of the differential judgment calculation unit 16 is delayed from being sent before the output of the exciting inrush current countermeasure element 67.

As a result, the NOT operation circuit 19 inverts the output of the return delay timer 23 that delays the output of the flatness determination operation section 31, and the AND operation with the operation delay timer 30 that delays the output of the differential element 5. Is performed by the AND operation circuit 20, the output of the differential element 5 that operates with the exciting inrush current can be blocked, and the malfunction of the differential relay 1 can be prevented.

Further, in the fault current having no flat section,
The output of the flatness determination calculation unit 31 does not occur, and the differential determination calculation unit 1
The output of 6 becomes the output of the differential relay 1 as it is through the operation delay timer 30 and the AND operation circuit 20, and the normal operation can be performed.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
= 1, 2, ..., X), the deviation value is obtained by dividing the sum of the values by N, and when the deviation value is equal to or less than a certain value, the excitation inrush current countermeasure element 67 that determines the excitation inrush current and produces an output is generated. In addition to detecting the flatness of the differential current Id, an operation delay timer 30 for delaying the output of the differential element 5 for one cycle or more is provided between the differential element 5 and the AND operation circuit 20. Further, the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is activated on the condition that the output of the differential determination calculation unit 16 of the differential element 5 is sent, and the differential determination calculation unit 16 of the differential element 5 is activated. Since the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is stopped on the condition that the output of the excitation inrush current is restored, the excitation inrush current and the fault current can be more reliably irrespective of the magnitude of the excitation inrush current. Can be distinguished into
Even for the transformer Tr of the electric power system, which was difficult to apply in the above-mentioned conventional method and in which the internal fault current includes the harmonic current in the vicinity of the second harmonic, the inrush current of the transformer surely does not work. It is possible to obtain a digital protective relay that can reliably operate without an operation delay in the event of an internal transformer failure.

(Eighth Embodiment) FIG. 12 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer according to the present embodiment, and the same portions as those in FIG. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
12 is omitted, so that part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 12, an operation delay timer 30 for delaying the output of the differential element 5 by a time of 1 cycle or more is newly provided between the differential element 5 and the logical product operation circuit 20 in FIG. The logical product arithmetic circuit 32 for calculating the logical product of the output of the differential judgment arithmetic unit 16 of the moving element 5 and the output of the return delay timer 23 of the excitation inrush current countermeasure element 61 is provided. , Operation delay timer 3
The output of 0 is blocked.

Next, the operation of the differential relay 1 of the present embodiment configured as described above will be described.

The operation of the differential element 5 is the same as in the case of FIG. 22, and therefore its explanation is omitted here.

In FIG. 12, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 61, and the flatness operation unit 21 causes the first current to flow. The calculation based on the equation (3) described in the embodiment is performed to calculate the average deviation D of the differential current Id for each sp in a certain section.

Further, in the flatness determination calculation unit 22, the average deviation D in a certain section is constantly determined and calculated for each sp.

However, the determination is always made because the differential determination current Id is zero when the load current is flowing or the passing current is flowing due to an external accident. Therefore, the output of the differential element 5 is always blocked. If an internal accident occurs at this time, the output of the flatness determination calculation unit 22 is restored, but the operation time of the differential relay 1 is required for the output of the return delay timer 23 of the exciting inrush current element 61 to be restored. There will be a time delay.

In this respect, in the present embodiment, the logical product arithmetic operation of the output of the differential judgment arithmetic unit 16 and the excitation inrush current countermeasure element 61 is performed by the logical product arithmetic circuit 32, and when the differential element 5 does not operate. The output of the excitation inrush current countermeasure element 61 is blocked,
When the differential element 5 operates, the excitation inrush current countermeasure element 6
By allowing the output of No. 1, the excitation inrush current countermeasure element 61 does not unnecessarily block the output in a steady state where there is no differential current Id, and even if an internal accident occurs from this state, the differential relay The operation time delay of 1 can be reduced.

The operation delay timer 30 for delaying the output of the differential judgment calculation unit 16 is for time coordination with the excitation inrush current countermeasure element 61 activated by the output of the differential judgment calculation unit 16, During the exciting inrush current, the output of the differential judgment calculation unit 16 is delayed from being output before the output of the exciting inrush current countermeasure element 61.

As a result, the operation delay timer 3 delays the output of the differential element 5 by the operation output of the logical product operation of the output of the differential element 5 and the output of the excitation inrush current countermeasure element 61.
By blocking the output of 0, the malfunction of the differential relay 1 can be prevented.

Further, in the fault current having no flat section,
The output of the flatness determination calculation unit 22 does not occur, and the differential determination calculation unit 1
The output of 6 becomes the output of the differential relay 1 as it is through the operation delay timer 30 and the AND operation circuit 20, and the normal operation can be performed.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
= 1, 2, ..., X), the deviation value is obtained by dividing the sum of the values by N, and when the deviation value is equal to or less than a certain value, the excitation inrush current countermeasure element 61 that determines the excitation inrush current and produces an output is generated. In addition to detecting the flatness of the differential current Id, an operation delay timer 30 for delaying the output of the differential element 5 for one cycle or more is provided between the differential element 5 and the AND operation circuit 20. Further, a logical product arithmetic circuit 32 for calculating a logical product of the output of the differential judgment arithmetic unit 16 of the differential element 5 and the output of the return delay timer 23 of the excitation inrush current countermeasure element 61 is provided. Since the output of the operation delay timer 30 is blocked by the output, the magnetizing inrush current and the fault current can be more surely distinguished regardless of the magnitude of the magnetizing inrush current. Difficult, inside Even for the transformer Tr of the electric power system in which the current contains a harmonic current in the vicinity of the second harmonic, the transformer inrush current surely becomes inoperative, and the internal operation of the transformer does not occur without delay. It is possible to obtain a digital protective relay that can be used.

(Ninth Embodiment) FIG. 13 is a functional block diagram showing a structural example of a differential relay for protecting a transformer according to the present embodiment, and the same parts as those in FIG. The description is omitted, and only different parts will be described here.

Note that the configuration of the differential element 5 is shown in FIG.
Therefore, a part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 13, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and instead of this, a new exciting inrush current countermeasure element 67 is provided, and the current change width detection (hereinafter, Δ
The element 33 (referred to as I) is provided.

The excitation inrush current countermeasure element 67 is composed of a flatness calculating section 21, a flatness determining calculating section 31, and a return delay timer 23.

Here, the flatness calculator 21 has the same function as in the case of the first embodiment.

Further, the flatness determination calculation unit 31 determines whether or not the flatness calculated by the flatness calculation unit 21 is less than or equal to a certain value, and when it is less than the certain value, it is determined as an exciting inrush current and an output is output. This occurs, and the determination operation is activated on the condition that the output of the return delay timer 35 of the ΔI element 33, which will be described later, is given as a condition, and the determination operation is stopped on the condition that the output of the return delay timer 35 of the ΔI element 33 is returned. It is a thing.

Further, the return delay timer 23 has a delay time of one cycle or more, and is for making the output of the flatness determination calculation section 31 continuous.

On the other hand, the ΔI element 33 is the ΔI determination calculation unit 3
4 and a return delay timer 35, and activates the determination operation of the flatness determination calculator 31 of the excitation inrush current countermeasure element 67 on the condition of the output of the return delay timer 35 of the ΔI element 33, and On the condition that the output of the return delay timer 35 is restored, the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is stopped.

Here, the ΔI determination calculation unit 34 calculates the differential current Id calculated by the differential current calculation unit 14 of the differential element 5.
It is determined whether or not the magnitude of has changed by a certain value or more, and an output is generated when it changes by more than a certain value.

The return delay timer 35 has a delay time of one cycle or more, and is used to make the output of the ΔI determination calculation section 34 continuous.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

The operation of the differential element 5 is the same as that in the case of FIG. 22, so the description thereof will be omitted here.

In FIG. 13, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the exciting inrush current countermeasure element 67, and the flatness operation unit 21 causes the differential current Id to be calculated. The calculation based on the equation (3) described in the embodiment is performed to calculate the average deviation D of the differential current Id for each sp in a certain section.

On the other hand, the flatness determination calculation section 22 of the first embodiment always determines and calculates the average deviation D in a certain section for each sp.

However, the constant determination is that the differential determination current Id is zero when the load current is flowing or the passing current is flowing due to an external accident. Therefore, the output of the differential element 5 is always blocked. When an internal accident occurs at this time, the differential element 5 operates and the output of the flatness determination calculation unit 22 returns, but the operation time of the differential relay 1 is the delay of the return of the excitation inrush current element. Timer 23
There will be a delay corresponding to the time required to restore the output of the.

In this respect, the present embodiment is provided with the ΔI element 33 which operates by detecting the change amount of the differential current Id which suddenly changes from zero when an internal accident occurs or when an exciting inrush current occurs.
The determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is started by sending the output of the ΔI element 33, and Δ
By stopping when the output of the I element 33 is restored,
In the steady state in which there is no differential current Id, the excitation inrush current countermeasure element 67 does not prevent unnecessary output,
Even if an internal accident occurs from this state, it is possible to eliminate the operation time delay of the differential relay 1.

The ΔI determination calculation unit 34 of the ΔI element 33 is
For this, a known calculation algorithm may be used. For example, the instantaneous value of the previous instantaneous value i _m and 1 cycle of current i _m-96
Taking the difference between _{(Δi = i m -i m-} 96), obtains a ΔIm is more a result of the amplitude value operation, this ΔIm predetermined value k6
Output is generated in the above cases. In addition, the ΔI determination calculation unit 34
Produces an output only when a change in current occurs,
It is necessary to continue the output for a certain time after the current change (time until the exciting inrush current is attenuated). Then, the return delay timer 35 is for ensuring this operation duration time.

As a result, the output of the differential element 5 is blocked by the output of the exciting inrush current countermeasure element 67 activated by the ΔI element 33 which operates when the exciting inrush current flows. It is possible to prevent malfunction.

Further, in the fault current which does not have a flat section,
The output of the flatness determination calculation unit 31 does not occur, and the differential determination calculation unit 1
The output of 6 becomes the output of the differential relay 1 as it is through the AND operation circuit 20, and normal operation can be performed.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
= 1, 2, ..., X), the deviation value is obtained by dividing the sum of the values by N, and when the deviation value is equal to or less than a certain value, the excitation inrush current countermeasure element 67 that determines the excitation inrush current and produces an output is generated. In addition to detecting the flatness of the differential current Id, an output Δ is produced when the magnitude of the differential current Id changes by a certain value or more.
The I element 33 is further provided, and the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is activated on the condition of the output of the return delay timer 35 of the ΔI element 33.
Since the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is stopped on the condition that the output of the return delay timer 35 of No. 3 is returned, the excitation inrush current is determined to be irrespective of the magnitude of the excitation inrush current. It is possible to more reliably distinguish fault currents, which was difficult to apply in the above-mentioned conventional cases.
Even for a transformer Tr of a power system in which the internal fault current includes a harmonic current in the vicinity of the second harmonic, the transformer inrush current surely becomes inoperative, and at the time of an internal fault of the transformer, there is no delay in operation, and there is no delay. It is possible to obtain a digital protective relay that can operate.

(Tenth Embodiment) FIG. 14 is a functional block diagram showing a structural example of a differential relay for protecting a transformer according to the present embodiment, and the same portions as those in FIG. 13 are designated by the same reference numerals. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
Since it is the same as 3, the part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 14, the ΔI element 33 in FIG. 13 is omitted, and instead of this, a plurality of new Δ (two in this example) Δ is provided.
The logical sum (OR) operation circuit 3 is provided with the I element 33.
6 is provided.

Here, each ΔI element 33 determines whether or not the magnitude of each of the terminal currents I ₁ and I ₂ converted into a digital amount has changed by a certain value or more, and when it has changed by a certain value or more, Each produces an output.

Further, the OR operation circuit 36 determines that each ΔI
The output of the element 33 is logically ORed, and the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is activated on the condition that the output is sent, and the excitation inrush current is activated on the condition that the output is restored. The determination operation of the flatness determination calculation unit 31 of the countermeasure element 67 is stopped.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

The operation of the differential element 5 is the same as in the case of FIG. 22 described above, and therefore its explanation is omitted here.

In FIG. 14, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 67, and the flatness operation unit 21 causes the differential current Id. The calculation based on the equation (3) described in the embodiment is performed to calculate the average deviation D of the differential current Id for each sp in a certain section.

On the other hand, in the flatness determination calculation section 22 of the first embodiment, the average deviation D in a certain section is constantly determined and calculated for each sp.

However, the constant determination is that the differential determination current Id is zero when the load current is flowing or the passing current is flowing due to an external accident. Therefore, the output of the differential element 5 is always blocked. When an internal accident occurs at this time, the differential element 5 operates and the output of the flatness determination calculation unit 22 returns, but the operation time of the differential relay 1 is the delay of the return of the excitation inrush current element. Timer 23
There will be a delay corresponding to the time required to restore the output of the.

In this respect, in the present embodiment, the ΔI element 33 that operates by detecting the change when the input current (terminal current) suddenly changes at the time of an internal accident or the occurrence of an exciting inrush current is input to each terminal. For the currents (terminal currents) I ₁ and I ₂ , the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is performed when the output of the ΔI determination calculation unit 34 of any of the ΔI elements 33 is transmitted. Start up and all ΔI elements 3
When the output of the return delay timer 35 of the ΔI determination calculation unit 34 of No. 3 is restored, the determination operation of the flat determination calculation unit 31 of the excitation inrush current countermeasure element 67 is stopped, so that the excitation in the steady state without the differential current Id is performed. Inrush current countermeasure element 6
Even if an internal accident occurs from this state, the delay of the operating time of the differential relay 1 can be eliminated without performing unnecessary output blocking by 7.

As a result, the output of the exciting inrush current countermeasure element 67 activated by the output of the ΔI element 33 provided for the input currents I ₁ and I _{2 of} the respective terminals operating when the exciting inrush current flows By blocking the output of the differential element 5, malfunction of the differential relay 1 can be prevented.

Further, in the fault current having no flat section,
The output of the flatness determination calculation unit 31 does not occur, and the differential determination calculation unit 1
The output of 6 becomes the output of the differential relay 1 as it is through the AND operation circuit 20, and normal operation can be performed.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
= 1, 2, ..., X), the deviation value is obtained by dividing the sum of the values by N, and when the deviation value is equal to or less than a certain value, the excitation inrush current countermeasure element 67 that determines the excitation inrush current and produces an output is generated. In addition to detecting the flatness of the differential current Id, a ΔI element 33 that produces an output when the magnitude of the input current changes by a certain value or more is provided for the input currents I ₁ and I ₂ at each terminal. Return delay timer 35 of each ΔI element 33
Of the excitation inrush current countermeasure element 67, the determination operation of the flatness determination calculation unit 31 of the excitation inrush current countermeasure element 67 is started, and the output of the reset delay timer 35 of all ΔI elements 33 is restored. 67 flatness determination calculation unit 3
Since the determination operation 1 is stopped, the exciting inrush current and the fault current can be more reliably distinguished regardless of the magnitude of the exciting inrush current, which is difficult to apply in the above-described conventional case. Even for a transformer Tr of a power system in which the internal fault current includes a harmonic current in the vicinity of the second harmonic, the transformer inrush current surely becomes inoperative, and at the time of an internal fault of the transformer, there is no delay in operation, and there is no delay. It is possible to obtain a digital protective relay that can operate.

(Eleventh Embodiment) FIG. 15 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer according to the present embodiment, and the same parts as those in FIG. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
15 is omitted, so that part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 15, the input of the output of the return delay timer 23 of the excitation inrush current countermeasure element 61 in FIG. 1 to the NOT operation circuit 19 is omitted, and instead of this, a new ΔI element 33 and a logical product operation are added. The circuit 37 is provided.

Here, the ΔI element 33 has the same function as that of the ΔI element 33 of the ninth embodiment described above.

The AND operation circuit 37 calculates the AND of the output of the return delay timer 23 of the excitation inrush current countermeasure element 61 and the output of the return delay timer 35 of the ΔI element 33, and performs a NOT operation on the output. It is provided as an input to the circuit 19.

Next, the operation of the differential relay 1 of the present embodiment configured as described above will be described.

The operation of the differential element 5 is the same as that in the case of FIG. 22, so the description thereof will be omitted here.

In FIG. 15, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the exciting inrush current countermeasure element 61, and the flatness operation unit 21 causes the differential current Id to be calculated. The calculation based on the equation (3) described in the embodiment is performed to calculate the average deviation D of the differential current Id for each sp in a certain section.

On the other hand, the flatness determination calculation unit 22 always determines and calculates the average deviation D in a certain section for each sp.

However, the constant determination is that the differential determination current Id is zero when the load current is flowing or the passing current is flowing due to an external accident. Therefore, the output of the differential element 5 is always blocked. When an internal accident occurs at this time, the differential element 5 operates and the output of the flatness determination calculation unit 22 returns, but the operation time of the differential relay 1 is the delay of the return of the excitation inrush current element. Timer 23
There will be a delay corresponding to the time required to restore the output of the.

In this respect, in the present embodiment, the output of the ΔI element 33, which operates by detecting the change amount of the differential current Id that suddenly changes from zero when an internal fault occurs or when an exciting inrush current occurs, and an exciting inrush current countermeasure. By the output of the logical product calculation circuit 37 that performs the logical product calculation with the output of the element 61, the output of the differential element 5 is blocked, so that there is no need for the excitation inrush current countermeasure element 61 in the steady state where there is no differential current Id. Therefore, even if an internal accident occurs in this state, the delay of the operation time of the differential relay 1 can be eliminated.

As a result, the output of the ΔI element 33, which operates when the exciting inrush current flows, and the exciting inrush current countermeasure element 61.
By blocking the output of the differential element 5 by the output of the logical product calculation circuit 37 that performs the logical product calculation with the output of
It is possible to prevent the malfunction of the differential relay 1 due to the excitation inrush current.

Further, in the fault current having no flat section,
The output of the flatness determination calculation unit 22 does not occur, and the differential determination calculation unit 1
The output of 6 becomes the output of the differential relay 1 as it is through the AND operation circuit 20, and normal operation can be performed.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
= 1, 2, ..., X), the deviation value is obtained by dividing the sum of the values by N, and when the deviation value is equal to or less than a certain value, the excitation inrush current countermeasure element 61 that determines the excitation inrush current and produces an output is generated. In addition to detecting the flatness of the differential current Id, an output Δ is produced when the magnitude of the differential current Id changes by a certain value or more.
Since the output of the differential element 5 is blocked by the output of the logical product operation of the output of the excitation inrush current countermeasure element 61 and the output of the ΔI element 33, the magnitude of the excitation inrush current is increased. Regardless of the above, it is possible to more reliably distinguish the inrush current and the fault current, and it is difficult to apply the above-mentioned conventional technique to the internal fault current that includes a harmonic current in the vicinity of the second harmonic. Even for the transformer Tr of the system, it is possible to obtain a digital protective relay that is surely inoperative due to the transformer exciting inrush current and can reliably operate without an operation delay in the case of an internal transformer failure.

(Twelfth Embodiment) FIG. 16 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer according to the present embodiment, and the same portions as those in FIG. 1 are designated by the same reference numerals. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
16 is omitted, so that part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 16, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 68 is provided.

The exciting inrush current countermeasure element 68 is composed of a flatness calculating section 21, a flatness determining calculating section 22, and a shift calculating section 3.
8, a logical product operation circuit 39, and a return delay timer 23.

Here, the flatness calculation section 21 and the flatness determination calculation section 22 have the same functions as those of the flatness calculation section 21 and the flatness determination calculation section 22 of the first embodiment, respectively. Is.

The shift calculation section 38 is for delaying the output of the flatness determination calculation section 22 by one cycle.

Furthermore, the AND operation circuit 39 outputs the output (current output) of the flatness determination operation unit 22 and the shift operation unit 38.
And the output (output of one cycle before) are ANDed.

Furthermore, the return delay timer 23 is set to 1
It has a delay time of more than one cycle and is for making the output of the AND operation circuit 39 continuous.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

The operation of the differential element 5 is the same as in the case of FIG. 22, and therefore its explanation is omitted here.

In FIG. 16, the differential current Id derived by the differential current operation unit 14 of the differential element 5 is introduced into the excitation inrush current countermeasure element 68, and the flatness operation unit 21 described above (3). The calculation based on the equation is performed, and each sp of the differential current Id
The average deviation D of a fixed section in each case is calculated.

Further, in the flatness determination calculation unit 22, when the average deviation D becomes equal to or less than the predetermined value k, it is determined as an exciting inrush current and the output is sent out.

Due to the relationship of the transformer core saturation, the exciting inrush current has a periodicity of a period in which the current flows and a period in which the current does not flow for each cycle. Therefore, the output of the flatness determination calculation unit 22 due to the inrush current of excitation is always sent once for each cycle, and the output is an intermittent output having periodicity for each cycle.

On the other hand, the fault current is a superposition of the fundamental wave current or the unspecified harmonic current and does not cause a non-current period, but rarely a transient flat portion due to the superposition of harmonics. It is possible to have

FIG. 17 is a diagram showing an example of a case where there is a transient flat portion due to the fault current. The average deviation D at the portion A of the differential current Id becomes a predetermined value k or less, and the flatness determination calculation portion 22 is shown.
Outputs a sporadic output, but the output of the flatness determination calculation unit 22 at this time does not have periodicity.

Then, the outputs of these flatness determination calculation units 22 are delayed by one cycle by the shift calculation unit 38, and the output of the flatness determination calculation unit 22 which is the current determination result and the shift calculation unit 38 which is the determination result one cycle before are output. By performing the logical product operation with the output in the logical product operation circuit 39, the periodicity of the flat portion in the differential current Id can be seen.

FIG. 18 is a diagram showing an example of detection of the periodicity in the exciting inrush current and the fault current. The exciting inrush current (a) is ANDed for the periodic output of the flatness determination operation unit 22. Output of circuit 39 occurs, but fault current (b)
The output of the AND operation circuit 39 does not occur due to the sporadic output of the flatness determination operation unit 22.

Since the AND operation result in the AND operation circuit 39 based on the exciting inrush current is an intermittent output, it is made continuous by the return delay timer 23 and used as the output of the exciting inrush current countermeasure element 68.

As a result, with respect to the exciting inrush current, the exciting inrush current countermeasure element 68 operates reliably and the differential relay 1
The malfunction of the differential relay 1 can be prevented and the unnecessary output of the excitation inrush current countermeasure element 68 does not occur, and the differential relay 1 can operate normally even with respect to a fault current that causes a transient flat portion.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
= 1, 2, ..., X), the deviation value is obtained by dividing the sum of the values by N, and the output generated when the deviation value is less than a certain value is compared with the flatness determination calculation 22 output one cycle before. Since the periodicity of the differential current Id is detected by providing the exciting inrush current countermeasure element 68 that produces an output when the logical product condition of both is satisfied, the exciting inrush current and the exciting inrush current are detected regardless of the magnitude of the exciting inrush current. For the transformer Tr of the power system, which can more reliably distinguish the fault current and which is difficult to apply in the above-mentioned conventional case, in which the internal fault current includes the harmonic current in the vicinity of the second harmonic. Also, it is possible to obtain a digital type protective relay that surely becomes inoperative with the transformer inrush current and can reliably operate in the case of an internal transformer failure.

(Thirteenth Embodiment) FIG. 19 is a functional block diagram showing a structural example of a differential relay for protecting a transformer according to the present embodiment, and the same parts as those in FIG. The description is omitted, and only different parts will be described here.

The structure of the differential element 5 is shown in FIG.
19 is omitted, so that part of the configuration is omitted in FIG.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 19, the exciting inrush current countermeasure element 61 in FIG. 1 is omitted, and in place of this, a new exciting inrush current countermeasure element 69 is provided.

The excitation inrush current countermeasure element 69 includes a flatness calculating section 21, a shift calculating section 40, a maximum value detecting calculating section 41, a flatness determining calculating section 42, and a return delay timer 23.
It consists of

Here, the flatness computing section 21, the above-mentioned first
The flatness calculator 21 has the same function as that of the flatness calculator 21 in the above embodiment.

The shift calculator 40 is for delaying the value of the average deviation D output from the flatness calculator 21 by one cycle.

On the other hand, the maximum value detecting / calculating section 41 has the average deviation D output from the flatness calculating section 21 and the shift calculating section 40.
The average deviation D _MAX which is the output of the above is compared and the larger average deviation D _MAX is output.

Further, the flatness determination calculation section 42 determines whether or not the average deviation D _MAX which is the output of the maximum value detection calculation section 41 is smaller than a predetermined value k, and when the average deviation D _MAX is smaller than the predetermined value k, an output is generated. It is a thing.

Moreover, the return delay timer 23 is set to 1
It has a delay time of more than one cycle and is for making the output of the flatness determination calculation unit 42 continuous.

Next, the operation of the differential relay 1 of the present embodiment configured as above will be described.

Since the operation of the differential element 5 is the same as that in the case of FIG. 22, the description thereof will be omitted here.

In FIG. 19, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced into the exciting inrush current countermeasure element 69, and the flatness calculator 21 described above (3). The calculation based on the equation is performed, and each sp of the differential current Id is
The average deviation D of a fixed section in each case is calculated.

Then, the average deviation at the present time which is the output of the flatness calculating section 21 is set as D _m , this average deviation D _m is delayed by one cycle by the shift calculating section 40, and this delayed average deviation is set as D _m-96 . To do.

On the other hand, the maximum value detecting section 41 compares the average deviation D _m and the average deviation D _m-96, and the larger standard deviation is output as D _MAX .

[0347] In the flat determination computing unit 42, when the average deviation D _{MA X} is the output of the maximum value detecting section 41 becomes equal to or lower than a predetermined value k, and outputs the determined magnetizing inrush current is delivered.

Due to the relationship of the transformer core saturation, the exciting inrush current has a periodicity of a period in which the current flows and a period in which the current does not flow for each cycle. Therefore, the average deviation D calculated by the flatness calculating unit 21 also becomes an output having a periodicity that becomes minimum every cycle, and the average deviation D _m at the present time and the average deviation D _m-96 one cycle before are obtained. Are equal.

As a result, since the maximum value detection calculation unit 41 outputs the average deviation D _m (= D _m-96 ) as it is, the output of the flatness determination calculation unit 42 has the periodicity of outputting every cycle. It is an intermittent output.

Since the intermittent output of the flatness determination calculating section 42 is made continuous by the return delay timer 23 and is used as the output of the exciting inrush current countermeasure element 69, the malfunction of the differential relay 1 does not occur.

On the other hand, the fault current is a superposition of a fundamental wave current or an unspecified harmonic current and does not cause a no-current period, but rarely a transient flatness due to the superposition of harmonics. It is possible to have parts.

FIG. 20 is a diagram showing an example in the case of having a transient flat portion due to the fault current, and shows the change of the average deviation D which is the output of the flatness computing section 21.

FIG. 20A shows the output of the flatness calculating section 21 and the flatness determining calculating section 22 in the first embodiment.
The average deviation becomes equal to or smaller than the predetermined value k at the point of time B, and the flatness determination calculation unit 22 transiently outputs one shot as shown in FIG. 20 (b).

On the other hand, FIG. 20C shows FIG.
The average deviation D _m of the output of the flatness calculation unit 21 in (a) and the average deviation D _m of the output obtained through the shift calculation unit 40
_{It is} the output (average deviation D _MAX ) of the maximum value detection calculation unit 41 comparing with _m-96 , and, for example, the value of the average deviation B at the present time in FIG. Is compared with the value of, whichever is larger (here, C)
Is the average deviation D of the maximum value detection calculation unit 41 of FIG.
Since the average determination calculation unit 42 does not operate, the excitation inrush current countermeasure element 69 does not generate an output, and the differential relay 1 can perform a normal operation.

As described above, in this embodiment,
As a quantity representing the variation (flatness) of a certain section of the N instantaneous values i _m through i in 1 cycle _m-(N-1) of the differential current Id, the N mean of each instantaneous value and the instantaneous value The difference from the value is the power of x (x
, 1, 2, ..., X), the deviation value obtained by dividing the sum of the values by N is compared, the deviation value at the present time and the deviation value one cycle before are compared, and the deviation value of whichever is larger is a predetermined value. Since the exciting inrush current countermeasure element 69 that produces an output when k or less is provided to detect the periodicity of the differential current Id, the exciting inrush current and the fault current are detected regardless of the magnitude of the exciting inrush current. The transformer Tr of the electric power system, which can be more surely distinguished and which is difficult to apply in the related art described above and which includes the harmonic current in the vicinity of the second harmonic, in the internal fault current is also used. It is possible to obtain a digital type protective relay that is surely inoperative due to the inrush current of the transformer excitation, and is capable of operating reliably in the event of an internal transformer failure.

The present invention is not limited to the above-described embodiments, but can be implemented in the same manner as described below.

(A) In each of the above embodiments, the transformer Tr
However, the present invention is also applicable to a differential relay for protecting a transformer having a plurality of terminals of three windings or more. It is possible.

(B) If the sampling frequency of the A / D conversion is a value that can distinguish between the fault current and the exciting inrush current by observing the variation of the instantaneous value, the above-mentioned 4.8 is particularly preferable.
It is not limited to kHz.

(C) In the seventh embodiment described above, the flatness determination calculation unit 31 determines the start condition based on the output of the differential determination calculation unit 16.
However, the present invention is not limited to this, and the activation condition by the output of the differential determination computation unit 16 may be the activation condition of the flatness computation unit 21, and the same effect as the above case can be obtained. It is possible.

(D) In the seventh embodiment, the case where the flatness determination calculation section 22 in the first embodiment is applied has been described. However, the present invention is not limited to this, and each of the second to sixth embodiments is applied. Flatness determination calculator 24, 25, 27, 2
The start condition may be given to 8 and 29 by the output of the differential judgment calculation unit 16, and the same effect as the above case can be obtained.

(E) In the eighth embodiment, the differential element 5 is operated by the operation output of the logic operation of the output of the differential element 5 and the output of the exciting inrush current countermeasure element 61 in the first embodiment. The case where the output of the operation delay timer 30 that delays the output is blocked has been described, but the present invention is not limited to this, and the output of the differential element 5 and the respective excitation inrush current countermeasure elements 62, in the second to sixth embodiments. 63, 64, 65, 66
The output of the operation delay timer 30 that delays the output of the differential element 5 may be blocked by the operation output of the logic operation with the output of the above, and the same effect as the above case can be obtained. .

(F) In the ninth embodiment, the case where the activation condition based on the output of the ΔI element 33 is given to the flatness determination calculation section 31 has been described, but the present invention is not limited to this.
The activation condition by the output of the element 33 may be the activation condition of the flatness calculation unit 21, and the same effect as the above case can be obtained.

(G) In the ninth embodiment, the case where the flatness determination calculation section 22 (31) in the first embodiment is applied has been described, but the present invention is not limited to this. Each flatness determination calculation unit 24, 25 in the form
The starting condition may be given to 27, 28, 29 by the output of the ΔI element 33, and the same effect as the above case can be obtained.

(H) In the tenth embodiment described above, the flatness determination operation unit 3 determines the start condition by the output of the logical sum operation circuit 36.
Although the case where it is given to 1 has been described, the activation condition by the output of the OR operation circuit 36 may be the activation condition of the flatness operation unit 21, and the same effect as the above case can be obtained. It is possible.

(I) In the tenth embodiment described above, the case of application to the flatness determination calculation section 22 (31) in the first embodiment has been described, but the present invention is not limited to this, and the second to sixth embodiments are not limited to this. Each flatness determination calculation unit 24, 2 in the form
The starting condition may be given to 5, 27, 28, 29 by the output of the ΔI element 33, and the same effect as the above case can be obtained.

(J) In the eleventh embodiment, the case where the ΔI element by the differential current Id is applied has been described, but the present invention is not limited to this, and the ΔI element by each input current may be used. It is possible to obtain the same effect.

(K) In the eleventh embodiment, the output of the AND operation of the output of the flatness determination operation unit 22 and the output of the ΔI element 33 in the first embodiment is used to output the differential element 5
However, the present invention is not limited to this, and the output of each flatness determination calculation unit 24, 25, 27, 28, 29 in the second to sixth embodiments and the output of the ΔI element 33 are described. The output of the AND operation of
May be blocked, and the same effect as the above case can be obtained.

(L) In the above twelfth embodiment, a case has been described in which the outputs of the flatness determination calculation unit 22 one cycle before are compared with each other. However, the present invention is not limited to this. The outputs of the calculation unit 22 may be compared, and the same effect as the above case can be obtained.

(M) In the above twelfth embodiment, the case where the output at the present time of the flatness determination calculation unit 22 in the first embodiment and the output one cycle or a plurality of cycles before are compared has been described. Not limited to the above, the second
Thru | or each flatness determination calculating part 24,2 in 6th Embodiment
The current outputs of 5, 27, 28 and 29 may be compared with the output of one cycle or a plurality of cycles before, and the same effect as the above case can be obtained.

(N) In the thirteenth embodiment, the case where the current deviation and the value of each average deviation one cycle before are compared has been described, but the present invention is not limited to this, and the value of each average deviation before the current cycle and plural cycles before. May be compared, and the same effect as the above case can be obtained.

(O) In the thirteenth embodiment, the case where the current value of the average deviation D in the first embodiment is compared with the value one cycle or a plurality of cycles before has been described, but the present invention is not limited to this. However, the ratio of the average deviations (D ₀ / D _max ), (D
₀ / | Id _1f |), or the standard deviation σ in the fourth to sixth embodiments and the ratio of standard deviations (σ ₀ /
σ _max ), (σ ₀ / | Id _1f |) may be compared with the current value of one cycle or a plurality of cycles before, and the same effect as the above case can be obtained. is there.

[0372]

As described above, according to the present invention, the difference between the waveforms of the transformer exciting inrush current and the transformer internal fault current, that is, the exciting inrush current is the transformer to be protected during one cycle. While there is always a section where current flows due to magnetic flux saturation of the iron core and a flat portion (no current period) where the current does not flow due to saturation of the transformer iron core, the fault current is the fundamental current or Paying attention to the fact that a flat portion in a certain section does not occur due to the superposition of an unspecified number of harmonic currents, the flatness of the differential current is calculated by calculating the average deviation, standard deviation, or a value based on these An internal inrush current, which was difficult to apply in the past, is provided by including an exciting inrush current countermeasure element that determines that it is an exciting inrush current when the value is less than or equal to a predetermined value, and reliably distinguishing the inrush current from the fault current. The second harmonic Even for a transformer of the power system that includes a harmonic current beside reliably become inoperative in magnetizing inrush current, the transformer internal fault digital protective relay capable of operating reliably at the time can be provided.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a first embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 2 is a waveform diagram showing characteristics of a fault current waveform and an excitation inrush current waveform.

FIG. 3 is a diagram for explaining the operation of the digital protective relay according to the first embodiment.

FIG. 4 is a view for explaining the operation of the digital protective relay according to the first embodiment.

FIG. 5 is a functional block diagram showing a second embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 6 is a functional block diagram showing a third embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 7 is a functional block diagram showing a fourth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 8 is a view for explaining the operation of the digital protective relay according to the fourth embodiment.

FIG. 9 is a functional block diagram showing a fifth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 10 is a functional block diagram showing a sixth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 11 is a functional block diagram showing a seventh embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 12 is a functional block diagram showing an eighth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 13 is a functional block diagram showing a ninth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 14 is a functional block diagram showing a tenth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 15 is a functional block diagram showing an eleventh embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 16 is a functional block diagram showing a twelfth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 17 is a view for explaining the operation of the digital protective relay according to the twelfth embodiment.

FIG. 18 is a view for explaining the operation of the digital protective relay according to the twelfth embodiment.

FIG. 19 is a functional block diagram showing a thirteenth embodiment of a digital protective relay (differential relay) according to the present invention.

FIG. 20 is a view for explaining the operation of the digital protective relay according to the thirteenth embodiment.

FIG. 21 is a circuit diagram showing an example in which a differential relay is applied to a transformer.

FIG. 22 is a functional block diagram showing a configuration example of a conventional differential relay.

[Explanation of symbols]

G ... Power system power supply, CB ... Circuit breaker, CT1, CT2 ... Current transformer (CT), Tr ... Transformer, 1 ... Differential relay, 2 ... Transformer (CT), 3 ... A / D converter, 4 ... CPU, 5 ... Differential element, 6 ... Excitation inrush current countermeasure element (2f element), 11, 12 ... Amplitude value calculation section, 13 ... Suppression current (scalar sum) calculation section, 14 ... Differential current (vector sum) Calculation unit, 15 ... Amplitude value calculation unit, 16 ... Differential judgment calculation unit, 17 ... Amplitude value calculation unit, 18 ... 2f judgment calculation unit, 19 ... NOT (inversion) calculation circuit, 20, 32, 37, 39 ... Logic Product (AND) operation circuit, 21, 26 ... Flatness operation section, 22, 24, 25, 27, 28, 29, 31, 42 ... Flatness determination operation section, 23, 35 ... Return delay timer, 30 ... Operation delay timer , 33 ... Current change width (ΔI) detection element, 34 ... ΔI judgment performance Arithmetic unit, 36 ... Logical sum (OR) arithmetic circuit, 38, 40 ... Shift arithmetic unit, 41 ... Maximum value detection arithmetic unit, 61, 62, 63, 64, 65, 66, 67, 68, 6
9 ... Inrush current countermeasures.

Front Page Continuation (72) Inventor Takafumi Maeda 1-3-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Company (72) Inventor Hiroshi Yamakawa 1-3-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Inc. In-house (72) Inventor Mitsuru Yamaura 1 in Toshiba Fuchu factory, Fuchu, Tokyo (72) Inventor Rikio Sato 1 in Toshiba Fuchu, Tokyo Fuchu factory (72) Inventor Satoshi Nakano 1 Toshiba Town, Fuchu City, Tokyo Inside Toshiba Fuchu Factory (72) Inventor Masao Hori 1-1-1 Shibaura, Minato-ku, Tokyo Inside Toshiba Head Office

Claims (13)

[Claims] 1. An alternating current for each phase is introduced across a protected object having a plurality of terminals, the introduced alternating current is sampled at constant time intervals and converted into a digital amount, and the converted value is converted. A first determining means for calculating a differential current for each phase by using the digital amount, and for generating an output by determining an internal accident when the amount of electricity based on the calculated differential current is a predetermined value or more. In a digital protective relay provided with a differential protection element having: N of a certain section in one cycle of the calculated differential current.
As a quantity representing the variation (flatness) of the number of instantaneous values _{i m ~i m- (N-1} ), the difference between the N average value of the instantaneous value and the instantaneous value th power x (x = 1, 2 , ..., X) is added to obtain a deviation value by dividing the sum of the calculated values by N, and it is determined whether the obtained deviation value is less than or equal to a certain value, and an output is generated when the deviation value is less than or equal to the certain value.
And an exciting inrush current countermeasure element having a return delay means for delaying the output of the second determining means by a predetermined time, and the output of the differential protection element is determined by the output of the exciting inrush current countermeasure element. A digital protective relay characterized by blocking. 2. An alternating current for each phase is introduced across a protected object having a plurality of terminals, the introduced alternating current is sampled at constant time intervals and converted into a digital amount, and the converted value is converted. A first determining means for calculating a differential current for each phase by using the digital amount, and for generating an output by determining an internal accident when the amount of electricity based on the calculated differential current is a predetermined value or more. In a digital protective relay provided with a differential protection element having: N of a certain section in one cycle of the calculated differential current.
As a quantity representing the variation (flatness) of the number of instantaneous values _{i m ~i m- (N-1} ), the difference between the N average value of the instantaneous value and the instantaneous value th power x (x = 1, 2 , ..., x) The sum of the calculated values is divided by N to obtain a deviation value, and the obtained deviation value and the section in which the deviation value is obtained include the past one cycle or another fixed section within one cycle. Ratio of maximum value deviation value D _max (D
/ D _max ) is a predetermined value or less, and an excitation having a second judgment means for producing an output when the value is less than the constant value and a return delay means for delaying the output of the second judgment means by a predetermined time. A digital protective relay, comprising an inrush current countermeasure element, wherein the output of the excitation inrush current countermeasure element blocks the output of the differential protection element. 3. An alternating current for each phase is introduced across a protected object having a plurality of terminals, the introduced alternating current is sampled at constant time intervals and converted into a digital amount, and the converted value is converted. A first determining means for calculating a differential current for each phase by using the digital amount, and for generating an output by determining an internal accident when the amount of electricity based on the calculated differential current is a predetermined value or more. In a digital protective relay provided with a differential protection element having: N of a certain section in one cycle of the calculated differential current.
As a quantity representing the variation (flatness) of the number of instantaneous values _{i m ~i m- (N-1} ), the difference between the N average value of the instantaneous value and the instantaneous value th power x (x = 1, 2 , ..., X) is added to obtain a deviation value by dividing by N, and a ratio (D / I) between the obtained deviation value and the quantity I indicating the magnitude of the calculated differential current is An exciting inrush current countermeasure element having a second judging means for judging whether or not the value is less than or equal to a fixed value and producing an output when the value is less than or equal to the fixed value, and a return delay means for delaying the output of the second judging means by a predetermined time. A digital protective relay, comprising: the output of the excitation inrush current countermeasure element to block the output of the differential protection element. 4. An alternating current for each phase is introduced across a protected object having a plurality of terminals, each of the introduced alternating currents is sampled at a constant time interval and converted into a digital amount, and the converted value is converted. A first determining means for calculating a differential current for each phase by using the digital amount, and for generating an output by determining an internal accident when the amount of electricity based on the calculated differential current is a predetermined value or more. In a digital protective relay provided with a differential protection element having: N of a certain section in one cycle of the calculated differential current.
Number of a standard deviation σ of a quantity representing the variation (flatness) of the instantaneous value _{i m ~i m- (N-1} ), and the value of the the obtained standard deviation σ is whether less than a predetermined value Second determining means for producing an output when the determination is made below a certain value, and the second determining means
Is provided with an excitation inrush current countermeasure element having a return delay means for delaying the output of the determination means of the above for a predetermined time, and the output of the differential protection element is blocked by the output of the excitation inrush current countermeasure element. Digital type protective relay. 5. An alternating current for each phase is introduced across a protected object having a plurality of terminals, the introduced alternating current is sampled at constant time intervals and converted into a digital amount, and the converted value is converted. A first determining means for calculating a differential current for each phase by using the digital amount, and for generating an output by determining an internal accident when the amount of electricity based on the calculated differential current is a predetermined value or more. In a digital protective relay provided with a differential protection element having: N of a certain section in one cycle of the calculated differential current.
The standard deviation σ of an amount representing a number of instantaneous values _{i m ~i m- (N-1} ) dispersion of (flatness), and the the obtained standard deviation σ and the standard deviation σ of the obtained interval Including past 1
Second judging means for judging whether or not the ratio (σ / σ _max ) to the maximum deviation value σ _{max in a} cycle or another constant section within one cycle is a fixed value or less and producing an output when the ratio is the fixed value or less And an excitation inrush current countermeasure element having a return delay means for delaying the output of the second determination means by a predetermined time, and the output of the differential protection element is blocked by the output of the excitation inrush current countermeasure element. A digital protective relay that is characterized by 6. An alternating current for each phase is introduced across a protected object having a plurality of terminals, the introduced alternating current is sampled at constant time intervals and converted into a digital amount, and the converted value is converted. A first determining means for calculating a differential current for each phase by using the digital amount, and for generating an output by determining an internal accident when the amount of electricity based on the calculated differential current is a predetermined value or more. In a digital protective relay provided with a differential protection element having: N of a certain section in one cycle of the calculated differential current.
Number of a standard deviation σ of a quantity representing the variation (flatness) of the instantaneous value _{i m ~i m- (N-1} ), and the size of the the obtained standard deviation σ the calculated differential current Second determination means for producing an output when the ratio (σ / I) with the amount I indicating the value is less than or equal to a certain value and less than or equal to the certain value, and the output of the second determination means for a predetermined time. A digital protective relay, comprising an exciting inrush current countermeasure element having a return delay means for delaying a return, wherein an output of the exciting inrush current countermeasure element blocks the output of the differential protection element. 7. The method according to claim 1, wherein
In the digital protective relay according to the item 1, the operation of the second determining means is activated on the condition that the output of the differential protection element is sent, and the second protection device is activated on the condition that the output of the differential protection element is restored. The excitation inrush current countermeasure element is configured to stop the operation of the determination means, and an operation delay means for delaying the operation of the output of the differential protection element for a predetermined time is added, and by the output of the excitation inrush current countermeasure element. A digital protective relay, characterized in that the output of the operation delay means is blocked. 8. The method according to claim 1, wherein
In the digital protective relay according to the item 1, an operation delay unit that delays the output of the differential protection element for a predetermined time, and a logical product of the output of the differential protection element and the output of the excitation inrush current countermeasure element. A digital protective relay, further comprising a first logical product calculating means, wherein the output of the first logical product calculating means blocks the output of the operation delaying means. 9. The method according to claim 1, wherein
In the digital protective relay described in the paragraph (3), a third judgment unit that produces an output when the magnitude of the calculated differential current changes by a certain value or more, and a delay for restoring the output of the third judgment unit for a predetermined time. A current change width detection element having a second return delay means for activating the second judgment means of the excitation inrush current countermeasure element on condition that the output of the current change width detection element is sent, and A digital protective relay, characterized in that the operation of the second judging means of the excitation inrush current countermeasure element is stopped on condition that the output of the current change width detecting element is restored. 10. The digital protective relay according to any one of claims 1 to 6, wherein any one or all of the terminal currents of the introduced electric quantity of each terminal converted into the digital quantity. Third judging means for producing an output when the magnitude of the terminal current of the device changes by a certain value or more,
And a plurality of current change width detection elements each having a second return delay means for delaying the output of the third determination means by a predetermined time, and at least one of the current change width detection elements has a current The operation of the second determination means of the excitation inrush current countermeasure element is activated on condition that the output of the change width detection element is sent,
Further, the digital protective relay is characterized in that the operation of the second judging means of the exciting inrush current countermeasure element is stopped on condition that all outputs of the respective current change width detecting elements are restored. 11. The digital protective relay according to claim 9 or 10, wherein a second logical product for calculating a logical product of the output of the current change width detection element and the output of the excitation inrush current countermeasure element. A digital protective relay, characterized in that an arithmetic means is added, and the output of the differential protection element is blocked by the output of the second AND arithmetic means. 12. The digital protective relay according to any one of claims 1 to 6, wherein the current output of the second determination means and one cycle or a plurality of cycles of the second determination means. A third logical product calculating means for calculating a logical product with the previous output is added, and the output of the third logical product calculating means is used as an input of the return delay means. Type protective relay. 13. An alternating current for each phase is introduced across a protected object having a plurality of terminals, the introduced alternating current is sampled at constant time intervals and converted into a digital amount, and the converted value is converted. A first determining means for calculating a differential current for each phase by using the digital amount, and for generating an output by determining an internal accident when the amount of electricity based on the calculated differential current is a predetermined value or more. Current value of each electric quantity (mean deviation or ratio of standard deviations, or standard deviation or ratio of standard deviations) in the digital protective relay with differential protection element having And one cycle or a value before a plurality of cycles are compared to obtain the larger value, and it is determined whether the larger value is a certain value or less, and an output is generated when the value is less than the certain value. 2 format And an excitation inrush current countermeasure element having a return delay means for delaying the output of the second determination means by a predetermined time, and the output of the differential protection element is blocked by the output of the excitation inrush current countermeasure element. The digital type protective relay characterized by the above.