JPH09172728A - Digital type overcurrent relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent relay which is not influenced by the overlapping angle of commutation even for a rectangular wave input and has a small error. SOLUTION: A sanpling (an instantaneous value) data (iR, iS, ir ) is obtained from a three-phase rectangular wave current in a P-wave an N-wave extracting part 11 in place of detection by a conventional fundamental wave extraction. The absolute value of the respective instantaneous values of three-phase components is sought and the three-phase addition of the values is performed in a |IP| and |IN| data preparing part 12, thereby obtaining the quantity of electricity (|If =|iR|+|is |+|ir |) corresponding to a DC current in |If | data preparing part 13. It is detected in a decision part 14 that the value |If | becomes not less than the setting value |Ik | of an overcurrent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital type protective relay device, and more particularly to a digital type overcurrent relay used in a protective relay device for an excitation transformer around a generator.

[0002]

2. Description of the Related Art FIG. 10 shows an example of a conventional overcurrent relay 1 applied to an exciting transformer _Tr . The protection purpose of this protection relay is to protect the withstanding capacity of the excitation transformer and thyristor rectifier of the generator field circuit, and FIG. 12 is a diagram for explaining a conventional overcurrent relay. A rectangular wave input (I _U ) as shown in FIG. 11 flows through CT of FIG. 10 and is input to the overcurrent relay 1.

First, the relationship between the input current I _U and the field current (I _dc ) shown in FIG. 10 is shown below. The current (i _UP ) flowing through the thyristor is as follows when the field current (I _dc ) is used.

[Equation 1]

[0004] Next, the transformer direct current (i _U), the value of the fundamental wave contained in the effective value and i _U of using the i _U the field current (I _dc) is as respectively below.

[Equation 2]

Next, the transformer alternating current (I _U ) is expressed by the equation (1) using the field current (I _dc ).

(Equation 3)

The value of the fundamental wave contained in I _U is expressed by equation (2).

(Equation 4)

Next, the operation of the overcurrent relay will be described. Input current (I _U ) input from CT shown in FIG.
Is converted into a digital amount through an analog filter (AF) 2 and an A / D converter 3, and only a fundamental wave component is extracted through a digital filter (DF) 4. This fundamental wave corresponds to I ₁ shown in equation (2). The extracted fundamental wave is subjected to an amplitude value calculation as shown below in the amplitude value calculation unit 5 to calculate an amplitude value | I _f | '.

An amplitude value calculation algorithm that is generally used is shown below as an example.

(Equation 5)

The difference Id (= | I _f | '-| Ia |) between the value | I _f |' calculated by the above-mentioned amplitude value calculation and the set value (Ia) for overcurrent determination in the Id creation unit 6 To calculate. ｜ I
_{When f} | '> | Ia |, the following calculation is performed in the integrated amount ΣId creating unit 7.

ΣId _m = ΣId _m-1 + Id _m (4) where ΣId _{m is the} current integrated amount. ΣId _m-1 : Integrated amount before sampling. Id _m : Current Id amount.

In the judging section 8, the integrated amount ΣId obtained above is calculated.
_{When m} is the condition of Eq. (5), it will be output. This means that the time required to operate varies depending on the magnitude of the input current | I _f | ′. The time characteristics at this time are shown in FIG.

[Formula 7] ΣId _m ≧ k …………………… (5)

[0011]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
_{On the} other hand, in the conventional system, the input amount corresponding to the input amount of the fundamental wave (equation (2) above) 0.78 × I _dc is input. In the actual field circuit, as shown in the circuit of FIG. 14, thyristor 1 (SCR1), thyristor 2
It is assumed that the thyristor 3 (SCR3) is ignited while the (SCR2) is in the ON state and the current I _DC is being supplied to the DC side. When SCR3 is ignited, SCR is generated between power supplies U and V
3 and the short-circuit current i _s flows through SCR1.

[0012] Here, a forward current of SCR1 (i _SCR1) Because represented by i _DC -i _s, i _s is i _DC
When a current equal to is reached, SCR1 extinguishes and i
_s does not increase further. At this time, the path of the output current i _DC shifts from SCR1 to SCR3. This is called the commutation phenomenon from SCR1 to SCR3, and what is expressed in electrical angle is called (commutation) overlap angle (6).
It is expressed by an equation.

(Equation 8)

As described above, the commutation overlap angle changes depending on the power supply voltage, the output voltage, the power supply impedance, and the phase control angle α. The commutation overlap angle (U angle) described above changes from about 26 ° to 13 ° from the measured data. Accordingly, the value of the fundamental wave is 0.764 × I _dc (U angle = about 26 °) to 0.
It becomes equivalent to 798 × I _dc (when U angle = about 13 °), and this becomes a detection error of the relay, and the error of the operating time with respect to 0.78 × I _dc equivalent input becomes large.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a digital overcurrent relay which is not affected by the commutation overlap angle and has a small detection error.

[0015]

A digital overcurrent relay according to claim 1 of the present invention is a three-phase current input (i _R ,
i _S , i _T ) is converted into a digital quantity through an analog / digital converter, and the positive wave (I _PR , I _PS , I _PT ) and the negative wave (I _NR , I _NR , I _NS , I _NT )
P-wave and N-wave extractor for extracting the absolute value of each phase extracted and the three phases are added to obtain | IP |, | IN
| Amount (| IP | = | I _PR | + | I _PS | + | I _PT |, | I
N | = | I _NR | + | I _NS | + | I _NT |) is created | I
P |, | IN | data creation unit and the created | IP
|, | IN | average value of the sum of | I _f | calculates the | I _f |
Creation unit, the created | I _f | and overcurrent set value | I _k
|, And a determination unit for outputting when | I _f | data is equal to or more than the overcurrent set value.

In the digital overcurrent relay according to claim 1 of the present invention, the value | _{if f} | obtained by adding the absolute values of the instantaneous value data of the rectangular wave current input for three phases for three phases is equivalent to the DC current. Become. In order to detect an abnormality in the rectangular wave input for three phases, | i _f | ≧ using the above calculated amount (| i _f |)
| I _k | is determined, and if | if _f | is greater than or equal to | I _k |, the relay outputs.

The digital overcurrent relay according to claim 2 of the present invention is the digital overcurrent relay according to claim 1, wherein | IP | and | IN | created by the | IP | A determination unit that individually compares the value | I _k | and an AND circuit that produces an output when both of the individual determination outputs are greater than or equal to the overcurrent settling value | I _k | . Therefore, the determination formula is | IP | ≧ | I _k |, | IN |
≧ | I _k |.

A digital overcurrent relay according to a third aspect of the present invention is the digital overcurrent relay according to the first aspect, wherein the absolute value of each phase extracted from the P-wave and N-wave extractor is taken to obtain an amplitude value (| I _PR | ' ，
| I _PS | ', | I _PT |' | I _NR | ', | I _NS |', | I
_NT | ′) amplitude value calculation processing unit and the amplitude value 3
Adding the phase components, | IP |, | IN | amount (| IP | '=
| I _PR | '+ | I _PS |' + | I _PT | ', | IN |' = |
I _NR | ′ + | _{IN S} | ′ + | I _NT | ′) | IP
| ', | IN |' data creation unit and the created | IP
Average of sum of | ′ and | IN | ′ | I _f | ′ ((| IP
| I + | IN | ') / 2) for calculating | I _f |' and the above-prepared | I _f | 'and the overcurrent set value | I _k | to compare | I _f |' And a determination unit that outputs when the data is equal to or more than the overcurrent set value.

[0019] the digital overcurrent relay according to claim 4 of the present invention, in claim 1, | I _f | created by creating unit | I _f | overcurrent setting value | I _a | and the difference I and I _d creation unit that creates a _d, integral quantity ΣI by integrating the I _d
The integrated amount calculation unit that calculates _d and the determination unit that compares the integrated amount ΣI _d with a predetermined value K and outputs when the integrated amount is a predetermined value or more are provided. Therefore, the judgment formula is Id _m ≧ K.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining a digital overcurrent relay that detects a rectangular wave. In FIG. 1, a digital overcurrent relay is an analog / digital converter (A / D) 10 that converts a three-phase input electric quantity into a digital quantity, and three-phase input quantities i _R , i _S , and i _T for each phase. of Seinami _{(I PR, I PS, I} PT), Funami (I _NR, I _NS,
I _NT ), a P-wave / N-wave extraction unit 11 and the extracted absolute values of I _PR , I _PS , I _PT , I _NR , I _NS , and I _NT of each phase, and the three phases are added. Then, | IP |, | IN | amount (|
IP | = | I _PR | + | I _PS | + | I _PT |, | IN | = |
I _NR | + | I _NS | + | I _NT |) | IP |, |
IN | Data creation unit 12 and created | IP |, | IN |
Average value of | I _f | (= | I _R | + | I _S | + | _IT |)
To calculate | I _f | data creation unit 13 and created | I _f
It is composed of a determination unit 14 for comparing | and the overcurrent set value | I _k |.

Next, the operation will be described. FIG. 2 is a diagram illustrating a method of calculating a rectangular wave input. In FIG.
(a) Three-phase input quantities i _R , i _S , i _T , (b) Positive wave (I _PR , I _PS , I _PT ) of each phase, Negative wave (I _NR , I _NS , I _NT ). ,
Addition amount of absolute value of positive wave of each phase to (c) | IP | (= | I _PR
| + | I _PS | + | I _PT |), amount of addition of absolute value of negative wave | I
N | (= | I _NR | + | I _NS | + | I _NT |), | I in (d)
P |, | IN | average value of the sum of _{| I f | (= | I} R | + |
I _S | + | _IT |) and overcurrent set value | I _k |.

First, the three-phase input quantities i _R , shown in (a),
When the positive wave component and the negative wave component of each phase are extracted by the P wave N wave extraction unit 11 with respect to i _S and i _T , I _PR , I _PS , I _PT , I _NR , and I in (b).
_NS, it is as I _NT. Here, these I _PR , I _PS , and I
_{PT is set} to | IP |, | IN |
As shown in (c), when the absolute values of I _PR , I _PS , I _PT , I _NR , I _NS , and I _NT are taken and the values are added, a certain amount of DC current equivalent to that shown in (c) is obtained. Electricity becomes | IP |, | IN |.

Next, in the | I _f | data creation section 13, | I _f |
By taking the average value of the sum of P | and | IN |, a | I _f | waveform as shown in (d) is obtained, and the overcurrent set value | I _k | shown in FIG. _If the determination formula | I _f | ≧ | I _k | holds, the relay outputs.

Next, the influence of the commutation overlap angle according to the present detection principle will be described. FIG. 3 is a diagram illustrating a method of calculating a rectangular wave input when the commutation overlap angle is taken into consideration. In FIG. 3, (a) shows three-phase inputs i _R , i _S , and i _T on the field circuit side when the commutation overlap angle is taken into consideration.

Looking at the overlapping angle portion in FIG. 3A, the sum of the falling edge of I _{R and} the falling edge of I _S results in I _dc . Similarly, when I _S and I _T and I _T and I _R are added, it becomes equivalent to I _dc . In a similar idea, showing the (b) to the respective phases in consideration of the commutation overlapping angle Seinami _{(I R, I S, I} T).

As shown in FIG. 4 (b), considering the same as on the field circuit side, the sum of the rising portion and the falling portion of the overlapping angle portion becomes a current equivalent to direct current. As a result, the amount of addition of the absolute value of the positive wave of each phase | IP |
(= | I _PR | + | I _PS | + | I _PT |) is the same as I _dc shown in FIG. 2 (c).

Similarly, on the negative wave side, it becomes the same as I _dc shown in FIG. 2 (c). Average value of the sum of | IP | and | IN | obtained above | I _f | (= | I _R | + | I _S | + | I
_T |) and overcurrent set value | I _k | and comparing | I _f | ≧
If the | I _k | judgment formula is satisfied, the relay outputs.

By using the above method, it is possible to protect the exciting transformer and the thyristor rectifier of the generator field circuit, which is the purpose of protection of the protective relay, and also to protect the rectangular wave input. It is possible to provide an overcurrent relay having a small error without being affected by the flow overlap angle.

According to the present embodiment, the rectangular wave input currents i _R , i _S , and i _T for three phases are input, and the absolute values of the instantaneous values of the positive and negative waves of each phase are calculated as three phases. By adding the positive and negative waves of three phases, the added amount (| IP |, | IN |) becomes equivalent to the direct current, and the calculated amount (| IP |, | IN
│) is used to calculate the average value | I _f │ (= │I _R │
+ | I _S | + | _IT |) is calculated.

This | I _f | is the overcurrent set value | I
_{If k} is larger than _k |, the relay outputs to protect the exciting transformer and thyristor rectifier of the generator field circuit, which is the purpose of protection of this protective relay, and also for rectangular wave input. It is possible to provide an overcurrent relay that is not affected by the commutation overlap angle and has a small error.

FIG. 4 is a block diagram showing another embodiment of the digital type overcurrent relay. In FIG. 4, FIG.
The same parts as those described above are denoted by the same reference numerals and description thereof is omitted. 14 is the | IP |, | IN | individual value of the | IP |, | IN | amount created by the data creation unit 12 and the overcurrent set value | I _k
The determination units 14-1 and 15 that compare | with each other are AND circuits.

Next, the operation will be described. FIG. 5 is a diagram illustrating a method of calculating a rectangular wave input. In FIG.
Fig. 2 shows up to the positive side extracted waveform and the negative side extracted waveform shown in (b).
Is the same as The different part is the judgment content of the judgment unit 14-1. As shown in (c), the positive wave side absolute value three-phase added waveform | IP
| And negative-wave-side absolute value three-phase added waveform | IN | are individually compared with overcurrent set value | I _k |, and | IP | ≧ | I _k |, |
If the judgment formula of IN | ≧ | I _k | is established, the relay outputs.

According to this example, it is possible to realize an overcurrent relay intended to protect the excitation transformer and the thyristor rectifier of the generator field circuit. Moreover, it is possible to provide an overcurrent relay having a small error without being affected by the commutation overlapping angle even with respect to a rectangular wave input.

FIG. 6 is a diagram showing still another embodiment of the digital type overcurrent relay. In FIG. 6, FIG. 1 and FIG.
The same parts as those described above are denoted by the same reference numerals and description thereof is omitted. What is newly added in the present embodiment is the amplitude value calculation processing unit 16, and by the addition of this processing unit, the | IP | ', | IN |' data creation units 12-1 and | I existing thereafter are added.
The calculation contents of the _f | ′ data creation unit 13-1 and the determination unit 14-2 inevitably differed.

Reference numeral 16 denotes an amplitude value calculation processing unit, which is I _PR , I _PS , I _PT , I _{NR of} each phase extracted by the P wave and N wave extracting unit 11.
I _NS, using the value of I _NT, performs amplitude value calculated by the formula showing the data between the half-cycle or one cycle below.

[Equation 9]

Next, the operation will be described. FIG. 7 is a diagram illustrating a method of calculating a rectangular wave input. In FIG.
(a) Three-phase input quantities i _R , i _S , i _T , (b) Positive wave (I _PR , I _PS , I _PT ) of each phase, Negative wave (I _NR , I _NS , I _NT ). ,
In (c), the amplitude value of the positive wave of each phase is calculated, and the absolute value addition amount | IP | '(= | I _PR |' + | I _PS | '+ | I
_PT | '), negative wave amplitude value calculation processing, and absolute value addition amount | IN |' (= | I _NR | '+ | _INS |' + | _INT
| '), (D) is the average of the sum of | IP |' and | IN | '
I _f | ′ and overcurrent set value | I _k | are shown.

First, the three-phase input quantities i _R , shown in (a),
When the positive wave component and the negative wave component of each phase are extracted by the P wave N wave extraction unit 11 with respect to i _S and i _T , I _PR , I _PS , I _{PT of} (b),
I _NR , I _NS , I _NT . Where these I _PR ,
The amplitude value calculation processing unit 16 performs the above-described amplitude value calculation on I _PS and I _PT .

Then, the values are set to | IP | ', | IN |'
In the data creation unit 12-1, as shown in A of (b), I _PR ,
When the absolute values of I _PS , I _PT , I _NR , I _NS , and I _NT are taken and the values are added, a certain amount of electricity | IP | ′ corresponding to the DC current as shown in (c), | IN | '.

Next, in the | I _f | ′ creating section 13-1, | IP
By taking the average value of the sum of | ′ and | IN | ′, (d)
'A waveform, and the overcurrent setting value shown in FIG. | | Is compared _{with, | | I k I f |} ' as shown in | I _f ≧ | I _k
If the | judgment formula is satisfied, the relay will output.

According to this example, it is possible to realize an overcurrent relay intended to protect the excitation transformer and the cycle rectifier of the generator field circuit. Moreover, it is possible to provide an overcurrent relay having a small error without being affected by the commutation overlapping angle even with respect to a rectangular wave input.

FIG. 8 is a block diagram showing still another embodiment of the digital type overcurrent relay. In FIG.
The same parts as those in FIG. What is newly added in the present embodiment is the Id data creation unit 17 and the integration amount creation unit 18, and the determination processing contents of the determination unit 14-3 are different accordingly.

Next, the operation will be described. FIG. 9 is a diagram illustrating a method of calculating a rectangular wave input. In this example, the processing up to the | I _f | data creating unit 13 (up to the waveform of (c) in FIG. 9) is the same as in the case of FIG. In (d) | IP
_||||| | and the overcurrent setpoint | _Ia |
The relationship is shown.

That is, in (e), the difference Id between the | I _f | waveform and the overcurrent set value | I _a | is shown, and the integral amount ΣId corresponding to the shaded area in the figure is obtained by the integration formula described later. The integrated amount ΣId and the determination amount k are compared, and if they are larger, the relay outputs.

As described above, by adding the absolute values of the positive and negative waves of the instantaneous value data of the rectangular wave current input for the three phases, the positive and negative waves of the three phases are added. The added amount (IP |, | IN |) corresponds to the DC current. In order to detect an abnormality in the rectangular wave input for three phases, the calculated value (IP |, | IN |) is used and its average value | I _f |
(= | I _R | + | I _S | + | I _T |) is calculated and | I _f
The difference Id between | and the overcurrent setting value | I _a | is calculated, and the integrated amount ΣId thereof is calculated as follows.

[0045]

[Formula 10] ΣId _m = ΣId _m-1 + Id _m where ΣId _{m is the} current integrated amount. ΣId _m-1 : Integrated amount before sampling. Id _m : Current Id amount. The data calculated above is used to determine ΣId ≧ k (k: constant), and if the integrated value ΣId is equal to or greater than the k value, the relay outputs. By adding this embodiment to the above-mentioned embodiment, it is possible to realize the anti-time limit characteristic.

By using the above method, it becomes possible to protect the excitation transformer and the thyristor rectifier of the generator field circuit, which is the purpose of protection of this protective relay, and commutation overlap occurs even for rectangular wave input. It is possible to provide an overcurrent relay that is not affected by corners and has a small error.

[0047]

As described above, according to the present invention, 3
By inputting the rectangular wave input processing i _R , i _S , and i _T for three phases, and adding the absolute values of the instantaneous values of the positive and negative waves of each phase by three phases, Negative wave added amount (IP |, |
IN |) corresponds to the DC current, and the calculated amount (IP
|, | IN |) is used to calculate the average value | I _f |
(= | I _R | + | I _S | + | _IT ) is calculated and | I _f |
Is larger than the overcurrent set value | I _k |, the relay outputs to protect the excitation transformer and the thyristor rectifier of the generator field circuit, which is the purpose of protection of this protective relay, and the rectangular shape. It is possible to provide an overcurrent relay that is not affected by the commutation overlapping angle even with respect to wave input and has a small error.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a digital overcurrent relay of the present invention.

FIG. 2 is a waveform diagram illustrating the processing content of FIG.

FIG. 3 is a waveform diagram illustrating a method of calculating a rectangular wave input in consideration of a commutation overlap angle.

FIG. 4 is a block diagram showing another embodiment.

FIG. 5 is a waveform diagram illustrating the processing contents of FIG.

FIG. 6 is a block diagram showing another embodiment.

FIG. 7 is a waveform diagram illustrating the processing content of FIG.

FIG. 8 is a block diagram showing another embodiment.

FIG. 9 is a waveform diagram illustrating the processing content of FIG.

FIG. 10 is a transformer system diagram to which an overcurrent relay is applied.

Fig. 11 AC current (I _U ) and DC current (i _U ) of the transformer
FIG.

FIG. 12 is a block diagram of a conventional overcurrent relay.

FIG. 13 is a diagram showing characteristics of a conventional overcurrent relay.

FIG. 14 is a diagram illustrating a commutation overlap phenomenon.

[Explanation of symbols]

1 Digital type overcurrent relay 2 Analog filter 3,10 A / D (analog / digital conversion part) 4 Digital filter 5 Amplitude value calculation part 6 Id creation part 7 Integrated amount creation part 8,14 Judgment part 11 P wave, N wave Extraction unit 12 | IP |, | IN | Data creation unit 13 | I _f | Data creation unit 15 Logical product 16 Amplitude value calculation processing unit 17 Id data creation unit 18 ΣId integrated amount creation unit

Claims (4)

[Claims] 1. A three-phase current input (i _R , i _S , i _T ) is converted into a digital amount through an analog / digital converter, and a positive wave (I _{PR) of} each phase is converted from the input waveform of these three phases. , I
_PS , I _PT ), P for extracting negative waves (I _NR , I _NS , I _NT )
Wave and N wave extractor and the absolute values of the extracted phases are added, and the three phases are added to calculate | IP |, | IN | amount (| I
P | = | I _PR | + | I _PS | + | I _PT |, | IN | = | I
_NR | + | I _NS | + | I _NT |) | IP |, | I
N | Data creation unit and the created | IP |, | IN |
Average value of the sum of | I _f | calculates the | I _f | is compared with, | | a creation unit, the created | I _f | overcurrent setting value | I _k I _f | data overcurrent settling A digital type overcurrent relay, comprising: a determination unit that outputs when the value is greater than or equal to a value. 2. A three-phase current input (i _R , i _S , i _T ) is converted into a digital quantity through an analog / digital converter, and a positive wave (I _{PR) of} each phase is converted from these three-phase input waveforms. , I
_PS , I _PT ), P for extracting negative waves (I _NR , I _NS , I _NT )
Wave and N wave extractor and the absolute values of the extracted phases are added, and the three phases are added to calculate | IP |, | IN | amount (| I
P | = | I _PR | + | I _PS | + | I _PT |, | IN | = | I
_NR | + | I _NS | + | I _NT |) | IP |, | I
N | Data creation unit and the created | IP |, | IN |
And an overcurrent settling value | I _k | individually, and both of the individual determination outputs are the overcurrent settling value | I _k |
And a logical product circuit that produces an output when it is detected that I _k | 3. A three-phase current input (i _R , i _S , i _T ) is converted into a digital amount via an analog / digital converter, and a positive wave (I _{PR) of} each phase is converted from these three-phase input waveforms. , I
_PS , I _PT ), P for extracting negative waves (I _NR , I _NS , I _NT )
Wave and N wave extractor and the absolute values of the extracted phases are used to obtain amplitude values (| I _PR | ', | I _PS |', | I _PT | '| I _NR
│ ', _{│I NS} │', │I _NT │ ') and the amplitude value calculation processing unit for the three phases of the amplitude value are added to obtain | IP |, |
IN | Amount (| IP | ′ = | I _PR | ′ + | I _PS | ′ + | I
_PT | ', | IN |' = | I _NR | '+ | I _NS |' + | I _NT
| IP | ', | IN |' data creating section and the average value of the sum of the created | IP | ', | IN |' | | _f | '((| IP |' + | IN | ') / 2) to calculate the | I _f |''compared with the, | | overcurrent setting value | | I _k I _f |' a creation unit, the created | I _f data overcurrent A digital-type overcurrent relay, comprising: a determination unit that outputs when the value is equal to or greater than a set value. 4. A three-phase current input (i _R , i _S , i _T ) is converted into a digital quantity via an analog / digital converter, and a positive wave (I _{PR) of} each phase is converted from these three-phase input waveforms. , I
_PS , I _PT ), P for extracting negative waves (I _NR , I _NS , I _NT )
Wave and N wave extractor and the absolute values of the extracted phases are added, and the three phases are added to calculate | IP |, | IN | amount (| I
P | = | I _PR | + | I _PS | + | I _PT |, | IN | = | I
_NR | + | I _NS | + | I _NT |) | IP |, | I
N | Data creation unit and the created | IP |, | IN |
Average of sum of | I _f | (= (| IP | + | IN |) /
2) to calculate the | I _f | a creation unit, and the created | I _f
| An overcurrent setting value | I _a | to create a difference I _d and I _d
A creating unit, an integration amount calculating unit for calculating the I _d integrated to the integrated amount .SIGMA.I _d, comparing the integrated amount .SIGMA.I _d and the predetermined value K, outputs when integrated amount is equal to or greater than the predetermined value determination And a digital type overcurrent relay.