JPH11262167A - Proportion differential relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid unnecessary output even if exciting inrush current including DC component occurs at the time of incorporating large capacity load into a power system, by discriminating occurrence of an accident, conducting instantaneous tripping if an absolute value is beyond a preset value, and conducting time tripping if the absolute value is not beyond the preset value. SOLUTION: Respective set values are inputted through an external setting input part 16, and a comparative value (set value for discrimination) with |i1|+|i2| is set as a variable Y. A measured value |i1|+|i2|is computed as a variable X, and the magnitude of the computed value X is compared with that of the setting value Y. In the case of X>=Y, a variable T is taken as 0. In the case of X<Y, the variable T is taken as a value proportional to Y-X. Using i1, i2, and its difference current, proportion discrimination is made by a computing part 14 for proportion discrimination to discriminate presence of transformer failure. In case that accident occurrence is discriminated, instantaneous tripping is outputted from a trip output part (instantaneous) 17 if T=0. The time limit tripping of time T is outputted from a trip output part (time limit) 18 if T≠0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential relay for detecting an accident such as a short circuit in an electric power system.

[0002]

2. Description of the Related Art Ratio differential relays have been widely used to protect power systems. FIG. 6 is a configuration diagram of a power system when a conventional ratio differential relay is used. In FIG. 1, a three-phase AC power supply 1, a transformer primary circuit breaker 4, a transformer 2, and a transformer secondary circuit breaker 5 are sequentially connected. A load (or transformer) side circuit breaker 8 is connected from a lower power system connected to the transformer secondary circuit breaker 5, and a load (or transformer) 9 is further connected.
In this power system, a transformer primary side current transformer 6 and a transformer secondary side are provided between the transformer primary side circuit breakers 4 and 2 and between the transformers 2 and 2 respectively. The current transformer 7 is connected, and a proportional differential relay 31 is provided between the two.

The proportional differential relay 31 measures the magnitude and the phase difference between the current i1 flowing from the transformer primary side current transformer 6 and the current i2 flowing out of the transformer secondary side current transformer 7, and performs the measurement. Based on the result, a cutoff command is output to the transformer primary circuit breaker 4 and the transformer secondary circuit breaker 5.

In such a ratio differential relay 31 that detects an internal accident or the like in the transformer 2 by such an operation, for example, when the transformer secondary circuit breaker 5 and the load circuit breaker 8 are open, the transformer primary When the side circuit breaker 4 is turned on, the main transformer 2 is rapidly excited, and an exciting rush current flows into the primary side of the transformer.

[0005] The excitation inrush current includes a small fundamental wave, a second harmonic, and a DC component, and the current flows into the ratio differential relay 31 only from the transformer primary current transformer 6. In order to prevent malfunction of the ratio differential relay 31 due to the inflow current, in addition to the difference current between the currents i1 and i2 in FIG. When the second harmonic is detected, it is determined that the circuit breaker is closed, and the operation of the relay is suppressed.

On the other hand, when the load-side circuit breaker 8 is turned on while the transformer primary circuit breaker 4 and the transformer secondary circuit breaker 5 are turned on, the load (or transformer) 9 is turned on. Excitation is suddenly performed, and an inrush current is applied to the load (or transformer) 9.
Flows into At the same time, the exciting rush current also flows into the transformer 2. At this time, countermeasures against malfunction of the ratio differential relay 31 are performed in the same manner as described above.

[0007]

When a large-capacity load 9 is incorporated in a system, an exciting rush current flows into the load 9 and a current also flows into the transformer 2 at the same time as in the above case. However, in such a case, the secondary current i1 of the transformer primary current transformer 6 and the secondary current i of the transformer secondary current transformer 7
2, there may be a slight phase shift. On the other hand, the peak value differs depending on the current ratio of the two current transformers 6 and 7 and the voltage ratio of the transformer 2, but has substantially the same current waveform. In this case, the second harmonic component included in the difference current is used. Is significantly reduced. Therefore, at this time, while the difference current is generated, the operation suppression by the second harmonic content is not effective, and the ratio differential relay 31 malfunctions.

Further, one or both of the primary side current transformer 6 and the secondary side current transformer 7 of the transformer 2 are determined by a DC component included in an exciting rush current flowing in the system of the load (or transformer) 9. May be DC-magnetized and saturated, causing a difference current between i1 and i2, causing the ratio differential relay 31 to malfunction.

The present invention has been made in view of such circumstances. For example, even when an inrush current including a DC component is generated when a large-capacity load (or a transformer) is incorporated in a power system, the present invention is not limited thereto. An object of the present invention is to provide a ratio differential relay that can avoid unnecessary output of a trip command and can surely shut off when a deterministic abnormality occurs.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 is based on the first aspect of the present invention, wherein each current value measured on each of a primary side and a secondary side of a protection target by a ratio determining means is first determined. Is determined based on the difference between the two.

On the other hand, the unnecessary operation prevention determining means compares the absolute value of the current value with a predetermined set value, and determines whether or not the absolute value exceeds the set value. When the absolute value of the current value is small, even if it is determined that an accident has occurred based on the difference between the current values, it is not actually an accident,
This is because there may be a mere current fluctuation due to the inrush current. When the absolute value of the current value is also large, there is a high possibility that an actual accident has occurred.

In a situation where the occurrence of an accident and the determination of prevention of unnecessary operation are being performed by the ratio determination means and the unnecessary operation prevention determination means, the occurrence of an accident is determined by these means and the absolute value is set to a set value. When crossing
The instantaneous trip is performed by the instantaneous trip output means. Thus, the protection target is reliably protected.

On the other hand, when it is determined that an accident has occurred and the absolute value does not exceed the set value, the timed trip is performed by the timed trip output means. In this case, there is a possibility that the accident may not actually be an accident. In other words, if the current fluctuation due to the inrush exciting current is reduced and the state in which it is determined that an accident has occurred within the set time period is avoided, no trip output is performed. If the accident occurrence state is not avoided, a trip output is made and the protection target is protected.

As described above, unnecessary output of the trip command can be avoided, and reliable shutoff can be performed when a deterministic abnormality occurs. Next, the invention corresponding to claim 2 is the invention according to claim 1, wherein the absolute value is:
It is the sum of the absolute values of each current value.

Therefore, it is possible to perform more reliable unnecessary operation prevention determination than to determine the current value on either the primary side or the secondary side. According to a third aspect of the present invention, in the first or second aspect of the invention, the timed trip output means performs trip output having a time limit inversely proportional to the absolute value.

If this absolute value is small, it is considered that the object to be protected can be maintained for a certain period of time.
Conversely, if the absolute value is large, it is considered that the object to be protected cannot be kept for a long time. Therefore, a time limit inversely proportional to the absolute value is provided to more appropriately prevent unnecessary operation.

Further, according to a fourth aspect of the present invention, the presence / absence of an accident is determined by the ratio determining means based on a difference between respective current values measured on each of the primary side and the secondary side to be protected. .

On the other hand, the endurance time calculating means calculates the overload endurance time of the protection target based on the current value and the overload tolerance of the protection target. When the ratio determining means determines that an accident has occurred, the timed trip output means performs a timed trip with a time limit within the overload durability time.

Therefore, unnecessary output of a trip command can be avoided, and in the event of a deterministic abnormality, reliable shutoff can be performed, and unnecessary operation corresponding to the overload withstand capability of the protection target can be prevented. can do.
Furthermore, the invention corresponding to claim 5 is based on claims 1-4.
In the invention corresponding to the above, the protection target is a power system transformer.

[0020]

Embodiments of the present invention will be described below. (First Embodiment of the Invention) FIG. 1 is a diagram showing an example of the configuration of a power system to which a ratio differential relay according to a first embodiment of the present invention is applied, and is the same as the conventional device shown in FIG. The same reference numerals are given to the portions, and the detailed description is omitted.

This power system is the same as the conventional FIG. 6 except that the ratio differential relay 3 is a ratio differential relay according to the present invention. In the figure, circuit breakers 4, 5, and 8 are turned on to supply power to a load (or a transformer) 9 via a transformer 2. At that time, a current I flowing through a primary side of the transformer 2 is supplied.
1 is transformed into a current i1 via a transformer primary side current transformer 6. The current I2 flowing on the secondary side of the transformer 2 is transformed into the current i2 via the transformer secondary side current transformer 7. These i
1 and i2 are input to the ratio differential relay 3 of the present embodiment.

The ratio differential relay device 3 applied to such a system will be described. FIG. 2 is a block diagram illustrating a configuration example of the ratio differential relay according to the present embodiment. The ratio differential relay 3 is provided with an input conversion module 11 for converting currents i1 and i2 and inputting the converted current to an analog / digital (A / D) converter 12. | I1 | + | i2 | as a means for determination 1
3. The arithmetic unit for ratio determination 14, the storage unit 15, the external selection input unit 16, the instantaneous trip output unit 17, the timed trip output unit 18, the interface unit 19, and the display LCD unit 20 are connected to the data bus 21.

The ratio differential relay 3 is a computer having a CPU, a memory, and other elements.
Each of the units 13 to 20 connected to 1 is a processing unit as a program module including hardware components and software components of the computer.

Here, the external settling input section 16 outputs | i1 | + | i2 in addition to the set values in the ratio setting and the tap setting.
And accepts an input of a set value or the like for comparison with |, and the storage unit 15 stores these set values, converted currents i1 and i2, and the like.

The display LCD unit 20 is a display device provided in the ratio differential relay device 3, and the interface unit 19 includes i1, i2 stored in the storage module 15.
It receives a request input for outputting various data such as i2 to the display LCD unit 20 and the outside, and serves as an interface for external output.

Next, | i1 | + | i2 |
The calculation unit 14 for determining the ratio 3 and the ratio is a unit that performs a predetermined calculation based on i1 and i2 and determines whether or not to perform a trip output. Here, | i1 | + | i2 |
3 is | i1 | based on the current value stored in the storage unit 5.
+ | I2 | etc. are calculated and | i1 | + | i2 |
On the other hand, the calculation unit for ratio determination 14 determines whether or not an accident has occurred by ratio determination based on the currents i1 and i2.

The instantaneous trip output unit 17 outputs | i1 | + |
i2 | When both the calculation unit 13 for determination and the calculation unit 14 for ratio determination receive notification that the respective set values have been exceeded,
Perform trip output. On the other hand, the timed trip output unit 18
Receives the notification that the set value has been exceeded from only the ratio determining operation unit 14, | i1 | + | i2 |
The time limit setting is performed by | i1 | + | i2 |

Next, | i1 | + | i2 |
A description will be given of a criterion for determining the trip output by the 3 and the ratio determination calculation unit 14. (When performing an instantaneous trip) Before and after the transformer, the current value I
1 and I2 are different from each other.
In step 4, the currents i1 and i2 are multiplied by a predetermined value in consideration of the current transformer ratio generated by the transformer 2, and id = i1 in a normal state.
The currents i1 and i2 are converted and stored in the storage unit 15 so that −i2 = 0 (conversion by tap). Hereinafter, unless otherwise specified, the currents i1 and i2 are assumed to be based on the converted values.

First, the data of the currents i1 and i2 before and after the conversion are always stored in the storage unit 15.
i1 | + | i2 | | I1
| + | I2 | is always | i1 | + |
i2 | is calculated. Then, comparison is made with a previously set value of | i1 | + | i2 | for determination, and the difference between the value of | i1 | + | i2 | and the set value is calculated. If there is no change in current values I1 and I2, | i1 |
The value of + | i2 | should be 0.

In the calculation unit 14 for ratio determination, id = i1-
i2 is calculated, and id / i1 or id / i2 is further calculated.
Is calculated. This calculated value is compared with the set value for ratio determination. If the set value is exceeded, it is highly likely that an actual accident has occurred, and this is set as one of the trip output conditions. This is referred to as detection of an accident or detection and determination of occurrence of an accident in the ratio determination calculation unit 14).

That is, the ratio determining arithmetic unit 14 determines that an accident has occurred, and | i1 | + | i2 |
If it is determined in step 3 that the value of | i1 | + | i2 | is larger than the set value, it is determined that a failure has occurred inside the transformer. In this case, both of the above conditions correspond to the instantaneous trip output unit 17.
And the instantaneous trip output unit 17 outputs a trip command to the circuit breakers 4 and 5.

It should be noted that | i1 | + | i2 |
The reason that the value of | i1 | + | i2 | is used instead of using the value of | i1 | or | i2 | alone in the determination in Step 3 is that the voltage transformation is performed in the determination of only the value of | i1 | This is because there is a risk of making an erroneous determination when an internal failure occurs. For example, when a short circuit accident occurs on the primary side inside the transformer, | i1 | may have a large value, while | i2 | may have an extremely small value.

When the value of | i1 | + | i2 | is larger than the set value, it is determined that an internal fault has occurred in the transformer because the short-circuit current is larger than the rated current. (In the case of performing a timed trip) Next, it is determined that an accident has occurred in the ratio determining arithmetic unit 14, and | i1 | +
If the value of | i1 | + | i2 | is determined to be smaller than the settling value by | i2 | determination operation unit 13, i1 and i
It is determined that a difference current occurs between the two, but does not necessarily mean a failure inside the transformer.

The timed trip output unit 18 having received the judgment to this effect automatically sets a time limit proportional to the difference between the set value and | i1 | + | i2 | each time. , 5 in a timed manner.

If the cause of the fault detection in the ratio determination unit 14 is a DC component included in the exciting inrush current generated when the load (or the transformer) 9 is turned on, the trip command is output from the fault determination for a limited time. The DC component is attenuated
As a result, unnecessary response of the ratio differential relay 3 can be avoided.

In addition, | i1 | + | i2 |
If it is determined in step 3 that the value of | i1 | + | i2 | is smaller than the set value, the reason for providing a time limit proportional to the difference between the set value and | i1 | + | i2 | in the trip output is as follows. It is as follows.

The large difference means that | i1 | + | i
2 | means that the transformer 2 which is to be protected by the ratio differential relay 2 can also be endured for a certain period of time, and conversely, the fact that this difference is small means that | This means that the value of i1 | + | i2 | is large, so that the transformer 2 to be protected by the ratio differential relay 3 cannot be endured for a long time.

Next, the operation of the ratio differential relay 3 according to the embodiment of the present invention configured as described above will be described. FIG. 3 is a flowchart showing the operation of the ratio differential relay of the present embodiment.

First, each set value is input via the external set input unit 16, and the set value is compared with | i1 | + | i2 | (| i
1 | + | i2 | settling value for determination) is set as a variable Y (ST1).

After the setting, each of the input currents i1 and i2 is sampled, and each waveform is calculated (ST2). next,
The measured value | i1 | + | i2 | is calculated as a variable X (S
T3), a magnitude comparison between the calculated value X and the set value Y is performed (ST4).

Here, if X ≧ Y, the variable T is set to 0 (S
T5). On the other hand, if X <Y, the variable T is set to a value proportional to YX (ST6). Then, the above-described ratio determination is performed using i1, i2 and the difference current id thereof (ST7), and the presence or absence of a transformer failure is determined (ST8). If it is not determined that an accident has occurred, the process returns to step ST2.

On the other hand, if it is determined in step ST8 that an accident has occurred, then it is determined whether T = 0 (ST9), and T = 0.
If so, a trip command is output at the time (ST10).
On the other hand, if T ≠ 0, a trip command having a time limit of time T is output in a timed manner (ST11).

As described above, in the ratio differential relay according to the embodiment of the present invention, | i1 | + | i
2 | is determined, and when both of the determination conditions are satisfied, an instantaneous trip is performed. When only the ratio determination condition is satisfied, a timed trip is performed in consideration of the | i1 | + | i2 | value. Even if an inrush current including a DC component occurs when a large-capacity load (or a transformer) is incorporated in a power system, the protection output can be set to an appropriate timed output, and both conditions are satisfied. When a deterministic abnormality occurs, the shut-off can be performed reliably. Therefore,
Unnecessary operation of the ratio differential relay can be avoided.

| I1 | + | i2 | determination operation unit 1
Since the value of | i1 | + | i2 | is used instead of using the value of | i1 | or | i2 | alone in the determination in step 3, it can occur by determining only the value of | i1 | or | i2 |. Erroneous determination can be prevented. However, |
Even if only the value of i1 | or | i2 | is determined, the above effect can be obtained to some extent, and the problem of the related art can be solved. (Second Embodiment of the Invention) In the first embodiment, the instantaneous trip output unit 17
Is provided, and the calculation unit 14 for ratio determination and | i1 | + | i2 |
When each of the determination calculation units 13 exceeds each settling value, an instantaneous trip is performed as a deterministic abnormality occurrence, and when only the accident occurrence condition by the ratio determination calculation unit 14 is satisfied, the time-limited trip is performed.

On the other hand, in the present embodiment, the transformer 2
Always calculates the transformer withstand time, and calculates the ratio determining operation unit 14.
When an accident occurrence condition is satisfied, a timed trip within the transformer withstand time is performed to cope with any accident occurrence detection.

FIG. 4 is a block diagram showing an example of the configuration of a ratio differential relay according to a second embodiment of the present invention. The same parts as those in FIG. Now, only the different parts will be described.

The ratio differential relay 3 of the present embodiment is provided with a transformer durability time calculator 22 instead of the | i1 | + | i2 | determination calculator 13 of FIG.
In addition, a single timed trip output section 18b is provided instead of the timed trip output section 18, and the configuration is the same as that of the first embodiment. In addition to the ratio setting and tap setting, the external setting input unit 16 receives overload capability of a transformer, a current ratio of a primary current transformer, a current ratio of a secondary current transformer, and the like. , And the storage unit 15 and the interface unit 19 can perform information storage, information request input, and output corresponding to the present embodiment, respectively.

Also in the present embodiment, the data of the currents i1 and i2 are always stored in the storage unit 15 and are simultaneously guided to the transformer durability time calculation unit 22. Transformer durability time calculation unit 2
2 is the value of the input currents i1 and i2 (the value before conversion by the tap), the current-input ratio of the transformer primary-side current transformer 6 and the input current of the transformer secondary-side current transformer 7 The current I1 flowing on the primary system of the transformer and the current I2 flowing on the secondary system of the transformer are constantly calculated from the current transformer ratio. Further, from the values of I1 and I2 and the overload withstand capability of the transformer input in advance, T1 (time) = transformer withstand capability / I1 ²
(Or T2 (time) = transformer durability / I2 ² ), and constantly calculates the transformer durability time T (T1, T2), and stores the determined transformer durability time T in the storage unit 15.

When an accident is detected by the ratio determining operation unit 14, the timed trip output unit 18b gives a trip time not more than the transformer durability time T calculated from i1 and i2 inputted at the time of detection. Timed output.

Next, the operation of the thus configured ratio differential relay 3 according to the embodiment of the present invention will be described. FIG. 5 is a flowchart showing the operation of the ratio differential relay of the present embodiment.

First, a set value is input, and the transformer 2
Is set as a variable X, and the primary / secondary current transformers 6, 7 are each input with a current ratio (ST21).

Subsequently, each of the input currents i1 and i2 is sampled, and each waveform is calculated (ST22). next,
System currents I1 and I2 flowing through the primary side and the secondary side of the transformer are calculated from i1, i2 and the current ratio of the transformer primary / secondary current transformers 6, 7, and a transformer is provided for each of I1 and I2. Are calculated (ST23).

The magnitudes of the calculated T1 and T2 are compared (ST24), and if T1 ≧ T2, T = T2 (ST24).
25), if T1 <T2, T = T1 (ST2
6). Next, a normal ratio determination is performed using i1 and i2 and the difference current id thereof (ST27), and the presence or absence of a transformer failure is determined (ST28). If no failure is detected, the process returns to step ST22.

On the other hand, when a failure is detected (ST28),
A trip command having a time limit of time T is output in a timed manner (ST29). As described above, the ratio differential relay according to the embodiment of the present invention has the same configuration as that of the first embodiment, calculates the transformer durability time T, and determines that an accident has occurred. Since the timed trip within the transformer durability time T is performed, the same effect as that of the first embodiment can be obtained. In addition, the factor of the accident detection in the ratio determination unit 14 is caused by the load (or the transformer) 9. If the DC component is included in the excitation inrush current that is generated when the system is turned on, the DC component is attenuated during the timed output of the trip command from the accident determination, and as a result, unnecessary response can be avoided.

The present invention is not limited to the above embodiments, but can be variously modified without departing from the scope of the invention. For example, each unit in each of the above embodiments is configured as a device that performs digital processing, but the present invention is not limited to such a case, and a part or all of the digital processing unit is realized by processing of an analog circuit. You may make it.

The method described in the embodiment may be implemented as a program (software means) that can be executed by a computer (computer), for example, a magnetic disk (floppy disk, hard disk, etc.), an optical disk (CD-ROM, DVD, etc.). ), Stored in a storage medium such as a semiconductor memory, or transmitted and distributed via a communication medium. The programs stored on the medium side include
A software program (including not only an execution program but also a table and a data structure) to be executed by the computer includes a setting program for configuring the computer. A computer that realizes the present apparatus reads a program recorded in a storage medium, and in some cases, constructs software means by using a setting program, and executes the above-described processing by controlling the operation of the software means.

[0057]

As described above in detail, according to the present invention, even when an exciting inrush current including a DC component occurs when a large-capacity load (or transformer) is incorporated into a power system,
Unnecessary output of trip command can be avoided, and
It is possible to provide a ratio differential relay that can reliably shut off when a deterministic abnormality occurs.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a power system to which a ratio differential relay according to a first embodiment of the present invention is applied.

FIG. 2 is an exemplary block diagram showing a configuration example of a ratio differential relay according to the embodiment;

FIG. 3 is a flowchart showing the operation of the ratio differential relay of the embodiment.

FIG. 4 is a block diagram showing a configuration example of a ratio differential relay according to a second embodiment of the present invention.

FIG. 5 is a flowchart showing the operation of the ratio differential relay of the embodiment.

FIG. 6 is a configuration diagram of a power system when a conventional ratio differential relay is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply 2 ... Transformer 3 ... Ratio differential relay 4 ... Transformer primary circuit breaker 5 ... Transformer secondary circuit breaker 6 ... Transformer primary current transformer 7 ... Transformer secondary transformer Current transformer 8 ... Load (or transformer) side circuit breaker 9 ... Load (or transformer) 12-Analog / digital conversion unit 11 ... Input conversion module 13 ... | i1 | + | i2 | Decision operation unit 14 ... Ratio determination Calculation unit 15 Storage unit 16 External selection input unit 17 Instantaneous trip output unit 18 Timed trip output unit 19 Interface unit 20 Display LCD unit 21 Data bus 22 Transformer durability time calculation unit

Claims (5)

[Claims] 1. A ratio judging means for judging occurrence of an accident based on a difference between respective current values measured on each of a primary side and a secondary side of a protection target, and an absolute value of the current value and a predetermined set value. An unnecessary operation prevention determining means for comparing and determining whether the absolute value exceeds a set value; and an instantaneous trip output means for performing an instantaneous trip when it is determined that the accident has occurred and the absolute value exceeds the set value. A timed trip output means for performing a timed trip when it is determined that the accident has occurred and the absolute value does not exceed a set value. 2. The ratio differential relay according to claim 1, wherein the absolute value is a sum of absolute values of the respective current values. 3. The ratio differential relay according to claim 1, wherein said timed trip output means outputs a trip output having a time limit inversely proportional to the absolute value. 4. A ratio judging means for judging occurrence of an accident based on a difference between respective current values measured on each of a primary side and a secondary side of a protection target, the current value, and an overload withstand capability of the protection target. A durable time calculating means for calculating an overload durable time of the protection target based on the time limit trip output means for performing a timed trip with a time limit within the overload durable time when it is determined that the accident has occurred. A ratio differential relay comprising: 5. The ratio differential relay according to claim 1, wherein the protection target is a power system transformer.