JP2005184956A - Electric feeder line protection method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately discriminate an accident in a protected section at high speed in a power station without a transmission path exclusive for a relay. <P>SOLUTION: The general-purpose transmission path 24 such as 9.6 kbps or 64 kbps is provided between protection devices 31, 32 of the power station. The presence or the absence of a short circuit accident in a protected section is discriminated by transmitting/receiving a positive phase current between opposite terminals in a normal state after detecting a bus bar voltage and a current by a voltage transformer 41 and current transformers 43, 44 in the protection device 31(32). A ground fault current instead of the positive phase current is transmitted during the occurrence of a ground fault accident. A differential current protection system having high section discriminating capability is applicable. It is possible to protect an electric feeder line at high speed and with excellent accuracy during the occurrence of an electric feeder line accident. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a protection device for a transmission line, and relates to a protection method that enables normal response using a general-purpose transmission line when a transmission line fails.

  A conventional power transmission line protection relay uses a relay-dedicated transmission line (for example, 54 kbps) to perform a differential current calculation using each phase current and zero phase current at its own end and each phase current and zero phase current at the other end. When the difference current exceeds a certain value (settling value), a differential current protection method is implemented in which an accident in the section is detected and the circuit breaker of the transmission line is cut off.

  Recently, however, the number of power transmission systems that do not have a dedicated relay transmission line has increased, and the transmission line for applying the above-mentioned differential current protection method has been stagnant due to the restrained capital investment of communication equipment. Despite being a protection method with high discrimination ability, it is difficult to apply.

  An object of the present invention is to provide a power transmission line protection device for accurately and quickly discriminating an accident in a protection section using a general-purpose transmission line such as 9.6 kbps and 64 kbps between electric stations without communication equipment dedicated for relays. It is in.

  In order to achieve the above object, the present invention provides a power transmission line protection method for detecting a power transmission line accident using a differential current protection method and protecting the corresponding protection section. Thus, the transmission data based on the two instantaneous values adjacent to each other in the positive phase current is always transmitted and received, and when the short circuit of the corresponding protection section is determined, the circuit breaker is opened. The data is transmitted through a general-purpose transmission line such as 9.6 kbps or 64 kbps.

  In addition, when a ground fault is detected, a zero-phase current is transmitted and received instead of the positive-phase current, and the circuit breaker in the corresponding protection section is opened.

  The transmission data of the two instantaneous values is compressed by the a-Law method. The transmission data is verified by a CRC verification method.

  The power transmission line protection device of the present invention is provided with a circuit breaker and a protection device for each protection section of the power transmission system, detects a power transmission system fault by a differential current protection method, and protects the power transmission line. A general-purpose transmission line is provided between the protection devices at the other end, and a communication means for transmitting and receiving transmission data based on a positive phase current is provided in the protection device at all times, and short-circuit difference current calculation is performed. The positive phase current is two instantaneous values at 60 degree intervals adjacent to each other.

  When the protective device detects a ground fault, the protective device is provided with switching means for switching the positive phase current to a zero phase current for transmission. At this time, a transient response timer is provided to satisfy the ground fault transient response time limit.

According to the present invention, an accident in a protection zone is detected with a small transmission amount (current information). At all times, the positive phase current that is the calculation result of IA + aIB + a ² IC is transmitted (a: vector parameter). In the event of a short circuit accident, transmission of positive phase current is continued, and internal / external (own end, other end) accident discrimination is performed. A voltage relay or the like is always used to determine whether there is a short-circuit fault or a ground fault. When a ground fault is detected, the positive phase current transmission is switched to the zero phase current for transmission.

  In order to make the device finishing time at the time of the ground fault accident the same as that of the conventional current differential relay, a timer (about 20 ms) is installed so as to satisfy the transient response time limit (50 ms) at the time of the conventional ground fault accident.

  As transmission monitoring, a CRC verification method with high error detection accuracy is applied to improve transmission monitoring capability. If there is other transmission data (information), CRC 12 may be used.

  According to the present invention, a current differential protection method with high section discrimination capability can be applied using the general-purpose transmission line even between electrical stations without a relay-dedicated transmission line (54 kbps, etc.). It can be protected with high accuracy.

  FIG. 1 is a single line diagram showing a three-phase AC power transmission system to which the present invention is applied, and this example shows a two-terminal system. The power transmission system in FIG. 1 has three-phase AC power supplies 11 and 12, terminals A and B are power supply terminals, and terminals A and B are connected by a power transmission line 21. When the circuit breakers 22 and 23 are “ON”, the power transmission line 21 is connected to the power supply system.

  The power transmission line protection device of the present invention takes in the voltage of the bus line by the voltage transformers 41 and 42 connected to both ends of the power transmission line 21, and takes in each phase current by the current transformers 43 and 44, respectively. An operation is performed to determine whether is a short circuit or a ground fault.

  When an accident occurs in the transmission line 21, the protection devices 31 and 32 calculate the vector sum of the current flowing from the A end and the current flowing from the B end by the differential current protection method, and if IA−IB = 0 is not satisfied. It is determined that the power transmission line has failed, and the circuit breakers 22 and 23 are set to “OFF”.

  A general-purpose transmission line 24 such as a general-purpose 9.6 kbps or 64 kbps is connected between the A terminal and the B terminal connected by the power transmission line 21. Although a two-terminal system is shown here, a multi-terminal system may be used.

  FIG. 2 is a block diagram showing the configuration of the protection device. The protection device 31 (the protection device 32 also has the same configuration) calculates the positive phase current I1 from the phase currents Ia, Ib, Ic measured by CT43, CT44 at all times. This positive phase current is transmitted as current data to the counterpart terminal through the general-purpose transmission line 24, receives current data from the counterpart terminal, performs a differential current calculation by the 87S relay, and detects a short circuit accident in the transmission line 21.

The positive phase current calculation means 51 calculates the positive phase current I1 from the currents Ia, Ib, and Ic of each phase according to the equation (1). Here, a and a ² are vector operators, which indicate that a: 120 degrees and a ² : 240 degrees are advanced.
I1 = Ia + aIb + a ² Ic (1)
The positive phase current to be transmitted transmits two instantaneous values adjacent to each other with an electrical angle of 60 degrees, that is, positive phase currents having instantaneous values of (t−1) and (t0). This is to transmit 120 degree data of a sine wave at a time. Note that when the sine wave exceeds 180 °, the phase calculation as a relay may exceed one period and an erroneous calculation may be performed. Therefore, the sine wave is set to 120 °.

When a ground fault is detected by the voltage transformer 41, the positive phase current is switched to the zero phase current and transmitted. The zero-phase voltage V ₀ is a vector sum of each phase voltage as shown in the equation (2), and is usually 0 or in the vicinity thereof. However, since the ground fault phase voltage is lowered during a ground fault, the zero phase voltage V ₀ becomes unbalanced. voltage _{V 0} exceeds a predetermined voltage.
V ₀ = Va + Vb + Vc (2)
When a ground fault is detected by the accident determination section 53, by switching the switching means 54, zero-phase current I ₀ in place of the positive phase current I1 is transmitted.

The zero-phase current I ₀ is a vector sum of each phase current as shown in the equation (3). Usually, it is 0 to the vicinity thereof, but during a ground fault, the current in the ground fault phase increases, resulting in an unbalance, and the ground fault current I ₀ exceeds a certain value.
I ₀ = Ia + Ib + Ic (3)
Note that a zero-phase current may be transmitted at all times in a system such as a cable system where there is no possibility of occurrence of a short circuit accident.

  On the other hand, when transmission data is received from the other end, the 87S relay and 87G relay in FIG. 2 operate as follows. The 87S relay detects the difference current between the positive phase currents at its own end and the other end, and outputs a trip command to the corresponding circuit breaker if the difference current exceeds a predetermined value. The 87G relay detects a difference current between itself and other zero-phase currents, and outputs a trip command to the circuit breaker if it exceeds a predetermined value.

  FIG. 3 shows a format of transmission data. The head is a frame synchronization bit, and then there are two current bits, one bit indicating a break every 6 bits. Normally, the binary data of the positive phase current with electrical angle of 60 ° is transmitted, and when the ground fault is judged, the binary data of the zero phase current with electrical angle of 60 ° is put on this positive phase current part, To transmit. Also, determination information (“ground fault” in the figure) as to whether a positive phase current or a zero phase current is transmitted is transmitted to the other end. (1) and (4) after “Ground fault” are sub-communication data (a plurality of data are transmitted at a rate of once every several times), and CB information (“OFF” or “ON”) and The format is used to transmit device health conditions.

  The amount of current data 1 is 12 bits (a digital amount of 2 12 bits). However, in order to send data in the range of 120 ° electric sine wave (total number of bits: 53 bits), it is necessary to send 1 amount of current data in 8 bits, considering the CRC test. In this embodiment, compression is performed by the a-Low method or the μ-Low method, and one amount of current data is transmitted as 8-bit data. Although this compression makes it difficult to detect the ground fault phase, the presence or absence of a ground fault can be determined. Of course, if a higher-speed general-purpose transmission line (for example, 64 kbps) is used, there is no need for such data compression.

Since CRC verification requires 16 bits, the transmission format is divided into CRC1 to CRC4 and transmitted. For CRC 16, CRC test expression becomes ^{X 16 + X 12 + X 5} +1. In CRC verification, transmission / reception data (transmission data) is divided by a CRC verification formula, and the remainder is transmitted. This enables transmission monitoring with high error detection accuracy.

  FIG. 4 shows a transient response countermeasure circuit when a ground fault is detected. Conventionally, in a ground fault, the circuit breaker is tripped 50 ms after detection. Also in this embodiment, in order to set the same time as the device finishing time of the conventional current differential relay, the value of the transient response time timer at the time of the ground fault is changed and installed.

  (A) is a conventional transient response countermeasure circuit. Since there is a high possibility that the ground fault relays 87G relay, 64 relay, etc. will operate unnecessarily when an accident occurs, an accident detection signal (interruption) once after a delay time of 50 ms after operation. ) Is output. Also, since the 87G relay input is transmission information, and an unnecessary operation occurs due to an abnormality on the transmission side, there is a possibility that the circuit breaker will be cut off and a power failure may occur. Treated. Further, in order to prevent both the short-circuit and ground fault indications from appearing in the case of fault type discrimination (short circuit) of two or more lines, the ground fault cutoff is locked by 27 relays which are undervoltage relays. (B) is the current transient response countermeasure circuit according to the present embodiment, and the input of the logic circuit includes the reception of the ground fault from the other end. This ground fault reception is delayed by about 30 ms from the prior art because the positive phase current is switched to the zero phase current and transmitted after the short circuit / ground fault determination. Therefore, the transient response time limit is set to 20 ms (50-30), and measures are taken so as not to cause a finishing time delay due to short circuit / ground fault discrimination.

  FIG. 5 is a flowchart showing an embodiment of the processing procedure of the present invention. It is processed by a computer provided by the protection device 31 (32).

  Step 51 is monitoring of the state of the power transmission line. When there is no accident, the transmission of the positive phase current is continued by step 57. Step 52 is a case where a short circuit accident occurs in the power transmission line, and since it is possible to determine an in-section accident based on the positive phase current, transmission of the positive phase current is continued. In step 53, a short circuit accident in the transmission line section is determined, and in step 54, the corresponding circuit breaker is interrupted.

  In step 55, a ground fault is determined based on the voltage element, and when the ground fault occurs, the amount of electricity to be transmitted is switched from the positive phase current to the zero phase current for transmission. In step 56, a ground fault in the transmission line section is determined, and the circuit breaker is shut off.

  In this process, the difference current relay calculation may be performed at each terminal, or the difference current calculation may be performed at the representative end and the calculation result may be transmitted to another terminal.

  As described above, according to the present invention, power transmission line protection using a general-purpose transmission line such as 9.6 kbps and 64 kbps can be performed even between electric stations that do not have communication equipment dedicated for relays.

1 is an overall configuration diagram of a power transmission line protection device according to an embodiment of the present invention. The block diagram which shows one Example of a protective device. Explanatory drawing which shows the format of transmission data, and switching of positive phase current / zero phase current. Explanatory drawing which shows a ground fault transient response circuit typically. The flowchart which shows the process sequence of a power transmission line protection apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11,12 ... Power supply end, 21 ... Power transmission line, 22, 23 ... Circuit breaker (CB), 24 ... General purpose transmission line, 31, 32 ... Power transmission line protection relay, 41, 42 ... Voltage transformer, 43, 44 ... Variable Current source 51... Positive phase current calculation unit 52. Zero phase current calculation unit 53. Accident determination unit 54.

Claims (8)

In the transmission line protection method that detects the accident of the transmission line by the differential current protection method and protects the corresponding protection section,
When the self-protection device always sends / receives transmission data based on the two instantaneous values of the positive phase current adjacent to the protection device at the other end, and determines a short circuit in the corresponding protection section based on the positive phase current A method for protecting a transmission line, characterized in that the circuit breaker is opened.   The transmission line protection method according to claim 1, wherein when a ground fault is detected, a zero-phase current is transmitted and received instead of the positive-phase current, and a circuit breaker in the corresponding protection section is opened.   3. The transmission line protection method according to claim 1, wherein the transmission data of the two instantaneous values is compressed by an a-Law method.   3. The transmission line protection method according to claim 1, wherein the transmission data is verified by a CRC verification method. In the transmission line protection device that protects the transmission line by providing a circuit breaker and a protection device for each protection section of the transmission system, detecting an accident in the transmission system by the differential current protection method,
A transmission line protection characterized in that a general-purpose transmission line is provided between the protective device at its own end and the other end, and communication means for transmitting and receiving transmission data by a positive phase current is provided to the protective device at all times, and short-circuit difference current calculation is performed. apparatus.   6. The transmission line protection device according to claim 5, wherein the positive phase current is two instantaneous values at intervals of 60 degrees adjacent to each other.   7. The transmission line protection device according to claim 5, wherein the protection device is provided with a switching means for switching the positive phase current to a zero phase current when a ground fault is detected. 8. The transmission line protection device according to claim 7, wherein the protection device includes a transient response timer for satisfying a ground fault transient response time limit.

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