JPH04312315A - Current differential relay unit - Google Patents

Abstract

PURPOSE:To prevent erroneous function of current differential relay by clearly discriminating between secondary discontinuity fault of current transformer and internal fault of transmission line. CONSTITUTION:A logic circuit makes a decision of secondary discontinuity fault of a current transformer for detecting current at this end based on outputs from overcurrent detecting circuits 12, 13 at this end and counterpart end, and then prohibits output from a differential decision circuit 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current differential relay device used to detect internal failures in power transmission lines and protect the power transmission line system.

0002

[Prior Art] Figure 6 shows, for example, the Institute of Electrical Engineers of Japan University Course, Protective Relay Engineering (published July 20, 1980), published by the Institute of Electrical Engineers of Japan.
Section 8.2.3, Carrier current differential relay system, 150-154
The conventional current differential relay device shown on page (hereinafter referred to as
This is a block diagram (abbreviated as relay), and in the figure, 1
2 is a power transmission line, and 2 is a current transformer (C) that converts the current flowing through power transmission line 1 into an appropriate amount as a relay input
T), 3 is the relay body. Also, this relay body 3
, 4 is an input transformer (I/V) that inputs the secondary current of the current transformer 2 and converts it into an appropriate voltage; 5
6 is a bandpass filter (BPF) that extracts the commercial frequency of the system from the output of the input transformer 4, and 6 is an analog/digital converter (
A/D), 7 is a transmission communication coupling circuit for transmitting the digital data to the other end relay, 8 is a reception communication coupling circuit for receiving the digital data transmitted from the other end relay, and 9 is the other end relay. A delay circuit that delays own-end data in order to synchronize end data with own-end data, and 10 a differential determination circuit that inputs temporally synchronized own-end data and opposite-end data and performs current differential calculation. If the calculation result indicates an internal failure in the power transmission line, the differential determination circuit 10 outputs a relay output.

Reference numeral 11 denotes a communication device, which is coupled to the transmitting communication coupling circuit 7 and the receiving communication coupling circuit 8 in the relay main body 3, and transmits data to the communication device of the other end relay via a microwave line. Have an exchange. Note that although this figure shows a circuit that inputs one phase of current flowing through the power transmission line 1 and performs transmission and relay calculations, it is actually performed for three phases of current.

Next, the operating principle of the current differential relay will be explained with reference to FIG. Now, (a) is the reference for the current direction, (b)
is the current direction when it is healthy, (c) is the current direction when there is an external fault,
Assuming that (d) indicates the current direction at the time of an internal fault, the sum of currents at both the transmitting and receiving ends A and B will be zero if the power transmission line is healthy. That is, IA +IB =0. Conversely, if IA +IB ≠0, it may be determined that there is an internal fault in the power transmission line, and this is the basis of the current differential principle. Therefore, the differential determination circuit 10 performs a current differential calculation on the own end data and the opposite end data, and if the calculation result is an internal failure in the power transmission line 1, the differential determination circuit 10 outputs a relay operation output.

[0005]

[Problems to be Solved by the Invention] Since the conventional current differential relay device is constructed as described above, in the event of a failure such as a disconnection on the secondary side of the current transformer 2, which is not an internal failure of the power transmission line 1, the disconnection side Since the current input to the relay body 3 is lost, if a load current is flowing through the power transmission line 1, the sum of the currents at both ends of the power transmission line 1 will be generated as the load current. There were issues such as misdiagnosis of internal accidents and malfunctions.

[0006] This invention was made in order to solve the above-mentioned problems, and it is possible to prevent a current transformer secondary side disconnection from being mistakenly determined to be an internal fault in a power transmission line. The purpose is to obtain a differential relay device.

[0007]

[Means for Solving the Problems] A current differential relay device according to the present invention includes a self-end overcurrent detection circuit that detects a self-end zero-phase overcurrent or a self-end individual phase overcurrent based on the self-end current;
A partner end overcurrent detection circuit is provided which detects a partner end zero-phase overcurrent or a partner end each phase overcurrent based on the partner end current, and each output of the own end overcurrent detection circuit and the partner end overcurrent detection circuit is Basically, the logic circuit determines whether there is a secondary disconnection failure in the current transformer for self-terminal current detection, and the output of the differential determination circuit is prohibited.

[0008]

[Operation] In the self-end overcurrent detection circuit and the opposite end overcurrent detection circuit in this invention, when a secondary breakage failure occurs in the current transformer at each end, an output signal is output at the broken end, but not at the non-broken end. . On the other hand, when a power transmission line fails, it is determined whether or not output signals are output from both ends, so that it can be clearly distinguished from the above-mentioned secondary disconnection failure.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 12 is a zero-sequence overcurrent element of a zero-sequence current as a self-end overcurrent detection circuit that calculates the vector sum of the three-phase currents at the other end, and 13 represents the vector sum of the transmitted three-phase currents at the other end. 14 is an exclusive OR circuit that outputs an exclusive OR signal of the output of each overcurrent element 12 and 13; 15 is an exclusive logic This is an AND circuit with an inhibit function that blocks relay operation output from the differential determination circuit 10 using the output signal of the summation circuit 14.

Next, the operation will be explained. The differential determination circuit 10 performs current differential calculation between own end data and opposite end data, and when there is an internal failure in the power transmission line 1, the operation of outputting a relay operation output is completely different from that of conventional current differential relay devices. are the same. In other words, the relay operation output is output when the sum of currents at both the transmitting and receiving ends is not zero, and specifically, when the current value is above a certain level (relay operation sensitivity current value),
It is determined that the above internal failure has occurred.

On the other hand, the zero-sequence currents at the own end and the opposite end are as follows depending on the presence or absence of a failure. That is, power transmission line 1
And when there is no failure in the current transformer 2 (in steady state), no zero-sequence current is generated. Furthermore, if the power transmission line 1 has a ground fault, zero-sequence current will be generated at both the transmitting and receiving ends, and if there is a short circuit, no zero-sequence current will be generated at both the transmitting and receiving ends. Further, when the current transformer 2 has a secondary disconnection, if a load current is flowing through the power transmission line on the disconnection side, a zero-sequence current corresponding to the load current is generated.

Furthermore, the detection setting value K of the zero-sequence overcurrent elements 12 and 13 newly provided for zero-sequence current detection is set to be higher in sensitivity than the differential relay operation sensitivity current value. Therefore, the differential determination circuit 10 and the zero-sequence overcurrent element 12 as described above
. can be activated and the relay operation output can be prevented from being output by mistake. FIG. 2 shows the operating status of such a differential determination circuit and zero-sequence overcurrent elements 12 and 13 at both ends A and B. In other words, when the load current is large (greater than the relay operation sensitivity current value) during the secondary disconnection of the current transformer 2, the differential determination circuit 10 attempts to malfunction, but at this time, for example, a zero-sequence overcurrent on the secondary disconnection side The element 12 is already operating, and the zero-sequence overcurrent element 13 on the non-disconnection side, for example, is not operating because no zero-sequence current is generated.
The exclusive OR circuit 14 outputs a signal, and this signal blocks the relay operation output of the differential determination circuit 10 in the AND circuit 15 with inhibit.

[0013] In the above embodiment, the zero-sequence overcurrent element 12
, 13 is shown, but in a power transmission line with power supplies at both ends, a reverse phase overcurrent may be used. This is because a negative phase component occurs when the secondary disconnection occurs in the current transformer 2, and when a failure occurs, a negative phase component either occurs or does not occur at both the transmitting and receiving ends, and the same effect occurs on the transmission line. It is possible to prevent misjudgment of internal accidents.

Furthermore, in the above embodiment, the zero feed overcurrent element 12
, 13 is shown, but it may also be constructed using overcurrent elements for each phase. FIG. 3 shows this configuration. The overcurrent element determination block P, which is a portion indicated by a dotted line in this figure, corresponds to the portion indicated by a dotted line in FIG. Here, 16 to 18 are overcurrent elements of each phase at the own end as an overcurrent detection circuit at the own end;
Reference numerals 19 to 21 designate overcurrent elements for each phase of the opposite end as overcurrent detection circuits, each of which detects a current equal to or higher than a set value K and produces an output. 22a to 22f are AND circuits. In this embodiment, the relay operation output from the differential determination circuit 10 is allowed only when current flows simultaneously to the own end and the opposite end, and if the current transformer 2 at one end has a secondary disconnection, the terminal Since the relay input current is eliminated, the output of the relay operation output due to the secondary disconnection can be prevented. In addition, when power transmission line 1 fails, if there is a power source at both ends, current will flow from both ends to the fault point, so the overcurrent element of the faulty phase will generate a relay operation output at both ends, ensuring reliable relay operation. becomes.

[0015] Furthermore, if one end of the power transmission line 1 is a non-power source (load), there may be no current at that load end, so relay operation may be blocked, and this needs to be taken into consideration. There is. FIG. 4 is an example of a circuit applied in this case. Focusing on the fact that the voltage drops at the load end when the transmission line 1 fails, in addition to the overcurrent element determination block P in FIG.
An undervoltage element 23 is added, and the output of the overcurrent element of the above embodiment is logically summed by OR circuits 25a to 25c to gate the output of the differential determination circuit 10. Here, 23 generates an output signal when the transmission line voltage signal obtained from the transmission line 1 via the voltage transformer 2 is below a certain set value, and does not generate an output under normal conditions. It is configured to produce an output in the event of a failure. Furthermore, this output signal is configured to be transmitted to the other end, and the OR circuit 24 calculates the logical sum of the outputs of the respective undervoltage elements 23 at the own end and the other end, so that it also operates at the load end. It has the feature that it always works even when there is no power supply.

In this case, even if the undervoltage element 23 does not have the overcurrent element of the above embodiment, it is possible to prevent malfunctions due to the secondary disconnection of the current transformer 2, but even this secondary disconnection will cause the voltage to drop. Therefore, if the distance of the power transmission line 1 is long and the impedance on the power supply side at both ends is large, even if a failure occurs inside the power transmission line 1, the voltage may not drop much. Therefore, in this case, operation due to overcurrent elements can be expected.

Furthermore, in the above embodiment, the zero-sequence overcurrent element 1
2 and 13 are used, but this takes advantage of the fact that even if one end is not powered, the zero-sequence is normally grounded, so even in the event of a ground fault, zero-sequence current will flow at both ends. , in a system where the zero-sequence impedance on the power supply side is extremely small compared to the impedance on the load side from the point of failure,
The zero-sequence current flowing to the load end becomes small, and the zero-sequence overcurrent element at the load end does not operate. In this case, even if a ground fault occurs, the output of exclusive OR 14 is established, and the relay operation is erroneously blocked. Sometimes it happens. Therefore, in this case, as a countermeasure against the above-mentioned malfunction, as shown in FIG. 5, the circuit shown in FIG.
Add an undervoltage element 23. Here, 26 is an inverter that inverts the output of the exclusive OR circuit 14 and inputs it to the OR circuit 25.

[0018]

As described above, according to the present invention, based on the respective outputs of the own-end overcurrent detection circuit and the opposite-end overcurrent detection circuit, the secondary Since the configuration is configured to determine a disconnection fault and prohibit the output of the differential determination circuit, it is possible to clearly distinguish between the secondary disconnection of the current transformer 2 and an internal failure of the power transmission line, and therefore to prevent the internal failure from occurring. This has the effect that it is possible to reliably perform determination and thereby block relay operation output for system protection.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a current differential relay device according to an embodiment of the present invention.

FIG. 2 is an operation explanatory table showing the operation of the current differential relay device of FIG. 1;

FIG. 3 is a block diagram showing main parts of a current differential relay device according to another embodiment of the invention.

FIG. 4 is a block diagram showing main parts of a current differential relay device according to still another embodiment of the invention.

FIG. 5 is a block diagram showing the main parts of a current differential relay device according to still another embodiment of the present invention.

FIG. 6 is a block diagram showing a conventional current differential relay device.

7 is an explanatory diagram showing the operating principle of the current differential relay device of FIG. 6. FIG.

[Explanation of symbols]

1 Power transmission line 2 Current transformer 10 Differential judgment circuit

Claims (1)

[Claims] Claim 1: A self-end current and a partner current detected at both ends of a power transmission line are transmitted and received via a communication line, and a differential current of the vector sum of the received partner-end current and self-end current is transmitted and received as a differential current. In a current differential relay device that detects an internal fault in a power transmission line by detecting it with a judgment circuit, a self-end overcurrent detection circuit that detects a self-end zero-phase overcurrent or a self-end individual phase overcurrent based on the self-end current; , based on the other end overcurrent detection circuit that detects the other end zero-phase overcurrent or the other end each phase overcurrent based on the other end current, and the respective outputs of the own end overcurrent detection circuit and the other end overcurrent detection circuit. A current differential relay device comprising: a logic circuit that determines a secondary disconnection failure of the current transformer for self-end current detection and inhibits output of the differential determination circuit.