JPH0124016B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a line selection relay device suitable for application to a parallel two-line system in which zero-phase circulating current exists.

In a power system with parallel multi-circuit lines, zero-sequence circulating current exists at all times, even when an accident is not occurring, due to unbalanced self-impedance of each phase of the system. If this zero-sequence circulating current cannot be ignored compared to the fault current, it will affect the detection sensitivity of the protective relay, especially in high-resistance grounding systems, and the direction of the fault may be misidentified, making high-sensitivity and high-speed protection impossible. The problem is that it could become.

To solve the above-mentioned problem, line selection relay devices that protect parallel two-circuit transmission lines from ground faults have been developed by detecting the change in zero-sequence difference current before and after the fault occurs, and In the case of an accident, a method (differential current change detection method) is adopted in which the fault line is determined by utilizing the fact that the change appears on the fault line side.

A line selection relay device, which is generally used as a main protection relay in a protection relay system for parallel two-line transmission lines, is designed to protect against accidents that occur near the electricity station busbar at the opposite end of a parallel two-line transmission line, as long as there is no zero-sequence circulating current. In this case, the zero-sequence currents of both lines are almost balanced, so the line selection relay at the own end cannot operate, and the fault is detected only when the fault current is biased toward the fault line due to the interruption of the fault line at the opposite end. It is configured to shut off its own end, that is, to perform sequential shut-off.

The above will be explained with reference to the figures.

FIGS. 1a, b, and c show an example of a system configuration of two parallel lines. In the illustrated system, between the electric station bus line 1a at one end and the electric station bus line 1b at the opposite end,
A first power transmission line 4 having circuit breakers 2a and 2c at both ends
A and a second power transmission line 4b having circuit breakers 2b and 2d at both ends are provided so as to constitute two parallel lines. Zero-sequence currents flowing through both transmission lines 4a and 4b on the self-end power station bus 1a side are detected based on phase currents obtained by current transformers (hereinafter referred to as CT) 3a and 3b, respectively, and the difference current ( A zero-sequence difference current (Is) is introduced into the line selection relay 5.

Figure 1a shows the steady state before the accident, and if there is no zero-sequence circulating current between the two lines and the grid current is balanced, the zero-sequence difference current Is is also zero,
Line selection relay 5 does not operate.

FIG. 1b shows a case where a one-line ground fault occurs at point F near the opposite end power station busbar 1b in the first power transmission line 4a. In this case, since the circuit impedance up to point F as seen from the power station bus 1a at its own end is almost the same on the transmission line 4a side and the transmission line 4b side, the fault current or zero-sequence current of both lines is also almost the same. The input current Is of the line selection relay 5 is also approximately zero, and the line selection relay 5 at its own end does not operate.

FIG. 1c shows a state in which the fault line (power transmission line 4a) is cut off by the circuit breaker 2c at the opposite end. In this case, the fault current is applied to the healthy line (transmission line 4
b), but flows only through the faulty line (power transmission line 4a), and conversely, the load current does not flow through the faulty line (power transmission line 4a), but flows only through the healthy line (power transmission line 4b). A zero-sequence current corresponding to the fault current flows through the line selection relay 5, and when it exceeds a predetermined value, the line selection relay 5 operates, allowing the circuit breaker 2a to break.

In this way, the protective relay at the non-fault side operates later than that at the opposite end, which is the fault side, so that the circuit breaker at the own end is tripped after the circuit breaker at the opposite end is tripped. This is called sequential shutdown. When this sequential cutoff is performed by the line selection relay, it is clear that an accident has occurred within the protected area, so it is common to have the line reclosed.

In the line selection relay using the differential current change detection method described above, the zero-sequence difference current between the two lines before the accident occurs is stored, and at the same time as the accident occurs, the zero-sequence difference current at the time of the accident is stored. The zero-sequence difference current before the occurrence of the fault is subtracted, the difference is taken as the zero-sequence difference current change, and the fault line is determined by looking at the direction (positive or negative sign). However, if a zero-sequence circulating current is constantly flowing between both circuits, the zero-sequence current change that occurs when the zero-sequence circulating current that was flowing before the accident becomes zero due to the opposite end being shut off will be Zero-sequence current caused by a fault (zero before the fault)
It acts to increase the amount of change in the positive or negative direction, and the amount of change causes misunderstanding of the direction and may cause the self-end circuit breaker on the healthy line side to malfunction. A system is adopted in which the operation of the zero-phase overvoltage relay causes the line selection relay at the self-end to be locked after a certain period of time and before the opposite-end circuit breaker is opened. For this reason, in systems where the zero-sequence circulating current cannot be ignored compared to the zero-sequence current equivalent to the fault current, the line selection relay cannot be expected to perform the sequential cutoff described with reference to Figure 1, so the line selection relay must have a time limit for operation. In most cases, the final cut-off is performed by a ground fault direction relay for backup protection. However, this method causes overload on the healthy line, especially in the case of a heavily loaded system.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide a line selection relay device that can perform sequential cutoff even in a system where zero-phase circulating current exists. It is something.

In order to achieve the above object, the line selection relay device of the present invention includes a differential current detection circuit that detects the differential current between two parallel lines for each phase, and a change in the output of this differential current detection circuit. A change detecting means, a level detecting means that generates an operation output when the output of the change detecting means exceeds a certain level, and a parallel 2
ground fault detection means for detecting an internal ground fault in a line; and change detection output means for producing an operation output when the operation output of the ground fault detection means continues for a certain period of time and there is an operation output of the level detection means. , a highly sensitive line selection relay that determines the ground fault line from the direction and magnitude of the zero-sequence difference current of two parallel lines, and the output of both the change detection output means and the line selection relay are set as an AND condition, and the circuit breaker at the own end is activated. The present invention is characterized by comprising a logic circuit means for opening the circuit.

According to the above configuration, based on the output of the change detection output means, it is detected that the circuit breaker at the opposite electric station bus end is opened when a change in the differential current between the lines exceeds a certain value due to a ground fault. However, under this condition, a highly sensitive line selection relay will be used to select the line, so it is necessary to lock the relay device so that the normal line at the own end will not be cut off due to the cutoff at the bus end of the opposite power station. , thus allowing sequence interruption.

FIG. 2 is a three-line diagram showing an embodiment in which the present invention is applied to a high-resistance grounding power system. Although this embodiment shows that the zero-sequence current of the ground fault relay is obtained from the residual circuit of the CT, it is of course possible to use the tertiary circuit of the CT.

In the system shown in Figure 2, the self-terminal power station bus 1a
, the first power transmission line 4a via the circuit breaker 2a,
In addition, second power transmission lines 4b are led out through the circuit breakers 2b, and both power transmission lines 4a and 4b connect two parallel
The line is configured. It is assumed that the opposite end electrical station busbar 1b side is constructed in the same manner as in FIG. 1a. Each phase current of both circuits is detected by CTs 3a and 3b on the busbar side of circuit breakers 2a and 2b, and a change in the difference current is detected by a difference current detection device 6. Each phase voltage of the power transmission line 4a is also introduced into the differential current change detection device 6 in order to detect a one-line ground fault. On the other hand, the zero-sequence difference current obtained based on each phase current detected by the CTs 3a and 3b is introduced into the line selection relay 7, and here, based on the direction and magnitude of the zero-sequence difference current between both lines, which It is determined whether there is an accident on the side line. It is assumed that the line selection relay 7 is set to be highly sensitive without considering the zero-phase circulating current. The outputs of the differential current change detection device 6 and the line selection relay 7 are indicated by symbols 6l and 7a, respectively.

FIG. 3 shows in detail one phase of the differential current change detection device 6 of FIG. 2. In FIG. Although the apparatus of FIG. 3 is shown as being of an analog type, it is of course possible to use digital processing as long as it performs the same function. In FIG. 3, a difference current 6a of the same phase in both lines is inputted to a delay circuit 6c and a comparator 4d via an input transformer 6b. The delay circuit 6c can be easily configured with a filter, a shift register, etc., and can also be configured as a memory circuit in some cases. The comparator 6d is a circuit that compares a signal input directly from the input transformer 6b and a signal input via the delay circuit 6c, and outputs a difference signal. The output level of the comparator 6d is detected by the level detector 6e.
If it exceeds a predetermined value, an operation output signal "1" is output and input to the first input terminal of the AND circuit 6j. An output signal of a one-wire ground fault detection circuit 6h that detects a one-wire ground fault fault based on each phase voltage is input to a second input terminal of the AND circuit 6j via a timer circuit 6i. Note that the timer circuit 6j is provided to confirm that a one-line ground fault fault continues, and its settling time is different from that of the conventional line, which uses the above-mentioned change detection method. The length may be approximately the same as the lock time of the selection relay, for example, approximately 0.1 seconds. The output signal of the AND circuit 6j is sent to the timer circuit 6k.
becomes the output signal 6l of the entire device. The timer circuit 9k is provided to extend the output of the level detector 6e for a time sufficient for the line selection relay 7 to operate.

FIG. 4 is a sequence block diagram of the apparatus of the present invention. In FIG. 4, the output signal 6l of the differential current change detection device 6 and the output signal of the line selection relay 7 are input to an AND circuit 9, and the output signals are sent to the self-end circuit breaker 3a via an OR circuit 11. Alternatively, it is used as a trip signal to open circuit 3b. FIG. 4 additionally shows a conventionally used line selection relay 10 that detects a difference current change, and its output signal 10a is also transmitted to a self-end circuit breaker 3a or 3b is configured to open the circuit.

In the above configuration example, there is a short-circuit priority circuit because it is a high-resistance grounding system that is normally installed, and a total ground fault direction relay that uses the sum of the zero-sequence current of both circuits to prevent malfunction of the variable ground fault direction relay. A ground fault overvoltage relay as a failure detection relay, etc. are not shown in the figure because they have no direct relation to the gist of the present invention.

The difference current change detection device 6 responds if a change occurs in each difference current in both lines while the single line ground fault continues,
By detecting this change, it is determined that the breaker at the end of the opposite electrical station is open. The detection level of this differential current change detection device 6 is the maximum value of the change in load current (excluding the opening of the self-section breaker) and the maximum value of the change in zero-sequence circulating current during a one-wire ground fault. Determined by considering the value.

Next, the operation of the apparatus shown in FIGS. 2 to 4 will be explained with reference to FIGS. 5a to 5c.

Figure 5a shows the state of each system before the accident occurs, b shows the state of each system when the single-wire ground fault occurs, and c shows the state of each system when the opposing circuit breaker opens.

Figure 5a shows a case where both circuits are healthy, and zero-sequence circulating current Ioc is circulating between both circuits.
A current corresponding to 2 Ioc is input to the line selection relay 7.

Fig. 5b shows a case where a one-line ground fault occurs at point F near the opposite end bus of the transmission line 4a. Since the impedances on both sides are almost equal, the zero-sequence current Iof due to the fault flows from the self-end electric station bus 1a side toward the fault point F in the fault phases of both power transmission lines 4a and 4b with almost the same magnitude, and The above-mentioned zero-phase circulating current Ioc flows in the opposite direction.
The zero-sequence current input to the line selection relay 7 at this point is the difference between (Iof+Ioc) and (Iof-Ioc), that is, 2·Ioc.

Figure 5c shows a case where the circuit breaker 2c is opened after an accident occurs, and in this case, the fault current is transmitted to the power transmission line 4.
Only the a side flows, and all the load current is transmitted through the transmission line 4.
The current flows only on the b side, and the zero-phase circulating current no longer flows. Therefore, the zero-sequence current input to the line selection relay 7 at this point is a current corresponding to the zero-sequence current flowing to the failed line (power transmission line 4a) side.

The difference current change detecting device 6 detects the phase current change when the state shown in FIG. 5B changes to the state shown in FIG. 5C. The value of the change is detected by the level detector 6e.
is determined to exceed a predetermined value, and since the one-wire ground fault detection circuit 6h has detected a one-wire ground fault fault, an operating output 6l is outputted via the timer circuit 6k.

The operation of the differential current change detection device 6 determines that the "opposite end circuit breaker is open", and the AND condition of this and the operation of the highly sensitive line selection relay 7 is determined by the AND circuit 9, and the output is determined via the OR circuit 11. Own end circuit breaker 2
Open circuit a. That is, under the circuit state shown in FIG. A highly sensitive line selection operation is performed regardless of the situation.

As described above, according to the present invention, in the event of a one-line ground fault at the opposite end, the opposite end is detected to be disconnected, and based on this, highly sensitive line selection is performed, thereby achieving an improvement that could not be achieved with conventional methods. Sequential shutdown may be possible.

[Brief explanation of drawings]

Figures 1a, b, and c are system connection diagrams of two parallel transmission lines to explain sequential shutdown;
The figure is a connection diagram showing the current and voltage input system for the differential current change detecting device and line selection relay according to the present invention, and FIG. 3 is a block diagram showing one phase of the differential current change detecting device in FIG. FIG. 4 is a block diagram showing the overall configuration of the device according to the present invention, and FIGS. 5a, b, and c are system connection diagrams for explaining the operation of the device according to the present invention. 1a... Own end electric station bus, 1b... Opposite end electric station bus, 2a, 2b, 2c, 2d... Circuit breaker, 6... Difference current change detection device, 6c... Delay circuit, 6d... Comparator, 6e... Level detection 6h...1 line ground fault detection circuit, 6i, 6k...timer circuit, 6j...AND circuit, 7...line selection relay, 9...AND circuit.

Claims (1)

[Claims] 1 A difference current detection circuit that detects the difference current between two parallel lines for each phase, a change detection means that detects a change in the output of this difference current detection circuit, and an output of this change detection means that is at a constant level. a level detection means that generates an operation output when the level exceeds the level, a ground fault detection means that detects an internal ground fault of the two parallel lines, and an operation output of the ground fault detection means that continues for a certain period of time;
and a change detection output means that generates an operation output when there is an operation output of the level detection means, and a highly sensitive line selection relay that discriminates a ground fault line from the direction and magnitude of the zero-sequence difference current of the two parallel lines. A line selection relay device comprising the change detection output means and logic circuit means for opening a circuit breaker at its own end by using both operation outputs of the line selection relay as an AND condition.