JPH01274616A - Current differential relay - Google Patents

Abstract

PURPOSE:To compensate recharge current with no trouble, even when system voltage is led through bus PT to a current differential relay by making the recharge current compensating function ineffective when a line circuitbreaker is opened and making the compensating function effective when the line circuitbreaker is closed. CONSTITUTION:When a circuitbreaker is opened, a high sensitivity current differential relay 11 is in erroneous operating state '1' and a low sensitivity current differential relay 12 is in non-operating state '0'. Since the output from a timer 13 is '0', output from a relay 12 functions to disable the output from a relay. When the circuitbreaker is closed, recharge current compensation functions normally after a predetermined time (t) later to disable the output from the relay 11. Output from the timer 13 goes to '1' after a predetermined time T later and the output from the relay 11 functions to protect a transmission line with high sensitivity. During this interval, the output from the relay 11 is never employed as the output of the relay.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a current differential relay device for a power system.

(Prior Art) In recent years, a current differential relay system has been widely used as a protection system for power transmission lines. In the case of a single-type current differential relay, the vector sum of the currents at both terminals becomes zero during normal times or an external accident.
The principle is that in the event of an internal fault, the current will be equal to the fault point current, and when the vector sum of both terminals exceeds a certain value, it is determined that there is an internal fault and a trip command is output to the breaker.

There are various error factors in the current differential relay type, one of which is the charging current of the line. Charging current is a current that flows through the capacitance between the line and the ground, and appears as a differential current between the two terminals. The ground capacitance of a line becomes large in long-distance power transmission lines and underground cable systems, and the charging current for current differential relays cannot be ignored. When the charging current cannot be ignored compared to the detection sensitivity of the current differential relay, charging current compensation becomes necessary.

FIG. 4 shows an overview of charging current compensation. If the currents at both terminals of the power transmission line in Fig. 4 are IA and I, the difference current between the terminals (vector sum) in normal conditions is given by the following equation.

However, C: Total sum of line-to-ground capacitance in the protection zone ÷
: Line voltage ω: Frequency (angular velocity) The right side of equation (1) shows the charging current of the line.

On the other hand, the principle of a current differential relay is as follows.
V 1d-kt(II, l±Ii, 1) -2≧...
-・(2) However, r, = I, 10I.

kl, 2: constant In equation (2), the second term represents the ratio suppression term, and the third term represents the detection sensitivity. As shown in equation (2), the difference current i includes the charging current even in normal times, and if the charging current is large, the value of k2 must be increased to reduce the detection sensitivity. It won't happen. Furthermore, if a decrease in detection sensitivity is not allowed, it is necessary to perform charging current compensation.

FIG. 5 shows an overview of the current differential relay and charging current compensation.

In the figure, the own terminal current i is introduced into the determining section 51 and transmitted from the transmitting device 52a to the other terminal. The other terminal current i and the own terminal voltage V received by the receiving device 52b are also introduced into the determination section.

The determination section is composed of software using a microcomputer. In software and software, the difference current is due to the following 2!
, is calculated.

In equation (4), the third term is a charging current compensation term, which is zero under normal conditions due to (2). Note that since the value of C in equation (4) is a known value, it is set as a constant and input into the software as instantaneous value data in advance, so calculations involving differentiation such as jω can be easily executed by the software.

(Problem to be Solved by the Invention) Strictly speaking, the ground capacity of a power transmission line exists as a distributed constant, but when considering charging current compensation for a current differential relay, it is generally sufficient to treat it as a lumped constant. Therefore, as the voltage V used in equation (4), the line voltage obtained from the voltage transformer (PT) of the electric station where the relay device is installed may be used. The voltage transformer includes a line PT for measuring line voltage,
Charging current compensation is normally performed correctly no matter which PT is used to measure the bus voltage. However, if the circuit breaker (CB) connecting the bus and the line is open, the line voltage cannot be measured correctly at the bus PT, and charging current compensation cannot be performed accurately. When the above-mentioned disconnector is open, the magnitude and phase of the bus voltage and line voltage are generally different, and the charging current compensation is either inaccurate or the difference current between the two terminals is different. It may even act in the direction of increasing it. FIG. 6 shows such an example. In the power transmission line shown in FIG. At this time, if the line voltage is Vt, a charging current jωC-Vt exists on the line, and the relationship between the line voltage Vt and the charging current jωC-Vt is shown in FIG. 6(b).

On the other hand, the bus voltage V, is asynchronous with the line voltage Vt,
In the worst case, Vt is 18 as shown in Figure 6(b).
There may be a phase relationship of 0°. At this time, the bus voltage V
The charging current compensation term jωC-V using the actual charge current jO)c-vt and the phase of 1800,
On the contrary, the error increases, and in some cases, the current differential relay may malfunction. In this case, the line is opened by a circuit breaker, so even if the current differential relay is activated, the device output is locked because the other fault detection relays are not activated, and the circuit breaker is open. By locking the device output under certain conditions, it is possible to prevent problems from occurring. However, immediately after the switch is turned on to save the line, the malfunction continues temporarily, and malfunction is unavoidable, especially when it coincides with an out-of-section accident.

From the above, it is preferable to introduce the voltage for charging current compensation of the current differential relay of the power transmission line from the line PT rather than from the bus line PT. However, in actual electrical stations, the line PT does not necessarily exist, and the voltage introduced from the bus line PT is often used.

The present invention has been made in view of the above circumstances.
It is an object of the present invention to provide a current differential relay device that does not cause problems even in a charging current compensation method using T.

[Structure of the Invention] (Means for Solving the Problems) In the present invention, in the current differential relay device, the charging current compensation function is disabled under the open condition of the line breaker, and the relay sensitivity is lowered than in the normal state, and - The charging current compensation function is enabled after a certain period of time from the closing condition of the circuit breaker, and the relay sensitivity is returned to the normal state. (Function) When the circuit breaker is open, the charging current compensation function is disabled. ,
It can only be used when closed. Therefore, even if the system voltage is introduced to the differential relay by the mother 1fJPT, charging current compensation can be performed without any problems.

(Embodiment) FIG. 1 is a block diagram of an embodiment of a current differential relay device according to the present invention. In the figure, reference numeral 11 indicates a current differential relay 87A that is set to be highly sensitive and performs accurate charging current compensation. 12 is a current differential relay 87B set to low sensitivity.
Charging current compensation is not provided. Reference numeral 13 is a timer, which delays and outputs the lateral characteristics of the breaker σ closed by a certain period of time. 1
4 uses the output of the timer 13 or the output of the current differential relay 11 when the distance is 1 m in the AND dart mode. 15 is an inhibit gate that locks the output of the current differential relay 12 when the output of the timer 13 is @l''.

16 is an or gate, and gate 14 and inhipip)r
-) Outputs 11" when there is an output in any of 15.

FIG. 2 is a time chart showing the operation of the apparatus according to the present invention. Figure 2 (,) shows the operation when normally turning on a line breaker or circuit breaker.In the initial state, the circuit breaker is open. The “closed” condition is @0”. At this time, the high-sensitivity current differential relay 87A is in the malfunction state @l”, but the low-sensitivity current differential relay 87B is in the non-operation state @0”. Therefore, the output of the timer 13 is "0", so the device output is 87B
The output of is utilized and becomes inactive. When the breaker is "closed", the current differential relay 87A output becomes inoperable after a certain period of time due to charging current compensation working normally. Then, after a certain period of time T, the output of the timer 13 becomes @1#, and the stain flow differential relay 87A output is utilized, and the power transmission line is protected with high sensitivity. During this time, the output of the current differential relay 87A will not erroneously become the device output.

Figure 2) shows the operation when there is a system fault when the breaker is turned on. The initial breaker is “open” (the “closed” condition is “O”)
”), 87A is in the operating state 11” and 87B is in the inactive state “0#” as in the case of Fig. 2 (a). After the breaker is turned on, there is a fault in the system, so 87A is in the operating state. The condition continues, but it is locked until the output of timer 13 is output.87B turns on the breaker and operates after a certain period of time.When 87B operates, the device outputs a trip output and the system fault is eliminated. be done.

In the method according to the present invention, the predetermined time T determined by the timer 13 after the breaker is turned on is a low-sensitivity current differential relay 87.
It works by BK. Usually, the sensitivity value is determined so that the minimum value of the fault current within the section is several times the detection sensitivity value of the current differential relay.

Therefore, even if the sensitivity value of 87B is lowered somewhat, it is possible to detect a system fault within the section. However, it may be slightly slower in terms of operation time, but it is within an acceptable range for system conservation.

The example in FIG. 1 shows a case where there are two current differential relay elements. However, two relay elements are not necessarily required to realize the present invention. FIG. 3 shows another embodiment of the invention. In the figure, reference numeral 31 denotes a current differential relay, which includes an operating amount calculating section 31a, a charging current compensating section 31b, and a detection sensitivity setting section 3.
1c is built-in. As in the example shown in FIG. 1, the timer 13 delays and outputs the condition for closing the circuit breaker by a certain period of time. When the output of the timer 13 is "0", the charging current compensator 31b is controlled to be disabled.

Also, at this time, the detection sensitivity setting section 31c is controlled to have low sensitivity. On the other hand, when the breaker becomes "open" and the output of the timer 13 becomes "l" after a certain period of time, the charging current compensator 3
1b is utilized, and the detection sensitivity setting section 31e is controlled to have high sensitivity. It can be understood that even in such a configuration, the same function as in the case of FIG. 1 can be achieved.

In the above example, no particular mention is made of the method of introducing the opening/closing status of the line breaker. Introducing the pallet switch conditions for circuit breakers can also achieve the objective. Furthermore, by highly sensitively detecting the current flowing through the line, it is possible to know whether the circuit breaker is open or closed.

Although the current differential relay has been described using a digital type relay using a microcomputer as an example, it is clear that the present invention is equally applicable to a current differential relay using analog elements.

〔Effect of the invention〕

As explained above, according to the present invention, the charging current compensation function is disabled when the circuit breaker that opens and closes the line is "open" and enabled when it is "closed." Charging current compensation can now be performed without any problems even when the grid voltage is introduced through the bus PTK.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a current differential relay device according to the present invention, and FIG. 2 is a time chart showing its response.
Fig. 3 is a diagram showing another embodiment, Fig. 4 is a diagram showing how charging current is generated in a power transmission line, Fig. 5 is a diagram explaining a conventional normal current differential relay, and Fig. 6 is a diagram showing a line It is a figure which shows the malfunction when a circuit breaker opens. 11... Current differential relay (high sensitivity) 12... Current differential relay (low sensitivity) 13... Timer 14 River and gate 15...
・Inhibit Gut 16...or dirt.

Claims (1)

[Claims] In a current differential relay device that uses bus voltage to compensate for the charging current of a line, when the line breaker is open, the charging current compensation function is disabled and the relay sensitivity is lowered than in the normal state; A current differential relay device characterized in that the charging current compensation function is enabled and the relay sensitivity is returned to a normal state after a certain period of time after a line breaker is closed.