JPH04355624A - Differential current monitoring method - Google Patents

Abstract

PURPOSE:To prevent the erroneous operation by exciting rush current by continuing the AND output of a circuit, which detects that the bus voltage is above a specified value, and a circuit, which detects the ON of a breaker, for a certain time. CONSTITUTION:A bus voltage detecting circuit 7 receives the voltage of an A terminal through PT, and outputs a level H when it is above the specified value. When a breaker 'ON' detection circuit 8 detects the 'ON' of the breaker CB-A on the side of A terminal, it outputs a level H. When the AND condition of the output of detection circuits 7 and 8 materializes, an AND circuit 9 outputs a monitor lock signal, which makes a one shot timer 10 continue for a certain time, and by this output, a NOT circuit 11 and an AND circuit 12 lock the output of a differential current monitoring circuit 3. Hereby, even with the device wherein line voltage is not introduced, the erroneous operation by the exciting rush current can be prevented surely in the case that voltage is applied to the transformer of a load terminal.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential current monitoring system for a current differential protection relay device for protecting a system including a transformer within a protection zone.

0002

2. Description of the Related Art Current differential protection relay systems are widely applied to protect equipment such as busbars, transformers, and shunt reactors, and to protect power transmission lines using data transmission means. As is well known, the principle of current differential protection is based on Kirchhoff's law, in which the current flowing into or out of the protected zone is introduced into the relay via a current transformer, and in the case of an internal fault, the vector of the current introduced into the relay is The presence or absence of an intra-section fault is determined by utilizing the fact that the sum, that is, the difference current (Id) is large, and in the case of an external fault, the difference current is small.

[0003] Equation (1) is one ratio characteristic determination formula of the operation determination principle of a current differential relay, where the vector sum Id of each current input is the operating amount, and the scalar sum Σ|I| of each current input is a predetermined ratio K. is multiplied by the amount of suppression, and when the amount of operation is greater than the amount of suppression by the sensitivity term Ko or more, the relay is activated. Id≧K・Σ｜I｜+Ko
......(
1)

[0004] In a current differential protection relay device using this relay, differential current monitoring is normally performed to check the accuracy of the analog input section and determine the quality of the differential circuit. The configuration will be described below using a current differential protection relay device for power transmission line protection as an example. In Figure 5, device 1 installed at electric station A
The own end current IA and the other end current of electric station B are inputted to the terminal via the transmission system. The current at both terminals is introduced into the current differential relay 2 to perform the current differential protection calculation of equation (1), and the operating amount and suppression amount calculated here are further introduced into the differential current monitoring circuit 3, and the on-delay timer 4 If the failure continues for a period of time or more, a monitoring failure is detected. Normally, the detection sensitivity of differential current monitoring is made higher than the operating sensitivity of a relay, so the determination is made using, for example, equation (2) or equation (3) in which the sensitivity term is smaller than Ko in equation (1). Id≧n・Ko

………(2) Id≧K・Σ｜I｜+n・
Ko
......(3) However, n is less than 1 and generally 0
．． 8 is used. FIG. 6 shows the defect detection area of this differential current monitoring on a ratio characteristic diagram in comparison with the operating area of the relay.

[0005]

[Problem to be Solved by the Invention] Here, if there is a branch load terminal within the protection interval that does not introduce terminal current to the current differential relay as shown in Fig. 5, the system voltage is applied to the transformer 5 of the load terminal. The excitation inrush current that occurs when the current is applied becomes the difference current. The difference current is within the range 6 shown on the ratio characteristic diagram in Figure 6.
, and the decay time is relatively long, so it is necessary to take measures to prevent the detection of differential current monitoring failures due to this influence.

Although there is a method of making the time of the defect detection timer 4 for differential current monitoring longer than the decay time of the excitation inrush current, this is not preferable because it causes a delay in the defect detection time when an actual defect occurs.

On the other hand, since the magnetizing inrush current occurs only immediately after the system voltage is applied to the transformer, there is a sufficient time and difference for the magnetizing inrush current to attenuate from the time when the voltage is detected to be applied. There is a method to prevent current monitoring failure from being detected. This method is excellent because it does not interfere with constant fault detection, but on the other hand, in devices that do not introduce line voltage, it is difficult to reliably detect that voltage is applied to the transformer at the load terminal. be.

The present invention has been made to solve the above problem, and even in a device that does not introduce line voltage, when voltage is applied to the transformer at the load terminal, monitoring by magnetizing inrush current can be reliably performed. The purpose of this invention is to provide a differential current monitoring method that can prevent false detection of defects. [Structure of the invention]

[0009]

[Means for Solving the Problems] The configuration of the present invention will be explained with reference to the configuration diagram of FIG. 1 corresponding to the embodiment. A circuit 8 for detecting whether the output is on, and a circuit 10 for outputting a signal for a predetermined time longer than the time that the transformer excitation inrush current continues after the output of the AND circuit 9 of both circuit outputs is provided. The configuration is such that differential current monitoring failures are not detected based on the output.

0010

[Operation] As a result, when a transformer is installed within the protection zone, the system voltage is applied to the transformer at the branch load terminal within the protection zone based only on its own terminal conditions without introducing line voltage. This makes it possible to prevent erroneous detection of differential current monitoring failure due to excitation inrush current.

[0011]

Embodiment An embodiment of the present invention will be described with reference to FIG. In FIG. 1, parts similar to those in FIG. 5 are given the same numbers and their explanation will be omitted.

In FIG. 1, 7 is a circuit for detecting the presence of bus voltage, which detects the level of the bus voltage using an undervoltage relay, and outputs "1" when the bus voltage is present. 8
is a circuit that detects whether the breaker installed between the bus bar and the power transmission line is "on".For example, the A contact condition of the pallet switch of the breaker is input, and when the contact is "closed", the circuit breaker is "on". input” and controls the output to “1”. When the AND condition of the outputs of both circuits 7 and 8 is satisfied in the AND circuit 9, the one-shot timer 10 outputs a monitoring lock signal for a predetermined period of time. The monitor circuit output is configured to be locked.

[0013] Regarding the above embodiment, the circuit operation in a case where a transformer excitation inrush current occurs will be explained using a time chart. Figure 2 shows that when the A terminal is the non-power terminal and the breaker is turned on,
This is a case where the breaker at terminal B at the power supply end is turned on. When the line voltage recovers, an excitation inrush current is generated, and the differential current monitoring circuit detects a failure, but the bus voltage also recovers at the same time and outputs a monitoring lock signal, so the monitoring failure detection is locked. FIG. 3 shows a case where the circuit breaker of the A terminal is turned on when the A terminal is the power supply terminal and the B terminal is the non-power supply terminal. As in the case described above, when the line voltage is restored, an excitation inrush current is generated, and the differential current monitoring circuit detects a fault, but since a monitoring lock signal is also output at the same time as the breaker is turned on, monitoring faults can be detected unnecessarily. There isn't.

Next, another embodiment will be explained with reference to FIG. In Fig. 4, the configuration is the same as that of the embodiment shown in Fig. 1 until the lock signal for differential current monitoring is output, but during the period when the lock signal is output, the detection sensitivity of differential current monitoring is changed to detect a failure due to the transformer excitation inrush current. The configuration is such that the sensitivity term n is controlled to a large value to prevent this. As a result, the same effects as in the previous embodiment can be obtained.

[0015] The above embodiments have explained the power transmission line protection device, but when the transformer terminal voltage cannot be introduced to the transformer protection device, the bus voltage and the breaker condition for connecting the bus and the transformer can be introduced. A similar circuit can be constructed by

[0016]

[Effects of the Invention] As explained above, according to the present invention, after detecting that the bus voltage is above a predetermined value and that the breaker is "on", the transformer magnetizing inrush current continues for a period of time or longer. Because the configuration is configured to lock the differential current monitoring for a predetermined period of time, branch loads within the protected area can be detected using only the conditions of the own terminal without adding functions such as introducing line voltage or transmitting a monitoring lock signal from the other terminal. It is possible to provide a differential current monitoring method that does not unnecessarily detect a monitoring failure using an excitation inrush current that occurs when a system voltage is applied to a terminal transformer.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a differential current monitoring method according to the present invention.

FIG. 2 is a time chart illustrating the operation of the differential current monitoring method of the present invention.

FIG. 3 is a time chart illustrating the operation of the differential current monitoring method of the present invention.

FIG. 4 is a configuration diagram showing another embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional differential current monitoring method.

FIG. 6 is a ratio characteristic diagram showing a defect detection range by differential current monitoring.

[Explanation of symbols]

1 Protective relay device 2 Differential current relay 3 Difference current monitoring circuit 4 On-delay timer 5　Transformer 6 Existence region of excitation inrush current 7　Bus voltage “presence” detection circuit 8 Breaker “on” detection circuit 9,12 AND circuit 10 One shot timer 11 Knot circuit

Claims (1)

[Claims] [Claim 1] In a differential current monitoring method of a current differential protective relay device that performs a protective operation by detecting the differential current obtained by the vector sum of each target current of the protected equipment, the system detects that the bus voltage is equal to or higher than a predetermined value. a first means for detecting, a second means for detecting that a breaker that controls the connection between the bus bar and the equipment to be protected is on, and a logical product of the output of the first means and the output of the second means. and a fourth means for outputting a signal for a predetermined period of time from the output point of the third means, and configured to invalidate the detection output of the differential current monitoring by the output of the fourth means. A differential current monitoring method characterized by: