JPH0622442A - Line selection relay - Google Patents

Abstract

PURPOSE:To prevent erroneous function due to circulation current by providing first and second current direction relays for detecting the direction of current flowing through each line of parallel two-line transmission line and tripping a circuit breaker when AND condition is satisfied for the outputs from an overcurrent relay, a short circuit selection relay, and the first and second current direction relays. CONSTITUTION:When a circulation current flows through a parallel two-line transmission line upon occurrence of bus short circuit fault, any one of first and second current direction relays 167, 267 functions but the other does not function because current flow in different directions through respective lines. Consequently, AND condition is not satisfied for the outputs from an overcurrent relay OC, a short circuit selection relay 50S, and the first and second current direction relays 167, 267, and no circuit breaker trip signal is delivered from an AND circuit 23. On the other hand, both of the first and second current direction relays 167, 267 function for forward fault to satisfy the AND condition and a circuit breaker trip signal is delivered from the AND circuit 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line selection relay device for selectively cutting off a faulty line of parallel two-line transmission lines of an electric power system.

[0002]

2. Description of the Related Art In a parallel two-line transmission line of an electric power system, the current distribution of each line is the same when there is always no fault in the system or when there is a fault outside the transmission line. However, in the case of an internal fault in the power transmission line, the magnitude of the current becomes larger than that in the sound line, and the direction of the current becomes opposite to the direction of the current in the sound line.

The line selective relay system utilizes the above phenomenon to selectively cut off an accidental line. For example, as shown in FIG. 3, current transformers are respectively inserted in parallel two-line transmission lines 1L and 2L, and the The secondary circuit of the current transformer is differentially connected, and the relay Ry is connected to the differential circuit.
It is configured by connecting. In FIG. 3, 3 and 4 are bus bars and 5
Is a transformer.

A conventional line selection relay device is constructed as shown in FIG. 4, for example. In FIG. 4, 11 is an AND circuit that obtains the logical product of the output of the short circuit selection relay 50S that receives the differential current and the bus voltage of the parallel 2 lines and the output of the overcurrent relay OC that inputs the differential current, and 12 is cut off. And AND circuit 13 and an AND circuit 13 for obtaining an AND condition for using the short circuit selection relay 50S, and an AND circuit 13 for obtaining a logical product of the outputs of the AND circuits 11 and 12. As can be seen from FIG. 4, conventionally, the trip signal of the circuit breaker is output when the AND condition of the outputs of the short-circuit selection relay 50S and the overcurrent relay OC is satisfied.

[0005]

In the electric power system as shown in FIG. 3, when a short-circuit fault occurs in the bus bar 3, the fault current is supplied from the upper system through the transformer 5. When the line in which the relay is installed and the upper system are arranged side by side as shown in the figure, a circulating current I _th is generated in the line (1L, 2L) due to mutual inductance between the lines.

As the difference current, difference current = I _th −
(−I _th ) = 2 × I _th occurs. Short circuit selection relay 50
In S, the bus voltage also decreases, and a differential current is generated, so it operates depending on the magnitude and phase of the differential current. The overcurrent relay OC also operates if a difference current larger than the set value is generated. Therefore, according to the conventional circuit of FIG. 4, there is a possibility that an erroneous trip output may be output despite a backward failure.

The present invention has been made in view of the above points, and an object thereof is to provide a line selection relay device which does not malfunction due to a circulating current flowing in a parallel two-line power transmission line.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to an overcurrent relay that operates when a differential current flowing in a parallel two-line power transmission line of a power system is a predetermined value or more, and a short-circuit selection that receives the differential current and a bus voltage. A line selection relay device, which includes a relay and selectively cuts off an accidental line of the parallel two-line transmission line,
First, a second current direction relays provided, setting value -K the setpoint K ₁ of the overcurrent relay the current direction relays to detect the direction of current flowing through each line of the parallel two-circuit transmission line
₂ is settled to a relationship of K ₂ <K _1/2, and the breaker is tripped when the AND condition of each output of the overcurrent relay, the short-circuit selection relay, and the first and second current direction relays is satisfied. There is.

[0009]

When a circulating short-circuit current flows in the parallel two-line power transmission line when a bus short-circuit fault occurs, the directions of the currents flowing in the respective lines are different from each other, so that either one of the first and second current direction relays operates. , The other does not work. Therefore, the AND conditions for the outputs of the overcurrent relay, the short-circuit selection relay, and the first and second current direction relays are not satisfied, and the circuit breaker trip signal is not erroneously issued.

Further, in the forward failure, the first and second current direction relays both operate, so that the AND condition is satisfied,
A breaker trip signal is issued.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1, the same parts as those in FIG. 4 are designated by the same reference numerals. The difference between FIG. 1 and FIG. 4 is that the parallel 2
A first current direction relay 167 that detects the direction of the current flowing through one of the line transmission lines, and a second current direction relay 26 that detects the direction of the current flowing through the other transmission line.
7 is provided, and the output of the current direction relays 167 and 267 is ANDed by the AND circuit 21, and the output of the AND circuit 21 and the AND used by this circuit are taken by the AND circuit 22, and the AND circuits 11, 12 and 22 are connected. The AND circuit 23 takes the AND of each output. Current direction relays 167, 2
The principle of 67 is expressed by the following equation.

[0012]

[Equation 1]

Here, it is assumed that the line selection relay device configured as described above is applied to the power system of FIG. At the time of the rear failure described above, for example, when a circulating current of I _th flows due to a short-circuit failure of the bus bar 3, one current direction relay, for example, 1
67 operates, but the other current direction relay 267 does not operate because it is in the opposite direction. Therefore, the AND condition of the AND circuit 21 is not satisfied, and the trip signal is not erroneously output from the AND circuit 23.

When a forward failure occurs, the current direction relay 167,
267 operates together, the AND conditions of the AND circuits 21, 22, and 23 are satisfied, and the breaker trip signal is output.

However, in the case of a near end failure, one of the current direction relays may not operate, so the current direction relay 1
The settling of 67 and 267 is negative. The current direction relay is set to a value smaller than a value obtained by dividing the set value of the overcurrent relay OC by 2 as shown in FIG. 2 (the set value of the overcurrent relay is K ₁ , current direction relays 167, 267). the setting value When -K _{2 of, K 2 <K 1/2} ). If the value is a negative value equal to or more than that value, it is impossible to prevent unnecessary operation of the current direction relay at the time of backward failure in FIG.

[0016]

As described above, according to the present invention, the first and second directions for detecting the direction of the current flowing in each line of the parallel two-line power transmission line,
Since the second current direction relay is provided and the circuit breaker is tripped when the AND condition of each output of the overcurrent relay, the short-circuit selection relay, and the first and second current direction relays is satisfied, the circulating current flows when the busbar short-circuit fault occurs. In the case of such a rear failure, the circuit breaker trip signal is not erroneously output, and at the time of the front failure, the trip signal can be reliably output for protection.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining set values of an overcurrent relay and a current direction relay of the present invention.

FIG. 3 is a power system diagram showing a configuration of a parallel two-line transmission line provided with a conventional line selection relay device.

FIG. 4 is a circuit diagram showing an example of a conventional line selection relay device.

[Explanation of symbols]

 1L, 2L ... Parallel 2-line transmission line 3, 4 ... Bus 5 ... Transformer 11, 12, 21, 22, 23 ... AND circuit 167, 267 ... Current direction relay 50S ... Short circuit selection relay OC ... Overcurrent relay

Claims (1)

[Claims] 1. A parallel 2 circuit comprising: an overcurrent relay that operates when a differential current flowing in a parallel 2-line transmission line of a power system is a predetermined value or more; and a short-circuit selection relay that inputs the differential current and a bus voltage. In a line selection relay device for selectively shutting off a faulty line of a line transmission line, first and second current direction relays for detecting a direction of a current flowing in each line of the parallel two-line transmission line are provided, and the overcurrent relay Settling value K ₁ and setting value of the current direction relay-K
₂ is settled to a relationship of K ₂ <K _1/2, and the circuit breaker is tripped when the AND condition of each output of the overcurrent relay, the short-circuit selection relay, and the first and second current direction relays is satisfied. Line selection relay device.