JPS5840407B2 - Residual circuit monitoring method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a residual circuit monitoring method for detecting disconnection of a residual circuit when a current transformer is connected to a three-phase power system.

FIGS. 1 and 2 are circuit diagrams showing conventional system protection relay devices.

1゜2.3 shown in Figures 1 and 2 are R, S, and T of the system.
Current transformers (hereinafter referred to as CTs) are inserted respectively, 4 is a short-circuit protection relay that responds to the unbalanced current of CTs 1 and 2, and 5 is a zero-sequence current of residual circuit 6.

This is a ground fault protection relay that responds to

If the system shown in Figure 1 is normal, R, S.

Since the secondary currents of CTI and 2.3 connected to each phase of T are balanced, no zero-sequence current ■o flows into the residual circuit 6.

Therefore, the earth fault protection relay 5 does not operate, but the R and S
, when a ground fault occurs in any of the T phases, CT1, CT2 .
The secondary current of 3 becomes unbalanced, and a zero-sequence current appears in the residual circuit 6.
.

is the flow. Ground fault protection relay 5 operates to protect the system.

However, in such a circuit, the zero-sequence current ■ appears in the residual circuit 6 as described above.

Since the system is considered to be normal because there is no flow, it is unknown even if the residual circuit 6 is disconnected.

Even if a system fault actually occurs, the protection relay will not operate and the system will not be protected.

On the other hand, as a method to compensate for this disadvantage, individual CT1s inserted into the R, S, and T phases of the ground fault protection relay 5 as shown in Fig. 2 are used.
, 2.3, there is a system that directly inputs the secondary current as input, but in order to actually adopt this method, CT1
．． Six secondary cables of 2.3 are required, and the zero-phase circuit must be combined within the earth fault protection relay 5, making the circuit complicated.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to propose a monitoring method that can reliably detect whether the residual circuit is healthy or not by adding a simple circuit.

FIG. 3 is a circuit diagram showing an embodiment of the system protection relay device according to the present invention.

1,2°3...6 shown in Fig. 3 is the above CTI,
2, 3, are the same or equivalent parts as the short circuit protection relay 4, the ground fault protection relay 5, and the residual circuit 6.

Reference numeral 7 denotes an intermediate tap that draws a current so small that the short-circuit and ground fault protection relays 4 and 5 provided in the secondary coil of the CT 1 do not respond.

8 is an auxiliary CT connected between this intermediate tap 7 and the residual circuit 6, which insulates the amplification of the current derived from the intermediate tap 7 and the secondary circuit of the CTs 1, 2, and 3; In response to the output current of this auxiliary CT8, the normally open contact 9
Auxiliary relay 10 closes a and sends out an alarm signal.Auxiliary relay 10 is a check switch that opens and closes the output current of the auxiliary CT8.

Next, the operation of the above configuration will be explained.

In fig. If the system is normal, the secondary current of CTI 2.3 is balanced and no current flows through the residual circuit 6.

In this state, when the inspection switch 10 is closed to check the health of the residual circuit 6, a part of the secondary current of the R-phase CT1 becomes unbalanced, and as shown by the dotted line in the figure, the intermediate tap 7 of the CTi and the auxiliary CT8 A small amount of current flows through the path of the primary coil residual circuit 6.

The output current of the auxiliary CT 8 energized by this current activates the auxiliary relay 9, which closes the normally open contact 9a and sends out a signal.

That is, it can be seen that the residual circuit 6 is healthy by sending a signal by closing the inspection switch 10.

As mentioned above, the value is selected to be lower than the response value of the ground fault protection relay 5 so that the ground fault protection relay 5 will not malfunction due to a slight unbalanced current derived from the intermediate tap 7. It is assumed that there is

In the above embodiment, the inspection switch 10 is pressed and if there is a signal, it is determined that the residual circuit 6 is healthy without any disconnection. The disconnection of the residual circuit 6 may be detected by turning off the light.

In short, the present invention provides a residual circuit of a CT in which no current flows in a normal balanced state, with the current transformed into the CT secondary winding for one phase and the current transformed into the CT secondary winding of the other phase. We created an unbalanced circuit that flows a small amount of current that cannot be determined to be a ground fault, and when this current disappears, it is detected that the residual circuit is disconnected, so we can reliably check the health of the residual circuit. Can be monitored.

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing an example of a conventional system protection relay device, and FIG. 3 is a circuit diagram showing an embodiment of the system protection relay device according to the present invention. In each of the above figures, the same reference numerals indicate the same or corresponding parts. In Figure 3, L2 and 3 are CTs, 4 is a short circuit protection relay, 5 is a ground fault protection relay, 6 is a residual circuit, 7 is an intermediate tap, 8 is an auxiliary CT-9, auxiliary relay 9a is a normally open contact, 10
is a check switch.

Claims (1)

[Claims] A CT inserted into a 13-phase power system and connected to the output side of its secondary winding, an earth fault protection relay that responds to the zero-sequence current flowing in the residual circuit on the output side of this CT, and 2 of the above CTs. An intermediate tap provided on one of the next windings and which derives a current that does not cause the earth fault protection relay to respond; an auxiliary CT connected between this intermediate tap and the residual circuit; presence or absence of output of this auxiliary CT; A method for monitoring a residual circuit, comprising means for detecting the health or failure of the residual circuit.