SU67775A1 - Device to protect synchronous machines, responsive to the rate of change of frequency - Google Patents

Description

The presence of synchronous motors and compensators or small synchronous generators at receiving substations makes it difficult to apply automatic reclosing of the automatic transmission lines.

The reasons are as follows:

First, after disconnecting the line from the supply end, the arc on the line can be maintained by e. d. synchronous machines installed at receiving substations; therefore, if the automatic reclosure is faster than the arc goes out, the activation will fail;

secondly, during the automatic reclose cycle, synchronous maschines at the receiving substations will go out of synchronism; therefore, typically, three-phase automatic reclosing is performed after the synchronous load of the receiving substation has been previously disconnected (after the occurrence of voltage at the receiving substation, automatic resynchronization is desirable).

To disconnect the synchronous load when the line is disconnected from the supply end, in the practice of the USSR, the relays of the minimum potential are the same as 1u. The time on this protection is usually set above the backup protection time in order to prevent tripping during short circuits in the system.

Occasionally, protective devices are used that respond to overloads or a long decrease in frequency.

Due to the reasons given above, a fast AR over three loads of synchronous load at the receiving end is difficult.

In American practice, relays that react to the rate of change of frequency are used for the above purposes, because after the line is disconnected from the main power supply side, the change in frequency (its decrease) proceeds faster than during any accidents in the system.

The present invention has to create a device responsive to the rate of change of frequency using a domestic relay.

For this purpose, the proposed device consists of two starting relays of different sensitivity with normally closed or open contacts, operating at a smooth change of electrical quantities non-simultaneously, and two auxiliary direct current relays. According to the invention, miniature frequency relays are used as starting relays.

The time delay of the opening contact of the auxiliary relay determines the magnitude of the rate of change, not the frequency.

The drawing shows two variants of the proposed device.

In the circuit of FIG. 1, when the frequency changes, first the frequency switch / I is activated, and then the relay / а. Installing the move.

If the frequency change is slow (which indicates any system failure, in which the switching off of the consumer synchronous power should not take place), then before the relay / 2 contact closes, time relay 5 will act. From the diagram it can be seen that in this case shutdown will not happen.

With a rapid change in frequency, the contact / 2 closes before the time relay operates. The output relay will act, which will remain in the triggered state if

even time relay 5 will subsequently open its contact.

FIG. 2 shows another embodiment of a circuit using a frequency relay with normally closed contacts. As an element of time used relay with delayed return.

Subject invention

A device for protection of synchronous masinas, which reacts to the rate of change of the frequency of the alternating current, consisting of two starting relays of different sensitivity with normally closed or open contacts, operating at a smooth change of electrical quantities non-simultaneous, and two auxiliary relays of direct current, characterized in as the starting relays, the minimum frequency relays are used, and the time delay of the opening contact of the auxiliary relay determines the magnitude of the rate of change of frequency.

/

FIG. one

Off

S1

FIG. 2