CS219795B1 - Wiring for direct tests of high voltage circuit breaker - Google Patents

Abstract

The invention relates to heavy-current electrical engineering and solves the problem of improving the adjustment of the recovered voltage curve by dividing the inductance of the power supply circuit into two parts, while a circuit for adjusting the recovered voltage curve is connected in parallel to the second part, consisting mainly of air reactors. The invention can be suitably used in short-circuiting plants.

Description

BACKGROUND OF THE INVENTION The present invention relates to a circuit for direct testing a high voltage circuit breaker with a circuit for adjusting the recovery voltage waveform.

There are known connections for direct testing of a MV circuit breaker in a current-carrying circuit, the magnitude of which is determined by the size of the reactors of the generator, the transformers, and is supplemented to the desired value by additional mostly air reactors. The reactance of this circuit thus determines the magnitude of the short-circuit current, and the inductance has a fundamental effect on the recovery voltage, which is further determined by the capacity of the generator, transformers and the whole distribution.

Until now, direct tests of MV circuit breakers are carried out by connecting a recovery voltage adjustment circuit, which in the simplest case consists of a series connection of capacitance and resistance, parallel to the MV circuit breaker under test. In more complex circuits, to achieve a linear recovery of the recovered voltage in the initial region, it consists of a series-parallel combination of capacitances, resistors, and inductances.

If the recovery voltage circuit is not connected at all, the recovery voltage circuit is predominantly single frequency and the supply circuit oscillates at a natural frequency given by the magnitude of the inductance and the capacitance of the circuit, especially the size of the short-circuit current setting reactors. The lower their inductance is, the lower it is. In real test circuits, this is a decrease from the order of tens of kHz at the minimum value of the inductance of the connected reactor, to kHz units where necessary, for example when testing at 10% or 30% of the rated trip current.

In power grids, a high frequency recovered voltage is generated because part of the inductance is downstream of the switch. When the MV circuit breaker is turned off, the recovery voltage is determined by the difference in the waveforms in the circuit before and after the circuit breaker. In the same way, the recovery of the high steep recovery voltage can also be set in the test room by means of an artificial oscillating circuit connected after the switch under test. The disadvantage of this modification, however, is that in the event of a voltage jump to the MV circuit breaker ground, the magnitude of the short-circuit current only limits the inductance upstream of the circuit breaker, which can lead to destruction of the tested circuit breaker and other devices.

In the aforementioned disadvantage, the circuit according to the invention is eliminated in that the inductance of the supply circuit is divided and a recovery voltage adjustment circuit is connected to the part preferably formed by the inductance of the at least one reactor.

The advantage of connecting the circuit for adjusting the recovery voltage parallel to the part of the distributed inductance of the supply circuit is to eliminate the drop in the attainable natural frequency of the circuit, if necessary increase the initial steepness of the recovered voltage above the given frame of tested MV switch.

An example of a circuit according to the invention is further described with reference to the drawing, in which Fig. 1 shows the connection with an RC member and Fig. 2 shows a series paralleling of the RLC member in the recovery voltage adjustment circuit.

In the power circuits of the MV circuit breakers, in addition to the G generators, transformers (not shown) for obtaining the required voltage and reactors for setting the rated current are connected in the drawing. Their inductances are divided into two parts, i and the part L _K , which consists mainly of machines, for example generators and transformers, and the part t _E , which mainly consists of air reactors. A known recovery voltage circuit O _N is connected in parallel to this second part L _{R of the} split inductance, which consists of a series RC member in FIG.

Inductance of the L-part _To minimize the inductance of the power supply circuit, corresponding to the reactance of the generators, transformers and the respective bus part, it must be selected. Together with the dashed parasitic capacitances C _{of the} individual circuit elements it forms one oscillating circuit. Second resonant circuit forms part of a distributed inductance L _R together with the parallel-connected _N O adjustment circuit during the return voltage. There are no inductances with iron in this circuit, the voltage recovery depression does not apply and the achievable overshoot is therefore high. Since the natural frequency of the air coils is considerably higher, of the order of hundreds of kHz, the desired circuit frequency can be set relatively easily. The resulting shape of the recovered voltage is given by the superposition of its components from both oscillating circuits, similarly as in the case of placing a part of the reactance behind the tested switch. It is important that the stress component with a linear initial waveform is predominantly applied. By suitable selection of circuit elements it is possible to achieve practically a linear increase of the recovered voltage.

Claims (1)

SUBJECT Circuit for direct tests of high voltage circuit breaker with recovery voltage adjustment circuit, characterized in that the inductance of the power supply circuit is divided and to the part (L _R ) BACKGROUND OF THE INVENTION formed by the inductance of the at least one reactor, a recovery circuit (O _N ) is connected.