GB1242400A - Method of and apparatus for testing circuit breakers - Google Patents

Abstract

1,242,400. Testing circuit breakers. ENGLISH ELECTRIC CO. Ltd. Oct.15, 1968 (Oct.20, 1967], No.47951/67. Heading G1U. A circuit breaker 20 is tested at "make" under short circuit current conditions and at "break" under alternating recovery voltage conditions by first applying across the open circuit breaker 20 and an auxiliary breaker 21 the rated voltage, which is derived from a low frequency, low voltage current source 10 summed with a low frequency, high voltage from a recovery voltage source 13. The test breaker is closed, and the build up of current monitored by detector 22, which detector triggers the spark gap 25 and subsequently the auxiliary breaker 21 to complete a short circuit current path for the current from the source 10. After four half cycles of short circuit at low frequency, the test and auxiliary breakers are opened, and a high frequency transient voltage from a voltage injection circuit 12 is applied across the auxiliary breaker, so as to suppress any current flow therein and subject the test breaker to the combined voltages from the low and high voltage sources and to the high frequency transient voltage. The alternators 14, 32 in the current and recovery voltage sources are coupled. The voltage injection circuit incorporates a series resonant circuit 28, 26, whose capacitor bank 26 is charged from a D.C. source 41, which is fired by triggering spark gap 27. Interruptors 17, 34, 29 enable the various circuits to be turned off. The circuit 38 simulates the length of the transmission line with which the test breaker will be associated, and the resistor 40 and capacitor 39 shunt the simulating circuit 38 and the test breaker. Prior to the break test a resistance current interrupter 42 is closed so that the test breaker will clear more easily. It is opened as soon as the test breaker clears. Following the break, the gap 27 is triggered as the first current zero is approached, so that the high frequency injection voltage is applied, to cause the current through the auxiliary breaker 21 to fall to zero more rapidly than normal. This means that the current through the test breaker falls to zero later than normal. It will then be stressed by the sum of voltages from the sources 10 and 13. Capacitors 23, 29, 31 control the waveforms applied to the breaker and resistors 30 and 40 damp parasitic oscillations in the injection transient. Following the decay of the transient voltage the isolating breaker 29 may be opened to allow recharging of the capacitor bank 26.