GB961882A - Improvements relating to apparatus for testing electrical circuit breakers - Google Patents

Abstract

961,882. Testing circuit breakers. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Feb. 19, 1963 [March 7, 1962], No. 8815/62. Heading G1U. Apparatus testing an electrical circuit breaker comprises a first circuit supplying a large low voltage current to the test breaker over an auxiliary breaker; a second circuit supplying a small additional test current to the test breaker followed by a restriking voltage when the auxiliary breaker is open, and means for injecting a re-igniting current pulse into the test breaker immediately before at least one zero value of the test current on interruption thereof in order to change rapidly the polarity of such current and maintain the test breaker arc. For testing a circuit breaker TCB, a voltage source V1 is connected in series with a stopper coil SC and an auxiliary circuit breaker ACB supplying a main low voltage test current to breaker TCB whose break time exceeds one half cycle of test current. A voltage source Y2 is switchably connected to charge capacitor C2 which is dischargeable over spark gap G1 and inductance L into capacitor C1. The latter is dischargeable over isolator I1 into breaker TCB to supply a small additional test current to the gap followed by a restriking voltage. An auxiliary circuit producing a re-igniting current pulse comprises capacitor C3 chargeable from source P1 and connectible over isolation gap G2, resistor R1 shunted by capacitor C6 and, triggered gap TG1 to discharge into ACB and TCB, the pulse maintaining the arc at TCB at each half cycle and being excluded from V1 by SC. An inductance L2 in series with TCB is associated with a further auxiliary circuit comprising capacitor C4 chargeable from source P2 and in series with spark gap G3 and triggered spark gap TG2, to discharge into TCB1 producing a further sharply peaked re-igniting current pulse assisting that derived from C3. TG1, TG2 are triggered from the secondaries of ferrite cored current transformers F1, F2 whose primaries are the test current conductor and a conductor carrying a further current derived from V1 over resistance R3 and leading the test current by 90 degrees. At a critical value of test current approaching zero of each half cycle the test current and the further current will cancel, and secondary pulses will trigger TG1, TG2 at an instant determined by R3. The test current rapidly traverses zero, and the arc is maintained at the gap of TCB, while isolator I1 opens before application of each re-igniting pulse and closes during the half cycle preceding application of the restriking voltage and small additional test current from C2, by triggering gap G1 A further relay circuit controls the application of triggering pulses to TG1, TG2 so that the re-igniting pulse is applied only when required. A cathode ray oscillograph may be connected across resistance R4 in series with the gap of TCB.