GB977732A - Improvements relating to apparatus for testing electrical circuit interrupters - Google Patents

Abstract

977, 732. Testing circuit breakers. ELECTRICAL RESEARCH ASSOCIATION. May 23, 1961 [Feb. 23, 1960], No. 6335/60. Heading G1U. In apparatus for the testing of A.C. circuit breakers which interrupt at current zero wherein a low voltage high current, and a high voltage are successively applied, an alternator is dispensed with and the high current is obtained from a D.C. source B through an inductance L1<SP>1</SP>, L1<SP>11</SP> and a variable resistance device SGB which cuts down the applied current to simulate the quarter cycle of an alternating current as it varies from its maximum to its zero value. The variable resistance device may comprise a D.C. circuit breaker with an arc-chute type suppressing circuit the resistance of which is designed to give the desired waveform, or it may be in the form of a number of resistors connected together each with its own switch, under the control of an automatic means which operates the switches in timed succession. The resistors may be in series, with their switches in parallel or in parallel, with their switches in series, and in the former the last switch may be an arc-chute type circuit breaker similar to that referred to above but much smaller, having a breaking characteristic to produce a desired rate of change of current at zero. To test the circuit breaker CB with a load comprising capacitor C1 and inductance L2 corresponding to that with which it is to be employed condenser C2 is charged with switch S2 open and circuit breakers SCB, ACB, FCB are closed to build up the direct current through the inductances L1<SP>1</SP>, L1<SP>11</SP>. The test performed by opening all circuit breakers together at the time t2 Fig. 2 feeds only a small amount of energy into the circuit breaker under test during one quarter of a cycle and it is desirable to open the circuit breaker CB at a point t6 or t7 before the opening of the variable resistance device SCB so that the energy received by the circuit breaker is the same order of magnitude as that normally experienced. Tests at a series of points can be used to indicate roughly the number of half cycles of alternating current which will pass before the circuit breaker clears. The inductances L1<SP>1</SP>, L<SP>11</SP>, are made large enough to prevent the arcing voltage of the test breaker forcing down the current D and switch S3 is time controlled to short section L1<SP>1</SP> immediately prior to the opening of the variable resistance circuit breaker SCB so that the desired wave form can be obtained. Circuit breaker ACB protects the battery against the high voltage and circuit breaker FCB is used to build up the D.C. current in place of breaker CB. In a modification described with reference to Figs. 3 and 4 (not shown) a condenser is provided in the high current circuit to discharge when the current passes through zero and thus provide the initial part of the re-striking voltage, and the high-voltage side, which does not include loading components as in Fig. 1, includes two time controlled spark gaps which connect the final re-striking voltage when that due to the condenser discharge has reached its peak. Specification 662,549 is referred to.