High-Current Tests on High-Tension Switchgear

The article describes a series of tests on oil circuit breakers and disconnecting switches to determine their strength at brush contacts and supports in withstanding the mechanical stresses engendered by the magnetic flux due to the flow of large currents of the order of 100,000 amperes, as may exist at times of short circuits on large systems. Other tests were made on current transformers and potential transformer fuses. For the first time, a synchronized motion picture machine and an oscillograph, were coupled to reproduce the coincident actions of the apparatus tested, and the variations of voltage and current in the circuit. The tests proved that practically all the circuit breakers then on the market had the brush contact placed in the wrong position, creating arcing before the operating mechanism had sufficient time to perform its function. The tests emphasized the importance of strong locks for disconnecting switches. Only single-turn primary-type current transformers and potential transformer fuses with resistance in series, were found adequate to give the service requirements.