In addition to the insulation testing mentioned above, for large switches and circuit breakers the following tests can be applied.
A. Circuit breaker time-travel analysis.
This test, used on medium and high-voltage circuit breakers provides information as to whether the operating mechanism of the circuit breaker is operating properly. This test can be used to determine the opening and closing speeds of the breaker, the interval time for closing and tripping, and the contact bounce. The test provides information that can be used to detect problems such as weak accelerating springs, defective shock absorbers, dashpots, buffers, and closing mechanisms. The test is performed by a mechanical device that is attached to the breaker. One device, a rotating drum with a chart attached, is temporarily connected to the chassis or tank of the breaker. A movable rod with a marking device attached is installed on the lift rod portion of the breaker. As the breaker is opened or closed, the marking device indicates the amount of contact travel on the chart as the drum rotates at a known speed. With another available device, a transducer is attached to the movable rod, and the breaker operation is recorded on an oscillograph.
Wuhan Huayi electric power developed the circuit breaker analyzer model number GKC-Y, which can accurately measure the mechanical dynamic characteristics of high-voltage circuit breakers of various voltage levels, such as less oil, more oil, vacuum and sulfur hexafluoride.
B. Contact-resistance testing.
This test is used to test the quality of the contacts on switches and circuit breakers. A test set designed for this purpose is available with direct-scale calibration in microhms, capable of reading contact resistances of 10 microhms or less. An alternate method is to pass a known level of direct current through the contact structures and to measure the do millivolt drop across the contacts. The data obtained can then be converted to resistance by applying Ohm's Law. The alternate method requires a source of at least 100 amperes with a mill volt meter of approximately 0-20 mV range.
Wuhan Huayi electric power developed the contact resistance tester, which has different models 100A/200A/400A/500A/600A. It has 0.01μΩ resolution, and a built-in printer. It can meet the requirements of on-site maintenance of high-voltage switches in power and power supply departments and circuit resistance testing in high-voltage switch plants. Suitable for high and low voltage switch contact (loop) resistance, cable line DC resistance value of high precision measurement, also suitable for other need large current, micro resistance measurement occasions.