An electronic method of controlling multiple reignition switching transients in vacuum contactors

Abstract

An electronic method of controlling the contact tip opening of a vacuum contactor in such a way that the probability of transient overvoltages caused by multiple reignitions during load switching is minimized is discussed. A description of the multiple reignition transient problem is provided, and the electronic hardware utilized to control the vacuum contactor is described. Tests of the effectiveness of the system were performed, and a brief description of the test procedure and results is provided. It was confirmed that control of the tip opening point on the load current waveform prevents vacuum contactors from producing multiple reignition transients even under severe conditions such as jogging duty. By varying the tip opening angle of the contactors under test, a range of arc angles was found where multiple reignitions did not occur. Other functions that can be provided by the microprocessor-based electronic control are also discussed. It is concluded that the utilization of this technique when vacuum contactors are applied to motor loads should result in reduced stress levels on motor windings and may lead to longer machine life. >