Synchronization of switchgear switching to waveform indices

Abstract

There is described method and apparatus to obtain synchronized switching of switchgear. A superposition of forces is used wherein the moving contacts of switchgear driven by a conventional operating mechanism has a secondary force, either opposing or aiding, superimposed upon the mechanism force under predetermined conditions to incrementally either slow down or speed up the moving contact. The computed secondary force is applied by a small servo-motor attached to the moving contact shaft. The energy of the secondary force is derived from a real time comparison of the measured position of the moving contact with its preprogrammed position in ROM at each predetermined point on the voltage or current waveform. From this comparison the required pulse energy is calculated and fed to the servo-motor which translates into the secondary force of appropriate duration thereby making the necessary incremental velocity correction. These corrections cause the moving contact to follow a preprogrammed time-distance curve such that there is a smooth time convergence of contact make and the zero voltage cross-over. The secondary force is much smaller than the mechanism force and serves only to correct for changes in moving contact travel time to closure caused by environmental effects such as temperature, pressure and age, as well as from waveform changes due to waveform distortion and frequency changes.