Vacuum switched capacitors to reduce induction motor caused voltage flicker on a 12.47 kV rural distribution line

The authors describe the use of solid-state controlled, vacuum-switched shunt capacitors to reduce the effects of simultaneously starting two 175 HP induction motors at the end of a rural 12.47 kV distribution line. A rather severe voltage flicker on the 12.47 kV feeder was caused by a 350 HP mining machine. The flicker was reduced to a tolerable level by installing shunt capacitors that are switched on the system in response to the current drawn by the mining machine. The scheme achieved approximately 50% reduction in flicker magnitude and significantly reduced the time of the voltage depression. The system has been in operation for one year with no maintenance problems. A complete analysis and computer simulation of the system is also presented. Verification of system operation prior to, and after, capacitor installation is provided by actual waveshapes from a computerized data acquisition system. The capacitor switching hardware is fully described