Point-on-wave capacitor switching and adjustable speed drives

In principle, capacitor switching disturbances can be eliminated by closing individual breaker poles when the gap voltage is zero. In practice random variations in pole timing, and prestrikes due to finite closing speed, limit the reduction possible. A real time digital simulator was configured with a commercial circuit breaker controller to study what levels can be achieved using typical independent pole breakers. It was found that disturbances reaching 1.7 pu with random timing can be easily reduced to 1.3 pu, sufficient to prevent trips on a 460-V adjustable speed drive. The study also reviewed resonance in a customer-owned capacitor bank, raising disturbances on random switching to 2.8 pu. Here a reduction to 1.3 pu is difficult to achieve through timing of existing breakers.