Advances in Capacitor Starting

An 8000-hp motor at the LOCAP Pipeline Clovelly Station is brought on line with three step capacitor starting and is protected from resonant overvoltage by a large metal oxide voltage limiter. Three-step starting is required to stay within the utility requirement of a maximum of ±1.5 percent primary voltage fluctuation during the entire starting operation. Cycle timers are utilized to obtain critical breaker sequencing as well as protect the system from breaker failure. Should the utility power fail while the motor is accelerating, the starting capacitor may cause severe motor overvoltage. Zinc oxide limiters are sized to absorb 1 MJ over a period of ten cycles allowing the breakers to clear the motor and capacitors.