SYNCHRONIZED OPERATION OF HIGH-VOLTAGE CIRCUIT-BREAKERS

The severity of transients introduced by switching of highvoltage circuit-breakers strongly depends on the phase instant of opening or closing the circuit. With synchronizing, the equipment automatically chooses the optimum instant for switching. Capacitor banks, off-load lines, reactors and transformers are typical cases where proper control of closing or opening instant of circuit-breaker reduces the switching transients. A microprocessor based control device identifies a suitable phase instant and withholds the switching command until the right moment. Since long-term variations of the circuit-breaker closing time can not be excluded, a self-adjusting feature has been included. The processor compares the predicted closing instant with the actual one, and adjusts the next prediction with half the measured error. Synchronizing of single-pole operated circuit-breakers is straight forward. Each separate pole is controlled and operated individually. For three-pole operated circuit-breakers, it is necessary to introduce a mechanical delay, "staggering", between the poles, tailored to the specific application. Intense studies and field tests have been made during the past few years in order to check the operation. Synchronized switching has the potential to solve virtually all the problems dealt with conventionally by using closing resistors, surge arresters, damping reactors, and the like. Since the efficiency and reliability is high and the investment cost is low, synchronized switching is subject of a rapidly increasing demand from utilities.