Circuit breakers for switching 230-kv lines

EXCESSIVE TRANSIENT VOLTAGES are the principal concern in switching long 230-kv lines. Such voltages are usually the result of commutation of line capacitance with respect to supply voltage by restriking of line circuit breakers. Experience has shown that restrikes will generally produce higher voltages on long lines than on relatively short lines. This is because the breakers will usually interrupt long-line restrike current at the first current zero, leaving the line charged at high potential, which in turn is apt to result in even higher transient voltage should further restrikes occur. Thus consideration must be given to breaker design safely to permit line switching.