Calculating the influence of the circuit breaker on overvoltage probability distributions

Small changes in element parameters which can be caused by manufacturing tolerances, wear, aging, and maintenance can cause significant changes in the overvoltage performance of a power system in which they are incorporated. To study the effect of such dispersion on the performance, a computer-controlled transient-network analyser capable of rapid, accurate estimation of overvoltage-probability distributions has been developed. This system has been used to study the sensitivity of the probability distribution of overvoltage peaks to changes in circuit-breaker characteristics. The effects of prestrike, mechanical dispersion of contact-closure instants between phases, and preferred pole-closing sequences were investigated in typical networks using both plain and resistor-equipped breakers. Significant changes in overvoltage-probability distributions which could cause up to tenfold increases in line-flashover probabilities were found.