The impact of line protection operate time on circuit breaker wear

In this paper the impact of relay operate time on circuit breaker wear, is analysed. The presented results show that the proposed concept of a fixed relay operate time (equal to half fundamental frequency cycle) is arguably the most beneficial, from an overall power system perspective. When ultra-fast relay operation (below 3 ms) is compared to the fixed operate time (10 ms), it causes >20% increase in circuit breaker wear. On the other hand, having a 3-6 times faster relay operate time brings only a very modest improvement in the average fault clearing time; of just around 13%. This leads us to question the main paradigm of transmission line protection, declaring that “faster is better”;; particularly when considering circuit breaker wear and power system stability aspects. The analysis supports the thesis from the International standards for circuit breakers that the initiation of circuit breakers operation while fault current asymmetry is high is damaging to the circuit breakers.