Pole Factor Calculation

This chapter discusses the current interrupting rating basis for circuit breakers to provide the context for the voltage calculations. According to IEC 62271‐100, the IEC standard for AC circuit breakers rated at 1 kV and above, circuit breakers are applied on either an effectively earthed system or a non‐effectively earthed system. When using symmetrical components to calculate fault currents, the equivalent circuit for the fault case is obviously that when the currents are still flowing, i.e. before current interruption. To calculate recovery voltage, the equivalent circuit is one step down, i.e. the current has been interrupted in the phase of interest while the fault currents in the other phases continue to persist or has been interrupted as in the case of a single‐line to earth fault. This chapter considers the following cases: effectively earthed systems (double‐line to earth fault, single‐line to earth fault); and non‐effectively earthed systems (line‐to‐line fault).