Short-circuit tests on current-limiting fuses: modelling of the test circuit

In the standard procedures for high power short-circuit testing of current-limiting fuses, the test circuit is conventionally characterised by the RMS test voltage, prospective current, frequency, closing angle, and power factor. From these parameters a constant RL equivalent circuit can be derived, which has been widely used in the modelling of fuse-breaking transients but recent studies have shown that this circuit model is inadequate. The frequency dependence of R and L has been investigated by fast Fourier transform analysis of fuse-breaking test transients obtained in a high-power short-circuit test laboratory, and the results show that, while L decreases slight, R increases greatly with frequency. The nominal power factor value provides only a measure of the DC resistance of the circuit. The frequency dependence of R must be taken into account for accurate modelling of the operation of current-limiting fuses