Modelling and Experimental Generation of 500 nanoseconds Virtual Front Time Current Impulse

The power system equipment is prone to various surges while in service. Surge arrester offers protection against the surges by maintaining a safe voltage level while bypassing them to ground. IEC 60099-4 standard classifies the current surges as switching, lightning and steep current impulses, while determining the protection voltage level offered by the surge arrester. Protection voltage level estimated for switching, lightning and steep current impulses is further utilized while performing insulation coordination study, in order to design the power system with optimum protection margin. Steep current impulse defined by the standard is the fastest among the three, with a virtual front time of 1μs. As the surge becomes faster, the protection voltage level developed by the surge arrester element will also increase. In certain scenarios like the circuit breaker current interruption, bushing flashover etc., the steepness of the current surge can be even faster than 1μs. Therefore, it was proposed to generate the current impulse with a virtual front time of 500ns in order to study the performance of surge arrester element during such scenarios. In this paper, the impulse current generator circuit that can create current impulse of 500ns virtual front time is modelled in EMTP and the same is generated experimentally.