Dynamic characteristics and cascaded coordination of limiting-type SPDs under subsequent negative strokes

Subsequent negative impulses are steep and common in lightning flashes. Under such currents, the dynamic behaviour of metal-oxide varistors (MOVs) is expected to be significant and would affect the coordination of cascaded surge protective devices (SPDs). This study experimentally investigates the dynamic behaviour of MOVs under steep currents. Based on the dynamic characteristics, simulations are conducted to investigate the coordination of two-cascaded limiting-type SPDs with different cascaded combinations, different separation distances, and different loads under subsequent strokes with 0.25/100 μs current waveform. Meanwhile, the results are compared with that under 8/20 and 10/350 μs currents. Experiments are performed to investigate SPD coordination performance under subsequent strokes. The results show that voltages on MOVs of low-voltage SPDs increase about 6.8-18.7% under steep currents, compared with that under 8/20 μs current. Thanks to the significantly changed dynamic characteristics, the cascaded SPDs could more easily realise effective coordination under subsequent strokes, compared with that under 8/20 and 10/350 μs currents. Moreover, effective coordination can be achieved in large ranges of separation distances and loads under subsequent strokes. The SPD combinations with clamping voltage of upstream SPD a little higher than downstream SPD have the best behaviour for lightning protection in low-voltage systems.