Energy ratings for metal oxide varistors under repetitively pulsed operation

Experimental tests done to determine appropriate energy ratings for ZnO metal oxide varistors (MOVs) for pulsed conditions from 10-to-20 ms long are described. Tests were performed first on single MOV units which were forced to failure in a small number of shots. Several sets of matched pairs were then operated under identical conditions to investigate current sharing and the failure statistics. Test results show that the standard rating method used by manufacturers (relating peak current, pulse length, and expected lifetime) are adequate but somewhat conservative. The manufacturers´ energy ratings hold the promise for a very economical nonlinear transfer resistor