FAILURE MODELING FOR ZNO VARISTORS

The energy-absorption capability of zinc oxide varistors depends on bo th the binder burn-out and shrinkage rate of the disc. This paper pres ents a study of the development of a failure model of a varistor disc with a nominal voltage V-nom = 5 kV and a diameter of 42 mm manufactur ed by rate-controlled sintering. The mathematical model has been devel oped in terms of the binder burn-out rate and the shrinkage rate for t he electrical-energy capability during initial failure and 50% failure of the samples, to secure the optimum temperature profile for the sin tering operation. The effect of the binder burn-out and the shrinkage rate has been investigated using design of experiments and response su rface methodology (RSM). Response surface contours were constructed by computer, giving the response in terms of the binder burn-out rate an d the shrinkage rate. (C) 1998 Elsevier Science S.A. All rights reserv ed.