Electro-thermal simulation studies for pulsed voltage induced energy absorption and potential failure in microstructured ZnO varistors

Time-dependent, two-dimensional simulations based on random Voronoi networks have been developed to study the internal heating and related breakdown effects in ZnO varistors in response to high-voltage pulsing. Our simulations allow for dynamic predictions of internal failures and the progression of hot-spots and thermal stresses. Results show that application of high voltage pulses can lead to the attainment of Bi₂O₃ melting temperatures in the grain boundaries and an accelerated progression towards failure. It is argued that reduction in grain size would help lower the maximum internal stress and enhance the hold-off voltage for a given sample size.