The Calculation of Energy Dissipation in Metal Oxide Varistors for Power Distribution Applications

Metal oxide varistors (MOVs) are used in power distribution engineering to suppress lightning and switching surges. Techniques from solid state engineering as well as laboratory experiments have been used to derive models for these devices. The models so derived are combined with circuit models for the distribution system to obtain an integrated, lumped parameter, nonlinear model. The model is used to assess the voltage and current waveshapes in the MOV and to evaluate the energy dissipated in the MOV. The application of such a calculation is illustrated to assess the energy rating of an MOV arrester for an electronically controlled distribution circuit. Comments on the switching time of the MOV are provided: the characteristic time of impact ionization events is typically on the order of femtoseconds to picoseconds.