On modeling and testing metal oxide resistors to evaluate the arrester withstanding energy

The determination of the energy withstanding capacity of metal oxide resistors is the starting point to evaluate the probability of failure of a complete surge arrester. The energy withstanding capacity of a resistor presents a statistical characteristic. A physical explanation and an associated mathematical modeling for the discharge considering the tunneling phenomena, responsible for the instantaneous failure of the resistor is presented. A testing method able to determine the reliability of metal oxide resistors for lightning and switching impulses is developed. Based on this it is possible to conclude that, at least for switching surge impulses, the energy withstand capacity of a metal oxide resistor is constant and independent on the impulse amplitude and shape. Finally, a model to compute the probability of failure of a complete arrester is developed and presented.