Stability of Metal-Oxide Varistor Characteristics in Exploitation Conditions

Abstract

Wide-spread use of metal–oxide varistors for non-linearity over-voltage protection results in a variety of possible working conditions. It is therefore essential to have a thorough insight into their reliability in various exploitation environments. The influences of temperature variation, aging and radiation exposure on metal–oxide varistors characteristics were investigated in this paper. Stable and effective over-voltage protection over a wide temperature range is always a desirable property, one which significantly contributes to overall system reliability. Behaviour of metal–oxide varistors in the temperature range from −50 ◦C to 150 ◦C was investigated. Aging caused by exploitation was investigated by applying 1000 consecutive double exponential over-voltage pulses to the varistors. Resistance of metal–oxide varistors to the radiation is of special interest in nuclear, military, and space technology. Radiation effects of californium-252 combined neutron/gamma radiation were examined. Voltage–current characteristics, voltage–resistance characteristics and the value of breakdown voltage were used to characterize metal–oxide varistors operation. Non-linearity coefficient, defined from the voltage–current curve, was also used as a parameter. Results are presented with the accompanying theoretical interpretations of the observed changes in metal–oxide varistors behaviour.