Stability of Metal-Oxide Varistor Characteristics in Exploitation Conditions

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