Ageing Characterisation of Varistor Arresters: A Statistical Model for Grain Response Under Applied Thermal Stress

In this work, regression analysis is invoked to predict relationship between varistor microstructure response and temperature for degradation characterisation or assessment of metal oxide surge arresters (MOSA). Accelerated degradation test is conducted on varistor samples—having similar electrical and physical characteristics—at randomly selected temperature points for equal period of time. The reference voltage—measured before and after accelerated degradation test—is used as the degradation criterion for varistor samples. Linear intercept performed on Scanning Electron Microscopy (SEM) micrographs is relied upon to estimate varistor average grain size at each applied thermal stress. The coefficients obtained for the developed regression model are statistically validated using the one-way analysis of variance (ANOVA). Results show that for each 1 °C variation in the accelerating temperature, which corresponds to 52. 6 h of service time, varistor average grain size increases by 0.143 microns.