Degradation assessment of metal oxide varistors using a statistical experimental design

The proliferation of metal oxide varistor (MOV) arresters in various industries prompts the need to improve reliability thereof. This is only achievable through first expanding current knowledge of these devices, particularly with regard to degradation mechanisms. Currently, there are no methods available to conclusively evaluate factors suspected of influencing degradation. This study investigates two such factors, namely, microstructural composition and distorted voltage supply (harmonic distortion). Furthermore, a statistical experimental design methodology is proposed to definitively assess the significance of the effects of these factors on the degradation of MOV arresters. The experimental methodology comprises thermally accelerated degradation under distorted and nondistorted voltage and scanning electron microscopy. Samples from three different manufacturers are used for the study. Results indicate that the differences in microstructural composition, owing to manufacturing differences, have a significant effect on the failure rate and, thus, on the reliability of MOV arresters. Distorted supply voltage is also found to have a significant effect on the failure rate of MOV arresters.