A Durability Model for Analysis of Switching Direct Current Surge Degradation of Metal Oxide Varistors

In this study, a durability model for predicting the lifetime of MOV devices used to prevent DC switch damage due to occasional switching surges is proposed and validated. In addition, MOV devices are subjected to induced switching DC surges of a constant amplitude and variable time durations. Each MOV of the 270 selected devices sourced from three different manufacturers with similar size and electrical specifications was subjected to 5000 degrading surges. Three samples of 30 of the selected MOV devices from each manufacturer were degraded by induced switching DC surge durations of 2, 3, and 4 ms in order to reach an undesirable degradation level of 10% change in V_{1 mA}. A statistical analysis of the three MOV manufacturer sample averages of the accumulated conduction charge transfer at 10% change in V_{1 mA} supported the proposed durability model irrespective of the surge charge content variation and MOV material differences. The results show that MOV device durability or resilience may be more accurately modelled by using the surge average accumulated conduction charge transfer of a statistically significant MOV device sample.