Experimental study on behavior of MOV based surge arrestors under distorted supply voltages

Surges due to lightning and various switching operations are a common phenomenon in electrical power systems. Due to surges, there can be transient overvoltages in the lines as high as many times the normal supply voltage. Equipment connected to the line cannot withstand these high voltages since the internal circuitry has not been designed to withstand surges. Metal oxide Varistor (MOV) is one of the best clamping devices used for electronic equipment from surges. Metal Oxide Surge Arrestor (MOSA) is made by stacking several numbers of MOV blocks to match system voltages for power system applications. Throughout life, MOVs are exposed to system voltage stress endlessly. Thus, the stress these devices experience is comparatively higher especially in the case of MOSAs. Supply voltage distortion due to harmonics is another common phenomenon found in power systems due to modem non-linear loads connected to power systems. This study is conducted to access the effect of supply voltage harmonics on the life expectancy of MOVs. Electrical and thermal experiments performed to validate relevant models for MOVs. Using simulations, and a life expectancy model, the effect of various cases of voltage distortion studied to find the effect on life expectancy. Based on the above results, recommendations have been made on how to select maximum continuous voltage of surge arrestors to minimize the effect of supply voltage harmonics on life expectancy