Abstract:
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.
