The effect of distribution system grounding on MOV selection

Since most MOV arresters do not incorporate a gap in their design, the arrester is always in conduction and considered to be much more prone to damage due to steady-state line-to-neutral overvoltage. The authors investigate design parameters that affect this overvoltage, using a calculation method that considers a detailed representation of neutral grounding electrodes and their resistances which are normally neglected when symmetrical components method are utilized. It is found that obtaining a 25 Ω ground footing resistance does not ensure low overvoltages during line-to-ground faults; the highest overvoltages during line-to-ground faults can be found on short feeders and for faults close to the substation; small neutral wire can significantly increase overvoltages; and broken neutrals can result in overvoltages exceeding 1.5 per unit during line-to-ground fault conditions (neglecting transformer saturation)