OVERVOLTAGE PROTECTION OF POLE MOUNTED DISTRIBUTION TRANSFORMERS

Abstract

The failure rate of pole mounted distribution transformers due to lightning is relatively high even if arresters are installed on their primary side. Dangerous voltage stresses resulted from the operation of the arrester connected to the primary terminals may appear in the transformer insulation. To clarify this phenomenon, a computer simulation has been undertaken. The authors have performed a sensitivity analysis in order to determine the main parameters influencing the stresses. It has been found that the most significant parameters affecting the voltage stresses in the transformer are the arrester current, the transformer connection and the transformer grounding resistance. The voltage stresses in the HV winding can be sufficiently reduced by means of spark gaps on the LV terminals besides the HV arresters.