Evaluating Overvoltage Protection Scheme of Pole Mounted Transformers Employed by ECG

Abstract

Pole-Mounted-Transformer (PMT) failures present a major threat to the Electricity Company of Ghana (ECG). These failures have been observed to occur frequently during thunder and lightning activities, raising strong suspicion that ECG’s existing pole mounted transformer protection scheme is inadequate. Over the years, the company has used and relied on the protection scheme that separates the primary surge arrester’s grounding from the low voltage neutral terminal of the pole mounted transformer. Unfortunately, literature on the subject is equally inconclusive . Whilst certain schools of thoughts encourage the interconnection of arrester grounding and LV neutral grounding, some codes do not allow it. In this study MATLAB Simulink is used to evaluate the effectiveness of the existing protection scheme adopted by the Electricity Company of Ghana. It was found that separating the HV grounding from the LV neutral grounding makes the transformer more vulnerable to lightning-induced overvoltage. The study recommends alternative solutions to deal with the problem.