Sizing and selection of grounding transformers-decision criteria

Within a period of two years, the Electricity Company of Ghana (ECG) lost a total of six grounding transformers in a particular substation. The situation created a lot of instability and resulted in huge productivity losses to both the company and its customers. The failures were believed to be related to wrong selection of grounding transformer rating. However, using the concept of capacitive charging current of a system, it was found that the short time rating of the grounding transformers were rightly selected. Analysis of the phenomenon strongly linked the damages to protection deficiency. This paper discusses analysis of the problem and proposes decision criteria for selecting a grounding transformer.