Through fault current effects on distribution transformer and prevention actions using backup protection : Case study of Kelapa Gading transformer

Failure due to external fault. This external fault, known as through fault current (TFC), determined as fault occur on low side of transformer. This condition become an issue in PLN transmission unit nowadays because this fault highly effected to the lifetime of transformer, especially distribution transformer (150/20 kV and 70/20 kV). Beside the loss of the material, it is also bring the consequence to the quality of the company services. To prevent this condition, some actions must be taken. TFC has three parameters that take effect directly to the transformer condition, i.e. magnitude, duration and frequency of fault. Controlling two of three parameters could be reduce the effect of TFC. Therefore, this paper will present about decreasing the impact of TFC to the transformer by using backup protection in transformer to limiting the value and duration of the TFC. This limitation is done by calculating the backup protection of the transformer for high setting in over current relay (OCR) installed on the incoming side. OCR high set must be calculated by considering equipment safety, system reliability and proper coordination among the OCRs. Hopefully, with the new setting calculation can reduce the number of transformer failure due to TFC.