Oil Insulation Analysis due to Electrical Arcing of Power Transformers Degradation

One of the causes of the power transformer failure is the breakdown of insulation due to excessive heat. The excessive heat usually caused by various factors, one of that is a short circuit. The magnitude of the short circuit current that exceeds the standard of the transformer's ability to withstand the fault current can trigger a temperature increase in transformer oil which can appear the harmful gases known as fault gases and can provide axial-radial forces in the transformer. To find out early on the failure that occur in the transformer due to a short circuit, it is to conduct electrical testing on transformers and test oil insulation transformers with DGA method. In this contribution, an experience of the 150/20 kV 60 MVA power transformer case in Brebes Substation, the result of the DGA test analysis obtained significant increase in the TDCG trend from the DGA test results. Then, using the Key Gas method, there is an indication of electrical arching from the result of gas formation increase in C2H2 and H2 gases. Afterward, using the Duval Triangle method, which has been analyzed from the composition of CH4, C2H4, and C2H2 gases, obtain the results of the thermal fault condition. Furthermore, the isolation resistance test indicate the short circuit on the core-yoke part with the test result of 0 MΩ. Therefore, it can be concluded that the cause of the increase key gases in the DGA test results is the short circuit between the yoke shunt and the transformer core.