The safe operation of power transformers in electrical network is crucial to the reliable of electrical power supply. Under electrical and thermal stresses, the insulation system will be degraded and increases the risk of transformer failure. The used of various diagnostic tools are become important to detect ageing and faults to avoid catastrophic failures. This paper presents the analysis results of dielectric response in time domain known as Polarization Depolarization Current (PDC) measurement on mineral insulating transformer oil under partial discharge, overheating and arcing conditions. The analysis result on the PDC pattern had show that arcing fault has higher polarization and depolarization current magnitude at the initial response compared to partial discharge and overheating fault. It concluded that faults in power transformer changes the oil properties and thus affect the dielectric response of the oil.
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