Comparison of partial discharge behavior in mineral oil and PFAE under influence of spherical metal particle

Partial discharge (PD) induced by the presence of free spherical metal particle in two commercial transformer oils has been measured in order to develop an effective monitoring system for high voltage transformer. The PD measurement result of the conventional mineral oil has been compared with vegetable-based transformer oil of Palm Fatty Acid Ester Oil (PFAE) under AC applied voltage in sphere-plane electrodes configuration. The partial discharge inception voltage (PDIV) for the single particle was measured to be 11kV and 15kV for PFAE and mineral oil, respectively. The positive PD and negative PD in PFAE were lower than mineral oil at 21kV. The Phase-Resolved Partial Discharge (PRPD) of PFAE and mineral oil at PDIV and 21kV were also obtained. A wideband 50Ω impedance matching circuit (IMC) used to measure the PD indicates that the frequency spectrum of PD due to metal particle for both oils is different at 21kV. The frequency amplitude of PD in PFAE has shown a marginal decrease than mineral oil. Only two dominant frequency peaks were detected in PFAE. In mineral oil, three dominant peaks in the PD frequency domain have been detected.