Investigations of Partial Discharge Characteristics of Moving Metal Particles in Transformer Oil Flow under AC Voltage

Abstract

Metal particles in transformer oil can seriously deteriorate the internal insulation states of power transformer via partial discharge (PD) and may ultimately lead to transformer failures. The moving metal particles within the transformer oil duct under the force of a submerged pump may have significantly different PD characteristics compared to free particles in static transformer oil. In order to investigate the PD characteristics, this study analyzed and simulated the forces and trajectories of the particles in a solid-liquid two-phase flow model under different oil flow velocities. Additionally, based on an ultra-high frequency (UHF) antenna, PD experiments of metal particles in flowing oil under alternate current (AC) voltage were carried out to obtain the variation of discharge number, PD amplitude, $\varphi-u$ and $\varphi-n$ diagrams under corresponding flow velocities. Results showed that as the flow velocity increased, both discharge number and PD amplitude decreased, whereas the shape of $\varphi-u$ and $\varphi-n$ diagrams changed little. Combing with the simulated trajectories, the cause for increasing flow velocity to suppress PDs was the decrease of the oscillating motions of metal particle between the oil duct.