Investigations of DC PD Characteristics induced by Metal Particles in Flowing Transformer Oil

The working transformer oil in practical converter transformers stays flowing state to cool the windings. In this paper, the partial discharge (PD) characteristics of metal particles in flowing transformer oil under DC voltage was investigated based on the time-resolved-partial-discharge (TRPD) patterns. On one hand, it was found that the voltage polarity had no obvious influence on the characteristics at any flow rate. On the other hand, with the flow rate increasing, the discharge number had a decreasing trend and the distribution of PDs in the patterns became more and more scattered. Besides, the PDs with a shorter time interval and lower discharge magnitude were the majority, regard less of the flow rate. The total discharge number was extracted and it significantly decreased with the flow rate. To explain the variation, the particle trajectories were simulated based on a two-phase flow model. The simulation results showed that as the flow rate increased, the collisions between particles and electrodes decreased, thereby reducing the discharge number.