Effect of magnetic nanoparticles on partial discharges in transformer oil

Abstract

We report on an experimental study of partial discharges (PD) in transformer oil with four different volume concentrations of superparamagnetic iron oxide nanoparticles (SPION) ranging from 0 to 0.0004 vol%. To investigate the PD, a specific high-voltage setup was designed. Thanks to the small amount of SPION in the oil (transparency), the PD events in the form of visible corona and streamer discharges were visualized by a CCD camera. Furthermore, the PD inception and extinction voltage, apparent charge and quantities derived from the PD recurrence, as pulse repetition rate and phase resolved patterns, were analyzed in dependence on SPION concentration. It was found that the PD inception voltage increases quasi linearly with increasing SPION concentration but the extinction voltage is practically unaffected. The pulse repetition rate decreases as a result of the increasing SPION concentration. The decreased PD activity is clearly concluded also from the reducing shape and growth of the visual corona discharge patterns. To interpret the observed suppression of PD in transformer oil-based magnetic nanofluids, the electric field modification and injected charge trapping by the dispersed nanoparticles is considered. Moreover, a possible effect of the local magnetic fields around the SPION on the space charge migration is taken into account, too.