Investigation on impact of magnetic field on the corona discharge activity in Punga oil using fluorescent fiber and UHF sensor techniques

This paper reports the experimental investigation of the corona discharge activity of punga oil under the influence of a local magnetic field and different voltage profiles (AC and DC voltages) using fluorescent fiber sensor as well as UHF sensor technique. The corona inception voltage (CIV) of punga oil is higher under negative DC voltage followed by positive DC and AC voltage, with a marginal reduction in its CIV magnitude observed on the impact of external magnetic field. The dominant frequency of the UHF signal obtained under AC voltage shifted towards lower frequency (0.6 GHz) with the influence of magnetic flux density to about 85 mT. The rise time, pulse width and energy content of the fluorescent signal formed due to corona activity under AC voltage is found to vary under high magnetic fields confirming the inception results. The fluorescent signals formed due to corona discharge under both AC and DC voltages have its dominant frequency at 1 MHz with no shift observed in the presence of magnetic field. Also, there is no variation in the phase resolved partial discharge (PRPD) pattern observed due to corona discharge (with and without magnetic field) signal using both UHF sensor and the fluorescent sensor. The fluorescent fiber-based technique provides a better accuracy on detecting the corona discharges in punga oil at an early stage compared to conventional UHF sensor. The breakdown voltage of punga oil under different voltage profiles with and without the effect of magnetic field follows normal distribution. The dielectric dissipation factor and electrostatic charging tendency (ECT) of punga oil is observed to be higher than the limit set for insulating fluids towards power transformer operation.