Effect of External Magnetic Fields on the Breakdown and Partial Discharge Characteristics of Vegetable Oil

Vegetable oil is based on natural ester oil, which is considered as the alternate natural source of traditional mineral insulating oil in electrical transformers. The oil applied in transformers performs dual functions of insulating and cooling materials. Partial discharges in an insulation system are incipient discharges that can damage materials and may eventually lead to complete failure of the electric transformer during operation. This paper presents an investigation on the effect of an external magnetic field on partial discharge (PD) characteristics of the vegetable oil applied in transformer. Although it has long been known that high magnetic fields are present in equipment, such as power transformers, where PD may occur, only a few investigations have been made on the effect of the magnetic field on the discharge characteristics of the traditional mineral oil. In the present study, magnetic fields of up to 500 mT were applied in the test oil samples with electric field stress simultaneously applied to produce PD. The PD characteristics along with the breakdown strength were recorded both before and after the application of the magnetic field.