Impacts of electrode geometry and gap length on the breakdown voltage of insulating liquids

This paper investigates the impact of different electrode geometries on the dielectric strength of insulating liquids under high-voltage direct current (HVDC). The study focuses on two electrode configurations sphere-to-sphere and mushroom-to-mushroom and two insulating liquids: soybean oil and mineral oil. Experimental tests were conducted at varying electrode gaps (1.0 mm to 4.0 mm) to determine the breakdown voltages (BV) for each liquid. The BVs were analyzed to understand the effects of both electrode geometry and liquid type on dielectric performance. Although the prospect of vegetable oils as alternative insulation liquid for high voltage applications have been reported in the literature, the statistical variability under the stated electrode configurations have not been covered, to the best knowledge of the authors. Results show that electrode geometry plays a crucial role in determining breakdown strength of liquids.The BV of the liquids increases with increasing gap length under both configurations. For the sphere-sphere configuration, soybean oil broke down at 6.90kV at a gap length of 1.0mm, while that of mineral oil occurred at 3.975kV. At 4.0mm, the breakdown voltages were recorded as 14.15kV and 11.225kV for soybean and mineral oils respectively. For the mushroom-mushroom configuration, Soybean oil broke down at 4.95kV at 1.0mm, while that of mineral oil occurred at 4.225kV. At 4.0mm, the breakdown voltages were recorded as 12.5kV and 12.925kV for the vegetable oil and mineral oil respectively. Thus, soybean oil demonstrated competitive dielectric properties compared to the mineral oil. However, statistical analysis revealed a lower variability in the performance of mineral oil compared to vegetable oil in which the highest standard deviations (SDs) were both obtained at gap length of 2.0mm as 0.45kV for the former and 0.86kV for the latter. Despite the higher BV of vegetable oil, the mineral oil is more stable over a range of operation conditions which suggests a complex nature of choosing appropriate liquid dielectrics for insulation purposes in HV equipment.