Experimental Study on Breakdown Characteristics of Transformer Oil Influenced by Bubbles

Abstract

Bubbles will reduce the electric strength of transformer oil, and even result in the breakdown of the insulation. This paper has studied the breakdown voltages of transformer oil and oil-impregnated pressboard under alternating current (AC) and direct current (DC) voltages. In this paper, three types of electrodes were applied: cylinder-plan electrodes, sphere-plan electrodes, and cone-plan electrodes, and the breakdown voltages were measured in both no bubbles and bubbles. The sphere-sphere electrodes were used to study the breakdown voltage of the oil-impregnated pressboard. The results showed that under the influence of bubble, the breakdown voltage of the cylinder-plan electrode dropped the most, and the breakdown voltage of the cone-plan electrode dropped the least. The bubbles motion was the key factor of the breakdown. The discharge types of the oil-impregnated pressboard were different with bubbles, and under DC, the main discharge type was flashover along the oil-impregnated pressboard, while under AC, the main discharge type was breakdown through the oil-impregnated pressboard.

A Short Review of Some of the Factors Affecting the Breakdown Strength of Insulating Oil for Power Transformers

“…Such observations are in agreement with those of [52]. Somewhat similar results were obtained in [61], where it was remarked that gas bubbles have a minimum effect with a nonuniform field arrangement because the movement of the bubbles and the corona will prevent the bubbles' discharge path. Discharge characteristics have been investigated in [62] with different electrode arrangements varying from point-plane to semi-homogeneous sphere-plane configuration, where it was reported that they depend on applied voltage, time of application and moisture content.…”

Applications of Plasma-Liquid Systems: A Review

“…Besides the above-mentioned applications, in which non-thermal plasmas are mostly being used in contact with aqueous solutions or solids containing high water amounts, non-thermal plasmas have also been applied in contact with or inside non-aqueous solutions, of which dielectric media are by far the most explored. Indeed, in literature, multiple studies focusing on plasma interactions with non-polar liquids, e.g., transformer oils, mineral oils, hydrocarbon oils, liquefied gases, etc., can be found [307,308,309]. More specifically, electrical discharges in hydrocarbon oils have been widely investigated and electron impact ionization was proposed as the primary mechanism driving a plasma discharge for both negative and positive polarities [310,311,312].…”

Engineering Dielectric Liquid Applications

“…Qin et al [1] experimentally investigated the influence of bubbles on the breakdown voltages of transformer oil and oil-impregnated pressboard under 50 Hz alternating current and direct current (DC) voltages while considering cylinder-plan, sphere-plan electrodes, and cone-plan electrodes. It is reported that, under the influence of bubble, the breakdown voltage of the cylinder-plan electrode dropped the most and the breakdown voltage of the cone-plan electrode dropped the least.…”