Effect of Static Floating Particle Shapes on Partial Discharge Characteristics in Mineral Oil

The existence of metal contaminants can reduce the performance of transformer oil by leading to partial discharge or even complete breakdown. Applied electric field will make particles move or even may float in the insulation. Many studies have been made to observe free moving particles effect on electrical performance of transformer oil. In this work, investigation on floating metal particle effect on partial discharge characteristics of mineral oil was conducted. The metal particle was artificially floated between 10 mm gap of plane-plane electrodes using a plastic stick. Two different shapes of particle but having similar volume, which were 2 mm diameter of ball and 2.8 mm length of cylinder with 1.5 mm diameter, were fabricated from copper material. In addition, the particle was positioned into three different points, which were having contact with electrode, floating in the vicinity of electrode, and floating near the gap center. Then, both electrodes system and floating particles were put in new mineral oil. Partial discharge measurements and observations were carried out under AC voltage. The results showed that both particles generated slightly different partial discharge pattern and more intense when placed near the electrode. It is expected that local field enhancement around the particle and the distance between the electrode and the particle play key role on the phenomena. It can be concluded that partial discharge characteristic of the particle was quite different with the floating particle position.