Partial discharge and breakdown characteristics of moving transformer oil contaminated by metallic particles

The presence of metallic particles in oil insulation degrades the performance of power transformers. At present, a large amount of research has focused on PD and breakdown characteristics initiated by particles in stationary transformer oil. However, in actual use, transformer oil flows which affect the movement of particles, and hence PD and breakdown characteristics change. In order to clarify these, PD parameters and breakdown voltage were measured in moving transformer oil in the presence of metallic particles, and the effects of flow velocity, particle size and concentration were investigated. It is found that as the oil flow velocity increased, PDIV became higher, whereas the discharge magnitude and frequency decreased. On the contrary, the discharge magnitude and frequency increased with particle size and concentration. Besides, the breakdown voltage increased with the circulation of oil, but it became lower with increasing particle size and concentration. A simulation model including electric field and fluid field was employed to study the moving trajectory of particles in flowing transformer oil. When the oil flow velocity increased, the collision number between particles and electrodes decreased and it became larger with particle size and number. In terms of the simulation results, the variation of PD characteristics could be interpreted. The breakdown voltage, as affected by oil flow velocity, particle size and concentration were discussed.