Variation of Discharge Characteristics With Temperature in Moving Transformer Oil Contaminated by Metallic Particles

During the operation of power transformers, the insulating oil is actually in a moving state due to the effects of various cooling systems. Therefore, the investigation on insulation characters of moving transformer oil is necessary. In this paper, the influences of temperature on partial discharge (PD) and breakdown characteristics of moving transformer oil contaminated by metallic particles were experimentally studied at first. It was found that the PD magnitude and frequency first decreased and then became higher when the temperature increased from 40 degrees C to 80 degrees C, and a minimum point appeared between 70 degrees C and 80 degrees C. On the contrary, the dependence of breakdown voltage on temperature showed an opposite tendency. In order to explain the experimental results, a simulation model involving multiple forces was constructed to obtain the movement trajectory of particles. The increase of oil temperature leaded to the decrease of dynamic viscosity of transformer oil, so the forces acting on particles and their movement characters changed. As the temperature increased, the collision frequency between particles and electrodes first decreased and then became higher, and there was a minimum point between 70 degrees C and 80 degrees C. This changing tendency was in accordance with the dependence of PD parameters on the oil temperature. In terms of the above results, the effects of temperature on PD frequency and breakdown voltage were discussed.