Surface Insulation Breakdown Behaviors in Liquid Nitrogen Environment of Epoxy/BN Composite

Epoxy resin as an insulating material is widely used in superconducting motors because it has excellent insulation properties under extremely low temperature. The insulation properties could be damaged by surface discharge. Our previous studies were focused on surface insulation breakdown behaviors in the room temperature condition, and the results showed that the accumulated heat at the discharge area was the main reason to cause insulation breakdown. The performance of surface discharge erosion resistance in a liquid nitrogen environment was not clear. In this paper, surface insulation breakdown behaviors in liquid nitrogen were studied to clarify the effects of extremely low temperature and BN particles on tracking performance. A digital camera and an infrared camera were used to measure the breakdown process. The camera was used to record the time to breakdown and observe the whole insulation breakdown process, while the thermal accumulation and decay process was measured by the infrared camera. Obtained results indicated that insulation breakdown performance was affected by BN fillers and low temperature significantly. In the liquid nitrogen environment, the time to tracking failure is much longer than that in air. It is concluded that the extremely low temperature in liquid nitrogen could produce an inhibitory effect on surface insulation breakdown.