Electrical insulation characteristics in the simulated electrode system of HTS double pancake coil

For the experiment the four types of spacer were distinguished by arrangement that could improve the dielectric strength with making long the path of flashover. One of the spacers could be applied to an insulator between windings of high temperature superconducting (HTS) transformer. The flashover characteristic of each type was investigated and. the, flashover phenomena were observed to understand breakdown mechanism in liquid nitrogen (LN2). In the first, the flashover characteristic in LN2 was compared with in air using the simulated electrode made from five turns of HTS tape. The dielectric strength of spacers was improved with arrangement in air but not in LN2. Through the observation, of flashover phenomena, micro gap between the spacer and the coil electrode generating bubbles was regarded as the main reason. In the second, the effect of micro gap on flashover was investigated with plane-plane electrode system. The micro gap decreased the flashover voltage by 70 percent. At last, the dielectric strength of spacer in LN2 also could be improved by filling an epoxy of small amount in the gap between the coil and the spacer.