The Barrier Effect on Breakdown for Design of 154 kV Class HTS Transformer

LN
₂
is used as an insulating material as well as a cryogen for a 154 kV class HTS transformer. However, main insulation with LN
₂
is not enough, and thus, research on barrier has been performed. The most of experiments on this barrier effect are combination of paper and air (air, SF
₆
, etc.), and also the results from these experiments on barrier effect are insufficient to be used practically for the electric insulation design of the 154 kV class HTS transformer. Moreover, there are insufficient researches regarding cryogenic liquid used for superconducting equipments. In this paper, we examined the breakdown properties of the barrier related to the position, number and materials. With the database in the electrical breakdown properties, the electric insulation design as the main insulation for the 154 kV class.