Influence of bubble size and flow velocity on AC electrical breakdown characteristics of LN2 Original Research Article

To evaluate insulation design of high voltage for high Tc superconducting (HTS) power apparatus, the effect of bubble and electrode arrangements on the AC breakdown characteristics of LN2 were investigated. Supposing that an outbreak of quench, the three electrode models were employed for breakdown voltage measurement in LN2 with bubbles. Experimental results for various quench conditions revealed that the breakdown voltage of LN2 with increasing the bubble size, flow velocity and electrode distance. Then, the relationship between the bubble conditions and the AC breakdown characteristics of LN2 were clarified. Also, bubble movement phenomena were observed with an electrode model which consist of plane to cylindrical needle electrode immersed LN2 for the simulation of the insulation environment in HTS pancake type coils and others of the quenching state.