Influence of bubble size and flow velocity on AC electrical breakdown characteristics of LN sub(2)

To evaluate insulation design of high voltage for high T sub(c) superconducting (HTS) power apparatus, the effect of bubble and electrode arrangements on the AC breakdown characteristics of LN sub(2) were investigated. Supposing that an outbreak of quench, the three electrode models were employed for breakdown voltage measurement in LN sub(2) with bubbles. Experimental results for various quench conditions revealed that the breakdown voltage of LN sub(2) with increasing the bubble size, flow velocity and electrode distance. Then, the relationship between the bubble conditions and the AC breakdown characteristics of LN sub(2) were clarified. Also, bubble movement phenomena were observed with an electrode model which consist of plane to cylindrical needle electrode immersed LN sub(2) for the simulation of the insulation environment in HTS pancake type coils and others of the quenching state. copyright 2002 Elsevier Science Ltd. All rights reserved.