Constant Voltage Breakdown Measurement of Lapped Insulation Under Cryogenic Conditions

A method for assessing constant (dc) voltage breakdown in lapped insulation under cryogenic conditions is presented, focusing on Kraft paper, Kapton and PPLP. Breakdown estimation under cryogenic environment can be greatly improved in terms of confidence and test duration by using a moving breakdown point along the sample. Experiments carried out in liquid nitrogen and gaseous helium at about 77 K show that Kapton offers the best breakdown electric field and that the improvement of PPLP is not so important compared to simple Kraft paper.