DC Breakdown Strength Of Dielectric Materials At Cryogenic Temperatures

The HVDC superconducting cable, under development at the Los Alamos Scientific Laboratory will operate at a temperature of 12 R and a helium pressure of 1.38 MPa. Because dc breakdown data of dielectric materials at these operating conditions were not previously available, extensive tests were performed on 11 dielectric materials in sheet form. Three of these materials were impregnated with mineral oil, which increased their dc withstand strength significantly. Four of these 11 materials were selected for further tests at varying temperatures and pressures. The dc-breakdown field of cellulose paper (with and without oil impregnation) and PP/C (cellulose paper/polypropylene-celulose paper) varied as the exponential of the inverse of temperature. For the two polyethylene materials tested, the dc-breakdown strength showed a peak between 12 nd 298 K. Higher pressure increased the breakdown strength of the materials. Higher pressure or lower temperature also decreased the probability of surface flashover.