DIELECTRIC-BREAKDOWN OF SUPERCRITICAL HELIUM

Results are reported of an experimental investigation into the dielectric-breakdown behavior of supercritical helium, in the range from 4 multiplied by (times) 2 to 30 K and 0 multiplied by (times) 4 to 1 multiplied by (times) 5 MPa under dc, ac and standard impulse voltages, to assist the development of superconducting power cables. At helium densities over 80 kg m** minus **3, the uniform-field breakdown voltage for dc or ac is about 55 MV m** minus **1 at 0 multiplied by (times) 8 MPa and has a slight pressure dependence. In nonuniform fields, the breakdown voltage with a negative electrode is considerably increased by corona stabilization in the density range from 30 to 83 kg m** minus **3.