Partial discharges in lapped polymer taped insulation impregnated with supercritical helium

Apparatus has been designed and constructed to evaluate the high-voltage parameters of lapped cable models impregnated with supercritical helium for pressures up to 1.5 MPa and for temperatures to 4.2K. The tape materials studied are as follows: high-density polythene, Valeron (cross-laminated polythene film), polypropylene, Nylon 11 and polysulphone with limited tests using polycarbonate. The variation of the maximum value of discharge with applied alternating voltage was obtained, and also the variation of inception stress (1 pC and 5 pC) with helium density and pressure. (author)