Assessment of the possible use of polythene/gas dielectrics in h.v. cables

From the point of view of its electrical and mechanical properties and its ready availability in thin tape form, polythene is one of the most promising dielectrics for possible application in h.v. cable construction. To predict the behaviour of the polythene/gas dielectric system, having a lapped-tape construction, experiments were carried out on thin-walled models in nitrogen and several electronegative gases. The effects on impulse strength of a number of variables, a.c. life tests, and factors affecting the discharge-inception stress were investigated. In addition, the gas-pressurisation time was determined. Optimum electric strength, consistent with good mechanical performance, was obtained with tapes of 3 mil thickness. It was concluded that a composite polythene-tape/gas dielectric system has many advantages to recommend it for full-scale h.v. cable development.