An assessment of the impregnated pressure cable

The impregnated pressure cable has a mass-impregnated dielectric which is maintained under a nitrogen pressure of 200 lb/in2 without an intervening membrane. After a survey of the installations which have been completed in Great Britain and of its increasing usage abroad, the modern design of the cable and its electrical and pneumatic accessories is described. Incidents which have occurred in service since the first commercial application of the cable system in 1940 are given in full detail. These include electrical faults, gas leakage and the effects which result from movement of the cable impregnant. Service experience and laboratory tests have shown that the system is sound but that its pneumatic performance, although adequate, is capable of improvement. The significance of pneumatic incidents in relation to the correct planning of the system is discussed. Prospective developments which will assist in improving pneumatic characteristics are indicated. Since the first commercial installation of impregnated pressure cable in 1940, about 140 feeder miles have been commissioned in Great Britain, and important installations are in progress abroad. Operational experience is detailed and the prospect of further improvement is discussed.