Gas insulated energy transmission systems twenty-third bernard price memorial lecture

The increasing demand for underground high power electric transmission systems has stimulated the development of new insulating media. Sulphur hexaflouride (SF6) has found wide applications for metalclad switchgear up to very high voltages and can also be used to insulate high voltage cables. The SF6 molecule tends to form negative ions, which, in turn, leads to high breakdown strength. However, in practical applications considerable reduction of the breakdown voltage may occur due to the movement of free particles and to the shapes and surfaces of the unavoidable insulator spacers. Three-phase gas insulated cables have very favourable electrical parameters and high power transmission capabilities which can exceed 1 000 MVA without artificial cooling. First installations started operating only a few years ago. High voltage testing of gas insulated cables is a special problem because it has to be done on site. The high capacitance of the test object makes it necessary to develop new test techniques to ensure high reliability in service. Finally, attention is given to practical installations of SF6 insulated transmission systems and expected developments of this very promising new technique as a means to improve the transmission and distribution of electrical energy.