Abstract :
AMERICAN engineers undoubtedly will be interested in some of the latest data and statistics on the use of a form of extra-high-voltage cable that has not yet been employed in America, namely, the pressure cable, which has been used in Europe since 1932 in increasing amounts. The main problem in high-voltage paper-insulated cable is the prevention of voids during contraction cycles when load is reduced. In an oil-filled cable, voids are prevented by the flow of oil from reservoirs into the cable while it is cooling, through channels in the cable itself. In the pressure cable, the same result is accomplished by gas pressure external to the lead sheath. To assist the lead in undergoing this slight diaphragm action, the sheath is made either slightly triangular or oval in shape and reinforced with a bronze tape to prevent cumulative bending. In the original form as described by Hochstadter, Vogel, and Bowden in Elektrotechnische Zeitschrift in 1932, page 145, the cable is placed in a steel pipe filled with nitrogen under a pressure of about 15 atmospheres. The cable itself is either a three-conductor cable with a triangular sheath, or a three-conductor SL (separately leaded) cable with individual elliptical sheaths. In the latest developments in England, a reinforced lead sheath has been substituted for the steel pipe as a pressure restraining medium, this type being known as the self-contained pressure cable. The latter type was described by K. S. Wyatt (A´32) at the Conférence Internationale des Grands Réseaux Électriques á Haute Tension, Paris, 1939.
