Outline of a flexible, SF6 insulated e.h.v. cable

A novel construction for a flexible, compressed SF6 insulated e.h.v. power cable is proposed. The main feature of the design is the use of a trefoil spacer held by three subconductors. This arrangement has a good stress distribution, which is independent of small gaps between the spacer and conductors; it also offers a practical way of manufacturing the cable without passing spacers over the conductor or moulding them in place. Experimental results show the effect of different gas pressures and sheath diameters on the impulse flashover strength of the cable. It is necessary to assemble and test the cable under very clean conditions, but even if this is done breakdown occasionally occurs at a low voltage. This phenomenon is discussed, but a satisfactory and comprehensive explanation is not yet available. Development of the cable is in an early stage, but it is expected to be transported in lengths of 100¿200 m. Some details of possible joint and termination designs are given.