Novel spirally-wound insulation for straight HVDC conductors to avoid voltage stress inversion

Elpipes are polymer-insulated underground HVDC conductors designed for higher efficiency than is practical for overhead power lines (1% I2R loss/1000 km), based on rigid conductor segment modules linked together by flexible splice modules. Because elpipes are not wrapped on a reel for transport, they can use far more conductor than cables or overhead power lines, typically 3–18 times more than in an overhead HVDC transmission line. The rigid nature of the segment modules enables compact rigid insulations for the segment modules such as ceramic, glass, or spirally wrapped polymer films in which one polymer layer is stiff, and the other elastomeric. Such high stiffness insulating pipes (Fig. 1) could not be used as cable insulations because they are not flexible enough to be wrapped on a reel. We examine a spirally wrapped insulation consisting of two layers: a good insulator and a semiconductor.