Present and future developments in DC transmission cable insulation

A synthesis is presented of the possible types of insulation for DC cables. These are: a. impregnated paper insulation, either non-pressure assisted or pressure assisted; b. lapped synthetic insulation, either liquid-filled or gas-filled; c. lapped composite insulation; d. extruded synthetic insulation, e. compressed gas insulation. The main characteristics of each dielectric are reviewed and the prospects of use are briefly discussed.