Novel spacer coated with functionally graded ZnO film for HVDC gas insulated line

To achieve a more uniform electric field (E-field) distribution on a spacer surface in HVDC gas insulated lines (GILs), novel spacers were fabricated by depositing ZnO films onto spacer surfaces using magnetron sputtering method. Through measurement, the deposited ZnO films of different sputtering times were found to have nonlinear surface conductivities, which can relax the E-field distribution. An iterative method was applied to optimize the sputtering time distribution in the radial direction of spacer, and an almost uniform E-field distribution was achieved after five iterations. For fabricating the optimized spacer, a baffle with a designed gap was placed above the rotating spacer to control the sputtering time at different radial positions. From the E-field simulation results, it can be seen that the introduction of a novel spacer with a 30 min-sputtered ZnO film can greatly reduce the E-field concentration around the triple junction of HV electrode, air and spacer. By grading the sputtering time distribution in an optimal way, a further E-field strength reduction is obtained inside the GIL. Flashover tests were conducted under DC and polarity reversal voltages, and the optimized spacer shows the best insulation performance, followed by the 30 min-sputtered spacer, and finally the conventional spacer. By applying such novel spacers, higher compactness and reliability can be achieved in HVDC GILs.