On-line partial discharge detection and control on MV cable networks with ground fault neutraliser

The technique of controlling neutral voltage and current is applied in medium- and high-voltage electricity networks as a means of eliminating earth fault currents. The complete compensation of earth fault currents is achieved using modern power electronics developed by Swedish Neutral. The GFN Ground Fault Neutralizer uses beside traditional Petersen Coil technology a novel Residual Current Compensator (RCC) to archive a very fast and complete elimination of the earth fault current. Injection of voltage into the transformer neutral using this system, also allows control of the phase-ground voltages under normal operation. This in turn allows partial discharge (PD) activity in the cables and connected plant to be incepted and extinguished through voltage increase and reduction on a phase-by-phase basis, providing a very powerful diagnostic system. The paper presents results from on-line partial discharge (OLPD) testing combined with neutral voltage displacement on MV networks. Case studies are presented from testing with fabricated defects and on two MV networks as part of GFN system commissioning.