An improved optically based PD detection system for continuous on-line monitoring of HV cables

An optically-based remote sensing technique using a laser source, polarization scrambler, standard single mode fibers, fiber polarizer, electro-optic (EO) modulator and optical receiver, for continuous on-line monitoring of partial discharges (PD) in high voltage cable joints is proposed. Both the fiber polarizer and EO modulator, which are placed near cable joints, are passive without any power requirements. An EO modulator with no electrical bias, which operates close to the half-intensity point, was used and proved to have much better light transmission performance and higher measurement sensitivity than the bias modulator approach investigated earlier. Various multiplexing techniques including optical switches and a fused fiber coupler have been investigated in order to implement multi-channel monitoring so that one laser source can be used to provide light to several fibers. The revised PD optical remote sensing technique has been applied to practical PD measurements on both 132 kV cable joint at the University of Southampton in the UK and 400 kV cable joints at Sudkabel GmbH in Germany. Obtained results have verified the principle and demonstrated the effectiveness of the developed technique.