Partial discharge on-line monitoring for HV cable systems using electro-optic modulators

A technique for the remote inspection and monitoring of partial discharge (PD) activity using an optical network is described. The network uses a LiNbO₃, modulator to modulate the intensity of the transmitted laser light approximately proportional to the voltage applied across the modulator. The laser light is transmitted along an optical fibre and measured remotely by a high-speed optical receiver. A capacitive coupler has been used to detect partial discharge activity and act as the modulator´s input voltage source. The electro-optic modulator is passive and does not require a power supply at the site of the PD detection sensor. The system has the additional advantages of being immune to electromagnetic interference, having very little signal transmission attenuation, with good sensitivity, compact size, as well as being convenient to use and safe. Both simulation experiments and practical PD tests on two cable systems have indicated that the optical system provides a feasible remote PD monitoring technique for high voltage cable systems.