Application of Superluminescent Light Emitting Diode to Electrooptic Modulator Based PD Continuous On-line Monitoring System

Partial discharge monitoring provides effective evaluation of power cables, particularly of joints that are installed on site. Continuous on-line monitoring can provide information about progressing degradation under operational stresses, thus reducing the likelihood of breakdown. A novel PD continuous online monitoring technique has been developed by the authors. The mechanism applies PD signals across a LiNbO3 electro-optic modulator to modulate the intensity of the transmitted light. This technique does not require a voltage supply near the cable joints as the EO modulator is passive. In earlier investigations a fibre laser was used as the light source. The polarisation state of the laser light needs to be maintained to suit the polarisation dependent EO modulator. This paper investigates the application of a superluminescent light emitting diode, which provides unpolarised light, as the light source. The alternative monitoring system is investigated using both simulated experiments and practical PD tests on a 132 kV prefabricated cable joint.