An optical technique to detect the degradation of electrical insulation

An experimental technique which can simultaneously measure the amplitude and phase of the electroluminescence (EL) pulses emitted prior to electrical tree inception is described. A digital oscilloscope is used to acquire the light pulses and 3-D plots of the number of light pulses versus their amplitude, and phase with respect to the AC waveform are obtained. Long-term aging tests are also performed on polymeric insulation. The results show that the light inception voltage and not the partial discharge (PD) inception voltage is the thereshold voltage at which the polymer starts to degrade