Development of capacitive sensor technique for partial discharge detection in high voltage cable

The phenomenon of partial discharge (PD) is a hidden activity that happens in insulators due to stresses of high voltages. Furthermore, due to aging effect it may lead to breakdown of insulation, and it is also a main cause of severe failure of electrical appliances and instruments installed in the grid power station. The earlier detection of PD can save a huge amount so its detection and localization is important. In current scenario, the conventional techniques of detection for partial discharges are expensive and have many drawbacks regarding its accuracy. In this study, a simple capacitive sensor technique has been developed for the detection of the partial discharge phenomenon in high-voltage cables. The capacitive sensor could be of any size and shape that could be easily mounted on the high-voltage cables. The designed capacitor was mounted on high-voltage cable, and it was capable to pick the partial discharge signal successfully through the high-pass filter. The partial discharge data was captured along with high-voltage discharge parameters using digital oscilloscopes. The data was then processed and analysed in the time domain to deduce the information about the level of partial discharge. The results show that the PD signal is prominent in the range of 100 nsec, which has many peaks similar to oscillatory motion than the other explored ranges. The capacitive sensor was also used for the detection of high-voltage signal and compared with the high-voltage probe signal. The attenuation factors for the four sensors have been determined and compared. The results show that as the high voltage increases the attenuation factor decreases and in some cases the attenuation curve has a crinkle for the sensors, which may be due to change of position on the cable. The results show linear behaviour in the explored range that suggests the capacitive sensor might be useful for the measurements of high voltage without high-voltage probe. In the comparison of the attenuation factors without high-pass filter results show that attenuation factor decreases as the high-voltage increases but for two samples of sensors, the trend was very close to linear behaviour. These results suggest that capacitive sensor could be used as an alternative cost effective approach for the detection of both high voltage and monitoring the PD signal in high-voltage cables.