Improving UHF partial discharge location in high voltage equipment

Insulation degradation in high voltage equipment may be caused by partial discharge (PD) activities. The ultra high frequency (UHF) PD detection has been successfully implemented in the field because it can provide on-line diagnostic information about insulation defects and endure to external interferences. PD can be located using a triangulation method when three or four UHF sensors are fixed on a tank. Benefits from locating PD accurately can be valuable for maintenance and repair proposes. Locating PD using the triangulation method is reliant on time differences obtained from the arrival times. A few methods for determining arrival times are available such as threshold crossing method of instantaneous signal power waveform, knee point of cumulative energy curve, energy criterion method, time-frequency analysis [1],[2]. These methods have some limitations such as the selection of percentage of signal power to be the threshold, the difficulty to identify the arrival time by choosing from the knee area, the mathematical formulas for determining the accurate arrival time, etc. In addition, determining the exact arrival times is dependent on signal characteristics. In this paper, several techniques that may help to identify the exact onset of PD signals will be presented. These can offer improvements to the accuracy of locating PD in high voltage equipment using time differences.