Electromagnetic radiation due to partial discharge and fault detection method for overhead distribution lines

Partial Discharge (PD) is a major problem in aging electrical power systems. PD causes damage to electrical hardware, power losses, and issues with power quality. It also creates electromagnetic (EM) interference that may couple into communication systems. PD activity can be an indicator of impending power line insulator failures, leading to catastrophic events such as pole top fires, bush fires and power outages, potentially costing millions of dollars and put the safety of people at risk. Therefore prevention, detection and eradication of PD are hence vital. Real time monitoring of overhead power lines for the EM radiation signatures emitted by PD can be employed for this purpose. <br><br>The four main types of PD are investigated in this thesis: cavity discharge, corona discharge, dry-band arc discharge, and surface discharge. EM radiation due to cavity discharges has been examined with respect to an increase in the number of cavities in defective Perspex and Epoxy insulator samples. Cavity discharges in Perspex exhibit EM radiation significantly above the noise level in the 10 – 170MHz and 760 – 1120MHz bands, whilst the similar activity has been shown in 30 – 140MHz and 840 – 1120MHz bands for Epoxy nano-composite insulators. <br><br>The EM radiation characteristics of corona discharge between water droplets and the dry-band arc discharge have also been investigated. An electromagnetic identification of the transition from corona to dry-band arc discharge has been discovered. The transition from corona discharge to dry-band arc discharge can be identified via EM sensing in the 800 – 900MHz and 1.25 – 1.4GHz bands. Investigations have shown it is notionally possible to monitor the degradation of the insulation surface by sensing the reduction of the voltage spectral density due to dry-band arc discharges in the 800 – 900MHz band. <br><br>An EM detection mechanism to monitor the variation of contamination level of a polluted insulator is proposed. By studying the EM radiation spectrum of surface discharge/creeping discharge activity, variations in salt concentration of a pollution layer on nano-composite epoxy insulator samples can be electromagnetically monitored in part or all of the 520 – 600MHz, 700 – 740MHz, 860 – 890MHz, 1.09 – 1.11GHz and 1.53 – 1.57GHz frequency bands. A link between the pollutant salt concentration, breakdown voltage, surface conductance and the magnitude of the electromagnetic radiation has been identified. <br><br>The propagation and radiation characteristics of the UHF frequency components of a PD signal along an uninsulated Aluminium power lines have been numerically evaluated. Bare Aluminium overhead cables show very low attenuation levels, even at GHz frequencies. Hence high frequency components of a PD signal will travel for a significant distance along a cable, allowing for remote real-time detection. The radiation patterns for the high frequency components of PD propagating on single wire and three phase systems exhibit travelling wave radiation patterns.<br><br>An initial practical methodology and demonstration of PD detection and localisation was implemented on live power distribution lines. The results and findings gathered from field trials conducted with a pilot PD detection and localisation system have demonstrated the success of the PD monitoring system in identifying faults on power lines.