A study of pole top fires on 22kV wood pole power lines in KwaZulu-Natal.

Abstract

The majority of Eskom's 22kV lines use wood as the support structure material. The economics of wood pole cross arms and their flashover withstand capabilities outweigh those of steel cross arms. However, wood pole structures are vulnerable to what is known as a Pole Top Fire. When insulators and wood cross arms become polluted, small and sustained leakage currents flow along the surface of the insulator and thereafter into the wood itself. This eventually leads to burning of the wood. Many of the 22kV lines traverse vast rural lands, going over people's path ways. If this fire is not discovered timeously, it can cause breakage of the relevant cross arm or the pole itself. A broken cross arm usually causes the outer phase conductor to hang between one and two meters above ground. When it's dark, rural inhabitants cannot see clearly and walk directly into these low lying energized conductors which cause severe injuries and often fatalities. Low hanging conductors cannot be detected electrically and are potentially hazardous to humans and animals. Safety is currently one of the highest priorities for Eskom Distribution and hence there is a dire need to mitigate Pole Top Fires. The researcher hypothesizes that the implemented mitigating technique of bonding does not eliminate Pole Top Fires. In this study accurate statistics on Pole Top Fires in KwaZulu - Natal are provided and causes of fires investigated to provide an understanding thereof. Two basic mechanisms of burning have been identified and explained. These are surface tracking and sparking, and internal sparking. This has helped to explain what mitigation techniques will be effective. A critical analysis on the performance of recommended mitigation techniques is conducted. This study therefore aims to conclude on the effectiveness of implemented techniques to mitigate Pole Top Fires. By comprehensive and critical analysis of a complex operational and safety related problem technical options for mitigating or eliminating the fires are identified, critically analyzed and only those options that are really technically feasible are proposed. This has not been properly done in Eskom before. It is within this context that this research has been undertaken.