A study of the variation of electric distance and electric strength with the type of voltage stress and portion of the gap covered by flames.

Abstract

South Africa has a large network of high voltage substations and transmission lines (over 28 000 kilometers) across the country designed to supply power to households, industry and businesses, railways and mines. This transmission system must be strong and capable of withstanding the loss of any single circuit without loss of supply to key customers. Veld fires burning under or near high voltage transmission lines are a potential hazard capable of disrupting transmission and distribution of power. Forest fires under high voltage transmission lines reduce the breakdown strength of the air insulation due to the influence the heat and particles have on the electric field surrounding electrical conductors and insulators. The performance of the high voltage transmission lines is most likely to be affected by the occurrence of veld fires under these power lines. The fire under high voltage transmission lines generates heat and increases the temperature of the air surrounding the conductors and insulators. The increase in temperature due to the presence of the fire decreases the breakdown strength of the air insulation, this results in flashovers and undesirable power supply interruptions in the electrical transmission network. Due to the past experience of AC transmission lines tripping as a result of sugar cane fires that occurs under these lines during cultivation seasons, this study was initiated to provide an understanding of how burning can cause outages of transmission lines and give recommendations on how to prevent outages due to burning. This dissertation is a research based modeling aimed at giving an understanding of how the electric distance and electric strength vary with the type of voltage stress and the portion of the gap covered by flames. The study reviewed how different authors have conducted studies related to this dissertation and compared the results. The different failures due to burning occurring next to the transmission lines and contamination was grouped and analysed in terms of the time of occurrence, time of the day, season of the year and time of the day. The results shows that most of the faults on contamination occur on the DC lines and that the voltage level that’s affected the most is 220 kV. The time of the day analysis shows that most of the faults occur between 13:00 to 15:00, this is because the temperature around those times are very hot and temperature has a direct influence on the fire behavior.