Abstract
Outdoor insulation design with regard to saline contamination and cold fog performance is a critical factor for secure and reliable operation of overhead transmission lines and substations in the vicinity of the shoreline. Several types of contamination contribute to insulator surface degradation and consequent surface flashover; some less severe and more prolonged than others. Severe types of contamination include contamination from the desert, coast, chemical plants and bird droppings. Saline contamination accumulation on the insulators of overhead transmission lines and substations in the vicinity of the shoreline has been recognised as a major problem. The joint effect of saline contamination and cold fog on the outdoor insulators in the vicinity of the shoreline has been recognised as a major cause of insulators surface degradation and flashover. Extensive studies are therefore required to explore the mechanisms of sea salt originating, transportation and deposition from the shoreline to inland and for modelling the surface flashover phenomenon of outdoor insulators near the shoreline.The main objective of this research is to investigate the mathematical and physical mechanisms involved in sea salt accumulation and surface flashover on outdoor insulators in the vicinity of the shoreline. In the current research, three mathematical models were presented, these three sub-models simulating three different processes were combined into one model, which was based on the mechanisms of sea salt transportation and deposition, dry band formation and development of arc burning on outdoor insulators near the shoreline,taking into account the saline concentration, oceanic winds, gravitational settlement of saline on outdoor insulators and the distance from the shoreline to transmission lines. The model was successfully applied to the artificially contaminated insulators, and the calculated parameters based on this model were in good agreement with those obtained from experimental tests. These results, together with studying the saline transportation and deposition, moisture diffusion and saline penetration, dry band initiation and development on outdoor insulator surface, provide background information for understanding the complete surface flashover phenomenon.
The effects of wind speed and direction on pollution accumulation rate on top and bottom surfaces of weather shed was investigated. The experimental results show that wind speed and direction have an obvious influence on pollution accumulation rate, it increases with increased wind velocity and decreases with increased distance from the shoreline to transmission lines. However, during periods of high wind, some parts of the contaminants can be removed from the insulator surface. A relationship between the moisture diffusion and saline penetration on insulator surface was established, showing how important the transfer of moisture with saline particles. It was found that the transfer of moisture significantly accelerates the penetration of saline ions on insulation material. To establish the reasons for the uneven wetting effect on insulator surfaces near the shoreline, experimental set up was adopted and installed in environmental chamber. The experimental investigations reveal that during un-even wetting effect electric field distribution across dry band regions was found to be dominant. Finally, in order to interpret the natural environmental condition on insulator surface near shoreline, the leakage current and surface flashover voltage tests along the contaminated insulator under various types of contamination and environmental stresses were carried out. Experiments results showed that leakage current magnitude changes with the variation of wetting rate and contamination degree, however, the amplitude was different under cold fog and rainfall wetting rates. Also, the major factors which influence and decrease the surface flashover voltage were contamination severity, cold fog-water conductivity and the number, location and length of dry bands.
| Date of Award | 2018 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Shahab Farokhi (Supervisor) & Scott McMeekin (Supervisor) |