Energy Transfer between Low Current Discharge and Insulation Surfaces

UoM administered thesis: Phd

  • Authors:
  • An Xiao

Abstract

With the development of electricity transmission systems, more and more insulators have been used in the system to isolate the high potential conductors from the earth. In order to secure the reliability of power system, it is necessary to understand the ageing mechanism of the insulators. A model for energy (heat) transfer between low current discharges and insulation surfaces has been built in this project which contributes to the understanding and prediction of insulator ageing.Within the experimental work, the temperature of low current discharges under different conditions has been measured with the "Best-fit" method. The temperature was found to vary between 1200 K and 2300 K with current level, sub cycle duration, gap length, electrode conductivity and polarity of DC discharges. The discharge temperature increases with the growth of current and sub cycle duration by means of the elevation of energy, while the discharge temperature is hotter between salt water droplets than between tap water droplets even though the former has a lower energy (I^2 Rt). The temperature is insensitive to a change of gap length and a positive discharge has a higher temperature than an equivalent negative one. The specific measurement shows the middle part is hotter than the electrode areas.Within the simulation work, the presence of water droplet(s) on the insulation surface concentrates and enhances the electric field over the surface which increases the risk of partial discharge. For practical insulators, this means the core, rather than the sheds, suffers more from discharges between water droplets as they are aligned to the electric field. This highlights the importance of keeping the core dry.The simulation of heat transfer between low current discharges insulation surface was achieved using COMSOL software. The simulated results show that the surface temperature increases rapidly in the first few seconds and arrives at a thermal equilibrium state after 20 seconds of discharge, which meets the experimental observation. The insulation surface temperature distribution under AC discharge is symmetric and the surface centre has the highest temperature which decreases towards the water droplets. In DC, the surface around the cathode is the hottest and the anode area is the coldest.

Details

Original languageEnglish
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Supervisors/Advisors
Award date1 Aug 2015