EM field effects on the surface of polluted HV insulators
Outdoor high voltage power plant is exposed to environmental pollution which is an important cause of failure. Knowledge of conditions leading to flashover is essential to design insulation levels. Discharges on the surface of polymeric insulators are one of the ageing mechanisms responsible for eventual failure. In this thesis, we examine water droplets on insulator surfaces. Chapter 1 discusses pollution on the surface of high voltage insulators, and chapter 2 considers water droplets on insulator surfaces. Chapter 3 reviews recent work in this area. Chapter 4 presents the aims of the present work to examine partial discharges at the edge of water droplets and to investigate droplet vibration with an applied ac field. Chapter 5 identifies the apparatus and procedures that were developed. Chapter 6 describes an experimental study of electrical breakdown at the edges of sessile water droplets on a PE surface subject to ac electrical stress up to of 2.0MV/m at 50 Hz. The study involves observing the motion of water droplets using a high-speed video camera operating at 3000 frames per second whilst electrically detecting any partial discharge activity. The significance of droplet vibration on electrical stress enhancement is investigated along with the effects on partial discharge activity. Chapter 7 describes test sample geometry and electric field modeling using finite element analysis. Chapters 8 and 9 describe an experimental study of breakdown at a sessile water droplet on a planar, polymeric, insulating surface subject to ac stress, parallel to the insulator surface, up to 2. OMV/m. The contact angle between droplet and surface was varied by controlling the physical properties of the droplet and by inclining the insulator plane from the horizontal. A theoretical model is developed which shows that it is possible to sustain partial discharges in the air around a droplet above the polymer surface.