| In cold climate regions, ice accumulation on insulators decreases their insulating strength, sometimes resulting in flashover faults and the consequent power outages. This problem has been paid great attention by many researchers and a large number of publications and reports have been available. It was found that one of the most common evidence on ice-covered energized insulators is the presence of air gaps along the ice surface due to corona discharge activities.;This present thesis aims to study the fundamental and initial processes of electric discharge in the air gap on the ice-covered insulators, within the framework of the NSERC/Hydro-Quebec Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE) and the Canada Research Chair on Atmospheric Icing Engineering of Power Network (INGIVRE), at the Universite du Quebec a Chicoutimi in collaboration with The Key Laboratory of High Voltage Engineering and Electrical New Technology of the Ministry of Education at Chongqing University (CQU). In order to simplify the study, a physical model, an icicle/iced-plate electrode system, is introduced based on numerous previous investigations to simulate the icicle tip and ice-covered insulator surface on real ice-covered insulators. Experimental investigations are systematically carried out in an artificial climate chamber in the High-Voltage Lab of CQU. Using a measurement system consisting of a ultra-violet camera, CoroCAM IV+, and a special-designed pulse current sensor, the corona discharge characteristics such as the corona inception voltage (Vinc), the discharge volume at Vinc, the repetition rate of discharge pulses, and the current pulse waveform are investigated in detail under different parameters. These parameters include the gap distance, the environmental temperature, the freezing water conductivity, the atmospheric pressure and the voltage polarities as well as the voltage types. Subsequently, the statistic analysis is applied to the experimental results and the influence of these parameters on the discharge current pulse characteristics is determined.;In order to reveal the physical mechanism underlying the corona discharge and determine the influence of space charge on the consequent discharge processes, a dynamic physics process of space charge is proposed to analyze this discharge phenomenon. A mathematical model is established to simulate the drift and diffusion process of the space charge clouds. From this model, the critical time of space charge clouds are calculated and are validated with the experimental results. Finally, the possible influences of space charge on the flashover of iced-covered insulators are analyzed and discussed.;The study results give a better understanding of the corona discharge at the tip of icicles on the ice-covered insulators. However, due to the time limitation and the complexity of this phenomenon, further studies are necessary to complete the model and theory. Several recommendations are proposed for future studies.;The corona discharge at the icicle tips in the air gap is the first stage of the flashover process. During these corona discharge activities, a large number of space charges, including the positive and negative ions, are generated and, in turn, they influence the electric field distribution in the air gap and the consequent sequential discharge activities. However, due to its invisible properties and its complexity, the influence of the space discharge on the electric field distribution and on the flashover process is generally ignored in previous studies. |
