UHVDC Casing Of The Electric Field Distribution Study

Ultra-high voltage (UHV) direct current (DC) bushing is the significant high-end equipment in the UHVDC transmission whose characteristic and quality are crucial to the safe and reliable operation of the UHVDC transmission system. Due to the complicated insulation system of the UHV DC bushing, its inner potential distribution is complex. The space charge, which is accumulated on the medium of the insulation material, can distort the electric field around the equipment. The concentrated and uneven distribution of the electric field could easily lead to flashover or breakdown discharge in insulation materials, threatening the safe operation of UHVDC transmission. This dissertation studies the calculation method of the electric field of UHV DC High-end equipment considering the influence of the space charge under strong electric field environment, aiming at solving some key and fundamental problems of the UHV DC bushing encountered in the analyzation and optimization of insulation structure.Under the strong electric field environment, the accumulated space charge has a significant effect on the compound insulation materials, which will distort the electric field and bring difficulty to the calculation of electric field and the optimization of insulation structure. According to the research on the evolution mechanism of the space charge, the dissertationhas summarized the inner link between the space charge and breakdown. The model of the space charge has been built in polarity reversal and under temperature field.Thanks to a finite element commercial software ElecNet from Infolytica, the paper built a finite element model concerned with the electric field calculation of UHV DC bushing. Furthermore, the space charge model is embed into the finite element model in terms of the designed UHV DC bushing.This dissertation calculated the electric field distribution and potential distribution of DC bushing on two kinds of special working conditions- polarity reversal and temperature field. As far as polarity reversal is concerned, a new calculation method of instantaneous electric field value has been presented to obtain the electric-field and potential distribution at the instant moment polarity reversal occurs and the any moment after polarity reversal happens. What's more, the trends of the electric-field and potential distribution with the time changing can be also obtained at the key part. With regard to the temperature field, temperature gradient has been added to the finite element model of the bushing, in order to get the comparison charts of the electric-field and potential distribution at the key parts under the conditions that whether the temperature factors are taken into account or not.