| The neutral point grounding mode selection of low voltage distribution network has always been a comprehensive, worldwide and professional power system technical problem. Because it needs comprehensively to consider the problems of the current operation mode characteristics of the power supply reliability requirements, equipment insulation and insulation technology development level, circumstances of relay protection and safety automatic device, the stability requirement, impact on the communication equipment and personal safety. In terms of current world situation, there are two neutral point grounding modes:grounding and ungrounding (so-called neutral dangling), and the neutral point grounding modes include neutral point directly grounding, neutral point grounded by resistance, neutral point grounded by extinction coil. Distribution network is an almost not directly grounded system. In recent years, along with the process of global economic integration, the economy of all over the word develops rapidly, the investment of power grid construction also increases. In our country, with the speed of urbanization, city scale is more and more big, the tension of land use and the increase of load density put forward new challenges to power grid. So the overhead lines put into underground in large-scale distribution networks, the cabling and insulation reconstructing in distribution network lines are in full swing. Area overhead line transformation of cable lines of power grid development brought new technical problems, because the increase of cable means not only a substantial increase in capacitance current, but also easily due to take long time to broaden the scope of the accident, and current of neutral point grounding often can meet the demand of new operation mode, will gradually be eliminated. And the distribution network grounding methods have their own characteristics, have their different applicability, can not be blindly determined. Therefore, the choice of the neutral point of China’s distribution network needs specific analysis of specific issues.With the development of urban economy and urban construction in Dalian City, the scale of distribution network has been expanded year by year. At the same time, the proportion of the cable line in distribution network 66 kV power distribution line is increasing year by year. Dalian power distribution networks are facing the biggest challenge is 66 kV distribution line as the cable line increased, when the case of single-phase grounding fault, capacitive current than the previous increase significantly, grounding residual often exceeds 10 A current becomes large, extinction is not easy, resulting in personal injury and other social accident, expand the scope of fault and cause insulation damage and other practical problems.This paper starts from the principle of low voltage distribution network neutral grounding mode and different types of theoretical calculation, in-depth analysis of its essence and characteristics, comparison of several grounding methods advantages and disadvantages, carries on the classified summary from the applicable conditions and applicable scope; combining with the characteristics of 66 kV power system in Dalian area unique, explores the situation of 66 kV in Dalian power grid area and the neutral point connection mode, analysis of the current situation and existing problems, through in-depth analysis of relevant cases mainly solved three kinds of refine existing typical problems, theoretical analysis and model reduction, targeted proposed way technical improvement scheme for the neutral point, and by the MATLAB simulation software of power system simulation toolbox of Dalian 220 kV high Chengshan, to verify the scheme of application and the Dalian area Scope of application. Finally analyzes the problems needing attention in the process of implementation of the selected resistance and relay protection. The research of this paper can provide references for the selection of neutral point of 66 kV power network in Dalian area. |
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