The Influence Of The Increasing Of Urban Cable Lines On The Grounding Mode And The Improvement Of Low Resistance Grounding

With the increase of urban cable lines,two major problems are brought to the current distribution network.One is that the capacitive current of the distribution network is gradually increasing,which leads to the occurrence of single-phase grounding in the neutral point low current grounding method,which is prone to arc grounding overvoltage.,Which seriously endangers the safety of power distribution system equipment and the personal safety of users.The second is that too many cables will cause problems such as reactive power reverse transmission,which will cause the end of the system voltage to be high or even exceed the limit and other hazards.Aiming at the problem of excessive capacitance current,this paper proposes the low resistance grounding method and related reform methods,and re-studies the problems such as the low resistance grounding protection system easily refuses to operate when a high transition resistance ground fault occurs.First,it introduces the current research status of neutral grounding methods at home and abroad,as well as the problems caused by urban cable.Then,the characteristics of single-phase grounding faults are analyzed in four grounding modes of neutral point ungrounded,neutral point directly grounded,arc suppression coil grounded,and low resistance grounding,and the basic principles,advantages and disadvantages of the four methods are analyzed.And expound the influencing factors of choosing the neutral point grounding method.Then analyze and study the influence of cableization on the distribution network and the solutions.Including the increase in cable lines to the requirements of the grid structure,and proposed a cable automation transformation plan.And analyze the hazards caused by the magnitude of the earth current of the cable line and the overhead line and the excessive capacitance current when a ground fault occurs,and propose the main solutions currently used.At the same time,it analyzes the reactive power generated by the distribution network based on cable lines,explores the principle of causing the line end voltage to exceed the limit,and conducts simulation analysis through the IEEE 14-node method.This paper proposes a small-resistance grounding reconstruction plan,focusing on the in-depth analysis and research on the selection of grounding resistance,and proposes to take technical requirements as constraints and the lowest economic cost as objective function modeling.Combining the calculation examples,the grounding resistance value is determined by the traditional particle swarm optimization algorithm,and a model of selecting the resistance value is obtained.And make corresponding adjustments to the relay protection after the transformation.When the distribution network is grounded with high transition resistance,the zero sequence current of the fault line is small,and the low-resistance grounding protection system is difficult to detect and easy to cause misoperation,which seriously affects the safety of the distribution network.Therefore,this article revisits the low-resistance grounding protection system.Research and propose a method based on zero-sequence power feature to identify high-resistance grounding.