Study On The Way Of Neutral Point Grounding And Fault Characters Of Distribution Network Influenced By The Cable Ratio

The problem of neutral grounding modes of the network is closely related to many aspects,such as the reliability of power supply,security,insulation and so on.These years,a higher rate of cable usage on the network makes the capacitance current and the failure ratio of intermittent arc grounding increase.In order to solve the problems,people put forward the improvement of neutral grounding mode s.With the introduction of new grounding methods,new problems also arise.How to improve the model of single phase earth fault in the current situation,and put forward a more perfect grounding method are worth studying.At the same time people found an actual condition.That is when transformers' neutral point is grounding through gap,the motor leads to the effect of feedback when the single p hase has grounding faults.Zero sequence voltage increases and cannot decay to a safe value,gap protection acts,and the transformer is removed.After the reclosing device acting,the lines will be affected.So,how to select the grounding mode of transformer is studied.First,based on the understanding of the arc model existing,on the high frequency of occurrence of high rate cable usage,under the condition of intermittent arc grounding fault we analyzed the situation,and the mathematical model is fur ther improved,and the simulation analysis verified using simulation software.Second,based on the study of the existing grounding mode,and on the situation of high rate of cable usage,we analyzed the badness of the grounding modes,and pointed out the inproved one.The simulation analysis software is used to deal with the analysis,using the fault model in the first step in place of the traditional single phase grounding fault.Finally,an improved grounding method is got which is called arc suppression coil parallel resistance by different time sections.In the new point grounding mode,study the original protection to find out the unreasonable points and improve the relay protection configuration.Then we analyzed the transformer neutral point grounding structure.Seeing the actual distribution network problems as the starting point,we study the transformer gap protection and the influence of feedback to the neutral point of the transformer.Using the simulation software to study electrical of the neutral point of transformer.Finally we obtained the transformer's safety conditions on which transformers can be grounding through gap.