Research On Analysis Of Overvoltage Based On Neutral Point Of Power Transformer And Technology Of Insulation Protection

The neutral point insulation of the power transformer is damaged due to various overvoltage during operation,resulting in transformer damage accidents from time to time,causing power supply interruptions.At present,most of the neutral points are protected by discharge gaps,metal zinc oxide lightning arresters or both,but transformer damage accidents cannot be completely avoided.It is necessary to further study the overvoltage of the neutral point insulation and its damage mechanism,and establish a complete insulation protection system to improve the reliability of power supply.Transformers generally choose metal zinc oxide lightning arrester and discharge gap in parallel to achieve insulation protection of the neutral point,but the discharge gap has the disadvantages of inaccurate distance adjustment and easy to be eroded by the discharge arc when working for a long time.The discharge voltage of the discharge gap has greater dispersion and poor concentricity,resulting in the possibility of burning or even deformation in the rod electric extreme.These drawbacks will lead to metal zinc oxide lightning arrester and rod gap can not work normally as planned.The site operation is prone to insulation coordination disorder,often leads to the system in the process of effective grounding single-phase ground short circuit and causes discharge gap breakdown,resulting in an increase in the range of power outages.The discharge gap refusal action is easy to cause the explosion of the lightning arrester and the insulation of electrical equipment is damaged,so it is urgent to better improve the insulation protection of the neutral point of the transformer to ensure the safe and reliable operation of the power system.In this thesis,the 110 k V substation is taken as the research subject,and the overall model of the 110 k V substation is established by using the simulation software ATP-EMTP.The neutral point overvoltage of the main transformer caused by the lightning strike of the inlet section of the 110 k V substation is simulated and studied,and the neutral point of the main transformer is effectively insulated by grounding by small reactance grounding.The finite element simulation of the station metal zinc oxide arrester was used to study the electric field and potential distribution,temperature rise and potential distribution,and the relationship between current density and temperature rise distribution of the metal zinc oxide arrester used in the station under lightning impact according to the simulation software COMSOL Multiphysics.The insulation protection effect of the metal zinc oxide lightning arrester on the neutral point of the main transformer of the substation was analyzed,and the insulation protection measures of the neutral point of the transformer were proposed according to the simulation results of two kinds of simulation software.This thesis through two schemes to study the transformer neutral point overvoltage analysis and insulation protection problems.The first scheme is the 110 k V substation main transformer in this thesis using a neutral point through a small reactance grounding mode.Simulation results show that the neutral point overvoltage of the main transformer can be reduced by small reactance grounding,provided that the value of the grounding small reactance should be selected within the specified range,that is,the neutral point of the main transformer is connected to a certain value of the small reactance.The second scheme is to install a metal zinc oxide lightning arrester at the neutral point of the main transformer of the 110 k V substation in this thesis.According to the simulation results,it can be concluded that the metal zinc oxide lightning arrester of the station has a certain restrictive effect on the neutral point overvoltage of the main transformer,thereby improving the insulation protection ability of the neutral point of the main transformer.