Research On Measurement Method Of Electric Field Intensity On Surface Of Metal Conductor

With the increase of the grid voltage level,the requirements for the insulation level of power equipment have increased,and the cost of power equipment has increased obviously.During normal operation,high-voltage electrical equipment will bear high voltage and generate high electric field intensity(EFI),and insulation failure is the main cause of electrical equipment failure.The variation of insulation strength of electrical equipment is related to many factors.The insulation level often depends on the EFI of electrode surface and internal dielectric.For this reason,experts and scholars have done a lot of research on the measurement of the EFI generated by high-voltage electrical equipment,and have made fruitful achievements.However,EFI sensors can only measure the EFI in the air gap far away from the electrical equipment,and cannot directly measure the EFI on the electrode surface.In this paper,a method for measuring the EFI on the surface of metal conductors is proposed,and a physical model for measuring the EFI is designed.The intensity of the EFI is measured at many different points on the metal surface of the high voltage conductor in the physical model.The analytical solutions of the electric fields at different positions on the surface of the high voltage conductor are obtained by combining the mirror image method with the electric axis method.The calculated results are compared with the measured results.The relative error between them is less than 5%.The effectiveness of the method is verified.The fault diagnosis method of power equipment proposed in this paper can be used for the research of compact power equipment,on-line detection,state evaluation and power grid security and stability research.The main work of this paper are as follows:(1)Based on Maxwell’s equations,the method of measuring the EFI on the surface of metal electrodes of high-voltage electrical equipment is introduced.The principle of EFI measurement on the surface of high-voltage conductor metal is proposed,and the equivalent circuit model of the EFI measurement system is established,And explained the measurement model of EFI in detail;At the same time,this article also introduces the basic theories of this thesis,including:the finite element analysis theory,the principle of the method of images(MoI)of the electrostatic field,and the principle of the electric axis method(EAM)of the electrostatic field.Among them,the principle of MoI of the electrostatic field and the principle of the EAM are the calculation basis of the analytical value of the EFI on the surface of the metal conductor in this paper,which lays the foundation for the comparison and analysis of the analytical value of the EFI and the experimental value.(2)Describes the EFI analysis method of the conductor surface of the simplified model of the overhead bus based on the MoI and the EAM.The variation law of the average EFI on the surface of the slice with voltage when the distance from the ground remains constant and the azimuth angle changes,the azimuth angle remains constant,and the distance from the ground are calculated respectively.It shows the difference between the average EFI on the slice and the analytical EFI at the center of the slice.The magnitude and positive and negative errors are closely related to the position of the linear charge in the two-dimensional field.In addition,the difference between the average EFI and the analytical EFI at the center of the slice surface when the height of the high-voltage wire to the ground is sufficiently high is analyzed.This is of great significance for the application of the EFI measurement method of the power system,especially the substation bus.(3)Describes the EFI experimental measurement platform built in the laboratory.Aiming at the EFI experimental measurement model,the reason for designing an experimental model of a single hollow conductor at a certain height from the ground is explained.It is because there is analytical solution for the surface EFI of the overhead bus bar,so that the accuracy of the measurement method can be verified by analyzing and comparing the experimental and analytical values.The finite element method and field-circuit coupling method are used to study its output characteristics.This article also details the various devices that make up the physical model of EFI measurement and their respective characteristics.In addition,two measurement methods are used for the EFI experimental measurement,and the influence of changing the azimuth of the conductor and the distance to the ground on the measurement results of the EFI is also analyzed.The fundamental influence factors are the surrounding environmental interference(conductor)and nearby Impact of other experimental equipment.