Research On Short Gap Discharge And Its Anti-metal Measurement In Electrical Equipment

As a key industry in the development of national economy,the safe and stable operation of electric power industry largely depends on the operation condition of electrical equipment.Insulation performance is one of the key factor of electrical equipment.While in the long-term operation process,insulation defects and short-gap discharges are easy to occur due to overvoltage and other effects,which causes latent operational risk of the system.Therefore,it is of great significance to realize the calculation of electromagnetic propagation in large-scale space and to carry out anti-metal detection.These studies can enrich the calculation and detection of theory for short gap discharge in power transmission and distribution equipment.Because the short gap in insulation material of electrical equipment is the main cause of insulation failure when discharge occurs.In this paper,a short gap discharge model based on plasma-chemical reaction is established,and the physical process and macrodynamic law of short gap discharge under typical power frequency voltage and impulse voltage are calculated.Secondly,in view of the difficulties in excessive memory consumption and low calculation efficiency when using the existing direct calculation methods for electromagnetic propagation propagation in electrical equipment.The nearfar field transformation method is proposed and the electromagnetic propagation law of typical electrical equipment discharge is obtained.Finally,considering the theoretical design defects of the built-in antenna used in metal environment of electrical equipment,a broadband UHF anti-metal antenna is proposed.The accuracy and effectiveness of the antenna are verified by experiments.The main contents and achievements of this paper are as follows.(1)The plasma-chemical model of short-gap discharge for electrical equipment under long-time power frequency voltage is established,and the dynamic characteristics of short-gap discharge are obtained.Emphasis is laid on the calculation of short gap discharge model and chemical reactions of main particle collision.The dynamic distributions of the electron density,electric field intensity and so on in short gap under power frequency voltage and the dynamic characteristics of short gap discharge pulse current under impulse voltage are revealed by calculation.(2)A near-far field transformation method for calculating electromagnetic propagation of short gap discharge in large-scale electrical equipment is proposed and the size of equivalent near-field source is studied.The principle of near-far field transformation in the calculation of electromagnetic propagation is analyzed.On this basis,the numerical calculation theory and stability conditions of near-far field transformation for short gap discharge calculation are given.The truncation error caused by selecting the size of nearfield equivalent source in near-far field transformation numerical calculation is analyzed,and the principle of selecting the size of near-field equivalent source is established.(3)Based on the calculation method of near-far field transformation,the computational efficiency and the electromagnetic propagation for short gap discharge in two typical structures of electrical equipment is studied.The short gap discharge of inner winding of structural transformer is taken as an example and the near-far field method and direct calculation of electromagnetic propagation for internal discharge of transformer are compared.The results verify the accuracy and advantages of the proposed method.In addition,the high voltage switchgear with multi-component structure is also taken as a research objective,the electromagnetic propagation for short gap discharge in the high voltage switchgear is analyzed.(4)A broadband UHF anti-metal antenna for built-in discharge detection is developed according to the characteristics of metal background environment in electrical equipment.The refraction process of UHF electromagnetic wave on the surface of metal conductor is obtained by theoretical analysis.A multilayer coplanar waveguide antenna with ECCOSORB MCS and FR4 dielectric layers is proposed,and a broadband UHF antimetal antenna covering the main frequency band(400MHz~3GHz)of discharge in electrical equipment is obtained by optimization.(5)The anti-metal test of the antenna is carried out and a short gap discharge test platform is built to simulate the metal environment.The performance of the antenna in measuring discharge signal in metalic environment is compared and verified in this paper.By analyzing the parameters such as the return loss and the radiation pattern of the antenna,the accuracy of the design is verified.In addition,a typical short gap discharge test platform is built to simulate the metalic environment of electrical equipment in the laboratory,and the effectiveness of anti-metal detection of the designed antenna is further verified by comparing with the detected results of reference antenna.