Influence Of Humidity And Air Pressure On DC Corona Discharge Mode Transition

Corona discharge of high-voltage transmission lines will waste electric energy,and cause electromagnetic environmental problems,which will affect people's life.Therefore,corona discharge is a hot issue in high-voltage transmission engineering.China's UHV AC and DC transmission lines cover a wide range,and the climatic conditions in different regions have a greater impact on the corona discharge of transmission lines.Humidity and air pressure are the main influe ncing factors.The DC negative corona can be divided into the three modes: Trichel pulse,pulseless glow,negative streamer.Different corona discharge modes have different corona currents and discharge patterns,which will cause differences in wire energy loss and the electromagnetic environment impact.The existing research on the mechanism of negative DC corona discharge is mainly about the influence of various environmental factors(such as pressure,humidity,etc.)on the Trichel pulse characteristics,such as corona inception voltage,pulse frequency,etc.However,the impact of these factors on the transition of corona discharge modes and its mech anism analysis are lacking.First of all,this paper builds a set of discharge chambers with adjustable humidity and pressure to simulate different climatic conditions.The pressure range is 50kPa-101 kPa and the relative humidity range is 10%-90% during the experiment.Copper needle-plate electrodes with different radii of curvature were used with a gap distance of 2.5 cm.The effects of humidity and air pressure on the transition of DC corona discharge mode were studied by measuring transient current and c orona discharge voltage.The physical process of the transition of negative DC corona discharge from Trichel pulse to pulseless glow is discussed.The scientific rules of the influence of humidity and pressure on the Trichel pulse characteristics of negati ve corona discharge were analyzed by experiments,including the effects of humidity and pressure on the negative corona start voltage,pulse average corona current and pulse repetition frequency.Secondly,in order to investigate the transition mechanism o f negative DC corona discharge from Trichel pulse to pulseless glow,a negative corona discharge simulation fluid model was established in Comsol Multiphysics software.The effects of gas heating and electron detachment reaction on the negative corona Tric hel pulse to pulseless glow transition process were studied to clarify which factors led to the transition of the negative corona discharge mode.The simulation results show that the gas heating effect plays an important role in the transition process from Trichel pulse to pulseless glow.Finally,the effects of humidity and air pressure on the transition char acteristics of DC negative corona from Trichel pulse to pulseless glow are studied.The variation of transition voltage is analyzed,and the influence mechanism of humidity and air pressure on the transition characteristics of Trichel pulse to pulseless gl ow is revealed.The experimental results show that when the humidity is constant,the transition voltage increases with the increase of the air pressu re.When the air pressure is constant,the transition voltage increases as the relative humidity increases.This is because the relative humidity increases,and the formation of hydrated ions during discharge reduces the ion mobility and slows down the rec overy process of the electric field of the tip electrode.In addition,the needle electrode with a large r adius of curvature has a interim process in which the Trichel pulse and the pulseless glow mode exist simultaneously during the transition process.Th e research results in this paper can provide reference for the design of high-voltage DC transmission lines and the performance optimization of corona discharge applications.