Effect Of Air Pressure And Humidity On Corona Inception Voltages Under Combined AC And DC Voltages

As the widespread use of converter valves and other electrical equipment,more and more attention has been paid to the high-voltage environment under combined AC and DC voltages.The research about the effect of air pressure and humidity on corona inception voltages under combined AC and DC voltages has been done,to explore the safety net distance and improve the insulation level of electrical equipment under complex electromagnetic environment with low air pressure and high humidity.A calculation model was developed to determine the corona inception voltages under combined AC and DC voltages.At a fixed applied combined voltage,every'potential corona point' and its 'affect region' was enumerated in time steps.The continuity equations were solved by flux corrected transport algorithm and the Poisson equation was computed by the successive over relaxation method,and the charged-particle density and electric field in 'affect region' were calculated.The physical model of corona voltage basing on the calculation of electron photos on the electrodes surface was ameliorated to analyze each 'potential corona point',which considered the influence of the charged-particle density and electric field in 'affect region'.A corona voltage criterion which applicable to combined voltages was determined.The applied voltage in model was enumerated by digit,and the corona inception voltages under different combined AC and DC voltages were worked out.The variations of important parameters due to air pressure were analyzed,such as drift velocities and attachment,ionization,recombination and diffusion coefficients.The ionization zone and particles densities over a range of air pressures and humidities were computed.The enviromental parameter was introduced into the corona inception voltages model,and the inception voltages under combined voltages at various air pressures and humidities were calculated.Under combined AC and DC voltages,the corona inception voltages decreased with a decrease in the air pressure and increased with a decrease in the humidity.As the air pressure decreased,the inception voltages changed more obviously than as the humidity increased.And at low air pressure,the effects of the humidity on the inception voltages becomes large.The quantitative law between the inception voltages under combined voltages and the air pressures and humidities was also achieved.In a laboratory tank with 0.06MPa?0.1 MPa air pressure and 20%?90%humidity adjustable,a series of corona experiment under different voltage types has been done.The experimental results of corona inception voltages under AC voltages,DC voltages,combined AC and DC voltages at various air pressures and humidities were worked out.Under AC voltages or DC voltages,the inception voltages decreased as air pressure decreased and decreased as humidity increased.With the compare between the computed results in the new method and traditional method and the experimental results,the computed results of corona inception voltages under combined AC and DC voltages in the new method was closed to experimental results.At various atmospheric environment,the change rule of experimental results of inception voltages under combined AC and DC voltages was the same as the change rule of computed results,and the law between the inception voltages and the enviromental parameter got further validated.