Effect of Relative Humidity on the Surface Electric Field Intensity Characteristics under DC Voltage in a Corona Cage

The effect of relative humidity on the surface electric field (SEF) strength and a new non-contact assessment method based on space charge density were studied. The purpose of using space charge was to assess the SEF accurately, particularly after corona occurs. Space charge measurement and SEF evaluation were conducted at a relative humidity of 40% to 90%. The change law of SEF after corona occurs at different relative humidity was obtained. Results showed that under the same relative humidity, the space charge density increases with the applied voltage, while the SEF decreases with voltages after corona occurs. As the humidity condition aggravated, SEF first increases and then decreases, and the turning point is about 70%. The distribution of charge density has an opposite change trend. The variation of charge density and SEF demonstrates that the two have mutual inhibition. Meanwhile, the change formula of SEF shows that the electric field intensity on the wire surface is not constant after corona occurs. The corona discharge experiment and theoretical research can be further carried out based on the results in this paper.