The effects of humidity on the ground-level resultant electric field around positive DC conductors were studied both experimentally and numerically. Experiments were carried out in an artificial climate chamber, the results of which showed that the photon count and the groundlevel resultant electric field strength both increased with increasing relative humidity. Numerical calculations for different values of relative humidity were carried out, including solutions of the positive corona inception voltage and the ion-flow field, for which a photoionization model and the upstream finite element method were employed, respectively. In order to analyze the effects of humidity, three main factors were considered: the ionization coefficient, the attachment coefficient in the photoionization model and the modified ion mobility of the charged water particles. The results indicated that, with increasing relative humidity, increasing values of the effective ionization coefficient were responsible for a reduction in the inception voltage, and the reduction reinforced the ground-level resultant electric field. Moreover, due to the charged water particles and the lower ion mobility with increasing relative humidity, the space charge density distribution was enhanced, which also strengthened the ground-level resultant electric field.

This work was supported by National Key Research and Development Program of China Grant No. 2016YFB0900800, Fok Ying-Tong Education Foundation China Grant No. 151058, the State Key Laboratory of Advanced Power Transmission Technology Grant No. GEIRI-SKL-2018-014, the Fundamental Research Funds for the Central Universities Grant No. 2019MS011 and Young Elite Scientists Sponsership Program by CAST Grant No. 2016QNRC001.