Modified peek formula for calculating positive DC Corona inception electric field under variable humidity

The corona on conductors is of importance for ultra-high voltage transmission. Humidity in air is an important factor of affecting corona inception electric field. Due to long distances of the ultra-high voltage direct current (dc) transmission, the transmission line crossing a high humidity area is inevitable, and thus the humidity should be taken into account in evaluation of the corona inception electric field of positive dc conductor. In this work a modification of Peek formula of calculating the corona inception electric field of positive dc conductor has been performed for taking into account the effect of air humidity. Using the modified Peek formula, the corona inception electric fields for the conductors with different radii under different humidity are calculated and compared with the reported experimental results. Reasonable agreement between calculated results and the experiments is obtained, which shows that the modified Peek formula is a good one for the effective and easy calculations of the corona inception electric field of positive dc conductor under different humidity.