Experimental investigation on altitude correction factor of positive dc corona inception voltages of transmission lines based on the mobile corona cage

In order to obtain the altitude correction factor of corona inception voltage of HVDC transmission lines within the range 23 to 4000 meters, a mobile corona test cage was used to research the influence of altitude changes on positive DC corona characteristics of several kinds of conductors. Photons released as a result of corona discharge on the conductors were detected by the ultraviolet detection apparatus. According to the apparent change of photon number, corona inception voltage could be acquired by the tangent method. With the obtained corona inception voltage in four altitudes, the exponential and linear correction formulas were introduced, which fitted well with the experimental values. Based on the correction relation, a correction coefficient of about -9.5%/1000m was recommended.