Corona is the key issue in the design and operation process of high voltage DC transportation and transfer facilities.The corona space charges are accumulated to the equipment insulation surface under the action of DC electric field

which led to local electric field distortion of insulation surface and weakens the insulation performance of the equipment.At present

there is no effective numerical method to consider the additional effect of space charge on the electric field strength of insulating surface.Considering the negative corona in the sphere-plane gap

an experimental platform

based on the principle of active electrostatic probe

for measuring the insulation surface charge under DC corona is set up.Through this experimental platform

three kinds of round slices with different materials and two kinds of umbrella shaped discs with different curvature are selected to measure the surface potential under negative corona in the sphere-plane gap.Then the surface potential is converted to the density of surface charges using a kind of inversion algo-rithm.The distribution characteristics of the surface charge on the surface of the negative sphere-plate corona discharge are obtained preliminary

which provides references for the study on charge distribution characteristics of high voltage DC equipment insulation surface under the corona.Furthermore

it can be extended to surface composited electric field numerical calculation and optimization of insulation design of high voltage DC electrical equipment

which has a certain application value for projects.