Experimental study on surface charge distribution of insulating film under the HVDC test wire

With the rapid development of HVDC transmission projects in China, the situation of the greenhouses existing under the HVDC lines is becoming increasingly common. When the transmission lines are in corona, the ionic space charges produced by the corona discharge in the vicinity of conductors are basically driven by the electric field to the ground. The presence of greenhouses with insulating film under the transmission lines will accumulate charges, which makes the electric field nearby distorted. However, the accurate modeling of the electric field in the presence of the insulating film under the transmission lines hasn´t been achieved because of the difficulty in getting the charge distribution at the surface of insulating film. In this paper, a set of experiments with conductor-to-ground configuration under DC corona is performed in the laboratory. The charges at the surface of three types of insulating films underneath the dc test wire are measured using the Faraday cage method. Through analysis and discussion on the measured results, the characteristics of the surface charge distribution at the surface of the insulating films are obtained. Furthermore, the differences between the charge capture ability of several different materials are found.