Amelioration of the ionized field distribution near the field mill under the HVDC conductor

When the probe of field mill is directly mounted on the ground under the high voltage direct current (HVDC) transmission lines, the ionized field near the probe is distorted. In order to reduce the ionized field distortion on the top surface of the field mill probe, an electrode with semi-circular edge is added flush with the top surface of the probe. Finite element method is utilized to calculate the ionized field distribution. Calculation results indicate that the ionized field distribution could be ameliorated effectively by the electrode proposed in this paper. When the edge radius of the electrode increases from 0.01m to 0.04m, the ionized field at the electrode edge is reduced by 46%. The maximum of the ionized field on the surface of the semi-circular electrode occurs when the angle equals approximately jt/3. The design of the additional electrode may provide valuable reference for the measurement of the electromagnetic environmental factors of HVDC projects.