Analysis of the direct current ionised field near the field mill probe with a hat-shaped electrode

Ionised field strength on the ground level is one of fundamental electromagnetic environment parameters of high voltage direct current transmission lines. Field mill is generally employed to measure the ground-level ionised field. In order to reduce the field distortion caused by the field mill probe on the ground, a measurement method of the ionised field with a hat-shaped additional electrode is presented in this study. Ionised field distribution on the probe with the hat-shaped electrode is analysed through both calculations and measurements. The ionised field is computed by the upstream finite element method (FEM) and is measured between a corona wire net and a parallel grounded plate. Experimental results demonstrate that the relative error between measurements and calculations is approximately 3%. The field distortion can be ameliorated effectively by the proposed method.