Calibration Analysis of Field Mills in the Space Charge Modified Field above Ground Based on Convection-diffusion Equation

The field mills are normally operated on the ground plane to measure ground-level electric field under dc operating transmission lines. In order to use the field mills to measure the electric field in space, it is necessary to carry out the calibration of the space electric field. However, the calibration method of the field mills above the ground is lacking, which may lead to an inaccurate measurement. In order to analyze the feasibility of possible calibration methods, a simulation based on the convection-diffusion equation is presented for the space charged electric field. As the validation of the simulation, calibration experiment of ground-level electric field is carried out. Comparing the ion current of simulation result with experiment, the maximum relative deviation is 8.3%. In addition, the electric field and ion current in the calibration device of simulation are in accord with the analytical solution. Finally, in order to analyze how to calibrate the mills above the ground, simulations are carried out with and without ions. It shows that the distortion coefficients obtained by the two methods are basically the same, with a difference of only 1.53%. The method of simulation could provide a new way to solve the space charged modified field, and results obtained could provide a reference for the measurement and calibration for the mills measuring above the ground plane.