Analytical method for evaluating surface charge distribution on a dielectric from capacitive probe measurement-application to a cone-type spacer in +or-500 kV DC-GIS

The measurement of surface charging on a spacer in a +or-500-kV HVDC gas-insulated switchgear (GIS) is performed by a capacitive probe set inside the gas tank. The various factors that cause measurement errors are examined using a simple model. An analytical method to correct the measurement errors and transform the probe output into the charge distribution on the surface of the spacer is developed. The method is an extension of a numerical method for 3-D surface charge calculation. It is shown that the charge distributions from the probe measurement agree fairly well with dust figures.>