In order to study the accumulation and decay characteristics of surface charges on polymeric insulation materials under DC voltage

the epoxy composite insulating material was selected as the experimental samples with symmetric planar electrodes. After the samples being charged under different voltage amplitudes with different duration in SF

6

of atmospheric pressure

the surface potential distribution was measured with a Kelvin electrostatic probe. The results reveal that charges of the same polarity as applied voltage accumulate on the insulation surface. The surface potential of the center of electrode presents a bell-shaped distribution. The peak and half peak width of surface potential

increase with the applied voltage amplitudes. When the applied voltage is low（

<

10 kV）

the density of positive surface charge is higher than that of negative one under the same voltage magnitude

which is opposite when the applied voltage is high. When charging duration increases

the surface potential of the center of electrode also presents a bell-shaped distribution. The density of surface charge of the same polarity as applied voltage is higher and distributed intensively. There are two stages of surface charge decay

which satisfies a double exponential model. The decay rate is fast at earlier stage and slow at later stage. The initial decay rate is faster when the voltage amplitude is higher

but it takes much longer time to decay completely. The experimental results reveal that the surface charge decays mainly because of the contribution of surface conduction.