The study on the law of surface charge decay of silicone rubber materials may provide a theoretical basis for the design of DC insulators. In our research

sample surfaces are charged by a pair of needle plate electrode

then surface charge decay process is observed under different humidity of air. The surface charge distribution is derived from the measured surface potential distribution which is obtained by capacitance probe method. The results show that the surface charge distribution still maintains its concentric circle distribution during the decay process when the decay process occurs in low humidity air. The polarity of the surface charge near needle electrode is the same as that of the applied voltage

while the polarity of the surface charge far from needle electrode is contrary to that of the applied voltage. The initial surface charge distribution changes its shape when decay process occurs in high humidity air. The decay process of the surface charge is similar to exponential decay process

and the magnitude of the time constant is 103 s. The positive charges are easier to decay than negative charges. It is concluded that the surface charges mainly decay by volume resistivity in low humidity air

and the higher the volume conductivity is

the faster the decay rate will be. As the humidity of the surrounding air becomes higher

the decay rate by surface conductivity as well as the total decay rate grows faster.