Spectral Characteristics and Evolution Mechanism of Silicon Rubber Surface Discharge Under Thermal Ageing Condition

Surface discharge is a typical fault type in electric power equipment. High temperature in long-term operation can easily lead to ageing of materials, resulting in changes in surface characteristics and surface discharge faults. In this paper, a method of surface discharge identification of silicon rubber (SiR) based on spectral detection technology is presented. The surface discharge spectral characteristics of SiR with different ageing degrees are investigated, and the changes of microphysical and chemical properties and surface insulation properties caused by thermal ageing are analysed. The dynamic evolution of charge during surface discharge is simulated. The experimental results show that the spectral intensity of the surface discharge of the SiR material is mainly concentrated at 350, 600 and 750–900 nm bands. The spectral intensity reaches the maximum value when the ageing time is 168 h. With the intensification of ageing, no new characteristic peaks generate in the discharge spectrum, but the proportion of the same characteristic peaks to the overall wavelength is different. The type of discharge material and ageing state are determined by the characteristic light intensity ratio I_b. The evolutionary mechanism of the discharge spectrum is revealed by the variation of flashover voltage, trap charge density, resistivity and other parameters. The simulation results show that the increase of electron density will lead to more intense electron collision, which will release more photons, resulting in enhanced spectral intensity. This work can provide a reference for the detection of surface discharge and the evaluation of ageing state of the equipment inside the high voltage box.