Evolution of Trap and Dielectric Properties of Silicone Rubber Insulation Under Power Frequency Voltage with Harmonic Component

With the rapid increase of capacity of power grid and the wide use of electronic devices and nonlinear loadings, harmonic voltage and current are generated in power grid. The harmonic components in power grid affect the operational safety of power equipment, accelerating the ageing of insulating materials in power equipment and reducing the reliability of power system. In the present work, we applied a power frequency voltage with harmonic component on power cable termination. Then we measured the infrared absorption, dielectric spectra, conductivity, and surface potential decay properties of silicone rubber for power cable terminations with different applied power frequency voltage with harmonic component in different periods. The experimental results show that the dielectric constant and dielectric loss will increase with the increase in the time of voltage application. Especially, the dielectric loss at low frequencies will remarkably change, which means that the effect of DC conductivity will increase with the time of voltage application, leading to an inverse power law between the dielectric loss and power frequency. In addition, the surface potential decay rates of silicone rubber charged by both positive corona and negative corona will increase with an increase in the time of voltage application, which is consistent with the experimental result of conductivity as a function of the time of voltage application. Analyzing the trap distributions by the first-order charge detrapping dynamic theory, we found that shallow traps are generated for both electrons and holes. Furthermore, the carrier mobility was calculated via the charge hopping conduction model. The results show that carrier mobility will increase with the increase in shallow trap density and the decrease in trap energy, resulting in the increase in conductivity. When the conductivity reaches a threshold value, the insulating material may lose its insulation properties, causing the failure of insulation through breakdown or surface flashover. © 2019, High Voltage Engineering Editorial Department of CEPRI. All right reserved.