Charge injection into solid insulators

Abstract

Electrical conduction in insulators requires the presence of charge carriers. When an insulator is stressed at high fields between two electrodes, charge injection into the bulk can occur from the cathode. This injected charge is then able to influence the insulator and affect its voltage hold-off capabilities and other electrical properties. An experimental apparatus has been constructed to study insulators stressed under high fields in a vacuum. The equivalent circuit of the experiment consists of two meshes which oscillate at different frequencies. The point-plane geometry of the electrodes and insulator appear in a mesh that oscillates at a higher frequency and much lower amplitude than the applied high voltage signal. One capacitive probe is coupled to both frequency components with the necessary voltage division ratios needed to detect both frequency components simultaneously. Separation of the two frequency components by use of Fourier transform techniques allows charge injection information to be extracted from the measured voltage waveform. A description of this method and results, including charge injection inception voltages is presented.