Abstract:
This thesis presents the measurement and simulation of surface charge decay on a polymethyl methacrylate (PMMA) circular disc. The objective of the thesis is to calculate the surface charge density in the 2-dimensional (2D) and the 3-dimensional (3D) models for comparison with the estimated results obtained from experiments, and to study the mechanisms of charge which depends on the thickness of the dielectric disc. For the experiments, a rod-plane electrode arrangement was used to generate the positive corona discharge on surface of 1-, 2- and 10-mm thick PMMA disc. The measured surface potential was used to calculate the electric field by using the finite element method (FEM). The surface charge density was calculated from the electric field component. The surface potential distribution was initially bell-shaped then decayed with time. The surface potential in the case of 10-mm thickness decreased faster than that in the thinner cases. The physical phenomena related to the surface charge reduction were 1. charge neutralization, 2. surface conduction, and 3. volume conduction. In all cases of thickness, the surface charge density was remarkably decreased at the center position and then made as a crater-like shape due to the charge neutralization mechanism. In the case of 1- and 2-mm thickness, the charge density spread in the radial position of PMMA disc according to the surface conduction mechanism. Furthermore, the surface charge distribution was sunk overall due to the mechanism of volume conduction.
