Time lag in CM-II electrode system attributed to dielectric surface conditioning

This paper deals with a digest on discharge time lag characteristics in a cylindrical void bounded polymethyl-methacrylate (PMMA) and metal using the CIGRE method II (CM-II) electrode system. The specimens were treated by plasma irradiations (0, 3, 6, 11, 16, 21 seconds) simulating material ageing in service which are very difficult to measure. It was found that, under room temperature, the longer plasma irradiation to the void surface will result in higher degree of surface roughness indicated by the increase of surface protrusion sizes. The statistical discharge time lag (SDTL) has been studied using square pulse voltage with rising time 40 μs, through 64 pulses. The SDTL value is inversely proportional to the surface conditioning. For a particular time period of plasma irradiation (3 s), the specimens seem to recover its insulating property after given recovery time of 20, 60, and 180 minutes compared to that of without recovery time.