Degradation processes of voids in solid dielectrics under AC applied fields

Abstract

This Thesis is concerned with an experimental study into the degradation processes that occur when voids in solid dielectric materials experience high applied electric fields. A method has been developed for manufacturing 2 mm thick samples of silicone rubber that contain a single gas void of around 1mm diameter. Samples are simultaneously electrically stressed under an applied ac sinusoidal voltage of 11-12kV for 6 hours that is then increased to 12-17kV. During the stressing period, partial discharge (PD) data is regularly acquired. The samples are then inspected for signs of degradation. Degraded samples that have not suffered catastrophic failure and contain pits or evidence of damage were then cut open using an RMC MT-7 ultra- microtome equipped with a C R-21 cryo-system set at -110ºC in order to provide a surface containing open segments that can be assessed using spectroscopic techniques.

The experiment is repeatable and the obtained degraded samples and the degradation areas of microtomed samples have been analysed using Raman spectroscopy to identify the chemical content of the degraded areas and obtained improved images using a scanning electron microscope (S EM) at the void /silicone rubber interface. In addition, the obtained PD patterns have been used to make a comparison between measurement and simulation results obtained using a physical model implemented in Matlab.

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Identifiers

ORCID for P L Lewin: orcid.org/0000-0002-3299-2556

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