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Title: The chemical degradation of epoxy resin by partial discharges.
Author: Hepburn, Donald M.
Awarding Body: Glasgow Caledonian University
Current Institution: Glasgow Caledonian University
Date of Award: 1994
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Epoxy res~ a major component of solid electrical insulation systems, degrades when subjected to electrical discharges. Identification of the epoxy resin degradation mechanism might indicate improvements which can be made in the chemical formulation of the resin to enhance the insulation systems. Samples of a commonly used epoxy res~ bisphenol-A epoxy crosslinked with phthalic anhydride, were manufactured and then aged by applying lOkV AC to an electrode 2mm above the resin surface. The following experimental conditions were altered: manufacturing system: (i) moulded slab and (ii) slice cut from moulded cylinder; atmosphere: (i) nitrogen, (ii) dry, (iii) normal and (iv) moist air; high voltage electrode:(i) brass and (ii) copper. In addition, ageing due to chemical, thermal and radiative stressing was also examined. The changes in the stressed resin samples were determined using the following techniques: diffuse reflectance Fourier Transform infrared spectroscopy (DRIFT), attenuated total reflectance FTIR (ATR-FTIR), thermogravimetric analysis (TGA), thermogravimetric FTIR (TG-FTIR) and atomic force microscopy (AFM). The changes in the electrode materials were determined using X-ray diffratometry (XRD) and Fourier Transform infrared (FTIR) techniques. The method of production of the specimens was shown to affect the degradation. Silicone release agent, used in the moulding of the resin slabs, was found on the surface of degraded moulded resin slabs: the contamination of the moulded samples was not detectable prior to partial discharge stressing. Crazing and flaking of the stressed resin surface were found on the moulded slabs but not on the slices of resin. Anhydride, acid and amine species were identified on the surface of the electrically stresses resin slices. Chemical reactions accounting for the changes found on the surface of the stressed resin slices are given. The radical species formed by methyl group dissociation, reacting with hydroxyl and activated oxygen species, lead to the formation of linear anhydrides, acids and peracids on the resin surface. Reactive nitrous oxide species in the discharge atmosphere react with the resin to form amines. Zinc formate dihydrate was identified on brass electrodes after the resin ageing process, whilst basic copper nitrate was identified on copper electrodes. The difference in deposit found on the electrode indicates that zinc reacts with carbon species from the discharge environment; copper reacts, not with carbon species, but with nitrogen species. The variation in chemical interaction at the high voltage electrode, dependant upon electrode material, has been found to correlate with changes on the resin surface. Correlations are made between the effects of partial discharge and other stresses applied. None of the applied stresses generated the anhydride structure found in partial discharge stressed resin samples. However, in common with p.d. stress, UV radiation increases the level of crosslinking in the epoxy resin and produces carbonyl structures, nitric acid fumes produce acid, peracid and nitroso structures.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Dielectric; Insulation