The basic requirements for insulation for overhead transmission lines also the problems of 'ageing' by 'weathering' and the effects of surface contamination are briefly surveyed. Correlation between the basic properties of polymeric insulating materials and their structure is considered. The causes of progressive degradation are discussed in some detail, with particular consideration of degradation by 'tracking' and 'erosion' and failure by flashover, in the presence of surface contamination. Test procedures which are used to assess the relative tracking resistance of insulating materials are C:escribed, with particular emphasis on the tests recommended by the International electrotechnical commission, which have been used by the candidate to assess a variety of resin bonded and elastomeric materials. The equipment used for these tests is described and the results of investigations to determine factors which affect the reproducibility of results are presented. Factors which should be specified in the test recommendations are summarized in Section 9.1. The current v voltage characteristics of short, current limited discharges in air have been investigated and used to estimate the rete of power dissipation by single discharge across dry bands. If the rate of heat dissipation were uniform along the length of the discharges, the temperature rise at the surface of the insulation would be insufficient to cause thermal degradation, unless discharges recur at the sane site for several seconds. However, the temperature rise would beg greater, if heating were concentrated at the 'roots of the discharge. This is indicated by a marked polarity effect found when inclined plane tests were made with half wave rectified voltage. A limited number of tests on polyester matt glass mouldings showed that doubling the electrode spacing increased the voltage to cause track initiation and failure by 1.55 times. This is consistent with failure by thermal degradation when account is taken of the greater flow of contaminant at the higher test voltage.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:255070 |
| Date | January 1983 |
| Creators | Eldeen, Wamidh Dhyaa Eldeen Bahaa |
| Publisher | London South Bank University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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