The majority of high voltage gapped silicon carbide surge arresters on transmission and sub transmission systems have been in service for over 10 years. It is possible that many are now somewhat degraded. A diagnostic testing programme is required that can accurately and efficiently determine the condition of these high voltage arresters. If possible the programme should be easily adapted to in-field testing situations. This thesis details the development and evaluation of a testing programme designed to meet these criteria.
Initially the essential theory of silicon carbide arresters was investigated, focusing particularly on arrester construction, performance and the unique characteristics of high voltage arresters. The effectiveness of available diagnostic testing procedures was then evaluated and a set of tests selected, based on their expected performance, their ability to assess all facets of arrester behaviour, the ease with which they could be completed in the available laboratory and their possible application to in-field testing. It was also decided that the condition of an arrester would be judged primarily on the comparison of its performance with that of similar arresters subjected to the same tests, eliminating the need for restrictive failure criteria.
The testing programme implemented consisted of a series of diagnostic procedures including the lightning impulse sparkover voltage test, power frequency sparkover voltage test, power frequency withstand test, AC and DC leakage current measurements, 5 kV insulation resistance test, a non-standard current impulse test, and finally the partial discharge and radio interference voltage measurements. The tests were performed on a set of 6 ASEA type XAA station class arresters rated at 36 and 121 kV and a set of 5 arrester sections. The programme was concluded by completing an exhaustive visual inspection of arrester internal components.
The results of the investigation verified the effectiveness of the selected diagnostic procedure with a consistent and accurate assessment of arrester condition obtained for all arresters under test. All arresters exhibited satisfactory performance in the selected tests, indicating that high voltage gapped silicon carbide arresters are more durable than those used on distribution systems. The partial discharge and radio interference voltage tests proved to be more sensitive than other tests used, measuring arrester degradation not detected by the other tests and thus providing a more informative measure of comparative arrester performance. The partial discharge and radio interference voltage tests also appeared to correlate well with AC leakage current measurements. Together these tests may be able to be adapted for in-field testing programmes but more research is needed to confirm these apparent trends.