Oil in 11 kV switchgear. Service performance

There has been much interest in the adoption of condition based maintenance regimes. One area which has attracted particular interest is the maintenance of 11 kV oil filled switchgear. Electricity companies have undertaken considerable work assessing the availability and effectiveness of techniques to assess the condition of switchgear noninvasively. A number of companies have also completed detailed reliability centred maintenance (RCM) studies in order to identify the critical factors which affect the safe and efficient operation of this equipment. EA Technology on behalf of many of the RECs have undertaken both joint investigations of the condition of 11 kV switchgear and many individual investigations of switchgear failures. Combining the results of these various studies it has become clear that in general the condition of oil filled switchgear in service is very good and that the critical factor in determining the degradation of components within switchgear and therefore ensuring satisfactory and safe long term performance is the condition of the oil. In order to move towards condition based maintenance, information on the condition of the oil is therefore seen as paramount. As a result of this, EA Technology has carried out an assessment of the condition of oil in service and used this to consider critically the processes of oil degradation. The appreciation of these factors has enabled significant progress to be made towards a condition based maintenance strategy. This paper briefly summarises the outcome of this work and illustrates the benefits and opportunities that have resulted