Feb 2013
Electricity Distribution
Polymeric Investigation
Feb 2013
Electricity North West Limited
Electricity North West Innovation Team
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Innovation Funding Incentive
High Voltage Technology
Switchgear manufacturers have been increasingly turning to polymeric insulating materials in recent years as they exhibit very high electrical breakdown strength, low dielectric losses, high DC resistively, high mechanical strength and high corrosion resistance. However this widespread use of these materials is not matched by a good understanding of their mechanisms of electrical breakdown or the way in which applied voltages may cause eventual physical breakdown of the materials.

Recent examples of switchgear failures attributed to tracking and treeing across polymeric insulating materials have been recorded where two apparently identical circuit breakers have performed completely differently under similar environmental conditions and this has led to some fundamental questions about how these materials are behaving in service.

Furthermore, it is believed that the proportion of switchgear across the network that contains these types of materials is now becoming significant as the capital replacement programme is removing older style equipment (with predominantly oil and SRBP insulation) and replacing it with equipment containing polymeric cast resin insulation. A concern has been expressed that the population of newer types of equipment may now sufficient be to reveal phenomena and trends that were not apparent when we had much smaller populations of these types of equipment.

It would appear that different types of cast resin materials supplied as insulators, which outwardly appears to be the same, have huge differences in their performance regarding their ability to repel moisture and as users we have no idea which types of materials are used. We are at the moment completely reliant on the suppliers of switchgear whose only apparent response is to specify switchgear should only be used at levels of relative humidity that are unrealistic in many locations in our license area. There appears to be no connection whatsoever between the manufacturers of the cast resin components and the end user DNOs and we have no understanding of the implications of the different chemical compositions of the cast resin that are supplied to us. This project is intended to begin to develop our in-house expertise by asking some fundamental questions.