Oil/Paper Insulation HVDC Performance
National Grid Electricity System Operator
National Grid TO Innovation Team
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Innovation Funding Incentive
Recent work in International Conference on Large Electric Systems (CIGRE) has highlighted that oil resistivity can greatly influence the stress distribution within an oil-paper insulation system in a Direct Current (DC) stress environment especially during voltage changes such as polarity reversals. There
have been several failures of bushings at Sellindge during or shortly after polarity
reversals and there is evidence that the factory testing of DC transformers is
inadequate to cover service conditions. A new CIGRE group is being established
to look at this further and this work could usefully link to this group. The
measurement of the DC conductivity of oil is not routine and a repeatable
method needs to be established. This project will provide the knowledge to
specify appropriate tests on new transformers and make sure that oil quality in
service is maintained to suitable levels.
The project will investigate the performance of the oil-paper insulation system
used in HVDC transformers under a variety of electrical stress conditions. It will
attempt to determine the effects of oil resistivity and other insulation condition
parameters on the capability of the insulation to withstand the electrical stresses
seen within HVDC transformers particularly during polarity reversal or other
changes in stress.