Retrofilling a “wet” transformer, UK Customer: Devonport Management Ltd (DML) Location: Devonport Royal Dockyard, UK Application: Distribution Transformer Highest Voltage: 11kV Rating: 800kVA Date: 2003 DML had a 30 year old free breathing mineral oil distribution transformer located indoors within the dockyard. It had become extremely wet, with core insulation readings by Megger test of <20MO. Oil testing showed that the transformer had very wet insulation; the mineral oil water content was 51ppm with a breakdown voltage of only 22kV. Both of these values were well below acceptable limits and so the transformer was taken out of service and earmarked for removal. Following consultations with the MIDEL team from, DML chose to retrofill the transformer with MIDEL 7131. This decision was take

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