A major energy distribution company in Quebec was advised by its insurance company to review the electrical substation at one of its urban locations. Two mineral oil transformers, rated 25 kV and 6.9 kV, were installed in close proximity to the building housing the ancillary substation equipment, including critical switchgear. The insurance company told the client that modifications would be necessary in order to make the substation compliant with the latest building and fire safety standards.

An engineering consultant assessed the site and submitted two potential courses of action: the first option (and the most expensive) comprised constructing a fire wall between the building and the transformers. This action would, however, create connectivity problems between the transformers and the other elements of the substation. The second option proposed to replace the mineral oil in both transformers with another type of insulating fluid with less flammable characteristics – a process called retrofilling.

The customer decided to replace the mineral oil with MIDEL eN 1204, one of the MIDEL range of ester transformer fluids suitable for low temperature applications. Choosing this option avoided the high costs of modifying the existing building and the disruption of major construction work on the site.

MDL Énergie, a MIDEL Service Partner specializing in the maintenance, repair and modernization of medium and high voltage equipment, was commissioned to replace the mineral oil with MIDEL eN 1204 natural ester at the customer’s site.

The transformer retrofilling was carried out over two consecutive days, minimizing the duration of the necessary electrical shutdown. The existing mineral oil was drained and transported to MDL Énergie’s workshop for recycling. Then the transformers’ coils and the tanks were rinsed with MIDEL fluid. After removing the rinsing fluid, the transformers were filled with MIDEL eN 1204. The qualified MIDEL Service Partner team deployed a filtration unit in order to perform the fluid transfer at a best-practice temperature of around 70°C.

The retrofilling was completed safely in just two days compared to the weeks of construction work necessary to build a fire wall. Production losses were thus kept to a minimum, a major benefit for the customer, and the transformers are now fully fire-safe thanks to the special attributes of MIDEL ester transformer fluids.

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