The best transformer fluids for underground, subterranean and tunnels


Underground, or subterranean, transformers and substations face a unique set of challenges during installation and operation. Deploying transformers underground presents an ideal solution for energy provision where the availability of surface land is restricted, such as in densely populated urban areas. However, in such cases the need for fire and environmental risk mitigation becomes a critical issue.


The MIDEL Ester Fluids


MIDEL ester fluids present the ideal solution for transformers in subterranean projects – including hydro power stations, underground storage facilities, mines, train tunnels and urban installations. With a high fire point of >300°C and proven biodegradability, MIDEL transformer fluids have been used in underground installations worldwide, including:

Göteborg Energi, Sweden

Underground transformers installed where fire safety was a critical requirement.

Kraftwerke Oberhasli AG, Switzerland

Four 50MVA converter transformers along with a number of auxiliary distribution transformers in an underground installation. Using MIDEL translated into cost savings with the removal of expensive fire suppression systems.

Vattenfall Hydropower Station, Sweden

Located in an environmentally sensitive area, where any spillage of mineral could not be tolerated. MIDEL 7131 was selected as the cooling fluid rather than mineral oil because it is fire safe and readily biodegradable.


Case Studies: Underground Transformers