Oil transformer bund - retention tank
Many industrial devices such as immersed power transformers contain several thousand liters of transformer oil in their internal cooling or insulation systems. These oils belong to the hydrocarbons classification and may cause severe soil or water pollution in case of leakage.
In order to mitigate this pollution risk, such industrial equipment must be paired with retention equipment of a volume at least equal to the volume of hydrocarbons they contain: the full retention principle. The European standard EN 61936-1 (§ 8.6.2.) for transformers requires a watertight retention representing 100% of the oil volume oil contained in the transformer. Additional protection such as extinguishing cover or suffocating gratings are recommended to avoid slippery stones or pebbles below the transformer in the concrete retention pit. It avoid fire to take too much power, pass through fire protection wall and spread to all your installation.
Furthermore, when the equipment is installed outside it is subject to rainwater that can fill this primary retention tank. To overcome this rainwater/oil leak overflow risk, the tank must be equipped with a system that filters and continuously discharges rainwater while retaining hydrocarbons within a secondary retention device. Authorities have set the hydrocarbon contamination limit to no more than 5ppm hydrocarbon in discharged water (EN 858-1: "light liquid separations facilities").
