Y--Oahe Passive Transfer Oil Containment

1. Main Unit Transformer Oil Containment This project is to install passive oil containment systems on ten (10) Generator Step-Up(GSU) Transformers located on the tailrace deck at the Oahe Powerhouse. Transformer 1 is a three-phase 115 kV transformer rated 103MVA and holds 4050 gallons of oil. There are 3 single-phase 230 kV transformers for banks 2, 3, and 4 for a total of 9 transformers each rated about 69 MVA and hold 4400 gallons of oil per phase. Each transformer is enclosed in concrete walls on three sides, with the downstream side open. The upstream wall is the powerhouse while the other two are firewalls. A curb will be placed on the downstream side of the powerhouse to provide enough containment to hold all of the transformer oil and the water from a 25-year, 24-hour storm event. A passive oil containment system will be placed in the lower section of each transformer vault. The passive liner will allow storm water to flow through while containing any hydrocarbons. Six-inches of fire quenching stone will then be placed on top of the liner to help extinguish puddle fires. Oil absorbing mats placed on top of the rock will be used to help collect small chronic leaks of the existing transformer to protect the life of the passive system. In the event of a catastrophic oil failure, the passive liner will solidify creating a water-tight barrier inside the vault. This will prevent any hydrocarbons from reaching the drain and being discharged into the river. Stairs may be installed to allow personnel to easily access the transformer vault. In addition to the containment on the GSU transformers, a similar passive containment system may be required the two (2)-1MVA station service transformers.