An oil-immersed power transformer in a hydro power station has the potential for fire, explosion and oil leakage that can cause serious damage to equipment and the environment, because they are generally located in underground vaults or adjacent to watersheds. Many power stations have aged oilimmersed power transformers which have higher potential risks of failure and transformer owners must pay careful attention to the aged transformer. A SF 6 gas insulated and cooled transformer (GIT) is nonexplosive, non-flammable and oil-free. This technology can provide an effective solution to eliminate the risks of fire, explosions, water pollution due to oil leakage.