Abstract: A substation transformer is disclosed which includes a winding, a winding compression ring, which closes off the winding, a compression beam, and expanding spring elements. The expanding spring elements are disposed concentrically around a core portion of the winding, and are placed between the compression beam and the winding compression ring. Each of the spring elements includes a spring, a bushing receiving a spring, and a compression piston which has been provided to close an open end of the bushing. The compression piston is adapted to limit movement of the spring. A post-installation modification mechanism is provided which includes a compression mechanism for compressing the winding. The compression mechanism comprises hydraulic cylinders adapted to be removably inserted between the compression beam and the winding compression ring.