The core is built up from interleaved low loss cold rolled ,grain oriented steel laminations.
Individual stampings are coated on both sides with an insulating material which is both oil and temperature resistant.
The core limbs are securely bound with heavy duty webbed cotton tapes and the yokes are firmly clamped between steel and channels. All cores have mitred joints.
Top and bottom clamps are secured to each other by means of tierods which serve the dual purpose of securing the winding in place and of transferring the load from the bottom to the top clamps when the core and winding are lifted. This prevents tensile stresses being set up in the core legs, which could adversely affect the iron losses.