Comparison of mechanical strengths of three materials used as pressure plates in oil-filled transformers

A comparison of the physical properties of three varieties of material used as pressure rings to clamp and hold the coils of core-form oil filled transformers is given. The data is presented to serve as a guide in the selection of materials for pressure ring applications. The materials studied are polyester bonded high density pressboard, epoxy bonded electrical steel and epoxy bonded filament glass. A brief history of the development of the three systems is presented, along with a list of the features of each material and general information regarding applications relative to transformers ratings.