Dynamic stiffness and damping of transformer pressboard during axial short circuit vibration

Data on the dynamic stress-strain characteristics of transformer pressboard during transient loading like that occurring in power transformer coils during short circuits are presented for wide ranges of preload stress, peak stress, and temperature. A nine-element dynamic stiffness and damping representation for pressboard is described which is based on these measured results and the physical nature of oil-immersed pressboard. It is shown that the representation accurately duplicates the highly nonlinear dynamic stress-strain characteristics of pressboard over wide ranges of conditions and provides a means for reliably calculating the large transient forces and displacements that can cause failure of transformer coils during short circuits.