Short Circuit Vibration Analysis of a Shell Form Power Transformer

The short-circuit axial vibration of a 250 Mva 500 kV single phase shell form transformer is calculated. The displacements of the coils and the stresses on the pressboard insulation between the coils are found for various design and operating conditions. Three different lumped mass models with nonlinear press-board representation are used for calculating the vibration in various parts of the coils because the frame which backs up the coils during short circuit is nonuniform. In shell form transformers manufactured by the authors´ company the frame consists of both the core and the tank which have considerably different mechanical impedances. These impedances are shown to be quite important and methods for evaluating them are given. The impedance of the tank is determined from the results of tests of a 1/7 scale model. The results show that dynamic effects are not large. The maximum calculated pressboard stress is 2290 psi (15790 kPa), which is only 27% higher than the statically calculated stress; and the maximum calculated coil displacement is .87 inch (2.21 cm). It is also found that friction in the interleaved core joints is sufficient to prevent core separation.