Thermal model of a disk coil with directed oil flow

Abstract

A model of a transformer disk coil with directed oil flow is presented which utilizes a network of oil flow paths. Along each path segment, oil velocities and temperature rises are computed. The oil flow is assumed to be thermally driven. The model includes temperature dependent oil viscosity, resistivity, oil density, and temperature and velocity dependent heat transfer and friction coefficients. Because of the nonlinearities, an iterative solution is necessary. Temperature and oil velocity profiles are computed. From this, the average winding rise and the hot spot temperature can be determined. The model can also be used for optimal positioning of the oil flow washers.