Estimation of Hottest Spot Temperature in Power Transformer Windings with NDOF and DOF Cooling


Department of Electrical Engineering,Iran University of Science and Technology


Power transformer outages have a considerable economic impact on the operation of an
electrical network. One of the most important parameters governing a transformer's life expectancy is the
Hot-Spot Temperature (HST) value. The classical approach has been established to consider the hot-spot
temperature as the sum of the ambient temperature, the top-oil temperature rise in the tank, and the hotspot-
to-top-oil (in tank) temperature gradient. In this paper, the heat conduction equation for temperature
is solved. For numerical solution of the heat conduction equation, the nite element method is used. The
selected model for simulation is a 32MVA transformer with Non-Directed Oil-Forced (NDOF) cooling and
Directed Oil-Forced (DOF) cooling.