Simulation of Convective Heat Transfer by Oil from the Distribution Transformer Surface

During operation of electrical equipment and its design there is always a need to solve the problem of its heating and cooling, and especially the heating and cooling problem of the windings insulation as the most sensitive construction element The successful solution of the problem promote creation economically reliable equipment and the formation of a reasonable usage. The result of the study is the expediency substantiation of heat balance equations drawn up for the active part of the voltage distribution transformer simulation results implementation, at the final and qualifying design stage. The active part is in the transformer oil environment, and emission of heat is carried out by convection and heat transfer. The heat balance mathematical model corresponds to the equivalent thermal circuit, consisting of two adjacent units with heat outlet – generalized winding and ferromagnetic core and the third unit which is adjacent to them - moving substance from the oil which additionally contacts with the environment of infinite heat capacity. The solutions of equations are obtained for the winding mean temperatures, magnetic circuit core and oil in function of time that allows to determine their expected values during the transformer operation, and especially with the uneven schedule of its load as well as to make the justified choice of magnetic induction in the magnetic circuit core and current density in the windings in terms of permissible heating temperatures in them.