High Speed Electric Locomotive Main Transformer Loss Analysis Of Three-dimensional Tank And The Temperature Field Calculation

Although there is no much difference in theory between electric locomotive main transformer and normal power transformer, electric locomotive main transformer is high leakage reactance and multi-winding one. The transverse leakage magnetic field is intensive when adopting cake and interleave windings, so the losses in tank is high. If no measurements have been taken, the tank wall may have local hot-spot which can deteriorate the transformer performance. It is necessary to calculate accurately the loss in the tank and estimate temperature rise of the hot-spot. The conventional calculating method is to estimate the loss in the tank according to empirical formula of normal transformer. It may have relatively large error for transformer made of high leakage reactance and cannot estimate the local hot-spot accurately, so more accurate finite element method (FEM) is needed. The large universal finite element software -ANSYS is introduced in this paper. The principal theory of quasi-static magnetic filed and rationale of FEM relative to the research is presented systematically, in which edge element method is emphatically discussed. 3-D leakage magnetic field model of high-speed electric locomotive main transformer tank is built using edge element method and accurate tank loss is calculated compared with 2-D analysis model. Result shows 3-D model is more accurate and eddy density distribution pattern provides intuitionistic help for taking better shielding measures. The tank shielding optimization model is presented by limiting maximum eddy density in tank and minimizing shielding volume. Optimization result through subproblem approximation optimization technique indicates eddy current density more uniformly distributed in tank and total losses decrease 4%, but shielding volume adds little, which can be accepted by practical engineering. 3-D steady state temperature field model of transformer tank is built and the local hot-spots and temperature rises before and after optimization are obtained using magneto-thermal weak coupling method. Results verify the rationality of tank shielding structure.