Modeling Method for Thermal Field of Turbulent Cooling Dry-Type On-Board Traction Transformer in EMUs

Adopting dry-type on-board traction transformer (OBTT) is one of the main ways to reduce the weight of electric traction systems, and its thermal characteristics are crucial for the safe operation of high-speed electric multiple units (EMUs). However, the existing thermal modeling methods either cannot realize the fast calculation of thermal characteristics of dry-type OBTT, or cannot accurately obtain the turbulence heat-transfer intensity when using the high-speed train-induced wind cooling. This article proposes an efficient method for dry-type OBTT thermal characteristics calculation. First, the thermal network of the winding area is proposed considering the thermal developing region of the air duct and the heat flow in the insulation paper between conductors. Then, the effects of key parameters on convective heat-transfer intensity are obtained by computational fluid dynamics (CFD) parametric sweeps, and then a novel local Nusselt number correlation for accurately calculating the turbulent convective thermal resistance is proposed. Finally, validation is performed with an experimental setup. The experimental results show that the computationally efficient thermal network model proposed in this article can quickly obtain the winding temperature distribution and the location of the hot-spot temperature. Moreover, the thermal analysis of a 6.3 MVA dry-type OBTT was conducted using the proposed modeling method.