Effects of end winding porosity upon the flow field and ventilation losses in the end region of TEFC induction motors

The cooling air circulation in the end region of high voltage TEFC induction motors is driven by a fan system consisting of the fan effect caused by the rotor bar extensions and wafters. This paper describes the effect of end winding porosity upon the flow field and the ventilation losses. A simulated end winding of simplified geometry was used in both experimental and computational approaches to determine the effects of porosity. Due to the close proximity of the end winding to the rotor, the end winding porosity has a significant effect on the flow generated by the rotor, the overall flow field and the ventilation losses. An end winding with low porosity had a choking effect upon the flow generated by the rotor. There are also large variations in the flow field around the end winding, which is mainly due to the reluctance of the predominantly tangential flow to penetrate the radial gaps in the end winding. One of the most important observations was that as flow passes through the end winding, the tangential momentum is removed. This effect significantly changes the overall flow field and the ventilation losses as the end winding through-flow increases with porosity.