Rotor Endwinding Cooling Analysis of Large Turbogenerators

Rotor Endwinding Cooling Analysis of Large Turbogenerators

Rotor windings in high-speed electrical machines such as a turbogenerator consist of concentric coils mounted in slots of a rotor which are typically connected transversely in rotor end regions. The power output rating of turbogenerators is often restricted by temperature limitations and effective cooling of turbogenerators contributes to more output ratings. In the present paper, the flow and thermal analysis of the rotor end winding of large turbo generators are investigated computationally to find the temperature distribution and hot spots as one of the main goals. Due to the complexity of the endwinding in shape and flow pattern, lumped-parameter model is used to find flowrates in the first step. Then, in the thermal analysis, the model is well simplified to apply finite difference method and thermal network method in an iterative approach. To validate the results, a comparison with empirical results is made. In order to obtain a more uniform temperature distribution and decrease the maximum temperature of the rotor endwinding, geometrical modifications are recommended.