Assessment of Systems for Cooling High-Speed Mini Turbine Generators
The results from a comparative study of cooling systems used for high-speed mini turbine generators are presented. It is shown that admissible temperature operating conditions can be set up by using liquid cooling of the stator and gas cooling of the rotor or by using fully gas cooling of the machine with different kinds of cooling media. However, the arrangement involving liquid cooling of the stator and gas cooling of the rotor is the most economically efficient option. With gas cooling of the rotor, the cooling gas parameters have an effect not only on the heat transfer coefficient, but also on the losses due to rotor friction against the cooling medium. The difference by which the rotor surface temperature exceeds the inlet gas temperature is a complex function of gas parameters, due to which the choice of cooling gas is not a trivial problem. For selecting a gaseous coolant, the linear programming problem involving the excess of rotor surface temperature as an objective function has been formulated and solved.