An Approach to Optimal Thermal Design of Superconducting Generator Rotor

To stabilize the superconducting condition of field winding of a superconducting generator and to ensure high-efficiency operation of the machine, heat penetrating the inner rotor of the superconducting rotor must be suppressed. This makes it necessary to recognize quantitatively and accurately heat penetrating from such parts as current leads, torque tubes, and radiation shields. Since the temperatures of such structures and the coolant rise from around 4K to 300K, such physical quantities as density of the coolant and thermal conductivities of the structures depend nonlinearly on temperatures. This prevents adequate accuracy from being obtained simply by the analysis of penetrating heat by using the mean values of properties. To improve this inaccuracy, we developed nonlinear thermal analysis methods. Many experiments, including those with a 3000kVA superconducting generator, have proved that this technique accurately estimates the temperature distribution in structures and the heat penetrating an inner rotor. The technique enabled us to obtain important knowledge on parameters concerning heat penetrating from current leads, torque tubes, and radiation shields for trial designing of a 1000MVA machine.