Electrical machines typically comprise a cylindrical rotor mounted to rotate around or within a cooperating stator. That is, an electrical machine may have an internal substantially cylindrical rotor mounted within an external stator or an outer cylindrical rotor mounted around an internal stator. In superconducting electrical machines the stator and/or the rotor may include a plurality of superconducting field coils mounted on a field coil support structure, thereby forming a surface that is substantially adjacent to, but spaced apart from, a surface of the other of the stator or rotor.
There are several problems that must be overcome in the construction of such rotors and stators. First of all, the superconducting field coils and the field coil support structure must be kept at cryogenic temperatures when operating. In contrast, it is preferable that the mounting upon which the field coil support structure is mounted is kept as close to ambient temperature as possible in order to allow the rotor or stator to couple to other equipment or components which operate at ambient temperature. Therefore, there is the need for an improved rotor and stator construction that provides a very good thermal barrier between the field coil support structure and the mounting for the field coil support structure.
It is also necessary that any such rotor and stator construction efficiently transfers torque and other stresses from the field coils to the mounting for the field coil support structure. It will be readily appreciated that the rotor or stator must be capable of withstanding all the forces that it may be subject to during operation of the electrical machine. This includes short circuit torque, which is oscillatory and is typically many times greater than normal rated torque.
The rotor or stator must also be capable of being built at ambient temperature and subsequently having the field coils cooled down to the cryogenic temperatures at which they will operate. This cooling produces large contractive forces which the rotor or stator must withstand.
There is therefore a need for a rotor or stator for superconducting electrical machines that provides an adequate thermal barrier between the superconducting field coils and the mounting for the field coil support structure and that is also capable of withstanding the mechanical and thermal stresses that it will be subject to during construction and operation.