Feasibility of turbogenerator with superconducting rotor and conventional stator

In a 660 MW turbogenerator, the losses associated with the rotor total some 4.5 MW, mainly due to direct current in the field winding. The feasibility of saving this by making the winding superconducting is examined. The stator coils carry alternating current, and so they cannot be made superconducting, and, in the concept proposed here, the stator is substantially conventional. The new rotor has no iron, except for shaft ends, and the winding is embedded in an insulating cylinder cooled with liquid helium from a refrigeration plant. The winding is protected from harmful a.c. fields by a copper cylinder which rotates with it. The gap is evacuated, and this screening cylinder is kept cold by thermal conduction in the residual gas to a stationary low-temperature shield. The machine has high steady-state-and transient-stability margins, and the need for rapid field changes is greatly diminished The new rotor allows the present stator to be uprated. The economic advantage of the machine, taking refrigeration into account, depends on the degree of uprating found possible, and is in the range £290 000¿£830 000 for an output range of 660¿1000 MW. Many problems, particularly of a mechanical nature, remain to be solved, but none appears insuperable.