Theoretical studies have demonstrated the advantages which would accrue from the use of high armature voltage ratings for turbine generators. Among these advantages would be the reduction in armature current and the concomitant reduction in the current-carrying requirements of associated equipment, as well as the possibility of directly connecting the generator to a power transmission or distribution system.
The voltage range for large turbine generators of conventional construction is on the order of 24 kV to 30 kV. In the past, special arrangements were used to achieve up to 36 kV ratings, but these are now principally of historical interest and have not been applied to practical turbine generators. Voltage ratings of up to 500 kV suitable for direct coupling with a transmission system have heretofore not been thought feasible.
The development of superconducting rotors has opened up the opportunity of operating a generator at extra high voltage ratings suitable for direct connection to transmission grids. However, armature windings and insulation systems of conventional design are not capable of operating at such extra high voltage ratings. Thus the need has been recognized for a winding design and insulating system suitable for extra high voltage operation.