Conductive Armature Shielding Design Concepts for Slow-Speed Superconducting Generators in the 40- To 400-MVA Range

Abstract

This study is concerned with the electrical dimensioning of passive, electromagnetic shields surrounding air gap armature windings for slow-speed multi-polar superconducting-field generators which make exclusive use of conductive rather than integrated conductive and ferromagnetic shields. Special reference is made to the problem of screening the composite stator winding and superconducting field for environmental and improved short-circuit protection rather than being applied to damp transient rotor oscillations. The conceptual machines used to illustrate the limitations on exclusive conductive shielding are 6–48 pole units with a corresponding stator rating ranging from 40 to 400 MVA at 60-Hz output. The specific cryogenic rotor circuit incorporates a Nb-Ti superconductor cable with design details included to calculate winding inductances and intermagnet forces. A high-voltage multilayer stator winding is dimensioned for numerically determining the Maxwell stress vector in the vicinity of the stator shield and reducing the load-dependent, radial magnetic forces on the superconductor.