Superconducting dynamoelectric machine having a liquid metal shield

Abstract

A superconducting synchronous motor or generator which utilizes separate radiation and damper shields around a superconducting field winding on the machine rotor. The damper shield includes a pair of concentrically disposed cylinders held in radial spaced relationship with each other by pillar type structural members. A liquid metal fills the space between the concentric cylinders and as the rotor, including the cylinders, is accelerated to its operating speed, the liquid metal likewise will reach synchronous speed as a result of viscous drag between the liquid metal and the cylinder walls. During operation, the rotor shielding function is performed by the electrically conducting liquid metal moving at synchronous speed during steady state operation. Current generated in the liquid metal shields the superconducting field winding from alternating flux generated in the armature due to phase imbalance and harmonics. During fault conditions, such as a terminal short circuit, currents are generated in the liquid metal to shield the high armature demagnetizing flux from the superconducting winding. These currents in the liquid metal react with the field flux in the air gap to produce body forces in the liquid metal which result in the motion of fluid particles. Forces moving in a radial direction would tend to establish a pressure gradient in the liquid metal, but since the liquid metal is free to move and the pressure gradient cannot be maintained, flow takes place in the space between cylinders to equalize the pressure in the annulus which contains the liquid metal. Also, since circumferential body forces can transmit shear only by viscous forces, the torque reaction is significantly reduced.