A Discussion on recent advances in heavy electrical plant - Superconducting reciprocating machines

Abstract

The superconducting reciprocating generator/motor has several advantages over the machines with rotating superconducting field windings on which most existing work is concentrated. It consists essentially of a number of armature conductors oscillating within a superconducting solenoid of rectangular cross-section, the conductors being parallel to the long side of the rectangle and at right angles to the directions of both the field and the movement. In the three-phase version the solenoid is wrapped into a toroidal shape, each armature phase being situated at an angle of 120° to its neighbour. The electrical phase relation is maintained by linking each phase-set of conductors through a connecting rod to a crank on the drive shaft. Electrical contact between the armatures and fixed terminals is made through flexible connectors. The chief advantages of the new machine are: 1. The superconducting field winding is stationary, while the armature does not require sliding contacts to carry the large output current. 2. The field flux is completely contained within the toroid without the need for iron or copper screens. 3. Because the armature conductors do not rotate, but reciprocate in the uniform toroidal field, it is possible to make them of superconductor since the a.c. losses, being due only to the self-field of the armature current, are tolerable. Even with normal conductors, eddy-current losses are greatly reduced. Among other points, the paper discusses optimization of the design, the problem of fatigue, seals and bearings, losses, and reactances. As the main disadvantage of this machine lies in the linkage converting rotary to linear motion, the prospect of an all-reciprocating system will be touched upon.