Patent GB-1435314-A (GB)
Title: Superconducting rotating electrical machines
IPC: H01L39/00
Filed: 1973-04-12
Abstract: 1435314 Dynamoelectric machines; control of AC motors MASSACHUSETTS INSTITUTE OF TECHNOLOGY 12 April 1973 [25 May 1972] 17549/73 Headings H2A and H2J A dual-armature superconducting rotating electrical machine comprises a superconducting field winding to provide a high-intensity D.C. magnetic field, a first armature having a fullturn winding, a second armature having portions to carry an electric current, both armatures being normally-conducting and having their turns and portions linked by the magnetic field which interacts with their currents to provide reaction forces therebetween, the force in the second armature acting to counteract that in the first thereby to allow a substantial portion of the forces to be taken up by the two armatures and reduce the reaction force on the field winding. In the embodiment of Fig. 8 the machine 101<SP>111</SP> is an alternator whose stationary first armature 1<SP>11</SP> is connectable to a load, whose second armature 2<SP>111</SP> is a free spinning conductive interial shell mounted on bearings 51, 51A, and whose field winding 3<SP>11</SP> is on a rotor 35<SP>1</SP>; the shell has sufficient inertia to relieve the field winding 3<SP>11</SP>, by slowing down, of reaction torque due to a fault in the load on the first armature 1<SP>11</SP>. The machine 101<SP>11</SP> of Fig. 6 is a commutated D.C. motor or generator whose field winding 3<SP>1</SP> is stationary and housed in a dewar 104, whose second armature 211 is either rotatable or also stationary, and whose first armature 1<SP>1</SP> is rotatable and has a commutator 42 engaged by brushes 41, 41A the windings of the two armatures being connected mutually in series, possibly also with a reistance. The machine 101<SP>1</SP> of Fig. 4 is an induction motor whose field winding 3 is rotatable, is energized from a D.C. source 6 via slip rings 4, 5, is in an evacuated cavity 103, and has a shield 20 also acting as a damper winding; the first armature 1 is stationary and may be 3 Ph.; and the second armature 2<SP>1</SP> has a load output shaft 23A rotatable in bearings 24, 24A and has a squirrel cage conductive shell or a conventional wound rotor winding in series via slip rings 27 with torquechanging resistances 26. The machines may have an outer eddy-current or magnetic shield 22. Motor control.-The latter 101<SP>1</SP> may be applied to a ship drive, Fig. 5, comprising a high speed turbine prime mover 30 driving a superconducting alternator 31 having a small number of pole pairs and supplying via a bus 34 the motor stator winding 1, which has a greater number of pole pairs. The torque of a propeller 33 driven by armature 2<SP>1</SP> via the shaft 23A may be varied in one of the following ways: (1) voltage control of motor 101<SP>1</SP> by changing the D.C. from source 6 to the alternator 31 and the winding 3, the change heing proportional to keep the alternator and motor voltages matched, (2) variation of resistors 26, (3) variation of the frequency difference between that f 2  of an A.C. supply replacing resistors 26 and that f 1  of the A.C. supply to armature 1. Dynamic braking may be effected by connecting the bus 34 to a bank of resistors instead of the alternator 31, the motor consequently acting as an induction generator controlled by variation of D.C. from source 6 and/or variation of resistors 26. Propellor reversal may be effected by disconnection of the alternator 31 from armature 1, reduction of the D.C. from source 6 to zero, subsequent increase of the D.C. to cause the damper winding to stop rotor 35 and accelerate it to near synchronous speed in the reverse direction and to cause winding 3 to pull rotor 35 into step, and reconnection of armature 1 in reversed phase sequence, armature 2<SP>1</SP> being open-circuited during the whole reversing procedure. Reclosure of the latter permits the propellor to be stopped and reversed by control of members 6 or 26. In a modification (not shown) the turbine 30 drives the induction winding of a superconducting induction generator at a negative slip relative to the free-spinning synchronous field winding, the propellor being driven by a superconducting multipole motor and locked at the synchronous speed ratio of the free generator rotor.