The present invention relates to dynamoelectric machines and more particularly to a winding configuration for an air gap armature winding for such machines, particularly machines with superconducting field windings on the rotor. In its broader aspects the invention is also applicable to machines having non-superconducting field windings.
Large alternating current generators with superconducting field windings offer great potential benefits. Such machines operate with no losses in the field winding itself and thus can provide higher magnetic fields than conventional generators and with greater efficiency. This makes it possible to achieve a greatly increased electrical rating for a machine of given size with high efficiency, and the substantial elimination of field copper losses during operation represents a very substantial saving in operating cost.
Such a machine has a rotating field member consisting of a cylindrical rotor with the field winding disposed in slots in its surface. The field winding conductors may be made of superconducting material; if so, means are provided for circulating a cryogenic coolant fluid during operation to maintain the windings in the superconducting state. Such a winding produces very high flux densities in the air gap, as compared to conventional machines, and in order to take full advantage of this high magnetic field, it is desirable to use the maximum number (or cross-section) of armature conductors. The gross cross-section of the conductors can be greatly increased by eliminating the conventional stator teeth and completely filling the enlarged air gap space thus provided with armature conductors packed together to extend over the entire circumferential extent of the air gap and preferably arranged in several layers. (A larger cross-section of the conductors is normally achieved by increasing the size of individual conductors. A greater number of smaller sized conductors can also be effective.) The stator core becomes a magnetic shield on the outside of the air gap winding.
The physical arrangement of such an air gap winding presents certain problems. In conventional windings for dynamoelectric machines, stator coils of the so-called diamond type are commonly used. In such coils, the end portions of each conductor, beyond the ends of the stator core, are inclined at an angle to the straight body portion of the conductor so as to extend in a substantially helical path around the circumference of the core for connection to the similar end portions of other conductors lying in circumferentially spaced positions in the stator. In an air gap winding as discussed above, however, where the conductors are packed together substantially in contact around the entire circumference of the air gap, the end portions cannot be bent as described because there is insufficient circumferential space for the inclined portions of the conductors. It has been proposed to avoid this problem by the use of other types of air gap windings such as concentric windings or helical windings as shown, for example, in Davies U.S. Pat. No. 3,529,192 and Anderson U.S. Pat. No. 3,761,752. Windings of these types, however, are undesirable as they are difficult and expensive to install and do not take full advantage of the air gap magnetic flux. Various other expedients have been proposed, therefore, to permit the use of a diamond-like coil. Thus, thin insulating spacers have been placed between conductors in the body portion of the machine, but this reduces the space available for conductors and is undesirable for that reason. It has also been proposed to lift alternate conductors radially outward in the end turn region to permit the coil end portions to be bent. The effect of this, however, is to double the radial thickness of the end turn portions of the winding which is undesirable.