Patent GB-331188-A (GB)
Title: Improvements in dynamo-electric machines
IPC: H02K3/12
Filed: 1929-03-20
Abstract: 331,188. Field, A. B., and Associated Electrical Industries, Ltd. March 20, 1929. Windings; coils and conductors; armatures, cooling; cores.-In an alternating- current machine, and particularly one wound for high voltage, the normal windings are grouped in a relatively small number of slots per pole-pair and the electromagnetic effect of these concentrated groups is distributed over the periphery of the air gap by a distributed winding which is inductively linked with the concentrated main windings so that on load the difference of magnetic potential at the stator core bore between two points spaced apart peripherally by the pitch of the distributed winding slots is in no place comparable with that corresponding to the main aggregate ampere conductors in one of the large slots. By these means the crossing of end connections at widely different potentials is avoided, saving is effected by concentrating the high-voltage insulation into a few slots, and the adverse electromagnetic effects of the concentrated windings, such as heavy rotor losses and the production of harmonics in the voltage wave form, are corrected. Fig. 1 shows a sixth part of a stator core for a two-pole threephase machine in which the main winding is concentrated in two tubes T<1>, T<2> in six single large slots A and the distributed correcting winding is in small slots 1 - - 8 at the gap periphery, and Fig. 2 shows the end connections of the distributed winding which comprises sixteen conductors 1 - - 8, e - - l connected in series in a closed circuit as shown in Fig. 3. The return conductors e - - l, shown dotted in Fig. 3, are placed in extensions C<1>, B<1>, B<2>, C<2>, D<2>, D<1>, Fig. 1, of the main slot and between the two tubes at A in inductive relation to the main conductors. The order of the conductors is immaterial, but the arrangement shown avoids the use of long end cross-overs. In place of the series connection shown parallel groupings may be employed, these being chosen with regard to the circulating current which will flow in the groups on no-load owing to the fact that the voltages induced in the slots 1 - - 8 differ by about 5 per cent. The main slot A may be connected to the air gap by a narrow slot S, optionally bridged for strength by narrow end-portions, as shown, and the pitch s and tooth-width t of the peripheral slots are preferably made uniform, the slot sides being offset by increasing amounts with regard to the pitch lines. A method is described for compensating the currents in the tubes T<1>, T<2> by means of two parallel-connected conductors symmetrically disposed in pairs, such as C', C<2> or B<1>, B<2>, or the main slot A. The arrangement of the main three-phase windings is shown in Fig. 4. These are disposed in two groups M, N, 0, m, n, o in two sets of main slots displaced by 60‹ and are connected in series, as shown in Fig. 5. In each group there are no end crossings and there is no interference between the end connections of the two groups. The Specification describes also the method of distributing the peripheral slots and their distributed correcting conductors so as to give an air gap effect corresponding either to an ordinary full-pitch main winding or one of chorded pitch. The groups of distributed windings may be connected in series or in a mesh or meshes by means of interconnecting tappings and bus rings or connectors equal in number to the phase number of the main windings. For ring-wound main windings, each of the six main slots A carries conductors of one phase only in a single tube, and there are no crossings of high-tension coils. For oil-filled stators the slot insulation may be of paper T<1>, Fig. 6, the main windings P being independently insulated, as at Q, and separated by insulating layers R. The conductors may be in straight lengths, which are subsequently bent to form the end connectors, or of hairpin form, the straight ends being subsequently bent to make the connectors. Cooling may be effected within the slots or in the end connectors by bare or insulated oil tubes U sandwiched with the conductors and dealt with in similar manner to the main conductors in building. up the coils. At each end of the machine the end connectors of the tubes are interrupted for the oil inlets and outlets and for breaking the conductivity of the tubes. The conductors of the distributed correcting winding may be similarly oil-cooled or, alternatively, they may be hollow so as to convey the oil themselves. Specification 164,114 is referred to.