Patent GB-190721584-A (GB)
Title: Improvements in Dynamo Electric Machines
Inventor: BURKE JAMES
Filed: 1907-09-28
Granted: 1908-06-18
Abstract: 21,584. Burke, J. Feb. 4, [date appliedfor under Patents Act, 1901]. Armatures.-Relates to windings for direct-current generators whereby one terminal is kept at a constant potential between the potentials of the main terminals. The invention is described with regard to machines for three-wire distribution, in which case the auxiliary winding has half as many turns as the main winding ; but two such machines may be employed in a five-wire system. Figs. 3, 5, and 6 show bipolar armatures carrying, in addition to the ordinary ring winding 12, an auxiliary winding 13 for keeping the slip-ring 6 at potential midway between the potentials of the brushes 4, the two windings being connected at the point 14. In Fig. 3, the sixteen maio conductors in the upper half of the armature are shown accompanied by eight auxiliary conductors 13, the two being wound in the same slots so as to be influenced by the same field strength throughout. Fig. 5 shows the same form but with one half of the auxiliary conductors wound 180 electrical degrees forward and in the reverse direction to correct the effect due to the two halves being under poles of opposite sign. The preferred arrangement is shown in Fig. 6, where the auxiliary conductor are statically balanced around the armature and still maintain the ring 6 at the required intermediate potential. This arrangement also minimizes the magnetic distortion by currents in the mid-wire 9. Fig. 7 shows a form having windings 13, 16 corresponding respectively to those of Figs. 3 and 5 for giving a very uniform distribution of the auxiliary conductors among the main turns 12. With two auxiliary windings, the tapping- points 14, 17 are preferably 90 electrical degrees apart, as shown, and with three or six windings they are 120 and 60 degrees apart; but these angular spacings are not essential provided that each set of auxiliary conductors is so arranged as to correspond completely with one of the circuits of the main winding. Although it is preferable for the main and auxiliary windings to correspond in phase position as shown, slight asymmetry may be allowed, the numbers of turns being altered to compensate this. Fig. 8 shows a four-fold parallel-wound drum armature with two auxiliary windings 18, 20 connected to diametrically opposed commutator segments by equipotential connectors 19, 21 and both feeding the slip-ring 6. The four conductors 18<a>, 18<b>, 18<c>, 18<d> correspond in phase respectively to the pairs of main conductors 3, 10 ; 5, 12 ; 7. 14 ; and 1, 8 ; and thus keep the slip-ring potential midway between the potentials of the conductors 1, 14 ; that is midway between the main brush potentials. Owing to the cross connexion 19, the auxiliary winding also corresponds in phase to the main conductors in the circuits starting from the bars 17, 22 and terminating through the bars 32, 9 at the other brushes. The winding 20 similarly corresponds to all the conductors in the main winding, and any number of further auxiliary windings may be similarly connected between the main windings and the slip-ring. The auxiliary conductors are preferably placed at the bottoms of the slots which contain the main winding. By using two or more such machines in series, a multiple-wire system may be obtained across the sections of which, for example, the armatures and fields of motors may be connected to obtain large speed ranges in the usual way.