GB190924126A - Improvements in and relating to Dynamo-electric Machines. - Google Patents

Abstract

24,126. British Thomson-Houston Co., [General Electric Co.]. Oct. 20. Rotary transformers; windings ; exciting. - A synchronous alternating-current machine adapted for use as a frequency-changer or double-current generator, in which the two voltages may be independently varied, has a single armature provided with two windings of different pole numbers, or with an electrically-equivalent single winding, the field magnet having coils which produce two component magnetizations corresponding in pole-number to the two pole-numbers 'of the armature winding. In a single-phase arrangement, Fig. 1, the armature is provided with four coils or g r o u p s of coils A<1>, A<2>, A<3>, A<4> forming mechanically a single winding. One armature circuit extends between the terminals a<1>, a<1> with the coils A<1>, A<4> connected in parallel with the coils A<2>, A<3>, the current directions in the conductors being indicated by the upper arrow-heads so that the winding constitutes an eight-pole winding. The terminals a<2>, a<2> of the second armature circuit are connected to equipotential points of the eightpole circuit, and, so far as this circuit is concerned, the armature winding is a four-pole winding with coils of half-pitch. The field magnet is provided with eight poles F<1> ... F<8>. The coils on alternate poles F<1>, F<3> ... are connected in series across the exciter C so as to give an eight-pole magnetization, as indicated by the top letters n, s. On the other poles F<2>, F<4> ... are placed a second series of coils, which are connected to the exciter through a rheostat D and superpose a four-pole magnetization on these poles, as indicated by the bottom letters n, s. The eight-pole and four-pole magnetizations induce voltages in the armature circuits without mutual interference, and the relative voltages are varied by means of the rheostat D. To utilize the armature copper more effectively, all of the field poles may be employed for the four-pole magnetization as well as for the eightpole, alternate pairs of poles being magnetized by the four-pole windings so as to have the same polarity. In a further modification, Fig. 3, the poles F<2>, F<4>, F<6>, F<8> only are wound and a resistance E<1> is adapted to be connected in shunt with a portion of the field coils. If the. resistance is open circuited, there exists an eight-pole magnetization only, but by closing the circuit of the resistance as indicated in dotted lines and moving the contact towards its dotted-line position, the poles F<2>, F<6> are strengthened and the poles F<4>, F<8> weakened, thus producing the equivalent of eight-pole and four-pole magnetizations. To avoid unbalancing, the numbers of poles should not be less than eight and four. Specifications 6223/06 and 15,711/06 are referred to.