GB274195A - Improvements relating to dynamo-electric machines - Google Patents

Abstract

274,195. Creedy, F. April 16, 1926. Addition to 249,579, Exciting; compensating - windings; rotary converters and transformers.- In an alternating-current machine having a commutator winding and in which two magnetic fluxes of different pole numbers coexist, as described in the parent Specification, a combined neutralizing and field-exciting winding is used, consisting of a closed drum system having taps about 90 electrical degrees apart, of which taps separated by 180 electrical degrees are connected in series with the brushes to give the neutralizing effect, while the remaining taps form the terminals of the field winding. In the form shown in Fig. 1, the dotted lines indicate a slot-wound two-circuit six-pole, main winding with leads brought out at points Y<1>, Y<2> 180 electrical degrees apart and connected in series with the commutator across the continuous current lines to form a neutralizing winding. Tapping-points X', X<2> displaced from the taps Y<1>, Y<2> by about 90 electrical degrees serve to convey current for exciting the field. Usually the potential difference is so low as to preclude excitation from the machine commutator and a separate low-voltage exciter is employed. Or, as shown, additional field windings F may be connected across X<1>, X<2>. Alternatively, the additional windings F may be replaced by two parallel-connected star groups of alternating current windings, as described in the parent Specification. By providing additional pairs of taps Y<1>, Y<2> making angles with the points X', X<2> different from 90 electrical degrees, a variable amount of compounding, or of reverse compounding, may be obtained. The winding shown at L is the three-phase two-pole winding of the machine. The number of sections in the alternating-current winding may be a multiple of the number of poles of the continuous-current field. Thus, with a two and six-pole combination, a 3- phase alternating-current winding giving six sections may be employed.