GB281344A - Improvements in or relating to induction motors - Google Patents

Abstract

281,344. Schwarz, B. Nov. 29, 1926, [Convention date]. Alternating-current motors.- The secondary winding of an induction motor is in two parts, located in separate sets of slots so as to have different inductances, the windings of one part being so connected to those of the other that the individual coils of phases of one part are short-circuited by corresponding coils or phases of the other part, there being no relative phase displacement of the currents in the mutually shortcircuiting coils or phases. Fig. 1 shows a winding comprising a single-turn coil W1 in the outer slots N1, N2 connected in series with a similar coil W2 in the inner slots N<I>1,N<1>2. The inner coils have greater magnetic leakage than the outer coils and at starting acts as choking coils. An additional highresistance starting winding Wa may be provided. Fig. 2 shows one phase of a three-phase four pole winding, the inner and outer coils W<1>, W being shown separately. The starting characteristics of the motor may be improved by connecting a resistance R to the coil terminals A, E or A<1>, E<1>. Instead of the phase winding shown, two continuous current type windings S, S', Fig. 3 may be employed situated respectively in the outer and inner sets of slots and interconnected to form shortcircuited coil groups. The number of interconnections X may be equal to or less than the number of coils and resistances R may be connected permanently between the interconnections. According to the Specification as open to inspection under Sect. 91 (3) (a) a closed coil has the conductors of one side in outer slots and the conductors of the other side in inner slots. The continuous-current type of winding shown in Fig. 3 may be connected to a commutator in which case the coil groups, which are connected together must be displaced angularly with respect to each other by an amount depending upon the purpose in view. For example in the case of a compensated shunt motor, Fig. 6 (Cancelled), in which the commutator brushes are fed from an auxiliary stator winding H the relative angular displacement of the commutator windings S, S<1> is chosen to give the desired power factor and/or speed regulation. Permanent resistances may be combined with the rotor windings or a starter r<1> may be included in the circuit between the commutator and the winding H. This subject-matter does not appear in the Specification as accepted, but forms the subject of divided applications.