Patent GB-190514401-A (GB)
Title: Improvements in Alternate Current Induction Motors.
Filed: 1905-07-12
Granted: 1906-07-12
Abstract: 14,401. Hunt, L. J., and Sandycroft Foundry Co. July 12. Armatures field magnets; motors, controlling. -The stator and rotor of a single-phase or polyphase induction motor are each provided with two or more independent windings producing different numbers of poles, the windings on the same body being in non-inductive relation with one another. One of the stator windings is supplied with current from the mains, and gives rise to a rotating field which acts inductively upon one of the rotor windings in the usual way. The current from this rotor winding is led into the second rotor winding, producing a field rotating in the opposite direction to the first and acting inductively upon the second stator winding. Starting or regulating resistances may be arranged in the circuit of the second stator winding. In order that the windings on the same body may be in non-inductive relation, it is preferred that the ratio of the number of poles produced by one set of windings to the number produced by the other set should be an even number, and that the numbers of poles produced by the two sets of windings when divided by their highest common factor, or, according to the Provisional Specification, an even number, should give an even quotient for one winding and an odd quotient for the other. The rotor windings may either be separate or in groups. The Figures show a three-phase machine in which the primary stator winding and the corresponding rotor winding each give eight poles, while the second rotor winding and the secondary stator winding give four poles. Fig. 1 shows the stator windings. The three phases a, b, c of the primary winding are connected at one end to the main terminals 1, 2, 3, and are short-circuited at their other ends through a ring 7. The three phases e, f, g of the secondary winding are connected at one end through a Y-connexion h, the other ends being led to the terminals 4, 5, 6, which are connected through suitable starting or regulating resistances. The conductor bars are shown at w, x. The rotor windings are shown in Fig. 2, and are lettered to correspond with the stator windings, the conductor bars being shown at y, z. The phases of the two windings on both the stator and rotor follow one another in opposite order. Points k, m, o on the rotor winding a, b, c are connected to points l, n, p on the rotor winding e, f, g. Figs. 3 and 4 show the arrangement of the conductor bars in the slots. The conductor bars y of the eight-pole winding are placed in all the slots, but for the four-pole winding there are bars z in alternate slots only, the intermediate slots being filled with dummy bars v of wood or the like. The method of connecting up the stator secondary windings e, f, g and the rotor inductive windings a, b c may be varied, and it is immaterial whether each element of these windings embraces one or any odd number of poles of the winding by which it is inductively acted upon. These two windings may be wound for any number of phases independently of the number of phases of the primary stator winding. Three or more sets of windings may be used on both the stator and rotor, each producing a different number of poles to prevent any inductive effect between the several windings on the one body. The pitch of the windings may be the full pitch corresponding to the number of poles, or it may be fractional, or the area of the pole faces may be equal or unequal. The functions of the stator and rotor may be reversed by introducing current through slip-rings to a primary winding on the rotor and connecting the two stator windings as above described, resistances being inserted in the secondary rotor winding by the aid of slip-rings.