Patent GB-147029-A (GB)
Title: Improvements in and relating to electric systems for the transmission of power and to multispeed induction motors suitable for use therein
IPC: B63H23/24
Filed: 1920-07-06
Abstract: 147,029. British Thomson -Houston Co., (Assignees of Macmillan, C.). May 31, 1917, [Convention date]. Alternating-current induction - machines; dynamos, regulating; motors, controlling.-In an electrical power-transmission system for driving ships' propellers or for other purposes in which an induction motor is used having primary windings adapted to give a variable pole-number when connected to supplies of different phase characteristics, the motor is supplied by a generator which is driven at variable speed and has switching arrangements for enabling it to give different numbers of phases. in the form shown, the primary winding of a multi-speed induction motor is arranged to produce n or 2n poles when connected to a three-phase source and 3n/2 poles when connected to a two-phase source. The primary winding 12 of the motor shown at the lower part of Fig. 3 comprises twelve circuits or groups of coils, each of which groups contains those conductors which carry current relatively in the same way for all the numbers of poles; switches 16, 17 are provided for effecting the polechanging connexions of the coil-groups, the various connexions for the different numbers of poles and phases being indicated in Figs. 4, 5, and 6. The armature winding of the alternator 11 is adapted to give either three-phase or two-phase currents, one phase being divided into two sections 60 electrical degrees apart. The alternator winding is joined to a phase-changing switch 15, which, in its upper position, supplies two-phase current, and in its lower position three-phase current to the motor primary winding 12; reversing- switches 18, 19 are included in the different busbars. The motor secondary may be phase-wound with external resistances, or it may be of the double squirrel-cage type. In a modified arrangement, each of the twelve groups of the motor primary winding is divided into two parts, one part remaining permanently in circuit, while the other parts are joined to switches so that. they may be disconnected from the main. The motor secondary member carries a high-resistance squirrel-cage winding 20, Fig. 7, and a low-resistance winding 31, the coils of which are joined to slip-rings 33, 34; for two-phase working and one number of primary poles, the low-resistance winding comprises twelve circuits connected in parallel between the rings 33, and twelve circuits (not shown) between the rings 34; adjustable resistances 35 are arranged between the slip-rings. For three-phase working and the other pole-numbers, the winding 31 is internally short-circuited. The Specification as open to inspection under Sect. 91 (3) (a) comprises also general claims for systems comprising means for producing polyphase energy of different phase numbers and induction motors with primary windings arranged to produce different pole members when supplied with energy of different phase numbers; also for induction motors with primary windings adapted to give n, 3n/2 and 2n poles for six, two and three or three, two and three phase running. This subject-matter does not appear in the Specification as accepted.