US1356936A

US1356936A - Induction-motor

Info

Publication number: US1356936A
Application number: US171917A
Authority: US
Inventors: Macmillan Campbell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1917-05-31
Filing date: 1917-05-31
Publication date: 1920-10-26
Anticipated expiration: 1937-10-26

Description

C. MACMILLAN.

INDUCTION MOTOR.

APPLICATION FILED MAY 31, 1917.

Patented Oct. 26, 1920..

5 SHEETS-SHEET l- Fig. l.

Inventor: Campbell VflaczrnillaflJ b5 MM His .'7qttorr1el`g.

C. MACMILLAN.

INDUCTION MOTOR.

APPLICATION FILED mman I9I.

Patented Oct. 26, 1920.

5 SHEETS-SHEET 2.

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Inventor: Campbell m acm il Ian b5 MM His aqttorneg.

C. MACMILLAN.

INDUCTION MOTOR.

APPLlcATxoN FILED MAY 31. 1917.

1,356,936. Patented. O01?. 26, 1920.

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C. MACMILLAN.

INDUCTION MOTOR.

APPucATloN HLED MAY31. 1917.

Patented Oct 26, 1920.

5 SHEETS-SHEET 4.

lign.

Inventor;

His Anker-neg.

C. MACMILLAN.

INDUCTION MOTOR.

APPLICATION FILED MAY sI. 1917.

Patented Oct. 26, 1920.

5 SHEETS-SHEET 5.

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lUNITED STATES PATENT OFFICE.

CAMPBELL MACMILLAN, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

INDUCTION-MOTOR.

Specification of Letters Patent.

Patented Oct. 26, 1920.

Application led May 31, 1917. Serial No. 171,917.

T 0 all whom t may concern:

Be it known that I, CAMPBELL MACMIL- LAN, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Induction-Motors, of which the following is a specification.

My invention relates to induction motors and has for its object the provision` of an induction motor having improved means for obtaining increased torque. The invention also relates to multi-speed induction motors and aims in this connection to provide simple andy convenient means for obtaining increased torque for any pole number of the motor without interfering with the efficient operation of the motor under normal conditions. Other objects of the invention will be brought out in the course of the following description: The ordinary polyphase induction motor with a low resistance secondary Winding does not possess sufficient starting torque for many purposes. The particular object of the present invention is to provide improved means for conveniently increasing .when necessary the starting torque of a polyphase induction motor without impairing its desirable operating characteristics under normal conditions. As is well understood in the art, the torque ofan induction motor is most effectively modified by changing the effective resistance of the secondary circuit of the motor; However, while increased torque at starting can be obtained by increasing the effective resistance of the secondary circuit, still, for efficient operation at speeds near synchronism, the resistance of the secondary circuit should be relatively low, and, accordingly, the increase in the effective resistance of the secondary winding' should be maintained only as long as the necessity for increased torque prevails. In carrying out my present invention, I provide means for increasing the Y effective resistance of the secondary circuit of an induction motor by a simple change in the connections of the primary Winding,

which change in connections can be conveniently made at starting or whenever increased torque is required without affecting the efficient operation of the motor under normal conditions when the primary winding is connected to produce a primary magnetie field of the usual type. The motor of my present invention therefore includes an improved secondary Winding so constructed as to provide a path of relatively low effective resistance for a normal magnetic field and a path of relatively high effective resistance for an irregular primary magnetic field such as results when the connections of the primary winding are changed to obtain increased torque. The irregular primary magnetic field may be produced in various ways, but I prefer to obtain this result by disconnecting a part of the primary winding from the source of supply so that the resulting primary magnetic field consists of alternate active and inactive belts. Therefore, in the preferred form of the invention, the primary Winding is divided into two components one of which is adapted to be independently disconnected from the source of supply thereby producing alternate active and inactive primary belts. The secondary winding is` arranged so that the secondary currents induced by the alternate active belts of the primary winding are caused to fioW through conductors of the secondary Winding corcent high resistance conductors of the sec-' ondary winding. The secondary Winding is preferably a compound or double Winding consisting of a low resistance winding comprising a plurality of closed circuits each of which includes in series relation one or more conductors influenced by active primary belts and one or more conductors under the influence of inactive primary belts and a high resistance winding having conductors inductively related to the conductors of the low resistance winding under the infiuence of inactive primary belts. The secondary currents induced in low resistance conductors by active primary belts are thus caused to flow by conduction through low resistance conductors'under the influence -of inactive primary belts and thereby induce by transformer action secondary currents in the inductively related high resistance conductors.

The novel features of my invention which I believe to be patentable are definitely set forth in the appended claims. The principles of the invention together with the pracmail tical embodiment of these principles will be fications and applications of the invention are illustrated, and in which g' Figure 1 isan explanatory diagrammatic viewof a polyphase induction motor embodying the invention, Fig. 2 is a conventional diagram of the same motor; Figs. 3 and 4 are `conventional diagrams of two modifications of the primary winding connections; Fig.` 5 shows'amodifiedtypelof the low resistance component of the secondary winding; Fig. 6 diagrammatically represents a quarter-phase induction motor embodying the invention. and having a modiiied low resistance winding; Fig. 7 diagrammatically represents a motor Ain which the primary winding is changed or distorted by reversal in part instead of by open-circuiting sections or belts thereof; Fig. 8 illustrates a modification of the secondary winding; Figs. 9 and 10 illustrate the application of the invention to multi-polar motors; Figs. 11 and 12 illustrate the application of the invention to a quarter-phase motor having an eight-circu`it primary winding arranged to be connected for two different pole members; -and Fig. 13 illustrates-the invention embodied in a ,motor combination having two separate motor units.

The fundamental principles of my invention will be best understood by reference to Fig.. 1. The legends @,5, c, l) and E at the top of the figure represent the six different phase-belts of an ordinary threephase primary winding. yll`he primary winding of the so-cal-led three-phase induction motor is usually wound six-phase with six phase-belts or coil-sections per pair of poles. rFhis result is obtained by providing per pair of poles two phase-belts in which the direction of current iow is relatively opposite or displaced in phase by 180 electrical degrees for each of the, three phases of the source of supply. rllhe currents in adjajacent phase-belts are then displaced in phase by 60 electrical degrees, and the winding may be called a 600 six-phase primary winding. Such' an 8-pole winding is diagrammatically represented by the irst complete Yrow of legends a, b, c, etc., of Fig. 1. rll'hus, a and represent the phase-belts or coil-sections connected to phase A in ywhich the currents are relatively opposite in direction of 180' out of phase, b and b represent the corres .p onding phase-belts connected to phase if and c and E the corresponding phase-belts connected to phaseC. All of the phase-belts of the same phase may be electrically connected together in any suitable mannemfor example in series, in parallel, or partly in series an -partly in parallel,

as will be understood by those skilled in the intense art. rllhe rst row of legends N, S, etc.',of" Fig. l-designates the polar distribution of l the primary winding. y

f yllhe motor diagrammatically represented in Fig. 1 has a double or two-part secondary winding. One part or component of this secondary winding is a high resistance squirrel cage winding 20. The second 'part or component ofthe secondary winding is a low resistance multiple -wave winding 21.- 'lFhe low resistance winding 21 has as many multiple circuits as there are slots per pole, and., since in Fig. 1 l have: shown only three slots per pole, the winding has onlythree multiple circuits. Fach circuit is wave winding including in series all 'bars or conductors which are similarly situated under successive poles. ln accordance with my present invention, thel primary winding of the motor is so arranged that certain coils or circuits thereof may be independently connected to or disconnected rom the source ofA supply in such a way as to leave alternate active and inactive or open belts. For example, all phasebelts ot two adjacent poles may be active while all phase-belts of the succeedin pair of poles are idle. This condition lghave diagrammatically represented b the last row of legends of Fig. l. lt wil be noted that the primary winding over alternate pairs of poles is inactive, so that the active torque-producing portionof the primary winding consists only of the remaining alternate pairs of poles thereof. Under these 100 circumstancesfthe active stator coils or conductors induce symmetrically disposed secondary currents which are of equal value under all active poles. Under idle or inactive poles, these currents will be opposed 105 by impedance only, and will induce by transformer action substantially equal and opposite currents in the high resistance squirrel cage winding 20. lin other words, these sections of the low resistance winding 21 110 which are located under inactive or open pairs of poles will act as the primary winding of a transformer, and the secondary currents Howing through such sections will induce currents in the adjacent conductors' of 115 the high resistance winding 20, which latter accordingly, acts as the secondary winding of the transformer.V The hi h resistance winding 21 thus forms a material part of the active secondary circuit of the motor and thev motor torque is correspondingly increased. v

ln Fig. 2 of the drawings, ll have (represented in a lessv diagrammatic way an induction motor embodying my present invention. 'llhis motor carries on its stator member a 60 siX-phaseprimary winding of eight poles and the phase-belts,are represented by they same letters as in Fig. 1'. A switch 22 is arranged when thrown to its right-hand 13 cordance with my present invention, divided active belts or sections.

` phase source of supp into two sections or components in such a manner that when one section is disconnected from lthe source of supply the primary -Winding consists of alternate active and in- For the sake of convenience, I shall hereinafter refer to that section of the primary winding which is always connected to the source as the basic component, While that section which is disconnected rom the source for obtaining increased torque I will refer to as the disconnectible component. Similarly disposed coils or phase-belts may be electrically connected together in any suitable manner. In the motor represented in Fig. 2, the two similarly disposed phase-belts of each component winding are connected in series, while the groups of phase-belts differing in phase by 180 degrees are also connected in series.V In other Words, all of the phase-belts a and of each component winding are connected in series, and so on for the other two phases of the primary Winding.

The two components of the primary winding may be connected in parallel, or in series, or partly in series and partly in parallel. In Fig. 2, I have shown these two components connected in parallel. A different diagrammatic representation of the primary winding of this motor is shown in Fig. 3. Here, all of the individual phasebelts a of each component winding, connect- /ed together 1n series, 1n parallel, or 1n seriesparallel, are represented by the winding A, all of the phase-belts of each component winding are represented by the winding A, and so on. The switch 22 in its right-hand position connects both components of the primary winding in lparallel to the threey 23, and in its lefthand position connects only the basic component to the source. In Fig. 4, the two components of the primary windinor are connected in series to the source when the switch 22 is `in its left-hand position, while only the basic component is connected to the source whenthe switch 22 is in its righthand position. y i

When the two component windings are connected in parallel, the same voltage is impressed on the basic component whether operating alone or in conjunction wlth the disconnectible component, whereas when the two component windings are connected 1n series a much higher voltage is impressed on the basic component when operating alone than when operating in conjunction with the disconnectible component. Any intermediate connection of the two component windings between straight series and straight parallel may of course be used.

The primary windingof an induction motor is usually a two layer lap winding. In such a winding each coil has two sides which are approximately 180 electrical degrees apart. VVhenmy present invention is applied to such a winding there will be intermediate spaces between the entirely active and entirely inactive belts in which one-half 80 of the conductors per slot are active. The inclusion of the high resistance squirrel cage winding as a part of the secondary circuit kof the invention I have assumed for the sake of clearness that the active and inactive belts of the primary winding were uniform, it will be well understood by those skilled in the art that my invention will usually be carried out with atwo layer lap winding, in which event there will be intermediate spaces half active and half inactive as just described. It willfurther be seen that other distributions of the primary winding may be used,r as for example, the proportion of active and inactive belt-smay be varied without preventing the formation of symmetrical groupings of all the coils, provided the tot-al number of available circuits is sufficient. Y

The low resistance secondary winding may be divided into short sections, each end of which is connected to special end rings o1' to 110 the end rings of the high resistance squirrel cage winding. In this way the maximum volt-age of the secondary circuits may be limited. The low resistance secondary winding may also be a lap winding. and these modifications will be clearly understood by reference to Fig. 5 of the drawings. The winding 25 of this figure isvto be considered as a substitute for the winding 21 of Fig. 1. Thus, the winding 25 cooperates with the 120 high resistance squirrel cage winding 20 to form the double secondary winding for a prima ry winding of the character represented by the legends of Fig. 1. The winding 25 is the usual lap winding with two layers of conductors per slot assembled so that each coil has the conductors of one side in the top of a slot and the conductors of the other side in the bottom of a slot. In F ig. 5. the full lines indicate thetop conductors and the removed from but otherwise correspond tol the other three. 'The c'oilsV of the winding 25 beneath phase belts la and are shown in heavier lines in Fig. 5 and only end connections for these coils are shown in order to better illustrate the principle of the arrangement.- lt will of course be understood that the coils beneath phase belts b and and c and are similarly connected to form short local circuits. `When alternate pairs of poles of the primary winding are inactive or idle,

it will be evident that each local circuit of the secondary winding 25 will be partly beneath an active section and partly beneath an inactive section, and, therefore, the high resistance secondary winding is effectively included by transformer action as a part of the secondary circuit of the motor.

.j As previously mentioned, `the primary winding of the ordinary polyphase induction motor ils generally a two-layer lap winding of the same t e as the winding represented in Fig. I5. ia-grammatically the secondary winding 25 may thus be substantially a counterpart of the primary winding. 'll` he coils of the secondary winding 25 are, there-e fore, designated by the same legends as the corresponding phase-belts of the primary winding, the coils being designated bythe legends of the` primary phase-belts correspending to thefconductors in the top `of the slots.l lf for the moment we assume that y represents the coils of a lprimary winding, it will be evident to those skilled in the art thatthe principles of the present invention may be applied to this winding by connecting the groups of coils in accordance with the corresponding diagram of Fig. 2. Therel will thus be obtained atWo-layer lap winding arranged to produce a primary magnetic field of eight poles when supplied with three-phase electromotive' Jforce and embodying the principles of the present invention.

yllhe conductor bars of the high resistance squirrel cage winding are pre'erablylocated 1n the same slots as the4 conductors of the low resistance winding. ln Fig. 2, the conductor bars of the high resistance winding 20 are positioned in the bottom of the slots while the conductors of the wave winding 21 are positioned in the topV of the slots. Where the winding 25 is substituted for the winding 21, the squirrel cage winding 20 The entire winding is thus com-l A Lacasse preferably has as many conductor bars as there are rotor slots and there will then be three concentric rows or layers of conductors in the rotor slots.

In F ig. 6, l have illustrated my invention embodied in a quarter-phase induction motor. Reference letters p and p represent the phase-belts of the primary winding connected to phase P, and respectively 180 electrical degrees out of phase, while letter g and Q represent the phase-belts of the primary winding connected 'to phase Q, also 180 electrical degrees out of phase with one another. ln accordancevwith the present invention, this quarter-phase primary winding is divided into basic and disconnectible components, alternate pairs of poles being in the basic component, while the other alternate pairs of poles are in the disconnectible component. The short-circuited low resistance'secondary winding 26 is of the same type as the winding 25 of Fig. 5. Instead of having a plurality of independent L.circuits as in winding 25, the winding 26 has all of its similar local circuits connected in parallel by four end rings or end-connections 27 at each end of the winding. ln a quarterphase winding of this type it will be evident that there are four different groups of local circuits. rllhefirst group includes the coils beneath phase belts p and p connected in series with similarly positioned coils beneath the next but one adjacent pair of poles. ln other words, similarly positioned coils under the influence of active sections of the primary winding are connected to common end-connections while coils slmilarly positioned beneath corresponding parts of inactive or idle sections are connected in the reverse manner to the same common endconnections. It will of course be understood that a high resistance short-circuitedsecondary"y winding similar. to the squirrel cage winding 20 will be used in conjunction with the low resistance winding 26. rl`he pitch of the

low resistance windings

21, 25 and 26 is in each case 100% or full pitch.

rll`he improved double secondary winding of vmy present invention may be advantageously used in conjunction with primary windings in which an irregular or distorted primary magnetic eld is obtained in other ways thanby open-circuited alternate sections of the;l primary winding. In Fig. 7 of the drawings, ll have shown how my improved secondary winding may be used in conjunction with. a primary winding in which an irregular or distorted primary magnetic field is produced by reversing all phases of a particular section or component of they primary winding. T he direction of the phase rotation of both components of the primary winding remains the same, because all phases of the distorting component are reversed, but the direction of current flow in the multiple circuits of a low resistance secondary winding embodying the principle of my present invention are reversed and the circuit for the secondary currents has a greater effective resistance. The first row of legends p, vg, etc., represents such a primary winding under normal operating conditions, while the second row of legends p, g, etc., represents the primary winding distorted. The primary winding represented is normally a l2-pole quarter-phase winding. I distort this winding by reversing all phases of six consecutive poles thereof. The letters N and S above the two rows of legends p, g, etc., diagrammatically designate the plar distribution of the primary winding under normal conditions and when distorted. It will be observed that when one-half of the primary winding is reversed as represented in Fig. 7 substantially equal and opposite electromotive forces are induced in the multiple circuit low resistance winding 2l', and consequently all of the secondary current is forced to flow in the high resistance winding 20. The synchronous speed of the distorted Will be somewhat different, usually higher, than the synchronous speed o f the Inormal primary winding, because of the overlapping of the poles where the basic and distorted components of the primary winding join. It will be understood that less than half of the entire primary winding may be reversed, in which case more or less secondary current will flow inthelow resist- A ance secondary winding 21.

The compound secondary winding of my present invention provides multiple circuits for the secondary currents, and in this rcspect is analogous to the double squirrel cage secondary winding 4in which one squirrel cage has low resistance and high inductance and the other high resistance and low inductance. A multiple circuit winding of the double squirrel cage type operates to Hatten the top of the torque curve at maximum torque, thereby making the torque more uniform, or more nearly uniform, over a larger range of speed. This flattening of the torque curve is sometimes of advantage. The multiple circuit secondary winding of my present invention probably possesses this characteristic to a slight degree, but the characteristic can be emphasized by increasingr the reactance of the low resistance winding, and this maybe very effectively accomplished by omitting some of the high resistance squirrel cage conductor bars. The omission of a high resistance bar of the squirrel cage winding increases the reactance of the conductors of the low resistance winding occupying the same slot, and consequentlyy increasesthe reactance of the circuit of which this conductor is a part. Preferably, the reactance of each multiple cirprimary" winding cuit of the low resistance winding is correspondingly increased by omitting one or more high resistance conductor bars for each multiple circuit. In order that the effective resistance of the secondary winding may not be so increased by the omission of high resistance conductor bars as to make the operation of the motor inefficient during the interval of operation'at low slip prior to the restoration ofthe primary connections to normal, I prefer to increase the size of thehigh resistance conductor bars of the same series circuit in which one or more bars are omitted. This modification of the invention is illustrated in Fig. 8 of the drawings. The roW of legends represents an 8- pole, six-phase primary winding having a basic component and a disconnectible component. winding 20 has three conductor bars omitted, one in each circuit-corresponding to the three multiple circuits of the low resistance winding 21. Thus, the first conductor bar omitted is in the same slot as one of the conductors ofphase-belt a, the second bar omitted is in the same slot as one of the conductors of phase-belt b, while the third omitted bar bears the same relation to phase-belt c. The symmetry of the winding is preserved as far as possible in omitting these three bars. The other bars of the squirrel cage winding are of slightly less resistance than if certain bars were not omitted. In this way one slot increases the reactance of the secondary circuit, by the omission of a high resistance conductor bar, while another slot reduces the resistance of the secondary circuit, by the substitution of a low resistance for a high resistance squirrel cage conductor bar. In this Way the power factor of the circuit may be reduced without necessarily increasing its impedance if desired.

My present invention is adapted to be embodied in multi-speed induction motors. Such a motor is diagramma-tically represented in Fig. 9 of the drawings, and the following description of this figure will in- The high resistance squirrel cage dicate the manner ofapplying the invention l to any multi-speed motor. The primary winding ofthe motor represented "in Fig. 9 is adapted to be connected to a three-phase source of supply as a'16-pole winding, and v to be connected to a. quarter-phase source of 16- and 24-pole numbers, respectively. 1n

inactive or idle sections of the *primary Winding embrace four and six poles for the other words, the basic component of the primary winding consists of alternate sections @of four and six adjacent poles on the 16- and 24-pole arrangement, respectivel while the disconnectible component of tide primary windin consists of the other alternatev sections o four and six poles. The minimum number of poles for ma etic symmetry with such a'combination o 4 and 6 poles is 16 and 24 poles.

lin Fig. 9 of the drawings, ll have shown a low resistance lap winding 30 embodying the principles of my present invention.-

'llhe coils of this winding arel connected to Aform a short-circuited secondary winding of low vresistance for either the 16-` or the 24-pole connection of the primarywinding, and also to coiperate by transformer action with a high resistance secondary winding when alternate sections of four or siX adjacentv poles for either the 16- `or 24-pole primary winding are inactive or idle. rllhe coils beneath phase-belt a are connected in a closed circuit with coils similarly positioned beneath phase belt a, four poles removed with respect to the 16-pole arrange- .ment. F or the sake lof clearness, only the circuits of the coils beneath phase-belts a and are completed in F ig. 9, but it will be understood that the other coils of the winding are similarly connected in local short-circuits. lt will also be understood that each local circuit may include more than two groups of coils. The high resistance squirrel cage Winding to be used in conjunction with the low resistance winding 30 has been omitted in'Fig. 9 in order to-simplify the drawings. llt will be noted that the pitch of the low resistance secondary winding 30 is 100% for the 16-pole larrangement of the primary winding and 150% for the 24-pole arrangement. lf the secondary winding Y30 is laid out as 100% of a full pitch winding with respect to 24 primary poles', it 'will be 66?;70 of full pitch wlth respect to 27 primary poles. 'llhe pitch of the winding 30 should be selected to best meet the` particular requirements of the case in and.

An external resistance may be included in circuit with the low resistance secondary winding if desired. Such Van arrangement Iis illustrated in Fig. 10 or' the drawings. f rllhe primary winding ot the motor diagrammatically represented in this ligure is adapted to be connected for three diderent pole numbers as indicated by the legends. Thus, the winding can be connected to a three-phase source voit supply as either a iti-pole winding or as fa {i2-pole winding, and'lto a quarter-phase source ot supply as a, 24-pole winding. The pitch at the lett intense of the legend-diagrams indicates the pitch of the primary winding and also 'of the low resistance secondary winding 31 with respect to that particular polar arrangement of the primary winding. F or the sake of clearness l have illustrated the winding 31 as having only one conductor per phase-belt, but in practice there will generally be a plurality of such conductors per phase belt. The primary winding of the motor as well as the secondary winding 31 are laid out with 100% pitch with respect to 24 primary poles, and, therefore, have 'a pitch of 663% and 1331;% with respect to 1b and 3-2primary poles, respectively. Y

rlhe coils of the winding 31 are connected to two sets of collector rings 33 and 3,4, so

that with` respect to 24 primary magnetic poles this secondary winding has twelve circuits connectedin parallel between the collector rings 33, and similarly twelve circuits connected in parallel between the rings 34. For the sake of clearness, only the connections to the collector rings 33 havebeen 90 fully indicated in the drawings. Every coil or group of coils beneath phase-belts p and 1? are connected in series to the similarly positioned coil or coils six poles removed with respect to the 24-pole arrangement, and the terminals of these seriesrconnected coils or groups of coils are connected to the collector rings 33. The coils beneath phase-belts g and q' are similarly connected to the collector rings 3 4. For the motor of 100 24 poles, there will, therefore, be twelve of these series-connected coils or groups of coils connectedto each set of collector rings 33 and 34. The transformer action bearrangement, and all of the secondary cur- `ll rent may then be forced to low in the high resistance winding 20.` Generally, however, it will be more desirable to provide external resistances 35 arranged to be connected between the collector rings 33 and. 434, respec- 12 tively, and thus to complete the circuits ot the winding31. The resistances 35 may be adjustable and when entirely cut out so as to short-circuit the

rings

33 and 34, respectively, the winding becomes electrically 12.5 equivalent to the winding illustrated in ilthough the winding 31 'is eectively open-circuited vfor 24 poles, it is internally short-circuited for either 16 or 32 poles. Alac For the 16-pole arrangement, the coils beneath phase-belts a, b and c are connected to the collector rings 33 to 'form in effect a short-circuited star-connected winding and the coils beneath phase belts b and E are similarly connected to the collector rings 34. For the S32-pole arrangement, the winding is similarly a short-ircuited star-connected winding. The only difference betweenthe short-circuits for the 16- and 32-po1e arrangements is that for 32 poles the p and g circuits connected to the collector rings 33 and 34, respectively, carry currents in the same direction, while for 16 poles the currents in these p and g circuits are 180 electrical degrees apart. In addition to permitting a connection to an external l'esist-ance for the 24-pole arrangement, this winding has a simpler system of end-connectionsconsisting of involutes spanning groups 4, 6 or 8 poles with respect to the 16%" 24-, or 32-pole arrangement'.

The application of my present -invention to a multi-speed motor of the ty )e described in the copending application of llrnst F. W'. Alexanderson, Ser. No. 67,387, filed December 17, 1915, patented April 23, 1918, No. 1,263,992, is illust-rated in Figs. 11 and 12. The Alexanderson motor represented in these figures has a quarterphase primary winding consisting of eight circuits. These eight circuits normally have one of their two terminals connected to a common neutral, while their other eight terminals are connected to av suitable switch for altering the connections of the circuits to the quarterphase source of supply in order to obtain two different pole numbeis. The eight circuits of the primary winding are designated and Qp-. The capital letters designate the phase in which the circuits are connected for one pole number, while the small letters designate the phase in which the circuits are connected for the other pole number. Letters l) and p represent phase I, while letter Q and y represent phase II. The circuits having a positive (Jr) sign have the same relative terminal connections with respect to the direction of current flow in both polar arrangements, while the circuits having the negative sign have their terminal connectlons relatively reversed in the two polar arrangements. Each circuit of the primary windlng is divided into two parts so as to form the basic and disconnectible components of my present invention. I have designated the disconnectible components in both Figs. 11 and 12 by prime marks Referring now particularly to Fig. 11, I will take a general case of an nand m-pole motor. The capital letters will be taken to represent the connections for n poles, and the small letters the connections for on poles. The circuits are vectorially arranged in Fig.

tion both the basic and disconnectible components of the primary winding are connected to the source P-Q as an n-pole winding. lVhen the main switch 40 is thrown to its right-hand position, the basic component of the primary winding is connected to the source as an m-pole winding, and the disconnectible component is connected to cooperate therewith When the switch 41 is in its left-hand position. If the switch 41 is now thrown to its off position, the disconnectible component of the primary winding will be inactive or idle, while if the switch 41 is thrown to its right-hand position, the'disconnectible component of the primary winding will be reversed with respect to the basic component, substantiall as explained in connection with Fig. 7. Ill will of course be understood that a suitable compound or two-part secondary winding of the general character previously described Will be provided for the motor represented in this figure.

A somewhat simpler circuit-controlling mechanism can be used in the arrangement shown in Fig. 12. Each phase of the source of supply is re resented by two positive terminals P and and two negative terminals P and Q. When the main switch 42 is thrown to its left-hand position, both the basic and .disconnectible components of the primary winding are connected to the source as an n-pole winding. When the switch 42 is thrown to its right-hand osition, the Circuits F19-, 1310+, Qqlw 9+, Q+= Qp*, PQ+ and Pgof the basic component are alone connected to the source so as to form complete circuits and carry currentsand these circuits will..produce a primary magnetic feld equivalent to m poles. The circuits Pp-, Pp+, Q q-, Q g+, QP+, Qzv-, PEV-t, and PQ 0f the disconnectible component are 1n effect opencircuited. `When the auxiliary switch 44 is now closed a neutral is provided for the circuits of the disconnectible component and the machine will then operate as a normal m-pole motor.

The manner of distributing the coils of the primary winding of the Alexanderson eight-circuit motor. or in fact of any motor, into the basic and disconnectible components will, it is believed, be understood from the foregoing description. The polar Width of the alternate active and idle belts or sections of the primary winding will first be determined by the ratio of the different pole numbers, n, m, etc., for which the primary winding is to bev connected. ln the case of the eight-circuit motor of Figs. 11l and 12, and generally inthe case of other motors, all of the coils in active sections undergoing the same electrical change in one pole numberto the other wi lbe grouped to form the circuits P12-t, i920-, etc, of the basic component, while all of the coils in inactive oridle sections undergoing the same electrical change in changing pole numbers will begrouped to form 'the circuits Pp-|, PpL?, etc. lt is believed that the design of4 a suitable low resistance sec-v ondary winding for the motors ofslfigs 11 and 12 will be obvious in view of the foregoing explanations. .lt 'willbe seen'that these motors may operate as normal high efficiency induction motors for both pole numbers n and m, but that a secondary Winding of high effective resistance may be pro-` vided for the m-pole connection by distort- 'ing the primary winding in accordance with the principles of my present invention.

ln Fig. 13 of thedrawings, l have illustrated a double or two-part motor combination embodying the principle of the'present invention. The combination includes two rotor cores 50 and 51 mounted on a common shaft 52. Polyphase

primary windings

53 and 54 are electrically associated with the rotors 5() and 51, respectively. rl`l1e-vsecondary winding is a duplex winding consisting of a low resistance squirrel cage winding common to both primary windings 53 `and l-and a high resistance squirrel.

cage winding 56 mounted on the lrotor 51.. rlhefprimary winding 54 is the disconnecti- Vble component of the motor combination,

and a switch 57, corresponding kto the switch 22 of .'lFigs. 2 and 3, is provided forl connecting the two primary. windings 53 andt in parallel to the source or for connecting only the primary winding 53 to the source.

When the primary winding 53 is alone connected to the source, the electromotive forces induced in the bars lof the common squirrel g cage winding 55 cause currents to circulate therethrough. lin the slots of therotor core 51 the long bars of this winding are lying side by side with the short bars .of the independent high resistance :squirrel cage winding 56 which latter consequently acts as the short-circuited secondary winding of a, transformer and carries a current equivalent to its 4transformer primary current. lln such a 1:1 ratio transformer, resistance in theffsecondary is exactly equivalent to resistance in the primary. Let R1 and lt, represent the relative resistances of the tvvo squirrel-cage windings in one rotor, where R1 refers to the winding 55 and R2 to the assing `from of heat are generated.

intense resistance of the winding 55 in both motor units is 2K1. By the 1:1 ratio transformer action in the rotory core 51, the independent squirrel-cage winding 56 is virtuall connected in series with the winding 55. herefore, the total virtual resistance of the secondary winding relatively'to the active motor unit` is 2R1|R2L rlFhe magnetizing current for the transe former formed by the secondary windings of the disconnected motor unit in the ap'- paratus of F ig. 13will be drawn frmthe source of supply as an additional wattless current, but at the reduced voltage required for starting, the sum of the two magnetizing currents relatively `to the energy currents at starting will not be at all excessive. |llhe operation ofthe apparatus with the) primary Winding of one motor unit unexcited ris particularly favorable for the condition encountered when relativel large amounts oth rotor cores are in this case available for, the storage and dissipation of heat. By such efficient transformer action between the secondary vconductors of the unexcited motor unit a considerablejamount of electrical energy 1s transferredto the high resistance secondary winding of the unexcited motor unit, where the thermal4 and mechanical conditions are most favorable for thefstorage and dissipation of theheat into which this lenergy is converted. The effective resistance ofthe secondary winding is thusv increased and its power of energy dissipation is also increased Without varying its electrical connections. -f

` ll have herein shown and particularly described'certain embodiments of my invention for the purpose of explaining its principlesl and Ashowing, its applications, but numerous-modifications ofthe details of construction and arrangement of these embodiments and other applications will present themselves to those skilled in the art. li, therefore, wish to cover by the following. claims ,allmodifications within the spirit of the invention. l y

What l claim asnew and desire tosecure by `Letters Patent of the UnitedStates, is:

l. An induction motor having a polyk -phase primary winding arranged in two.

the components undergo Aa predetermined change, a low 'resistancey secondary winding lhaving' conductors corresponding to both components ofv thel primary *winding included in the same series circuit, and a high resistance secondary Windingv 'havingl conductors inductively related'to conductors of :,ssepse the low resistance winding corresponding to the irregular field-producing component of the primary winding.

2. An induction motor havinga polyphase primary winding divided into two components one of which is adapted to be disconnected from the source of energy supply thereby producing alternate active and idle primary belts, a low resistance secondary winding having conductors corresponding to both active and idle belts of the primary winding included in the same series circuit, and a high resistance secondary winding having conductors inductively related to conductors of the low resistance winding corresponding to idle belts ofthe primary winding. v

3. An induction motor yhaving a polyphase primary winding arranged in two components such that a normal primary magnetic field is produced when the two components act in conjunction and an irregular primary magnetic field is produced when the electrical connections of one of the components undergo a predetermined change, a low resistance secondary winding having a plurality of closed series circuits inductively related to both components of said primary winding, and a high resistance short-circuited secondary winding.

4. An induction motor having a two-part primary winding, a low resistance secondary winding common to both parts of said primary winding, means for electrically disconnecting one part of 'said primary winding from the source of energy supply while the other part of the primary winding is connected to such source, and a high resistance secondary winding adapted to be included by transformer action between said secondary windings as a part of the effecltive secondary circuit of the motor when only one part of the primary winding is connected to the source of supply. 'i

5. An induction motor having a two-part primary winding, a low resistance secondary winding having a plurality of closed series circuits including conductors which are inductively related to both parts of said primary winding, means for electrically disconnecting one part of said primary winding so that only the other part of theprimary winding is connected to produce a magnetic Held, and a high resistance squirrel cage seconda ywinding adapted to be included by trans ormer action between said secondary windings as a part of the effective secondary circuit of the motor when only one part of the primary winding is connected to produce a magnetic/field.

6. An induction motor having a polyphase primary winding of two components which coperate when acting together to netic field, means for changing the electrical connections of one component of said primary winding so'that the resulting magnetic field produced by the entire primary winding is irregular, and a secondary winding including a high resistance component and a low resistance component inductively related to said primary winding, the components of said secondary winding being so arranged that a relatively greater proportion of the total secondary current flows in the high resistance component when said primary winding produces an irregular magnetic field than when the primar winding produces a normal magnetic fiel 7. Ano induction motor having a polyphase primary winding of two components, said components being adapted to act together to produce a normal polyphase primary magnetic ield when both components are electrically connected to a source of energy supply, means for electrically'disconnecting one of said components from the source of supply so that the primary magnetic field of the motor is produced by the other component acting alone, a low resistance secondary winding having a plurality of closed series circuits including one or more conductors inductively related to each component of said primary winding, and a high resistance secondary winding arranged to be included by transformer/action between said secondary windings as apart 0f the effective secondary circuitof the motor when only one com onent of the primary windinv is electrica ly active, the connections o said high resistance winding being identical for both connections of said primary winding.

8. An induction motor having a polyphase primary winding of two components adapted to act together to produce a normal polyphase primary magnetlc field, each component of said primary winding consisting of alternate sections embracing one or more pairs of primary magnetic poles, a low resistance secondary winding having closed circuits including in series relation one or more` conductors inductively related to each component of said primary winding, means for electrically disconnecting one component of said primary winding so that the primary magnetic-field'of the motor Ais produced by the other component acting alone whereby secondary current is induced in at least one of the conductors of each closed secondary circuit and flows-by conduction through atleast one conductor of the same circuit, and a secondary winding having high resistance conductors inductively related to the low resistance conductors through which'secondary current flows b conduction when one component of the primary winding is inactive. f

9. An induction motor having a polyphase primary winding of two components and inactive belts of the primary winding,

and a high resistance secondary winding having conductors inductively related to low resistance conductors situated under inactive belts of the primary winding. N/N, l0. n induction motor having a polyphase primary winding arranged to be connected so asto produce a plurality of primary magnetic fields of different pole numbers, said primary winding comprising two components one of which is adapted to be independently connected and disconnected from the source of energy supply, said components being so arranged that when only one component is connected to the source of supply the primary winding of the motor consists of active belts alternating with inactive belts, each of said active and inactive belts embracing one or more pairs of polesfor any polar arrangements for which said primary winding is arranged to be connected, a low resistance secondary winding having a plurality of series circuits including two or more conductors similarly situated under-active and inactive belts of the primary winding for any polar arrangement for which said primary winding is arranged to be connected, and a high resistance secondary winding having conductors inductively related to low 'resistance conductors situated under inactive belts of the primary winding. i v

'11. multi-speed induction motor having a primary winding, means for connecting said winding as an n-pole six-phase primary Winding and asia ZL-pole quarter-phase primary winding and as a Qz-pole threephase primary winding, said primary winding being divided into two components one of which is adapted to be independently connected and disconnect-ed from the source of energy'supply, said components being so arranged that a normal primary magnetic field is produced when the two components act in conjunction and an irregular primary magnetic field is produced when only one component is connected to the source of supply, a low resistance secondary winding having 'conductors corresponding to both components of the primary winding included in the same series circuit. and a high resistance secondary winding inductively reisaaeea lated to the low resistance secondary winding` and adapted to be included by transformer action between said secondary windings as a part of the eHective secondary circuit of the motorl when said primary winding produces an irregular primary magnetic field.

12. multi-speed induction motor having a primary winding adapted to be connected as an n-pole six-phase winding and as a rg-pole quarter-phase winding and as a Qn-pole three-phase winding, said primary winding being divided into two components one of which is adapted to be independently connected and disconnected from the source of energy supply, said components being so arranged that when only one component is connected to the source of supply the primary winding of the motor consists of uniform active belts alternating with uniform inactive belts, each of said uniform active and inactive belts embracing one or more pairs of poles for any one of the polar arrangements for which said primary winding is adapted to be connected, a low resistance secondary winding having a plurality of series circuits including two or more conductors similarly situated under active and inactive belts of the primary winding for any7 one of the polar arrangements for which said primary winding is adapted to be connected, and a high resistance secondary winding having conductors inductively related to low resistance conducmary winding.

13. An induction motor having a poly-` phase primary winding arranged to be connected so as to produce a plurality of primary magnetic felds of different pole numbers, said primary winding comprising a plurality of circuits each of which contains conductors which carry current relatively in the same way when the primary winding is connected for any of the pole numbers for which it is arranged, said primary winding being divided into two components one of which is adapted to be independently connected and disconnected from the source of energy supply, said components being so arranged that when only one, component is connected to the source of supply the primary winding is arranged to produce a primary magnetic field consisting of alternate active and inactive belts embracing one or more pairs of poles for any polar arrangement for which the primary winding is adapted to be connected, a low resistance secondary winding comprising a plurality of closed circuits each of which includes in series relation one or more conductors influenced by active primary belts and one orv ductors under the in uence of inactive primary belts.

14. An induction motor having a primary Winding-arranged in two components one of which is adapted to be independently connected and disconnected from the source of energy supply, said components being so arranged that when only one component is connected to the source of supply the primary Winding is arranged to produce a primary magnetic ield consisting of alternate active and inactive belts embracing one or more pairs of poles,- a low resistance secondary winding comprising a plurality of closed circuits each of which includes in series relation one or more conductors inuenced b active primary belts and one or more con uctors under the influence of inactive primary belts, and a high resistance secondary winding having conductors in the same slots with said conductors under the influence of inactive primary belts.

15. An induction motor comprising a two part primary winding, a low resistance secondary winding common to both parts of said primary winding-said primary and secondary windings being arranged for relative rotation, means whereby a predetermined change may be made in the electrical ccnnections of one part of said primary winding, and a high resistance winding mechanically fiXed with respect to said low 'i'esistance secondary winding arranged in inductive relation to conductors of said low resistance secondary winding.

In Witness whereof I have hereunto set my hand this 29th day of May, 1917.

CAMPBELL MACMILLAN.