CA1055095A - Rotor with form wound coils for synchronous dynamoelectric machine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A rotor is provided for synchronous generators and motors of relatively small size, and especially for high speed machines. The rotor has a laminated core with winding slots arranged in spaced groups around the core providing unslotted pole face regions between them. A progressive winding using form wound coils is placed in the slots to pro-vide a multi-pole magnetic field. Means are provided for bracing the end turns of the winding including insulating spacing means to fill the spaces between groups of coil end turns corresponding to the pole face regions.

Description

BACKGROUND OF THE INVENTION
The present invention rela~es to rctors for synchronous motors and generators, and particularly for machines of relatively small size and high speedO
Synchronous generators and motors of relatively small size, such as machines in the 3000 kilowatt range of ratings, have conventionally been built with s~lient poLe rotors. In machines of relatively low speed, the pole pieces are bolted on the shaft, ar on a spider, and the field winding consists of wire wound coils placed on the poles or wound on them in place, resulting in a relatively inexpensive construction. In high speed machines, however~
such as two and four pole machines, the rotational forces 45,842 are much higher and this inexpensive construction can~
not be used. High speed machines have usually used pole members with dovetails on the base of the pole engaging dovetail slots machined in a shaft forging and keyed or otherwise locked in place. Such a construction requires a relatively expensive shaft forging and strap wound field coils which are considerable more expensive tha~
the wire wound coils used on lower speed machines.
The slotted shaft forgings required involve very expen~
sive machining and long lead times in procurement, making this type of construction undesirable. It is ap~
parent, therefore, that a less expensive rotor construct~
ion is needed for relatively Small9 high speed synchronous machines.
There are other possible ways in which high speed synchronous rotors could be built without requiring shaft forgings and dovetailed poles. One method which has been proposed is to use a laminated core wlth the pole mem~
bers and spider formed by integral punchings assembled in 20i a unitary pole and spider assembly for mounting on a shaftO
This has the disadvantage that the field winding coils have to be wound in place on the poles after the core is assem~
bled, which is very difficult and time-consuming. The pole embrace, or arcuate extent, obtainable i~ this manner is necessarily so low that the electrical design may be unfavorably affected. This construction also requires very

-2-~5,842 1~55095 expenslve compound dies to produce the required punchings~
Another possible type of construction which has been pro~
posed for high speed synchronous machines involves the use oE a round or cylindrical rotor with distributed windings9 similar to the rotors used in large turbine generators. Such a rotor can be built up with a lami~
nated core of round, punched laminations which can easily be supported on the shaft and provided with vents to permit good ventilation9 and which can be readily protuced with inexpen~ive diesO Such a conætruction9 however7 presents a winding problemO Turbine generator rotors are wound with concentric field windings9 the coils being formed of heavy strap conductors and wound one turn at a time~ For the smaller size machines under discussion, such a winding is~ of course, not suitable because of the high costO The distance between adjacent slots varies with the radius so that the end portions of each turn are different, and conventional form wound coils could not be used because the length of each turn would be different from the other turns~ Such a coil would not lend itself to the usual manufacturing methods for form wound coils, and the cost of such a winding would be too high to be practical~

In accordance with the present invention, a rotor construction is provided for high speed synchronous

-3~

~5,842 1~:)55095 machines which avoids the winding problem discussed above and makes possible a satisfactory, relatively low cost construction for rotors for synchronous mzchines of relatively small size and high speed.
The rotor construction of the present inven~
tion utilizes round punchings~ preferably supported on radial spider arms on the shaft and built up in a cylin~
drical core. Winting slots are provided in the surface of the core arranged in spaced groups to provide pole face regions between them, the arrangement being similar to the slotting of the rotors of large turbine generators~
In order to avoid the winding problem discussed above which results from the conventional concentric type of winding used in large generators, the present invention utilizes form wound coils arranget in a progressive type of winding to provide the required multi-pole magnetic field. With this arrangement, the coils can all be of substantially identical dimensions, and can be of essen~
tially standard construction. The coils are full-pitch coils and are wound in the slots in the usual way with one coil side of each coil in the bottom of a slot and the other coil side in the top of another slot. Standard coils with the usual diamond end turns have sufficient flexibility in the end portions to permit them to be twisted or stretched as rèquired for insertion in the radial slots, and a relatively low~cost winding is thus ~4~

` 45,842 ~055095 made possible since the coils can be manufactured in the same manner and with the s~me tooling as stand2rd motor stator coils. A low-cost construction is thus provided for both the rotor itself and the winding.
This type of winding results in spaces between groups of end turns corresponding to the unqlotted pole face regions, and means must be provided for adequately sup~
- por~ing or bracing the end turns, Such supp~rts may be provided by suitable insulating blocks disposed in the spaces between groups of end turns, with circumferen-tial banding to draw the end turns together ln a tight arch-bound construction~
BRIEF DESCRIPTION OF ~HE DR~WINGS
.. . . . . . . . , .. _.
The invention will be more fully understood from the foll~wing detailed description, taken in con-nection with the accompanying drawings, in which:
Figure 1 i~ a longitudinal sectional view of a rotor member embodying the invention;
Fig. 2 i a transverse sectional view substan~
tially on the line II~II of Fig. l;
Fig. 3 is a developed plan view of a portion of one end of the rotor member of Fig. l; and Fig. 4 is a simplified schematic diagram of a winding arrangement.
DESCRIPTION OF THE PREFE~RED EMBODIMENT
.. .. . ...
The invention is shown in the drawings embodied ~5~

45,842 in a rotor for a relatively small synchronous generator or motor which may, for example, be in the range of 2000 to 3000 kilowatts rating. The rotor may, of course, be used with a stator member of ~ny usual or suitable con-struction. The particular rotor shown for the purpose of illustration is a four-pole rotor, but it will be understood that the invention is not limited to any specific rotor speed or number of poles.
As shown in Figs. 1 and 2 9 the rotor has a shaft 15 with a generally cylindrical laminated core 16.
The core 16 is built up of a suitable number of gener-ally annular punchings, as shown in Fig. 2, and the assembled core is supported on radial spider arms 17 welded or otherwise secured to the shaft 15~ The arms 17 provide axial passages 18 between them for axial flow of ventilating air so that effective cooling of ~he core is obtained, radial vents in the core also being provided if desired. The laminated core 16 is clamped together under suitable pressure by means of end plates 19 of usual ~ype secured to the shaft in any desired mannerO
Coil supports are also provided at each end consisting of axial arms 20 extending from the end ?lates 19 with circumferential coil support rings 21 mounted on themO
Suitable insulating pads 22 may be provided on the coil supports 21.
As shown more particularly in Figo 2, the core 45, 842 16 is provided with longitudinal slots 25 for receiving the rotor winding. The particular rotor shown in the drawing is a four-pole rotor having nine slots per pole for receiving a nine-coil-per-pole w~nding. As shown in Fig. 2~ the slots 25 are arranged in four spaced groups providing pole face regions 26 between them which are unslotted. This arrangement is similar to the 5 lot arrangement used in rotor forgings for large tur-bine generators. Concentric coils of heavy strap con~
ductors are usually used in such m~chines and the lengths of the end turns of different coils are differ~
ent. The end portions of each turn in a coil are also different in such a winding because of the radial dis-position of the slots. This is not a serious disadvan~
tage in large generators where strap conductors are used and the coils are placed in the slots one turn at a time. For machines of the sizes here involved, how~
ever, it would preclude the use of standard form wound coils because it is undesirable to use coils of several different sizes and it is not practical to provide coils having each turn of a different length at any reasonable cost.
In accordance with the present invention, a progressive winding is used instead of the conventional concentric winding, and standard form wound coils such as are used in stators can be utilized since all coils 7~

45,842 1()55095 can be identical. Each coil 27, as can be seen in Figs~
2 and 3, has straight coil sides lying in the slots 25 and has end turn portions 28 of the so-called diamond type. The coils are placed in the slots so that one side of each coil 27 lies in the top of one slot 25 and the other side lies in the bottom of another slot, the end turns 28 nesting together around the machine as can be seen in Flg. 3. Such form wound coils can be manuO
factured in the usual manner at relatively low cost using standard or existing tooling. The coils may be either stranded or wire wound, and are wound to the desired number of turns and mçan turn length and then pulled or formed to ~he desired configuration and dimen~
sions on standard pulling machines. Such coils have sufficient flexibility in the diamond portions 28 of the end turns to allow the necessary twisting or stretching to insert the coils in the slots, and the necessary num~
ber of identical coils can readily be placed in the slots 25 and connected together to form a multi~pole progressive winding.
The winding coils are preferably full~pitch coils and an illustrative winding connection is shown by way of example in Fig. 4. This is a simplified diagram showing a four-pole winding having only three coils per pole, with twelve slots. The positions of the slots axe indicated by dotted lines numbered 1-12, inclusive, and 45,842 it will be seen that the slots are arranged in four spaced groups having unslotted pole face regions 26 between them, as previously described. The coil sides of the form wound coils 27 are disposed in the slots with two coil sides in each slot, the lower coil side in each slot being shown by dotted lines and the top coil side in each slot being shown by solid linesO It will be seen that the winding i9 a progressive winding with all coils connected in series and extending from one pole to the next with three coils in each pole group, the direction of winding of adja~ent poles being reversed so as to form a multi-pole magnetic field with four poles of alternating polarity when the winding is excited with direct current.
The rotor shown in Figs. 1-3 is similarly wound except that there are nine coils per pole which are disposed and connected similarly to the coils of Fig. 4. The form wound coils 27 are multi-turn coils which are substantially identical and which are wound with the required number of turns. Both leads 31 of each coil are brought out at the same end of the coil so that all coil leads lie at the same end of the core 16.
~he coil leads 31 are brazed or welded together in any suitable manner, as can be seen in Fig. 1, and the nec-essary cross-connections, indicated at 32, may be sup-ported on suitable insulating cleats 33 attached to the 45,842 105S~95 coil support structure. The positive and negative field leads 34 preferably extend into an axial passage 35 in the shaft for connection to any suitable source of excitation (not shown) which may, for example, be the rotating rectifier assembly of a brushless exciter or which may comprise a set of slip rings on the shaft for use with a conventional exciter.
In high speed rotors, the end turn portions of the winding coils must be well braced and supported against the high centrifugal forces which occur during operation. In conventional wound rotors, such as are used in induction motors, the end turns are supported by circumfe~ential banding which holds them down against the coil supports. Adjacent end turns are separated by insulating pads or thin spacers and the entire structure is tightly arch-bound into a subs~an~
tially solid mass by the circumferential force applied by the banding. In the winding arrangement described above, as seen particularly in Figs, 3 and 4, the end turns 28 are disposed in groups with relatively large spaces between them corresponding to the unslotted pole face regions. The large spaces thus exist~n~ in both the upper and lower layers of end turns preclude the usual type of arch-bound construction and make it diffi~
cult to brace the end turns by the conventional banding alone ` 45,842 As shown in Fig. 3, effective bracing is pro~
vided ~y filling the spaces between adjacent groups of end turns by insulat~ng structures 38. These structures may comprise blocks molded of a~y suitable insulating material to the desired size and shape to substantially fill the spaces as shown in Fig. 3, a block being pro-vided for each of the spaces in both the upper and lower layers of end turns of the coils. The insulating spacing structures 38 may, if desired, be composite members built up of suitable materials, or may be mem~
bers of any desired construction having the necessary strength and rigidity. The blocks 38 may be of any suitable configuration, preferably being arcuate in the circumferential direction to conform to the disposition of the end turns, and each block may have an opening 39 formed in it to permit ventilating air to flow through the end turns. The closely-spaced end turn portions within each of the groups of end turns are separated by insulating pads or spacers 40 in the us~
ual manner.
The complete assembly of end turns 28 and insulating spacers or blocks 38 is supported by suitable circumferential banding 41 which may consist of the necessary number of turns of glass tape wound under tension around the end turns, as shown in Fig. 1, in position to bind them down on the winding supportsO

45,842 Any desired type of banding material could, of course, be utilized. It will be seen that this applies cir-cumferential forces to the end turns and since the structure includes the blocks 38 to complete the cir~
cumferential configuration, a solidly arch-bound structure results which is effectively braced against rotational forces. The spacers or blocks 38 may be composite structures of any suitable type of the neces-sary mechanical rigidity and strength with the required insulating properties, as discus~ed above, or other suitable spacing means might be used. Coil end por tions, for example, might be cut from complete coils and ~he appropriate number of such dummy end portions placed in the spaces between groups of active end por~
tions.
It will now be apparent that a synchronous rotor construction has been provided which is espec~
ially suitable for relatively small, high speed synchronous machines and which avoids previously-encountered problems and provides a very efective low~
cost construction for such machines. It will be evi~
dent that although a particular embodiment has been described for the purpose of illustration, various modifications are possible. Thus, the invention is not necessarily limited to use with a laminated core as the type of winding shown could be used with a slotted -12_ 45,842 forging. Any suitable materials or structures may be utilized for bracing purpoæes in the spaces between groups of end turns. It would also be possible to avoid this problem by arranging the slotting of the rotor nonsymmetrically about the pole center lines, 90 that by changing the end winding shape of each coil in a group, the spaces between groups of end turns could be eliminated and the coil ends evenly spaced about the circumference of the rotor. A similar result could be obtained with symmetrical slotting, such as that shown in the drawings, by changing the coil dimensions for each coil in each group so as to use unsymmetrlcal coils which could also result in evenly spaced coil ends about the circumferenceO In either case, conven~
tional bracing could then be used. Either of these arrangements, however, would involve different dimen~
sions or shape for each coil and would require a great deal of setDup time in manufacture with correspond-ingly increased costs.

Claims (9)

What is claimed is:

1. A rotor member fox a synchronous dynamo-electric machine, said rotor member comprising a gener-ally cylindrical core having a plurality of longitudinal slots in the surface thereof, said slots being arranged in circumferentially-spaced groups with unslotted pole face regions between the groups, and a field winding disposed in said slots, said winding comprising a plurality of form wound coils having coil sides placed in the slots and axially extending diamond end portions, the coils being connected in a progressive winding to form a plurality of magnetic poles of alternating polarity in said pole face regions.

2. A rotor member as defined in claim 1 in which said core comprises a plurality of coaxially dis-posed circular laminations and means for clamping said laminations together in a cylindrical core.

3. A rotor member as defined in claim 2 in which the rotor member includes a shaft having radially extending arms thereon, and said laminations are annular and supported on the outer ends of said arms.

4. A rotor member as defined in claim 1 in which all of said coils are substantially identical and said end portions have sufficient flexibility to permit the coils to be placed in radial slots.

5. A rotor member as defined in claim 4 in which each coil has one side disposed in the bottom of a slot and the other side disposed in the top of another slot.

6. A rotor member as defined in claim 1 in which the end portions of said coils at each end of the core are disposed in groups of closely-spaced coils with intervening spaces corresponding to said pole face regions, insulating spacing means in said spaces, and means for supporting said coil end portions against rotat-ional forces.

7. A rotor member as defined in claim 6 in which said spacing means comprise insulating blocks sub-stantially filling said spaces, and bracing means sub-porting said coil end portions in a solid, arch-bound structure.

8. A rotor member as defined in claims 6 is which each coil has one side disposed in the bottom of a slot and the other side disposed in the top of a slot, whereby the coil end portions are arranged in two circum-ferential layers, an in which said spacing means comprises an insulating block substantially filling each of said spaces in each layer.

9. A rotor member as defined in claim 8 including circumferential banding means for tightly supporting the coil end portions in the radial direction.