SYSTEME DE VENTILATION ET APPAREIL DE REFROIDISSEMENT D'AIR COMPRENANT DES POLES SAILLANTS EN SAILLIE AVEC BOUCLIERS JUXTAPOSES

VENTILATION SYSTEM FOR AN AC MACHINE HAVING OVERHANGING SALIENT POLES WITH JUXTAPOSED SHROUDS

Abrégé français

L'invention porte sur une méthode d'amélioration de l'écoulement d'air dans une machine dynamoélectrique à pôles saillants de faible à moyenne vitesse. La jante de rotor, sur laquelle les pôles saillants sont montés, est plus courte comparativement aux structures antérieures, de sorte que les extrémités des pôles saillants (et les enroulements du rotor) dépassent du bord de la jante de façon importante. Un bouclier fixe ou rotatif est juxtaposé aux extrémités rotatives des pôles saillants afin de créer une enceinte pour que les extrémités saillantes des pôles saillants puissent fonctionner comme un ventilateur rudimentaire à aubes radiales.

Abrégé anglais

A method of improving the airflow through a low to medium speed
salient pole dynamoelectric machine DEM is disclosed. The rotor rim on
which the salient poles are mounted is shortened in comparison to prior art
structures so that the ends of the salient poles (and the rotor windings)
protrude a substantial distance beyond the edge of the rim. A stationary or
rotating shield is placed in juxtaposed relationship with the rotating ends of
the salient poles to provide an enclosure so that the protruding ends of the
salient poles can function as a crude radial fan.

Revendications

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Claims
1. A salient pole DEM (dynamoelectric machine) comprising a stator
assembly and a rotor assembly mounted within said stator assembly for rotation
therein, said rotor assembly comprising a shaft integrally attached to a web
which
carries a cylindraceous rim integrally attached thereto at the extremities of
said
web,
said rim having a set of salient poles mounted thereon, said poles being
of such length that the ends of each pole extend beyond the rim of said rotor
assembly by a first predetermined distance, and,
said stator assembly includes magnetic core having a set of stator
windings whose ends protrude a second predetermined distance from said core,
annular shroud means attached to the stator assembly of said DEM in
such a manner as to enclose the ends of the windings projecting from said
stator
core in juxtaposition with said ends of said salient poles.
2. A DEM as claimed in claim 1 wherein said shroud is sealedly
attached to the stator assembly of said DEM and extends radially inwardly to
obscure a major portion of said poles.
3. A DEM as claimed in claim 1 wherein said shroud comprises two co-
operating parts, a rotary part attached to said rotor assembly, said rotary
part
having the general shape of an annulus, said co-operating parts of said shroud
obscuring a major portion of said poles.
4. A salient pole DEM comprising a stator and a rotor for rotating within
said stator,
said stator having a frame for supporting a core therein, said core
comprising groups of punchings of a suitable magnetic material stacked in such
a
manner as to produce an annular core having ventilation spaces formed between
said groups of punchings,
said core having a plurality of windings extending through slots formed in
said core,
said windings extending beyond the ends of said core to form end heads
for said windings,

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said frame also having ventilation ports provided therein in
predetermined locations radially outwardly of said endheads,
said rotor having a shaft mounted in suitable bearings for rotation in said
stator, and rotor hub assembly mounted on said shaft for supporting a rim
means
thereon,
said shaft and rim being interconnected by a rotor web,
said rim means having a plurality of salient poles mounted thereon at
predetermined spaced intervals,
each of said poles extending across said rim and slightly beyond the
edge of said rim,
shroud means mounted at the ends of the DEM in juxtaposition with the
ends of the salient poles
wherein said shroud means is sealedly attached to said stator of said
DEM radially outwardly of said end heads and extending radially inwardly to
obscure a major portion of said rotor poles.
5. A slow to medium speed salient pole DEM comprising a stator and a
rotor,
said stator comprising groups of laminations stacked together to form an
annulus having an interior and exterior cylindraceous surface and having
ventilation ducts formed in said stator at predetermined spaced intervals
along the
axis of said stator,
said stator having a set of axial slots formed therein near the interior
surface thereof for accepting stator windings therein,
said windings extending beyond the ends of the annulus in the form of
endheads for said windings,
said stator being supported in a frame; enclosure means surrounding
said frame and stator and extending along the ends of said stator so as to
extend
inwardly past the endheads of said stator windings into the rotor space,
said rotor having a shaft mounted in suitable bearings for rotation within
said stator,
said rotor shaft having a web mounted thereon for supporting a rotor rim

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thereon,
said rim having a plurality of salient poles mounted thereon such that the
ends of said salient poles overhang the edge of said rim by a predetermined
distance,
said enclosure extending radially inwardly toward said shaft in
juxtaposition with said salient poles to form a shroud for said rotor,
said enclosure obscuring at least a part of salient poles.
6. A salient pole DEM as claimed in claim 5 in which said frame has
spaced ventilation apertures in said frame outwardly of said endheads to
permit
communication between the endhead enclosure and the enclosure surrounding
said frame.
7. A salient pole DEM as claimed in claim 6 wherein said rotor rim is
provided with suitable ventilation apertures between said salient poles for
the
passage of ventilating air therethrough.
8. A salient pole DEM as claimed in claim 6 wherein a second shroud in
the form of an annulus is mounted on said rotor to co-operate with said
endhead
enclosure to form an interface,
said rotor shroud forming a partial seal at the interface of the endhead
enclosure and rotor shroud, said rotor shroud obscuring said salient pole.
9. A salient pole DEM as claimed in claim 6 wherein said rotor rim is
provided with suitable ventilation apertures between said poles for the
passage of
ventilating air therethrough.
10. A salient pole DEM as claimed in claim 9 wherein said rotor rim has
ventilation apertures formed therein at predetermined spaces between said
poles.
11. A slow to medium speed salient pole DEM comprising a rotor and
stator mounted in a suitable frame, enclosure means for said frame for ducting
ventilation air therethrough,
said stator comprising groups of magnetic laminations stacked together
to form an annulus having an interior and exterior cylindraceous surfaces, and
having suitable ventilation ducts formed in said stator at predetermined
spaced
intervals along the axis of said stator,

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said stator having a set of axial slots formed therein near the interior
surface thereof for accepting stator windings therein,
said windings extending beyond the ends of the annulus in the form of
endheads for said windings,
said endheads having sealing means applied thereto adjacent the ends
of the annulus to form a ventilation barrier,
said enclosure enclosing the frame and the exterior surface of said
annulus to form a ventilation space for the collection of air passing from
said
ventilation ducts of said stator,
said rotor having a shaft mounted in suitable bearings for rotation within
said stator, said rotor shaft having a web attached thereto for supporting a
rotor
rim thereon, said rotor rim serving as a suitable mounting means for a
plurality of
salient poles thereon, such that the ends of the salient poles overhang the
edge of
said rim by a predetermined distance,
said rotor having an annular shroud mounted thereon adjacent the ends
of said salient poles for rotation with said rotor, such that said rotor poles
are
obscured by said annular shroud, said shroud being aligned with said
ventilation
barrier of said stator to form a partial seal therewith.
12. A slow to medium speed salient pole DEM comprising a rotor and
stator mounted in a suitable frame, enclosure means for said frame for ducting
ventilation air therethrough,
said stator comprising groups of magnetic laminations stacked together
to form an annulus having an interior and exterior cylindraceous surfaces, and
having suitable ventilation ducts formed in said stator at predetermined
spaced
intervals along the axis of said stator,
said stator having a set of axial slots formed therein near the interior
surface thereof for accepting slator windings therein, said windings extending
beyond the ends of the annulus in the form of endheads for said windings,
said endheads having sealing means applied thereto adjacent the ends
of the annulus to form a ventilation barrier,
said enclosure enclosing said frame and the exterior surface of said

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annulus to form a ventilation space for the collection of air passing from
said
ventilation ducts of said stator,
said rotor having a shaft mounted in suitable bearings for rotation within
said stator, said rotor having a web attached thereto for supporting a rotor
rim
thereon, said rotor rim serving as a suitable mounting means for a plurality
of
salient poles thereon, such that the ends of the salient poles overhang the
edge of
said rim by a predetermined distance,
annular shroud means attached and sealed to said stator at said
ventilation barrier extending inwardly toward said shaft adjacent the ends of
said
salient poles of said rotor, said shroud obscuring at least a part of said
poles.
13. A salient pole DEM as claimed in claim 12 wherein said rotor rim
has ventilation apertures formed therein at predetermined spaces between said
poles.

Description

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21 96363
GECAN 3065
VENTILATION SYSTEM FOR AN AC MACHINE HAVING
OVERHANGING SALIENT POLES WITH JUXTAPOSED SHROUDS
This invention is directed to an improved method of cooling of large
low to medium speed self ventilating salient pole dynamoelectric machines
(DEM's) by a modification to the rim of the rotor which, when used in
conjunction with an air shroud which may be mounted on either the rotor or
stator produces an improved cooling efficiency of the DEM.
The improvement is brought abQut by having the ends of the salient
poles beyond the pole body protrude beyond the edge of the rotor rim.
This induces ventilation air to flow radially outwardly past the edge of the
rotor rim in spaces between the poles between the rim and the shroud.
Because the rotor is rotating, the natural fanning action of the protruding
pole ends pumps air outwardly, and because the shroud presents a barrier
to air which would otherwise flow axially away from the air gap in the
absence of the shroud, the air now is forced into the air gap and through
other stator parts in the air flow path.

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BACKGROUND OF THE INVENTION
Self ventilating low to medium speed AC salient pole DEM's have
traditionally exhibited a large radial depth. A typical construction for such a
DEM generally consists of a shaft on which a hub type frame is mounted,
on which a barrel type rim is attached so that the hub supports the rim at
some distance from the central shaft. Salient poles may then be bolted to
the rim to complete the rotor construction.
The salient poles are usually bolted to the rim at both ends of the
poles so that the ends of the poles are in line with the edge of the rim, in
other words, the axial length of the poles (with the pole windings in place)
is usually made to equal the axial width of the rim. The space between the
adjacent poles is called the interpolar space.
In salient pole DEM's of the above type which are designed for
parallel air flow, that is, where the ventilating air flows in two distinct paths
in the machine, i.e. radially past the ends of the poles into the end heads of
the windings and axially into the interpolar spaces and into the stator
ventilating ducts, a shroud or shield is used in the DEM to provide a barrier
adjacent the ends of the poles to cause the ventilation air to flow in the
prescribed manner. The air that enters the stator ducts is merged with the
air passing over the end heads of the stator windings in the stator frame at
the back of the stator core.
In order to improve the air flow through such DEM's, designers have
traditionally mounted scoop fans on the edge of the rotor rim immediately
adjacent the interpolar spaces. For unidirectional salient pole DEM's, the

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scoop fan is located to one side of the interpolar space, so as to attempt to
induce air to flow into the interpolar spaces during rotation of the rotor.
For bi-directional machines, a compromise must be made, and
designers have traditionally mounted two scoop fans back to back on the
S rim of the rotor at a point midway between the adjacent poles. The effectiveness of this solution is open to question.
When the above types of cooling are analyzed, it will be found that
while the scoop fans are primarily intended to move the air in an axial
direction, the fans predominantly move the air in radial direction in a
manner similar to a radial fan, with the result being that little air is moved in
the intended axial direction (between the poles).
The air stream which results from the presence of the scoop fan in
the presence of a surround barrier such as a shroud or shield tends to be
such as to create a positive pressure on the concave side of the blade,
l 5 with a negative pressure being generated on the convex side of the blade.
This condition leads to the generation of turbulence, which results in
increasing windage losses in the DEM.
The following patents will illustrate how the evolutionary process has
included shrouds and fans in various ways to improve the air flow through
salient pole machines.
U.S. Patent 4,383,181 to Miznyama et al (May 10, 1983) shows a
baffle system for a salient pole DEM wherein an annular baffle encircles
each end of the rotor but is spaced a short distance from the pole and the
rotor rim ends. The addition of the annular shield tends to captivate the air

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between the shield and the rotor so as to spin the entrapped air as the
rotor turns and then release the entrapped air into the interpolar spaces.
The invention claims a substantial reduction of windage loss.
Canadian Patent 1,019,397 (October 18, 1977) to Sapper shows a
salient pole DEM in Figs. 3 and 4 which describes an annular shield to
improve air flow through the machine. Alternately, a radial fan may be
substituted in place of the annular shield if efficiency is not a design
consideration or if it is desired to increase the nominal rating of the
machine.
Both the above references recognize the basic problem of
misdirected air flow at the ends of the rotor and stator of salient pole
machines. Both references provide a solution by placing large annular
shields adjacent the pole ends which must rotate with the rotor of the
machine.
The rotating shield of the Mizuyama patent is displaced from the
ends of the salient poles because the spider rim extends axially the entire
length of the pole. This means that the pole ends are obscured with
respect to radial air flow by the spider rim. There appears to be no radial
blades on the rotating baffle and as such it is not clear how any significant
static air pressure can be developed in the interpolar inlet region in the
absence of radial impeller blades somewhere in the machine's
construction.

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The Sapper patent provides a separate centrifugal radial fan which
in itself tends to block the flow of air at the inlet of the interpolar spaces, a
condition that is open to suspect.
SUMMARY OF THE INVENTION
The present invention seeks to overcome the deficiencies of the
prior art by providing a radial shroud having substantial radial length which
may be fastened to either the rotor or stator of a salient pole DEM. In
addition, the construction of the rotor of the DEM is modified so that the
pole ends protrude beyond the edge of the rotor rim. This feature along
with the deepened shroud provides the basic components of a crude air
pump. The protruding pole ends function as thick radial blades of an
impeller thus permitting a static air pressure head to be developed by the
rotating pole ends in the presence of the shroud.
The resulting increase in air pressure across the interpolar spaces
results in an improvement of the air flow through the interpolar spaces and
the elimination of the scoop fan blades from the rotor which yields an
increase in operating efficiency by the consequential reduction in windage
losses.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagram of a prior art medium to low speed salient pole
machine showing the cooling air flow paths.
Figure 2 shows a perspective view of a prior art scoop fan used in
unidirectional rotating DEMs.

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Figure 3 shows a perspective view of a double scoop fan used on
bi-directional rotating DEM's.
Figure 4 is an illustration of the air flow distribution of the stator of a
salient pole DEM in the absence of the rotor fans.
Figure 5 is an illustration of a parallel air flow salient pole DEM to
which this invention has been applied.
Figure 6 is an illustration of a portion of a series air flow salient pole
DEM to which this invention has been applied.
Figure 7 is an alternate form of this invention as applied to the DEM
of Figure 5.
Figure 8 is an alternate form of this invention as applied to the DEM
of Figure 6.
Figure 9 is yet another alternative form of the invention as applied to
the DEM of Figure 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, and to Fig 1 in particular, a prior art low to
medium speed salient pole DEM 10 is shown. This DEM is illustrated to
show how a prior art machine construction may be used to produce parallel
air flow, that is~ an air flow pattern wherein part of the air flow induced by
the rotor passes past the end heads of the windings, and another part of
the air flow passes into the interpolar spaces and passes through the air
gap and into the stator ventilation ducts.
DEM 10 has a rotor 12 and a stator 14 in which rotor is suitably
journalled in bearings (not shown) for rotation.

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Rotor 12 comprises a shaft 16 on which a hub 18 is mounted. A
web 20 completes the hub construction. A barrel rim 22 is suitably
attached to hub web 20 by welding or some other suitable means of
attachment.
Rim 22 is provided with apertures 24 placed at predetermined
spaced locations on the rim 22. Scoop fans 26 are shown mounted on the
edges of rim 22 to motivate air flow through the DEM 10 from the ends of
the rim 22.
Poles 28 are shown mounted on rim 22 for carrying a winding 30
thereon .
An air gap 32 exists between poles 28 and stator 14. Stator 14
comprises a frame 34 of which members 36 are shown, each having
ventilation apertures 38 shown therein.
A stator core 40 is mounted in frame 34 shown here mounted
l 5 between frame members 36. The stator core 40 is composed of stacks of
lamination punchings which are separated at spaced intervals by space
blocks in ventilation slots 42.
A set of windings shown as 44 are mounted in slots of the
lamination punchings of stator 40.
A pair of enclosures 46 are mounted on the stator frame members
36 to provide means to direct part of the ventilation air passing through the
machine.
It must be remembered that Fig.1 represents a partial sectional
view of a salient pole DEM and members 46 for instance, are fairly large

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annular shaped members. Members 46 are shaped such that flanges 48
extend inwardly a small distance radially inwardly to ward the center of the
DEM in juxtaposition with the ends of scoop blades 26.
The air flow pattern through the DEM is shown as entering the ends
of the DEM 10 at A and B. Air entering from points A is drawn into the
scoop fan areas and a large portion of the air which is moved by the scoop
fans 26 passes past end heads 44 and through chambers enclosed by
housings 46, through apertures 38 to the collection chamber formed by the
frame members 36 of the back of the core of the DEM 10.
A portion C of the A stream is directed into the interpolar spaces
where the rotor poles 30 and windings 30 are cooled and the C stream
gradually bleeds across air gap 32, to pass through ventilation slots 42 of
the stator 40 and form a portion of the exit air stream D.
The B air stream enters the interior of the rotor and is drawn through
apertures 24 in the rotor because of the pumping action produced by the
rotating poles 28. These apertures are located in the interpolar spaces so
that the B stream is able to provide additional cooling for the rotor poles 28
and windings 30. As with air stream C, the B stream bleeds across the air
gap 32 and passes through ventilation ducts 42 of stator 40 to become a
2() component of exit air stream D. The exiting air streams A and D are
ducted to atmosphere or to a heat exchanger.
Note that the prior art DEM of Fig.1 utilizes a rotor construction
wherein the rotor rim 22 has a width approximately equal to the length of
poles 28 and windings 30. The width of the stator 40 and frame members

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36 is almost the same dimension as the rim 22 and the poles 28 and
windings 30.
The scoop fans 26 are mounted on the outside edge of the rim 22
and will be mounted to one side of the interpolar space, so that during
S rotation, the scoop fans 26 attempt to "scoop" air into the interpolar spaces.
The presence of flanges 48 provide confinement for the ends of
blades 26 to allow a pressure build up of the air being moved by the blades
26.
The width of the flange 48 as indicated by R2 - R1 is the determining
actor in the development of the static pressure build up for air passing
through the scoop fans 26. The static pressure increase is proportional to
the difference of the squares of the radii R2 and R1 and if this distance can
be increased, the increase in static air pressure existing at R2 would be
substantial .
The machine illustrated in Fig. 1 is based on actual machine
dimensions, and as such gives a fair representation of the dimensions and
placement of the actual parts of a typical low speed salient pole DEM.
Note the distance "d" which is the distance by which the rotor extends
axially beyond the width of both the stator core laminations and the pole
laminations 31.
Fig. 2 shows a perspective of a scoop fan 60 used in prior art
machines. The fan is provided with a base portion 62 which is integrally
connected to air foil portion 64. This blade is bolted to the edge of rim 22

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of the DEM 10 and will be offset from the center of the interpolar space in
an attempt to scoop air into the interpolar spaces.
Fig. 3 shows the scoop fan arrangement for a bi-directional rotating
machine. Here a pair of identical scoop fan blades 60 are mounted in a
back-to-back relationship on the centerline of the interpolar space of the
edge of the rim of the DEM.
Fig. 4 shows the stator airflow distribution for a DEM similar to the
DEM illustrated in Fig.1 with the scoop fans removed. Similar parts bear
the same reference numerals. Note the uneven airflow across the width of
the stator core 40.
Fig. 5 shows a DEM 110 having the modifications of this invention.
In this instance, the fans 26 are absent and the rotor 112 has been
modified to reduce the width of the rotor rim 122 by a distance "2d". The
length of the salient poles 128 and windings 130 are of the same
dimensions as previously shown in the DEM of Fig. 1, but now protrude
beyond the shortened rim 122. The enclosures 146 have a substantially
different shape when compared to enclosures 46 in Fig.1 in that the flange
extensions 148 extend a much greater distance toward the center of the
DEM 110 than did flanges 48 in Fig. 1. The distance R2- R1 is much
greater in Fig. 5 than Fig. 1.
The airflow pattern in Fig. 5 is produced by the rotating poles in
combination with flanges 148 of enclosures 146. Because the rotor rim
122 is shortened, the protruding poles 128 and theirwindings 130 serve as
thickened fan blades of a radial fan to propel air through the DEM 110.

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Note that airstream E is roughly equivalent to the A stream of Fig.1
and the F stream corresponds the B stream, etc. Because of the
significant increase in the difference in the dimensions R2 and R1, the static
pressure of the air gap will be increase and thus, the airflow will be
substantially increased in DEM 110. Note that the width of the rotor 122
corresponds to the stator lamination stack length "S".
Fig. 6 shows a quarter section of a DEM 210 having a series air flow
through the DEM 210. Here a rotor 212 rotates within a stator 214. The
poles 228 and windings 230 again overlap rim 222. Instead of enclosures
surrounding end heads 244 of stator windings, a seal ring 250 seals the
outer circumference of end heads 244 to stator frame members 236. A
second intermediary seal member 252 extends in the spaces between the
endheads 244. Lastly, a stationary shroud 254 is attached to endheads
244. Member 254 extends nearly to the base of poles 228.
An additional winding brace 256 is shown so stabilize the ends of
winding endheads 244. In Fig. 6, the airflow pattern is quite difference
than previous figures. Here the inlet air enters at J and K and flows past
end heads 244 (in a direction opposite to previous figures) to point L where
the air stream makes substantially a 180~ turn and is pulled into the rotor
pole pump and into space M and into the interpolar spaces and thence into
space N and into airgap 232.
From space M the air stream moves through the frame 236 and into
ventilation slot adjacent frame member 236.

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Another branch of the incoming J-K airstream enters the rotor space
and passes through apertures 224 and into interpolar spaces at P and into
air gap 232. Airstreams N and P pass through the air gap and enter
ventilation ducts 242 and pass through the stator and joins the M air
stream at Q where the air exhausts to atmosphere or to a heat exchanger.
This is a series flow situation and the air pressure developed by the
pole ends is dependent on the depth of the annular shield 254, which in
this instance extends almost the entire height of the pole 228.
Fig. 7 illustrates a parallel air flow machine 310 which utilizes a
rotating shroud 348 in combination with stationary enclosure 346 which
produces an air flow pattern similar to that of DEM 110 in Fig. 5. The
rotating shroud 348 is attached at the rim 322 by bolts 360 and spacers
362 which are located at equally spaced intervals around the rim 322.
The static pressure of the head developed as the air passes
between shroud 348 and poles 330 is dependent upon the difference
between the squares R2 and R1 as previously described.
Fig. 8 illustrates a series flow DEM 410 which is similar to the DEM
illustrated in Fig. 6 with the exception of the shroud 454 which is attached
to rim 422 by means of bolts 460 and spacers 462. The static air stream
pressure generated by the protruding poles 430 is proportional to the
difference of the squares of the distances R2 and R1. It will be obvious that
rotating shroud 454 must be sealed in some suitable manner to winding
heads 444 to prevent excessive air leakage at this location.

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Fig. 9 illustrates a series air flow DEM 510 which utilizes a pair of
spaced air shields 554 and 564 to further increase the distance R2 - R1 to
increase the static air pressure generated by the rotating poles 530. Radial
blades 566 are attached between shields 554 and 564 at spaced intervals
inwardly of the poles 530.
In addition, tubular extensions 568 are mounted on the inside of
rotor rim 522 to increase the static air pressure at apertures 524 so as to
improve the airflow in the interpolar spaces through rim 522.
It will be seen that the elimination of scoop fans is of paramount
importance in improving the efficiency of low and medium speed salient
pole DEM's. Because of the deficiencies in the overall performance of the
scoop fans, this invention seeks to replace and augment the scoop fan
function with a salient pole which protrudes beyond the edge of the rim of
the rotor and rotates in juxtaposition with a rotary or stationary air shield.
The primary objective of improving the differential distance R2 - R1 leads to
a definite improvement in the static air pressure head built up in the vicinity
of the rotating salient poles protruding beyond the edge of the rim at the air
gap. The increased static pressure will result in increased air flow in both
the interpolar spaces and stator ventilation ducts. Most motors of this type
are limited by rotor field winding temperature, thus the increased air flow in
the interpolar spaces is of primary importance to the successful operation
of such machines.
In determining the reduction in rim width which is acceptable it will
be found that the rim width may be made to equal the stator lamination

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stack width "S" as shown in the drawings without any degradation in the
magnetic characteristics of the machine.
An additional benefit of the stationary shields results from the
relatively small distance between the stationary shield and the end of the
rotor winding of the rotating salient pole. The full tangential velocity of the
pole end relative to the stationary shield results in an increase in the
surface heat transfer co-efficient at the pole face ends. Rotating shrouds
are generally more difficult to implement in comparison to stationary
shrouds. Some shrouds may be composed of segments of a lightweight
non-metallic material such as a suitable polymeric material reinforced with
a glass fiber material. This material may be successfully used to fabricate
either stationary or rotating shrouds.

Dessin représentatif