U.S. patent application number 09/805995 was filed with the patent office on 2001-09-20 for electric machine.
Invention is credited to Leyvraz, Rene-Louis, Stallone, Francesco.
Application Number | 20010022482 09/805995 |
Document ID | / |
Family ID | 7635350 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022482 |
Kind Code |
A1 |
Leyvraz, Rene-Louis ; et
al. |
September 20, 2001 |
Electric machine
Abstract
In a generator with an indirectly gas-cooled, in particular
air-cooled, stator winding (21), the end regions of the stator bore
(23) are to be designed in such a way that the conductor bars are
shielded as effectively as possible by the laminated stator core
(20) against magnetic fields inducing eddy currents, but, on the
other hand, a specific radial dimension between the rotor retaining
ring (12) and the laminated stator core (20) is ensured. According
to the invention, for this purpose, the end region of the stator
bore is designed with four axial zones having a different diameter
profile. A first zone (I) is the interior of the stator with the
constant nominal stator bore diameter (D.sub.I). Toward the end
face of the stator is arranged a second zone (II) with a stator
bore diameter (D.sub.II) widening toward the end face. The stator
bore widens, there, to the diameter of a third zone (III) with an
at least approximately constant diameter (D.sub.III), this
diameter, on the one hand, being large enough to ensure a necessary
distance from the rotor retaining ring, but continuing to ensure a
good overlap over the stator conductor bars by the laminated
core.
Inventors: |
Leyvraz, Rene-Louis;
(Lupfig, CH) ; Stallone, Francesco; (Locarno,
CH) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
7635350 |
Appl. No.: |
09/805995 |
Filed: |
March 15, 2001 |
Current U.S.
Class: |
310/429 ;
310/201; 310/216.014 |
Current CPC
Class: |
H02K 1/16 20130101; H02K
9/04 20130101; H02K 3/42 20130101 |
Class at
Publication: |
310/254 ;
310/216; 310/201 |
International
Class: |
H02K 003/04; H02K
019/00; H02K 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2000 |
DE |
100 13 375.4 |
Claims
1. An electric machine with a rotor (10) and with a stator (20),
the rotor being inserted into a central stator bore (23) of the
stator (20), and essentially axially running stator slots (26)
being arranged on an inner cylindrical surface of the stator, said
cylindrical surface delimiting the stator bore (23); the stator
slots (26) being delimited in the circumferential direction by
stator teeth (27); conductor bars (21) of a stator winding being
arranged in these stator slots (26) in the circumferential
direction between the stator teeth (27); the conductor bars (21) of
the stator winding consisting of a conductor material (211) and of
an insulation (212) surrounding this conductor material, a radially
inner boundary of the insulation (212) defining a mechanical stator
winding diameter (D.sub.M) and a radially inner boundary of the
conductor material (211) defining an effective stator winding
diameter (D.sub.eff); the rotor containing a rotor barrel (11),
said rotor barrel defining in its axial extent essentially the
active part of the generator with magnetic fields which are high
during operation; rotor retaining rings (12), the outside diameter
of which is greater than that of the rotor barrel (11), being
placed onto the rotor barrel (11) at axial ends; the stator having
in the active part a first zone (I) with a constant diameter
(D.sub.I) of the stator bore, said diameter being greater than the
diameter of the rotor barrel by double an air gap dimension
(s.sub.I); the diameter (D.sub.I) of the stator bore in the first
zone (I) being smaller than the effective stator winding diameter
(D.sub.eff), such that the conductor material (211) of the stator
winding in the first zone (I) is overlapped at least completely in
the circumferential direction by stator teeth (27); the stator
having in the axial region of the rotor retaining ring (12) a third
zone (III) with a profile, at least approximately constant in the
axial direction, of the diameter (D.sub.III) of the stator bore,
said diameter (D.sub.III) being greater by a predetermined minimum
amount (s.sub.III) than the outside diameter of the rotor retaining
ring (12), and said diameter (D.sub.III) being greater than the
diameter (D.sub.I) of the stator bore in the first zone (I); the
stator having axially, between the first zone (I) and the third
zone (III), a second zone (II) with a stator bore diameter
(D.sub.II) increasing axially toward end faces of the stator; the
diameter (D.sub.III) of the stator bore in the third zone (III)
being at no point appreciably greater than the effective stator
winding diameter (D.sub.eff), such that the conductor material
(211) of the stator winding in the third zone (III) is overlapped,
at least for a predominant part, in the circumferential direction
by stator teeth (27) and a distance (s.sub.III) mechanically
necessary between the stator in the third zone (III) and the rotor
retaining ring (12) is ensured.
2. The electric machine as claimed in claim 1, the diameter
(D.sub.III) of the stator bore in the third zone (III) being
dimensioned such that the radial distance (s.sub.III) between the
rotor retaining ring (12) and the stator in the third zone at no
point appreciably exceeds the radial air gap dimension (s.sub.I) in
the active part of the generator between the rotor barrel (11) and
the first zone (I) of the stator bore.
3. The electric machine as claimed in claim 2, the diameter
(D.sub.III) of the stator bore in the third zone (III) being
dimensioned such that the radial distance (s.sub.III) between the
rotor retaining ring (12) and the stator in the third zone
corresponds at least approximately to the radial air gap dimension
(s.sub.I) in the active part of the generator between the rotor
barrel (11) and the first zone (I) of the stator bore.
4. The electric machine as claimed in claim 1, the diameter of the
stator bore (D.sub.III) in the third zone (III) being between the
mechanical stator winding diameter (D.sub.M) and the effective
stator winding diameter (D.sub.eff).
5. The electric machine as claimed in claim 1, a conductor exposure
coefficient Q.sub.D being higher than 0.5 and lower than 1.1, said
conductor exposure coefficient being defined by 2 Q D = D III - D I
D eff - D I ,in which relation D.sub.III represents the diameter of
the stator bore at an axial position of the third zone, D.sub.I the
diameter of the stator bore in the axially inner first zone and
D.sub.eff the effective stator winding diameter.
6. The electric machine as claimed in claim 5, the conductor
exposure coefficient Q.sub.D being higher than 0.9 and lower than
1.05.
7. The electric machine as claimed in claim 1, characterized in
that the stator winding is an indirectly cooled winding.
8. The electric machine as claimed in claim 7, characterized in
that cooling is carried out by means of air.
9. The electric machine as claimed in claim 1, characterized in
that the electric machine is a generator.
10. The electric machine as claimed in claim 1, there following on
the stator, axially outside the third zone (III), a fourth zone
(IV) with a stator bore diameter (D.sub.IV) increasing toward an
end face of the stator.
Description
[0001] The present invention relates to the technical field of
electric machines. It relates, in particular, to the configuration
of a stator bore in axial end parts of a stator, in the region of
rotor retaining rings.
[0002] In electric machines, such as generators or electric motors,
the air gap dimension between an active part of the rotor and a
laminated core of the stator constitutes an important parameter for
setting the machine characteristics. On the other hand, this
dimension also influences the mechanical handleability of the
rotors which often weigh several tons. It is therefore obvious that
a minimum radial dimension of the air gap is necessary in order to
move the rotor of, for example, a generator for a power output of a
few 100 MVA into the stator and out of the stator. The axial end
faces of such a machine constitute a critical region in this
context.
[0003] The rotors are normally provided at their ends with rotor
retaining rings. The task of the rotor retaining ring is, inter
alia, to fix the axial end regions of rotor windings. The outside
diameter of the rotor retaining rings is greater than the outside
diameter of the middle part of the rotor, the so-called rotor
barrel. Even at these locations, the minimum dimension of the air
gap must be ensured, without the air gap dimension inside the
stator, consequently in the active region of the machine, being
increased. The diameter of the stator bore must therefore be
increased in the axial end regions toward the end faces of the
stator, in such a way that, for reasons of loss, a minimum
necessary radial dimension relative to the rotor retaining ring is
ensured in the region of said ring. This minimum dimension must
also be maintained in order to make it possible to lift the rotor
when it is being drawn along. At the same time, it is highly
disadvantageous to increase the inside diameter of the stator bore
abruptly in the region in question, since this is located in the
still active part of the rotor. Sharp steppings of the bore
diameter of the stator laminations in this region would lead to the
stator laminations being subjected to axial magnetic fields and to
eddy currents resulting from these.
[0004] It is known, for example, from SU 1185498 to configure the
axial termination of the stator bore in such a way that the
magnetic field lines end as exactly as possible. For this purpose,
the stator bore is enlarged toward the end face with an increasing
gradient, the secondary effect of this being that a sufficient air
gap dimension in the region of the rotor retaining ring is also
ensured.
[0005] It is known, furthermore, from ABB Technik 1/96, page 20 ff,
for air-cooled generators to design the stator laminations toward
the end face of the stator with a more or less linearly increasing
inside bore diameter. This results in a conical widening of the
stator bore, which, with a corresponding geometric design of the
conicity, makes it possible to maintain the minimum dimension for
the air gap. As compared with an abrupt increase in size, the
conical widening of the stator bore affords the advantage that only
a small region of each stator lamination is subjected to axial
magnetic fields, with the result that the load on each individual
stator lamination by induced eddy currents remains low. It is
specified, moreover, in the case of air-cooled generators, to use a
solid aluminum press plate connected operatively to nonmagnetic
press fingers, instead of the laminated press plate known from
water-cooled generators with a higher unit rating. An advantage is
to be seen, here, in that the solid aluminum press plate ensures
that the stator laminations are shielded effectively against axial
magnetic fields in the end regions of the stator and assists in
reducing eddy current losses. A disadvantage of the cited version
of the so-called stair-like end stepping of the stator bore is, on
the one hand, from a manufacturing point of view, that a large
number of stator laminations with different bore diameters are
required. Furthermore, with the increasing diameter of the stator
bore, the overlap of the conductor bars of the stator is reduced.
In turn, however, the conductor bars are not provided for this
orientation of the magnetic field lines, and eddy currents which
locally cause high thermal load are induced in the conductor bars.
Particularly in the case of air-cooled generators and
further-increased power output densities, these eddy current losses
in the conductor bars may lead to undesirable or even inadmissible
local heating and to adverse effects on the efficiencies capable of
being achieved.
[0006] The invention is intended to remedy this. The object of the
invention, as defined in the claims, is, by means of a novel
geometry of the end region of the stator bore, to provide an
improvement in the magnetic flux, to reduce eddy currents, and,
consequently, lower local heating. The invention is suitable very
particularly advantageously for use under the special conditions of
the abovementioned air-cooled generators.
[0007] According to the invention, in an electric machine of the
type initially mentioned, the end region of the stator or the
stator bore is designed in axial profile with zones with a
different profile of the inside diameter of the stator bore. In
this case, a first zone of the stator bore has a constant clear
width. For a given rotor, this clear width is predetermined by a
radial air gap dimension between the rotor barrel and the laminated
stator core. Particularly with regard to the air-cooled generators
mentioned, which come within a power output range of up to, for
example, 500 MVA, this dimension is of the order of magnitude of a
mechanically necessary dimension which must be ensured for the
handling of the rotor within the stator bore, for example when the
rotor is being moved in and out. At the same time, this minimum
dimension must be ensured even in the region of the rotor retaining
rings which have a larger diameter than the rotor barrel. According
to the prior art, therefore, the stator bore is designed, as
mentioned above, with continuous stair-like stepping, along with
the problems, likewise mentioned there, of the losses induced by
radial magnetic fields in the conductor bars.
[0008] Too small a radial distance between the rotor retaining ring
and the laminated stator core not only causes problems with
mechanical handleability, but also an increase in the slot
harmonics induced in the rotor retaining ring.
[0009] The invention is intended to specify the configuration of
the stator bore end regions in such a way that, on the one hand, a
minimization of the eddy current losses in the stator conductor
bars is achieved, but, at the same time, it is also advantageous
with regard to the further aspects.
[0010] According to the invention, a second zone with a bore
diameter widening toward the end face of the stator is arranged
axially outside the first zone. There follows, in the axial region
of the rotor retaining ring, a third zone which, in turn, has a
substantially constant bore diameter which, however, is greater
than the bore diameter in the first zone. The bore diameter in the
third zone is dimensioned such that, at least where conductor
material is arranged, the conductor bars of the stator winding are,
at least for the most part, overlapped in the circumferential
direction by stator teeth. The diameter of the stator bore in the
third zone is dimensioned such that at no point in the third zone
is it substantially greater than an effective stator winding
diameter which is defined by a radially inner boundary of the
conductor material of the stator winding. As a result, the
conductor bars of the stator winding in the third zone are largely
shielded from radial magnetic fields which lead to losses in the
stator winding.
[0011] In a preferred variant of the invention, the diameter of the
stator bore in the third zone is designed in such a way that the
radial dimension between the rotor retaining ring and the stator in
the third zone does not appreciably exceed the air gap dimension in
the first zone of the stator. This, on the one hand, ensures, the
maximum overlap of the conductor bars; on the other hand, the
mechanical handleability of the rotor is restricted by the minimum
radial gap dimension present, and because of this an increase in
the radial gap dimension in the third zone above the air gap
dimension in the first zone is of no benefit. If, as stated above,
the radial air gap dimension in the first zone is already near the
minimum value necessary for handling reasons, the diameter of the
stator bore in the third zone will preferably have to be
dimensioned such that it exceeds the bore diameter in the first
zone by the same amount as that by which the diameter of the rotor
retaining rings exceeds the diameter of the rotor barrel.
[0012] A further design criterion for the diameters of the various
zones of the stator bore is a conductor exposure coefficient QD
which is defined as 1 Q D = D III - D I D eff - D I
[0013] In this, D.sub.III represents the diameter of the stator
bore at an axial position of the third zone, D.sub.I the diameter
of the stator bore in the axially inner first zone and D.sub.eff
the above-defined effective stator winding diameter. The conductor
exposure coefficient Q.sub.D is therefore to be interpreted as the
increase in diameter of the stator bore from the first zone to an
axial position of the third zone, in relation to the overlap of the
conductor bars in the first zone of the stator. According to the
invention, this conductor exposure coefficient is selected higher
than 0.5 and lower than 1.1, preferably in the range between 0.9
and 1.05. A selection of the conductor exposure coefficient near 1
is to be preferred, particularly in the case of very confined
conditions of space, since this value ensures, on the one hand, a
large radial gap and, on the other hand, a good overlap of the
conductor bars.
[0014] As compared with the prior art having the continuous
widening of the diameter of the stator bore, the design according
to the invention of the end region of the stator bore affords the
further advantage that a smaller number of differently manufactured
stator lamination variants is required.
[0015] Furthermore, in a preferred embodiment of the invention, a
fourth zone with a conical diameter profile widening toward the end
face terminates the laminated stator core axially. In further
conjunction with an aluminum press plate, this results in an
advantageous configuration of the laminated core in terms of
magnetic field lines running axially.
[0016] Further preferred and advantageous embodiments may be
gathered from the subclaims.
[0017] The invention is explained in more detail below with
reference to an exemplary embodiment illustrated in the drawing, in
which in particular:
[0018] FIG. 1 shows an electric machine with a stator bore, the end
regions of which are designed according to the prior art;
[0019] FIG. 2 shows an electric machine, in which the end regions
of the stator bore are designed according to the invention;
[0020] FIG. 3 shows a cross section of the stator of the machine
illustrated in FIG. 2; and
[0021] FIG. 4 shows an illustration of a detail of the machine from
FIG. 2, in which the essential features of the invention are
clearly emphasized.
[0022] The drawing and the following statements are to be
understood instructively and are intended to ensure that the idea
of the invention is thoroughly understood. By contrast, these
exemplary embodiments are not intended to be used to restrict the
invention which is defined solely in the claims and which discloses
to the person skilled in the relevant art a markedly wider range of
embodiments than can be illustrated within this framework.
[0023] A prior art is first illustrated in FIG. 1, so that the
essential features of the invention and their advantageous effect
become open to fully comprehensive assessment. An electric machine,
a generator in the example, consists of a rotor 10 and of a stator
20. The stator consists of a number of laminations 201, 202, 203,
204, 205, . . . , 20xx, . . . which are joined to one another in
the axial direction and are insulated from one another. As a
result, only comparatively low eddy current intensities are
generated in the stator. The stator laminations are held together
nonpositively, in a way known per se, by means of press plates
arranged in end regions of the stator. In this exemplary
embodiment, aluminum press plates 24 are arranged on the end face,
which are drawn together in the axial direction, for example, by
means of ties, not illustrated here, and act on the stator
laminations via press fingers 25 consisting of nonferromagnetic
material. This form of construction is known for air-cooled
generators from ABB Technik 1/96, page 20 ff; further embodiments
of the press plates are, of course, familiar to a person skilled in
the art. A stator bore 23, into which the rotor 10 is inserted, is
located centrally in the stator 20. The rotor forms, with the
stator, an air gap 22 having the radial air gap dimension S.sub.I.
The operating behavior of an electric machine can be influenced by
means of the radial air gap dimension. On the other hand, the
mechanical handleability of the rotor when it is being installed
and removed requires a specific minimum dimension of the radial air
gap which must be ensured. Slots, which cannot be seen here, but
are familiar to a person skilled in the art, and are also discussed
below, and which run in a main axial direction and in which
conductor bars 21 of the stator winding are inserted, are
introduced in the stator 20. The conductor bars are Roebel bars
readily familiar to a person skilled in the art. These conductor
bars are overlapped in the tangential direction by stator teeth
which, in particular, keep radially running magnetic fields away
from the conductor bars; this is likewise not explained in this
way, but is familiar to a person skilled in the art. An explicit
illustration is therefore dispensed with at this juncture. The
geometry of the conductor bars is optimized in terms of magnetic
fields running in the circumferential direction. The rotor 10
itself consists of a rotor barrel 11 which constitutes the actual
active part of the rotor and which carries the rotor windings. On
the end faces, rotor retaining rings 12, the outside diameter of
which is greater than that of the rotor barrel, cover the rotor
barrel. The task of the rotor retaining rings is, inter alia, to
fix the end regions of the rotor winding. The rotor retaining rings
are placed axially onto the ends of the rotor barrel. The rotor
magnetic field decreases rapidly away from there in the axial
direction. The shaft journals 13 of the rotor carry, in a way known
per se, bearing points and drive flanges which are not illustrated
in the figure. In end regions, the stator bore widens toward the
respective end face of the generator. This is necessary in order to
maintain the minimum radial dimension of the air gap, even in the
region of the rotor retaining rings, without increasing the air gap
dimension sI inside the generator. In the widening of the stator
bore, it is necessary to take into account the fact that this
necessitates a radial stepping of the stator laminations, this
being illustrated in the enlarged detail in the figure. Due to this
radial stepping, axial magnetic fields may generate eddy currents
in the laminations, specifically the higher, the larger the radial
step is. This is, of course, the more critical, the higher the
magnetic field intensities are, that is to say the nearer a step is
arranged to the inside of the generator. In the embodiments known
from practice, a linear stair-like stepping of the stator
laminations is selected. The embodiment which is specified in SU
1185498 has a stepping which is progressive toward the end face. As
a result, the tangential overlap of the conductor bars 21 by the
teeth of the stator laminations is reduced even near the active
part and even also in the axial region of the rotor barrel 11, that
is to say in the active part of the electric machine. The conductor
bars are consequently exposed to high radial magnetic fields for
which they are not designed. High eddy currents are thereby induced
in the conductor bars in the axial end regions of the stator
winding. This can be controlled perfectly well, for example in the
case of directly water-cooled windings, since, by virtue of the
water cooling, the thermal leakage power occurring is discharged
efficiently from the conductor bars. By contrast, in generators
utilizing the indirect air cooling of the windings which is very
simple per se to implement and is cost-effective, sharp local
temperature rises may occur at the relevant points of the conductor
bars, while it is scarcely possible per se to implement
appropriately an intensification of the cooling.
[0024] FIG. 2 shows an electric machine designed according to the
invention. The machine is basically constructed in a completely
similar way to the machine shown in FIG. 1. The stator 20 similarly
consists of stator laminations 20xx which are joined to one another
axially and are held together by press plates 24 and press fingers
25. A rotor constructed completely identically to that of FIG. 1 is
inserted into a central stator bore 23. Differences are found in
the configuration of the stator bore. The stator bore is divided
into four zones toward each end face of the stator. An axially
inner first zone I has a constant bore diameter DI. This
corresponds to the nominal diameter of the stator bore. This is
followed by a second zone II with a bore diameter D.sub.II
increasing axially toward the end face of the generator, in which
second zone the diameter of the stator bore increases toward the
zone III with the bore diameter D.sub.III. The opening angle is, in
this case, limited primarily by the requirement of limiting the
radial steps of the stator laminations, since axially running
magnetic fields otherwise induce high eddy currents in the stator
laminations. However, the inside diameter profile follows the
conventional contour line 30 only until the necessary radial air
gap dimension between the stator and a rotor retaining ring 12 is
ensured. The bore diameter in the zone III is at least
approximately constant, that is to say the stator bore in the zone
III is at least approximately cylindrical.
[0025] The criteria for dimensioning the diameter D.sub.III which
are relevant to the invention are understood better by including
FIG. 3 which illustrates a cross section of the stator of the
machine from FIG. 2. The abovementioned stator slots 26 which run
essentially axially can be seen in this figure. The stator slots 26
are delimited in the circumferential direction by stator teeth 27.
The heads of the stator teeth define the stator bore 23 of the
stator 20. Arranged in the stator slots 26, between the stator
teeth 27, are conductor bars 21 of the stator winding which are
designed as Roebel bars readily familiar to a person skilled in the
art and which are fixed in the slots by means of slot closing
wedges 28 and wedge shims 29. The conductor bars 21 are arranged
within the stator slots in such a way that a coolant, for example
air, is capable of flowing around them. The conductor bars 21
consist of a conductor material 211, for example copper, which is
surrounded by an insulation 212. In this case, a radially inner
boundary of the insulation defines a mechanical stator winding
diameter D.sub.M and a radially inner boundary of the conductor
material defines an effective stator winding diameter D.sub.eff.
The inside diameter D.sub.I of the stator bore in the first zone is
smaller than the mechanical stator winding diameter, thus resulting
in a complete overlap of the conductor bars by the stator teeth in
the circumferential direction. In this case, the diameter of the
stator bore in the axially inner zone I is dimensioned such that a
radial air gap dimension s.sub.I is established between the
laminated stator core and the rotor barrel 11 illustrated only in
longitudinal section in FIG. 2, as indicated in FIG. 2. In the
third zone III, the radial dimension s.sub.III is established
between a rotor retaining ring 12 and the laminated core and must
be greater than or at least equal to a minimum dimension necessary
for reasons of mechanical handleability. This condition is,
admittedly, also fulfilled in a version corresponding to the prior
art illustrated in FIG. 1; however, according to the prior art, the
diameter of the stator bore also follows the general contour line
30 in the third zone. Consequently, the diameter D.sub.III of the
stator bore in the third zone increases rapidly essentially over
the effective winding diameter. Conductor bars are exposed, and,
because of radial magnetic fields which are even higher at the
boundary of the active region, eddy current losses are generated in
the conductor bars. In the present invention, the conductor bars,
at least their conductor material, are overlapped completely or at
least for the most part by stator teeth in the zone III and are
thus shielded effectively from radial magnetic fields acting upon
them. The detailed dimensioning of the diameter D.sub.III in the
design according to the invention of the end regions of a stator
bore depends to a great extent on the particular geometry of a
generator. A preferred possibility, precisely when conditions of
space are confined, for, on the one hand, ensuring the overlap of
the conductor bars, but, on the other hand, ensuring the radial
distance between the rotor retaining ring and the stator in the
zone III, is illustrated in the exemplary embodiment. It can be
seen in FIG. 3 that the bore diameter D.sub.III in the zone III is
selected such that it corresponds essentially to the effective
stator winding diameter, and, if anything, is selected somewhat
smaller than this. In the machine illustrated here, the bore
diameter D.sub.III of the third zone is between the effective
stator winding diameter D.sub.eff and the mechanical stator winding
diameter D.sub.M. It is, in this case, essential to the invention
primarily that, in contrast to the prior art illustrated in FIG. 1,
the smallest bore diameter necessary for ensuring mechanical
handleability can be selected in the region of the rotor retaining
ring in the entire third zone, that is to say, therefore, in the
region which surrounds the rotor retaining ring and is directly
adjacent to the active part, thus resulting in an overlap of the
conductor bars which is increased, as compared with the prior art,
and consequently in low eddy current losses.
[0026] In the exemplary embodiment in FIG. 2, the zone III is
followed axially toward the end face of the stator by a fourth zone
IV. In the fourth zone, the diameter D.sub.IV of the stator bore
increases again toward the end face of the stator. This, in
conjunction with the aluminum press plates 24 and the press fingers
25, ensures a favorable termination of the stator with respect to
axially running magnetic fields.
[0027] FIG. 4 illustrates, enlarged, the stator bore end region,
designed according to the invention, from FIG. 2. The stator 20
consists of individual stator laminations 20xx joined to one
another in the axial direction. Conductor bars 21 of the stator
winding are arranged within stator slots which cannot be seen in
this view and are not illustrated. In the middle of the electric
machine, in the first zone I having the diameter D.sub.I, there is
a radial dimension s.sub.I between the rotor barrel 11 and the
stator 20. In an axial end region, the central stator bore, in
which the rotor is installed, must have an increasing diameter, in
order to ensure a necessary minimum dimension of the air gap, even
in the region of a rotor retaining ring 12, the outside diameter of
which is greater than the outside diameter of the rotor barrel 11.
In the figure, a contour line 30 is depicted, which follows the
contour of the stator bore according to the prior art. As can be
seen, in the case of this contour, the conductor bars 21 of the
stator winding would be exposed in the region of the ring seat and
be open to high radial magnetic fields, with the consequences which
were discussed above and which are undesirable per se. According to
the invention, the stator bore is divided in an end region into a
plurality of zones I, II, III, IV with a different diameter
profile. At the same time, in each case, a zone I, III having an at
least approximately constant inside diameter D.sub.I, D.sub.III of
the stator bore alternates with a zone II, IV having a bore
diameter D.sub.II D.sub.IV increasing more sharply toward the end
face. A first zone I has a constant inside diameter D.sub.I. This
is followed by a zone II, in which the diameter D.sub.II of the
stator bore increases. In this region, the bore is conically
configured in the example, and its contour follows essentially the
general contour line 30. The general conical profile is produced by
stator laminations with a larger inside diameter being joined to
one another toward the end face. This gives rise to a stair-like
contour in detail; a stair-like end stepping of a stator bore of an
electric machine is also referred to in this connection. According
to the invention, the stair-like stepping of the zone II is not
continued in this way as far as the end face of the stator, but
only until the bore diameter of the stator bore is large enough, in
a region located axially further toward the end face, to ensure a
necessary minimum radial dimension of the air gap, even in the
region of the rotor retaining ring 12. Consequently, the zone II,
which has a conical profile of the stator bore, is followed axially
toward the end face by a zone III, in which the diameter D.sub.III
of the stator bore is essentially constant and in which the stator
bore has an at least approximately cylindrical contour. In this
zone, according to the invention, the conductor bars of the stator
winding are still overlapped completely or at least for the most
part by stator teeth, with the result that the conductor bars are
effectively shielded from radial magnetic fields. In the example
illustrated here, the diameter D.sub.III of the stator bore of the
zone III is between the mechanical stator winding diameter D.sub.M
defined by the insulation 212 of a conductor bar 21 and the
effective stator winding diameter defined by the conductor material
211 of the conductor bar. This results, in the exemplary
embodiment, in a complete overlap of at least the conductor
material 211 of the stator winding 21 by stator teeth, as discussed
in connection with FIG. 3. As already described above, eddy
currents and undesirable local heatings of the stator winding which
result from these are thereby avoided. Finally, the zone III is
followed by a zone IV which terminates the stator on the end face
and in which the bore diameter increases again. This terminating
stair-like stepping avoids individual stator laminations being
subjected to high axial magnetic fields. In the zone IV, the
overlap of the conductor bars by the stator teeth decreases
rapidly. However, the zone IV is short, so that heatings occurring
locally can easily be discharged by axial heat conduction. A press
finger 25 can be seen axially on the far outside of the stator; the
press plate 24 is not illustrated in this figure.
[0028] Furthermore, the design according to the invention of the
end regions of stator bores of electric machines also affords a
series of other advantages. Thus, in the design according to the
invention, the number of different variants of stator laminations
is markedly smaller than in the case of a design according to the
prior art illustrated in FIG. 1. It also proves advantageous,
depending on the design of the cooling, that, in the design
according to the invention, as illustrated in FIGS. 2 to 4, an
aperture for cooling air is formed between the stator and the rotor
retaining ring in the region of the zone III.
[0029] In light of the above explanations of the invention,
together with the exemplary embodiments and with the primary
objects of the invention, further advantageous effects and
particular embodiments, not illustrated in the example, of the
invention defined in the claims will become readily evident to a
person skilled in the art.
LIST OF REFERENCE SYMBOLS
[0030] 10 Rotor
[0031] 11 Rotor barrel
[0032] 12 Rotor retaining ring
[0033] 13 Shaft journal
[0034] 20 Stator
[0035] 21 Conductor bar (Roebel bar) of a stator winding
[0036] 22 Air gap
[0037] 23 Stator bore
[0038] 24 Press plate
[0039] 25 Press finger
[0040] 26 Stator slot
[0041] 27 Stator tooth
[0042] 28 Slot closing wedge
[0043] 29 Wedge shim
[0044] 30 General contour line
[0045] 201 Stator lamination
[0046] 202 Stator lamination
[0047] 203 Stator lamination
[0048] 204 Stator lamination
[0049] 205 Stator lamination
[0050] 20xx Stator lamination
[0051] 211 Conductor material of the stator winding
[0052] 212 Insulation of the stator winding
[0053] I First zone of the stator bore
[0054] II Second zone of the stator bore
[0055] III Third zone of the stator bore
[0056] IV Fourth zone of the stator bore
[0057] s.sub.I Radial air gap dimension in the active part of the
generator
[0058] s.sub.II Radial gap dimension between the rotor retaining
ring and the stator
[0059] D.sub.I Diameter of the stator bore in the middle part of
the stator
[0060] D.sub.III Diameter of the stator bore in the region of the
rotor retaining ring
[0061] D.sub.eff Effective stator winding diameter
[0062] D.sub.M Mechanical stator winding diameter
[0063] Q.sub.D Conductor exposure coefficient
* * * * *