U.S. patent application number 09/444677 was filed with the patent office on 2001-08-16 for adjustable generator stator slot wedge system.
Invention is credited to BLAKELOCK, THOMAS RICHARD, BUTMAN, THOMAS RUFUS JR., IVERSEN, ALAN MICHAEL.
Application Number | 20010013736 09/444677 |
Document ID | / |
Family ID | 23765903 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013736 |
Kind Code |
A1 |
BLAKELOCK, THOMAS RICHARD ;
et al. |
August 16, 2001 |
ADJUSTABLE GENERATOR STATOR SLOT WEDGE SYSTEM
Abstract
A generator stator includes a magnetic core having a plurality
of axially extending radial slots arranged about the periphery
thereof with stator windings in each radial slot. At least one
adjustable assembly is located in an axially outermost end of each
radial slot, arranged to apply radial force to the windings in the
radial slot, the adjustable assembly including mating wedge and
slide components which interface along stepped matching surfaces
which lie at an acute angle to a center axis of the magnetic core.
The assembly is adjustable in situ to compensate for decreases in
radial pressure with time while stepped contacting surfaces of the
wedge and slide prevent axial regression of the slide.
Inventors: |
BLAKELOCK, THOMAS RICHARD;
(CLIFTON PARK, NY) ; BUTMAN, THOMAS RUFUS JR.;
(DELMAR, NY) ; IVERSEN, ALAN MICHAEL; (CLIFTON
PARK, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
GE POWER SYSTEMS, PATENT OPERATION
1 RIVER ROAD
BUILDING 37, 5TH FLOOR
SCHENECTADY
NY
12345
US
|
Family ID: |
23765903 |
Appl. No.: |
09/444677 |
Filed: |
November 22, 1999 |
Current U.S.
Class: |
310/214 |
Current CPC
Class: |
H02K 3/487 20130101 |
Class at
Publication: |
310/214 |
International
Class: |
H02K 003/48 |
Claims
What is claimed is:
1. A generator stator including a magnetic core having a plurality
of axially extending radial slots arranged about the periphery
thereof with windings in each radial slot; at least one adjustable
assembly in an axially outermost end of each radial slot, arranged
to restrain said windings in said radial slot, said adjustable
assembly comprising mating wedge and slide components which
interface along stepped matching surfaces which lie at an acute
angle to a center axis of the magnetic core, said wedge component
slidably received in a pair of dovetail grooves in said radial
slot.
2. The generator stator of claim 1 wherein, relative to a bottom of
said radial slot, said wedge component lies radially outwardly of
said slide component and wherein said wedge component and said
radial slot have mating surfaces which prevent radial outward
movement of said wedge component, and wherein said slide component
is axially driveable into a first position between said stator
winding and said wedge component.
3. The generator stator of claim 2 wherein upon loosening of said
stator windings, said slide component is axially driveable into a
second position beyond said first position.
4. The generator stator of claim 1 wherein a second adjustable
assembly is located axially inboard of said at least one adjustable
assembly.
5. The generator stator of claim 4 wherein a dowel extends
substantially axially through said wedge component of said one
adjustable assembly into engagement with a slide component of said
second adjustable assembly.
6. The generator stator of claim 1 wherein said wedge component is
fitted with non-abrasive pads along surfaces of said wedge
component received in said dovetail groove.
7. The generator stator of claim 1 wherein the stepped surfaces of
said wedge and slide components are formed as discrete parts.
8. A generator stator including a magnetic core having a plurality
of axially extending radial slots arranged about the periphery
thereof with stator windings in each radial slot; at least one
adjustable assembly in an axially outermost end of each radial
slot, arranged to restrain said windings in said radial slot, said
adjustable assembly comprising mating wedge and slide components
which interface along stepped matching surfaces which lie at an
acute angle to a center axis of the magnetic core, wherein said
wedge component comprises a pair of bonded laminates including a
first component having a stepped surface and a second component
having a dovetail adapted to be slidably received in mating
dovetail grooves formed in said radial slot.
9. The generator stator of claim 8 wherein, relative to a bottom of
said radial slot, said wedge component lies radially outwardly of
said slide component and wherein said slide component is axially
driveable into a first position between said stator bar and said
wedge component.
10. The generator stator of claim 9 wherein upon loosening of said
stator windings, said slide component is axially driveable into a
second position beyond said first position.
11. The generator stator of claim 10 wherein a second adjustable
assembly is located axially inboard of said at least one adjustable
assembly.
12. The generator stator of claim 11 wherein a dowel extends
substantially axially through said wedge component of said first
adjustable assembly into engagement with a slide component of said
second adjustable assembly.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to generator stators and, more
specifically, to a wedge and slide system used at the ends of the
stator core. The wedge and slide system is adjustable to permit in
situ radial correction for radial pressure and dimension losses
which occur over time.
[0002] Electric utility companies require large turbine-generators
to operate reliably for long periods of time, for example, thirty
years or more. Normal, steady-state electromagnetic forces acting
on the armature winding are capable of causing armature bar
vibration within a much shorter period than the expected generator
lifetime. Armature bar vibration can occur if radial clearances are
present within the stator core slot. Bar vibration can result in
armature bar insulation abrasion. The abrasion can become severe if
maintenance actions are not taken to retighten the slot support
system and arrest the vibration. Typically, a prolonged maintenance
outage is required to retighten the slot support system and
eliminate radial clearances within the slot.
[0003] The electrical windings at opposite axial ends of the stator
core slots may be particularly susceptible to accelerated abrasion
due to: 1) preexisting or rapidly-evolving radial clearances, 2)
the effects of excessive or continuous oil contamination, 3) the
effects of end winding electromagnetic forces, and 4)
abnormally-high electromagnetic design forces on the slot portion
of the winding. It is therefore important to provide an in situ
means for eliminating radial clearances that develop in this
location in order to prevent unscheduled or prolonged service
outages.
[0004] In an attempt to address these problems, a stepped wedge and
slide arrangement is proposed in U.S. Pat. No. 4,149,101 but for
the purpose of preventing axial displacement of wedges within the
core slot. A stepped bracing arrangement is proposed in U.S. Pat.
No. 3,842,303 but in the context of an end winding support fit-up
device between the coil end arms.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention seeks to provide a stepped dovetail
wedge and slide system which permits re-tightening of generator
stator end-of-slot wedges (or simply, end wedges), restoring the
required radial force on the winding bars in a location where
loosening is most likely to occur. Significantly, the re-tightening
process can be carried out without removal or replacement of parts,
and without removal of the generator field. The invention also
increases the long-term durability and reliability of the end
wedges by making design and materials improvements, and hence
contributes to a decrease in the frequency of generator inspection
outages.
[0006] Accordingly, the present invention relates to a dovetail
wedge and slide combination that can be used at the ends of the
stator core, and that has matching inclined surfaces that are
stepped to permit in situ radial correction for any radial pressure
and dimension losses which occur over time, and to prevent axial
regression of the slide after adjustment. The invention is
preferably applied to large turbine generator stators that have
relatively high electromagnetic forces during normal operation and,
in some cases, have exhibited the development of radial clearance
in the windings at the ends of the core and subsequent end wedge
loosening.
[0007] More specifically, the invention provides an adjustable
version of a restraining device commonly referred to as a "stator
slot wedge" that has the primary purpose of supplying a radial
force to the armature winding (stator bars) to prevent it from
vibrating under the influence of electromagnetic forces experienced
continuously during normal operation, and which can become much
more severe under conditions caused by misoperation or system
faults. There are several features which, in combination, yield a
unique support device, the main feature of which is adjustable
tightening of the wedges in place, while also increasing the radial
force on the stator bar.
[0008] In accordance with one embodiment of the invention, matching
stepped contact planes are machined on the sloped surfaces of the
slide and dovetail wedge components. In the initially installed
condition, the slide is driven tight to provide the required radial
force on the bars, but with the capacity to be driven an additional
distance in the axial direction, as needed at later dates, to
eliminate radial clearances and to restore radial wedge force.
[0009] In the preferred arrangement, the stepped surface is
machined on the sloped side of a slide component, made from a high
strength laminate. The wedge is formed by laminating a slide
component to a flat slidable dovetail piece made from a
non-abrasive laminate. The non-abrasive portion of the wedge is the
only part of the wedge-slide system in contact with the iron thus
eliminating core wear.
[0010] In another variation, the wedge component can be composed of
a high strength laminate, which may be abrasive, but to which
non-abrasive strips or pads have been bonded on any surface in
contact with the core.
[0011] A further enhancement of the invention is achieved by
designing the end wedge to incorporate a device which can be used
to tighten the next axially inboard wedge. This involves drilling
through the end wedge in an axial direction to allow insertion of a
movable part such as a hard, non-metallic dowel which can be
positioned to contact the outboard end of the next adjacent slide.
The outboard end of the dowel can then be driven inwardly if needed
at the same time the end slide is adjusted. The thickness of the
end wedge may be increased if necessary to accommodate the dowel
pin without sacrificing radial strength. The sloped surfaces of the
next adjacent inboard wedge and slide are also stepped (as in the
case of the end wedge and slide) to permit adjustable tightening
and to prevent axial regression of the slide after adjustment. This
arrangement allows radial load adjustment over a greater axial
length and compensates for any loosening of the inboard wedge
caused by re-tightening the end wedge.
[0012] Accordingly, in its broader aspects, the present invention
relates to a generator stator including a magnetic core having a
plurality of axially extending radial slots arranged about the
periphery thereof with stator windings in each radial slot; at
least one adjustable assembly in an axially outermost end of each
radial slot, arranged to restrain the windings in the radial slot,
the adjustable assembly comprising mating wedge and slide
components which interface along stepped matching surfaces which
lie at an acute angle to a center axis of the magnetic core.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a partial end view of a stator core slot with
slide and wedge components in place, so as to supply radial forces
to the armature winding or stator bars;
[0014] FIG. 2A is partial side elevation of wedge and slide
components in their initially installed condition;
[0015] FIG. 2B is a view similar to FIG. 2A but with the slide and
wedge components in a loosened condition;
[0016] FIG. 2C is a section similar to FIGS. 2A and 2B but with the
slide component driven fully under the wedge component in order to
correct the loosened condition shown in FIG. 2B;
[0017] FIG. 3 is a perspective view of a slide component which
illustrates the manner in which the stepped surface can be machined
or molded into a discrete part;
[0018] FIG. 4 is a bottom plan view of a composite laminate wedge
component with a non-abrasive flat dovetail bonded to a discrete
component having a machined or molded stepped surface in accordance
with the invention;
[0019] FIG. 5 is a side elevation of the composite wedge shown in
FIG. 4;
[0020] FIG. 6 is a perspective view of an alternative wedge
component in which the stepped surface can be machined or molded
into a wedge body fitted with longitudinally extending non-abrasive
pads;
[0021] FIG. 7 is a partial side elevation view illustrating an
alternative arrangement wherein a dowel is slidably engaged within
the outboard wedge for the purpose of tightening a next adjacent
inboard wedge; and
[0022] FIG. 8 is an end view of the arrangement shown in FIG.
7.
DETAILED DESCRIPTION OF THE INVENTION
[0023] Referring to FIG. 1, the stator core is partially shown at
10, it being understood that the core includes a plurality of
radial slots 12 which extend axially along the core and which
receive stator windings 14. Each slot 12 is formed adjacent its
mouth with dovetail grooves or undercuts 16, permitting wedge and
slide components 18, 20 to be inserted in an axial direction within
the slot.
[0024] For each radial slot, two sets of wedge and slide components
18, 20 are employed at opposite ends of the stator core. More
specifically, conventional wedges or components are inserted from
the axial center of the core outwardly in opposite directions. In
this regard, individual wedges are generally between about 4 and 7
inches in length, and the stator core may have a length of between
about 60 and 330 inches. The final two axially adjacent wedge
locations at respective opposite ends of the core are fitted with
the wedge and slide assemblies 18, 20 described in greater detail
below.
[0025] With reference also to FIG. 2A, the wedge 18 is formed with
a flat top surface 22 and an inclined lower surface 24 machined to
include a series of integral steps defined by vertical shoulders 26
which connect adjacent inclined surface portions 28, with the wedge
increasing in thickness in an "inward direction", i.e., in the
insertion direction toward the axial center of the core 10. Along
the axially extending sides of the upper portion of the wedge,
there are laterally extending dovetail projections 30 which mate
with the dovetail grooves 16 in the slot 12.
[0026] The slide component 20 has a flat bottom surface 32 and an
inclined upper surface 34 machined to include a series of steps
(i.e., 22 and 34 are stepped matching surfaces) defined by vertical
shoulders 36 which connect adjacent inclined ramp portions 38, with
the slide decreasing in thickness in the "inward" or insertion
direction. The slide 20 is preferably a high strength laminate. The
wedge and slide components 18, 20 thus interface along matching
stepped contact planes (the inclined surface portions 28 and 38 are
equal in length and have the same slope). Surface portions 28, 38
lie at an acute angle to the center axis of the core. It is
preferred that this angle lie in the range of from about 30 to
about 80. Between the winding 14 and the slide 20, there are one or
more axially extending filler strips 37, 39.
[0027] To facilitate the description of the invention, using the
bottom of the radial slot 12 as a reference, the wedge component 18
lies radially outwardly of the slide component 20.
[0028] During assembly, after the conventional interior wedges have
been inserted in the usual manner, the axially outer wedge and
slide components are inserted in the slot 12, with the wedge 18
inserted first, supported by the dovetail grooves 16. With the
filler strips 37, 39 located atop the winding 14, the slide 20 is
inserted axially as shown in FIG. 2A, i.e., radially between the
wedge 18 and the windings 14. As shown there, the slide 20 is
driven tight in the axial direction to provide the required radial
force on the winding bars, but with the capability to be driven
axially an additional distance L, as needed at later dates, to
eliminate radial clearances and to restore radial wedge force.
[0029] In FIG. 2B, the slide and wedge assembly is shown in a
loosened condition where radial clearances have developed in the
slot as a result of bar and wedge shrinkage and compaction over
time. Of course, the stepped configuration between the slide and
wedge prevents the slide from "backing out" of the slot even though
radial clearances have developed.
[0030] FIG. 2C illustrates a corrected and tightened condition
where the slide 20 can be driven axially further into the slot up
to the distance L, until the forward and rearward ends of the wedge
and slide lie flush with one another. It will be understood that
the depiction in FIGS. 2A-2C is schematic in nature and does not
reflect the exact step size, slope, or axial travel.
[0031] FIG. 3 illustrates the slide component 20 as also shown in
FIGS. 2A, B and C, and the manner in which the upper surface 34 is
machined or otherwise formed to include integral shoulders 36 and
inclined ramp surfaces 38.
[0032] FIG. 4 shows an alternative and presently preferred
embodiment for the wedge and slide components, although only the
wedge component is shown in FIGS. 4 and 5. The wedge component 40
comprises discrete bonded laminate portions including a stepped
wedge part 42 and a flat part 44 bonded thereto. Note that FIG. 4
illustrates the wedge component viewed from below and FIG. 5 shows
the wedge component inverted relative to its installation
orientation as shown in FIGS. 1 and 2A-2C. The flat part 44
includes laterally extending dovetail portions 48 with a pair of
notches or cut-outs 46 on each side thereof. These notches are
intended to align with ventilation ducts but are otherwise not
significant to this invention.
[0033] Turning to FIG. 6, a wedge component 50 is shown which is
generally similar to that shown in FIG. 1 but with the addition of
nonabrasive pads 52 on the dovetail portion of the wedge. The
non-abrasive pads can be made from a laminated material such as
which minimizes stator core wear but permits the main body of the
wedge to be constructed of a higher strength and possibly abrasive
material.
[0034] In still another embodiment, as illustrated in FIGS. 7 and
8, the outside or end wedge/slide assembly 54 can be used to
tighten the next inboard wedge/slide assembly 56. This can be done,
for example, by drilling through the end wedge 58 to provide a bore
60 generally parallel to the top surface, and at a location which
insures that the bore lie adjacent the next inboard slide member
62. A hard non-metallic dowel 64 can then be positioned within the
bore 60 so as to contact the trailing edge of the adjacent slide
62. The outboard end of the dowel 64 can be driven axially inwardly
(for example, at the same time that the end slide 66 is adjusted)
as described above. If necessary, the thickness of the end wedge 58
can be increased to accommodate the utilization of the dowel 64
without sacrificing radial strength. Moreover, the sloped surfaces
of the next adjacent inboard wedge and slide assembly 54 are also
stepped to permit adjustable tightening and to prevent axial
regression of the slide. This arrangement allows radial load
adjustment over a greater axial length and compensates for any
loosening of the inner wedge caused by increasing the load on the
end wedges.
[0035] As will be appreciated by those of ordinary skill in the
art, the utilization of a permanently installed dowel 64 could be
eliminated in favor of simply providing the bore 60 and then
employing an appropriate rod-like tool whenever necessary.
[0036] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *