U.S. patent application number 09/882176 was filed with the patent office on 2002-04-25 for high voltage generator stator with radially inserted cable windings and assembly method.
This patent application is currently assigned to General Electric Company. Invention is credited to Kliman, Gerald B., Shah, Manoj R..
Application Number | 20020047458 09/882176 |
Document ID | / |
Family ID | 23816904 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047458 |
Kind Code |
A1 |
Kliman, Gerald B. ; et
al. |
April 25, 2002 |
HIGH VOLTAGE GENERATOR STATOR WITH RADIALLY INSERTED CABLE WINDINGS
AND ASSEMBLY METHOD
Abstract
A stator for a high voltage generator has cable windings that
are radially inserted into the stator slots. The stator is
assembled as the cable windings are laid into the stator slots. The
stator slots are left wide open to allow the cable windings and
separator bars to be inserted in the slot as the stator is
assembled. The open slots have sidewalls that are defined by stator
teeth, which extend radially out from a rotor jig in the stator. As
each coil section is laid in a slot, a separator bar is inserted
over the coil so that another coil section can be laid into the
stator. The coils are stacked in a slot and sandwiched between
separator bars also in the slot. The separator bar is keyed to the
sidewalls of the teeth to provide structural support for the cable
windings.
Inventors: |
Kliman, Gerald B.;
(Niskayuna, NY) ; Shah, Manoj R.; (Latham,
NY) |
Correspondence
Address: |
NIXON & VANDERHYE P.C.
1100 North Glebe Road, 8th Floor
Arlington
VA
22201-4714
US
|
Assignee: |
General Electric Company
|
Family ID: |
23816904 |
Appl. No.: |
09/882176 |
Filed: |
June 18, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09882176 |
Jun 18, 2001 |
|
|
|
09457480 |
Dec 9, 1999 |
|
|
|
Current U.S.
Class: |
310/215 ;
310/214; 310/254.1; 310/60A |
Current CPC
Class: |
H02K 2203/15 20130101;
H02K 3/48 20130101; Y10T 29/49073 20150115; H02K 15/085 20130101;
Y10T 29/49009 20150115 |
Class at
Publication: |
310/215 ;
310/214; 310/60.00A; 310/218 |
International
Class: |
H02K 003/48; H02K
003/34; H02K 001/18 |
Claims
What is claimed is:
1. A stator for a dynamo electrical machine comprising: a circular
array of stator teeth extending radially outward from a rotor
opening, and stator slots defined between opposite sidewalls of
said stator teeth; separator bars in said slots and extending
longitudinally along said stator, said separator bars engaged with
the opposite sidewalls of the teeth, wherein a plurality of stator
bars are stacked in a stator slot, and cable windings seated
between adjacent stator bars in the stator slots.
2. A machine as in claim 1 further comprising an intra-cable space
between said cable and at least one of said opposite sidewalls.
3. A machine as in claim 2 wherein the inter-cable space is a
cooling fluid conduit.
4. A machine as in claim 2 wherein said separator bars comprise
insulating plastic.
5. A machine as in claim 2 wherein said separator bars comprise a
magnetic material, and include a gap extending axially through each
bar.
6. A machine as in claim 5 wherein said separator bars comprise a
powdered metal.
7. A machine as in claim 1 wherein said separator bars have
longitudinal channels on an upper or lower surface to seat said
cable windings.
8. A machine as in claim 1 wherein said separator bars have edges
with a key segment that slidably engage opposite key segments in
opposite sidewalls of the teeth.
9. A machine as in claim 1 wherein said teeth have upper edges
having a top key segment that slidably engage opposite yoke key
segments in said yoke.
10. A machine as in claim 1 wherein the cable windings have an
insulation sheath that gradually increases in thickness, and the
cable windings in the stator slot and near the rotor opening have a
insulation sheath that is thinner that the cable windings near an
opposite end of the slot.
11. A machine as in claim 1 having a yoke slidably mounted on said
teeth.
12. A machine as in claim 1 having a yoke formed of azimuthly
oriented silicon steel.
13. A machine as in claim 12 wherein said teeth are formed of
radially oriented silicon steel.
14. A method of forming a stator in a dynamo electrical machine
comprising the steps of: a. arranging a cylindrical jig that has an
outside diameter corresponding to an inside diameter of a rotor
opening of the stator; b. mounting inner edges of stator teeth on
the jig to form a circular array of teeth, where the teeth extend
radially out from the jig; c. sliding a first separator bar into an
axial end of a stator slot defined between adjacent stator teeth,
where the separator bar has a lower surface adjacent the jig and an
upper surface; d. seating a cable winding on the upper surface of
the first separator bar by inserting the cable winding radially
into the stator slot; e. sliding a second separator bar axially
into the stator slot and over the seated cable winding, where the
second separator bar has a lower surface seating on the already
seated cable winding, and has an upper surface to seat another
cable winding; f. repeating steps (d) and (e) until a sequence of
separator bars and cable windings are stacked in the stator
slot.
15. A method of forming a stator as in claim 14 further comprising
the step of (g) sliding an annular yoke over the outer peripheries
of the teeth and slots.
16. A method of forming a stator as in claim 14 wherein the step of
inserting separator bars includes sliding in an axial direction of
the stator a key segment of the bar into a matching key segment of
the sidewalls of the teeth.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to high voltage generators and other
dynamoelectric machines having stators with cable windings.
[0002] High voltage generators produce electric power at
transmission line levels, which are generally between 45 kilovolts
(kV) to 750 kV. These generators can connect directly to
transmission lines. They avoid the need for step-up transformers
that are required for generators that produce only lower voltage
levels. High voltage generators use windings formed of round
conductive cables instead of the winding bars typically used in
lower voltage generators. These round cables are able to support
the high voltages and carry the currents produced by high voltage
generators.
[0003] The round cables used as windings in high voltage generators
are insulated with a thick sheath formed of a cross-linked
polyethylene or similar insulating material. The sheath protects
and insulates the conductor core of the cable. In addition, the
cables typically have semiconductor layers on the conductor core
and on the outer sheath surface of the cable. These semiconductor
layers maintain uniform voltage stresses across the core and sheath
surface of the cable winding. The cables, especially their
insulation and semiconductor layers, are fragile and should be
handled carefully as the cables are inserted into the stator during
assembly of the generator.
[0004] The stators are large cylinders that encircle the rotor of a
generator. The rotor is coaxial to the stator, and the stator has a
cylindrical aperture to receive the rotor. The stators have radial
slots that extend from the rotor aperture outward into the stator.
The cable windings are mounted in the stator slots. The slots
extend from one end of the stator to the other and along the length
of the rotor. The slots form a circular array around the rotor. The
cable windings loop back and forth through the slots to form
electrical paths surrounding the rotor. In addition, the stator
sections between these slots are typically referred to as the teeth
of the stator.
[0005] Each turn of the cable must be separately and mechanically
supported in the slot. The cable cannot withstand the compressive
forces of a stack of cable loops in a stator slot. If the cable is
stacked in a slot without supports (such as the support provided by
bicycle chain type slot), the cable at the bottom of the slot would
suffer a broken or crushed insulation sheath due to electromagnetic
forces in the slot.
[0006] An example of a stator slot layout is disclosed in commonly
assigned U.S. Pat. No. 3,014,139, (the '139 Patent) entitled
"Direct-Cooled Cable Winding For Electromagnetic Device". The
bicycle chain slots of the stator shown in the '139 Patent support
the cable in the stator, transfer heat generated by electrical
current out of the cables, and protect the cables from mechanical
stresses that might damage the cable. The slot shape of the stator
has the cross-section appearance of the outline of a "bicycle
chain" and is designed to support each loop of the cable in the
stator slot without excessively compressing the insulation sheath
of the cable.
[0007] During assembly, the cables used as windings in high voltage
generators have traditionally been threaded through the stators by
inserting the cable into one end of the stator and drawing the
cable through to the other end of the stator. As it is threaded
through a stator slot, the cable extends out of an end of the
stator, is looped back towards that stator end, is inserted into
another stator slot, and drawn through that other slot. The
threading of the winding cable back and forth through the stator
continues as the cable is inserted into the stator slots. When
inserted in the slots, the cable forms the windings for the stator
of the generator.
[0008] A problem exists in threading cable windings through the
stator slots. Conventionally, the cables are inserted at one end of
a stator and drawn through a stator slot along the entire axial
length of the stator until the cable is pulled through the opposite
end of the stator. Threading the cable axially through a stator
slot tends to place the cable in excessive tension. The insulation
sheath of the cables is fragile, and does not tolerate excessive
tension or compression forces. Also, the structural and insulating
integrity of the cable surface may be compromised or damaged due to
the shearing forces between the cable and stator during cable
insertion. The cable must be carefully threaded through the slots
of the stator to prevent damage to the insulation sheath. The care
in threading the cable through the slot increases the complexity of
and time required for the cable threading process. Moreover, the
cable is susceptible of being damaged, even when the threading
process is carefully conducted.
[0009] Another difficulty with the conventional threading technique
is that a large room is required to thread the cable back and forth
through the stator slots. The cable windings are typically
stretched out in a long line as it is being threaded into an end of
the stator. Similarly, as the cable is pulled through the stator
slot, the end of the cable progressively extends further out along
a line from the opposite end of the stator. Accordingly, a large
amount of space in a stator assembly room has been needed to thread
cable through the slots of a stator.
BRIEF SUMMARY OF THE INVENTION
[0010] A novel stator has been designed for a generator or other
dynamoelectric machine. The stator has cable windings that are
radially inserted into slots in the stator. The radial insertion is
in contrast to the axial insertion of conventional cable threading
techniques. A segment of the cable is laid into the open slot from
a radial direction and from the outside diameter of the stator
teeth. In the present invention, the cable need not be pushed or
pulled through the slot, and there is no need to apply substantial
tension on the cable during assembly of the stator. In addition,
the present invention requires less floor space to insert the cable
windings into the stator because the cables do not have to be
extended out from the ends of the stator, as was done previously in
threading cables through the stator end-to-end.
[0011] In one embodiment of the present invention, the cable
windings are laid into the stator slots while the slots are open
radially. The stator slots are open to receive the cable windings
and separator bars, which are inserted in the slot as the stator is
assembled. The open slots have sidewalls that are defined by the
stator teeth. These teeth extend radially out from the rotor
aperture of the stator. The teeth together form a circular array
around the rotor. The coils are inserted in the slots formed
between the teeth. As each coil section is laid in a slot a
separator bar is inserted over the coil so that another coil
section can be laid into the slot. The separator bar is keyed to
the sidewalls of the teeth and provides structural support for the
cables.
SUMMARY DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is cross-sectional side view of a generator;
[0013] FIG. 2 is an cross-sectional view of a stator section
showing two variants of the invention;
[0014] FIG. 3 is an exploded view of the stator components shown in
FIG. 2, and
[0015] FIG. 4 is a perspective view of a stator tooth with tapered
sidewalls and a stator slot with parallel sides.
DETAILED DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a general side view of an electric generator 10
including a stationary stator 12 which is an annular body having a
cylindrical rotor aperture 14 to receive a rotor 16. The rotor is
mounted on shaft 18 which is coupled to a turbine or other power
source. The rotor has electromagnetic windings that create a
magnetic field surrounding the rotor and extending into the stator.
As the rotor spins within the generator, the rotating magnetic
field causes electrical voltage to be generated in the cable
windings of the stator. The current from the cable windings at a
desired voltage level is output from the generator as electrical
power.
[0017] FIG. 2 is a cross-section of a segment of a stator and
illustrates two possible embodiments of the invention. In
particular, the left half of the figure shows a first embodiment of
the invention having insulating separator bars 24, and the right
half of the figure shows a second embodiment of the invention
having magnetic separator bars 25. In an application of the
invention, a stator would likely include only one embodiment of the
invention, and would not have different embodiments, e.g.,
different types of separator bars, cables and stator teeth. The
particular type and shape of the separator bars, cables and teeth
may vary between different applications of the invention and
depending on the specific design requirements of each stator.
[0018] The stator 10 includes teeth 20 arranged in a circular array
about a rotor opening 15. Between the teeth are cable windings 22,
separator bars 24, 25 and inter-cable spaces 26 (which may be open
coolant conduits). A laminated magnetic yoke 28 surrounds the
assembly of stator teeth, cables, separator bars and cable spacers,
and provides a casing that holds this stator assembly together. The
yoke is an annular casing that slides over the assembly and teeth,
cables, separator bars and spacers. The yoke is separate from these
other stator components.
[0019] The stator teeth 20 form individual partition walls that
separate the stator slots 30. The teeth form walls that stand
radially outward from stator assembly jig 14. The annular jig may
be removed from the rotor opening 15 after assembly of the stator,
or retained to provide rigidity to the stator. The teeth may be
laminated layers punched from silicon steel sheets as individual
rectangular teeth or a group of multiple teeth. The teeth have an
inner edge 34 that is adjacent the stator assembly jig 14. The
outer edge 32 of the teeth abuts against an inner cylindrical
surface of the yoke 28. There may be an interference fit between
the yoke and sidewalls to ensure that the teeth and other stator
components are held in place by the yoke.
[0020] The pair of sidewalls 36 of each tooth 20 forms sidewalls to
the adjacent stator slots 30. Adjacent teeth define a stator slot
30 between opposite sidewalls 36 of the teeth. These opposite
sidewalls forming a slot provide support for the cable windings 22,
separator bars 24, 25 and inter-cable spaces 26 that occupy the
slot. The sidewalls 36 are notched to hold the separator bars that
support the cable turns. The notches in the sidewalls of the teeth
may be key slots 40 that receive key bosses 42 on the stator
separator bars 24.
[0021] The insulating separator bars 24 shown in the left-hand side
of FIG. 2 are formed of an insulating material, such as plastic.
The bars 25 shown in the right hand side of FIG. 2 are formed of a
material, such as a powered metal bound in a plastic matrix. For
magnetic powders the separator bars must be split to provide a gap
43 between a right bar segment 45 and a left bar segments 47. The
gap 43 separating the magnetic bar segments may be aligned with the
center of the cable 22. A similar gap between left and right bars
in a stator slot is not needed for bars made of an insulator or a
non magnetic composite, as shown in the left hand side of FIG.
2.
[0022] The teeth 20 have parallel sides 36 that form tapered slots
30. Widening the slots 30 from the rotor toward the yoke allows the
thickness of the cable insulation 48 to be graded according the
voltage to ground which, in a normal winding, the voltage to ground
(voltage level in cable) would be at its maximum near the bottom of
the slot (near the yoke 28).
[0023] The cable windings 22, separator bars 24, 25 and cable
spacers 26 are held in the stator slots 30. The cable windings 22
are high-voltage cables having a conductive core 50 that is
circular in cross-section and formed of wire strands comprising
copper, for example. The core may have a semiconductor sheath. In
addition, the core and semiconductor sheath is encased in an
annular insulation sheath 48, and another semiconductor sheath
covering the insulation. The thickness of the insulation sheath may
vary along the length of a cable, as is shown in FIG. 2. The
insulation sheath may gradually increases in thickness such that
the cable windings in the stator slot and near the rotor opening,
e.g., inner end, have a insulation sheath that is thinner than the
cable windings near an opposite end, e.g. outer end, of the
slot.
[0024] The separator bars 24, 25 are trapezoidal in cross-section,
but may have other cross-sectional shapes that bridge the slot 30
between the teeth and provide support for the cables 22. However,
magnetic separator bars 25 may have a gap 43 extending the axial
length of the slot 30 in order to separate the left and right
segments 45, 47. The separator bars 24, 25 extend the length of the
stator slot. The gap 43 may be utilized as a cooling conduit, and
may also be incorporated in insulating separator bars. The sides of
the separator bars have key bosses 42 that engage key slots 40 in
the teeth, as is shown in the right-hand side of FIG. 2.
Alternatively, the sides of the separator bars 24 may fit entirely
into slots 52 in the sidewalls of the teeth, as is shown in the
left-hand side of FIG. 2. The arrangement of key slots and key
bosses, and the means by which the separator bars engage the
sidewalls of the stator teeth may vary with different applications
of this invention.
[0025] The separator bars 24, 25 may be proportioned to leave an
open space (intercable space 26), which is used as a fluid conduit
through which a dielectric coolant such as oil may be circulated to
cool the surface of the cable. The cross-sectional shape of the
separator bars may increase from the bars near the rotor aperture
to the yoke to compensate for the increasing width of the slot. If
the inter-cable spaces 26 are to be left as open coolant conduits
they have no structure themselves. Alternatively, the cable spacers
may be structural supports that are sandwiched between an upper and
lower separator bars 24 and bracket the cables.
[0026] As shown in FIG. 3, the channels 58 in the separator bars
24, 25 extend along the length of the bars and the stator. The
channel 58 may be a semi-circular groove in an insulating separator
bar 24, or a pair of opposite concave shoulders on the left and
right segments 45, 47 in a magnetic bar 25. The separator bars may
be formed of an insulating plastic, a powered metal (such as a
powered molded iron composition) or other material suitable for use
in a stator as a support member. Molded iron is finely divided
particles of iron (or steel) pressed into final form. Several types
of molded iron are commercially available. A common form of molded
iron is fine iron powder with an organic binder. Another type of
molded iron comprises powdered iron with an inorganic binder and
that is annealed has recently become commercially available. A
third type of molded iron consists of iron flakes without binder,
is also annealed, and is held together by interlocking in the
molding process. The separator bars may be multiple pieces, shorter
than the length of the stack of laminations forming the stator.
Each separator bar may be only a few inches long, especially if the
bar is a magnetic composite material. A train of separator bars may
be axially inserted into the stator slot to extend the length of
the stator and may be interlocked axially.
[0027] In one embodiment, during assembly of the stator, the stator
teeth are stacked in an annular jig 14 positioned at the rotor
opening 15 in the stator. The outer surface of the jig 14 matches
the inner cylindrical surface of the stator surrounding the rotor.
The jig supports the teeth of the stator during stator assembly. To
assemble the stator, the inner edges 34 of the teeth are mounted in
grooves 56 on the outer surface of the jig. In this initial
assembly arrangement, the teeth extend out in a circular array from
the jig. The open stator slots 30 are defined between adjacent
pairs of the teeth.
[0028] The innermost separator bars 60 (the bar nearest the rotor
aperture 14) are inserted axially between a pair of teeth and on
the jig. The separator bars are inserted axially into the stator to
engage the longitudinal key slots or grooves of the sidewalls of
the teeth. If the tooth is formed with overhangs (an inner surface
in the tooth to the slot), the first layer of separator bars is
unnecessary. The innermost cable segment 62 is inserted radially
into the slot (between the inner edges of the teeth 34) and seated
in the concave channel 58 of the bar. The separator bars 24 have
channels 58 along their upper and lower surfaces to hold the cables
22. The channels are shaped to provide an upper or lower cradle for
the cables.
[0029] The cable extends out of the axial end of the stator slot
and is looped over to another stator slot where the cable is again
seated in that other stator slot. The cable is looped from stator
slot to slot until the cable-segments are stacked in the stator
slots. After a segment of cable 22 is seated in a stator slot 30, a
second separator bar 24, 25 is axially inserted into the slot and
over the cable segment already seated in the slot. Another segment
of the cable is seated over the second separator bar. This
procedure of axially inserting separator bars and radially inserted
cables and spacers is repeated until the turns of the cable are
stacked in the stator slot.
[0030] Alternatively, as is shown in FIG. 4, the sidewalls 42 of
the teeth 44 may form a wedge such that the thickness of the stator
slot 46 increases from the bottom edge 32 near the rotor to the top
edge 34 of the tooth near the yoke 28. Wedged teeth 44 may form
stator slots 46 that have parallel sides and a constant width (in
contrast to the wedged slots 30 shown in FIG. 2). The cost may be
prohibitive, in certain applications, for cables having increasing
thickness. Accordingly, it may be more economical for some
applications to use a cable having a constant thickness of
insulation. In this case all the holes would be the same size, the
teeth trapezoidal and the slot approximately rectangular. This
configuration may result in reducing the number of different parts
needed to form the stator.
[0031] Once the cable windings and separator bars are fully stacked
in all of the stator slots, the yoke 28 is assembled around the
teeth and winding section as shown. The yoke and stator teeth may
be formed from oriented silicon steel laminations which provides
good magnetic properties in the appropriate and best direction for
the magnetic flux being carried through the stator yoke and teeth.
The orientation of the silicon steel laminations may be radial in
the teeth and azimuthal in the yoke. In addition, keys 60 at the
outer edge 32 of the teeth to slide into matching key slots in the
yoke can provide good flux transfer and enhanced mechanical
integrity. In addition, flanges, bolts and other known mechanical
fastening devices may compress the stator slot stacks of cables and
bars, the teeth and yoke and to firmly lock them all together.
[0032] The invention has been described in context with what is
presently considered to be the best mode(s) of the invention. The
invention is not limited to the disclosed embodiments. Rather, the
invention covers the various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims.
* * * * *