Note: Descriptions are shown in the official language in which they were submitted.
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A RESIN IMPREGNATED AROMATIC POLYAMIDE
C WERED GLASS BASED SLOT WEDGE FOR
LARGE DYNAMOELECTRIC MACHINES
BACKGROUND OF THE INVENTION
Slot wedges are strips of electrically insulating
material, used to retain conductors in the coil slots of
stators of dynamoelectrlc machines such as generators and
motors. Prlor art slot wedge structures have included
phenolic resin lmpregnated, flat, Kraft paper sheet lamin-
ates. However, when subJected to temperatures on the order
of 100C, after several years use, ln large generators and
motors, some shrinkage o~ the Kraft paper laminates was
encountered. In addition, the Kraft paper-phenollc wedges
had poor interlaminar shear length, and were abra~ive to the
inner surface edges of the iron stator teeth during the
wedge driving operation. Asbestos-phenolic slot we~ges have
found wide acceptance, having good stabllity and lubrlclty
characteristlcs, but the use of asbestos ls now consldered
to be a potential health hazard.
White, ln U.S. Patent 3,437,858, trled to remedy
shrinkage and shear strength problems, by provlding a poly-
ester resln lmpregnated, parallel glass ~lber, extruded slot
wedge, havlng a core of low shear strength. This structure
lncluded at each end, a metal or glass fiber tube, rod, tape
or cord, having a very high shear strength. Thus, the
hlghest shear strength was at the portlon of the wedge that
contacted the inner surface of the stator teeth. Thls wedge
was faced wlth a 5 to 30 mll ~hick tape of wrapped woven
~, glass, whleh provided a hlgh transverse bondlng strength,
and allowed lncreased drlving pressure durlng wedge lnser-
tion. The tape coverlng also added to the shear strength
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of the wedge, since 1~2 of the glass ~lbers were transverse
to the slot wedge core fibersO Such wedges would, however,
still be abrasive to the lnner sur~ace edges of the iron
stator teeth, during the wedge driving operation.
Balke, in U.S. Patent 3,735ll69, provided plural
layers of Kapton polyimide ~ilm, or Nomex tpoly 1,3 phenylene-
isophthalamlde) polyamide, high density, fibrous sheet,
laminated together with adhesive, to ~orm flat composites.
These sheets, with applied adhesive, were placed ln a clamp-
ing ~ixture, and then laminated, to cure the adhesive. Theyformed rigid plastic wedges, with high temperature dimen-
sional stability, having the desired channel shaped slot
wedge configuratlon, without using a supporting core. Such
a construction, however, relies upon the thin adhesive layer
~or rigidity, and would provide wedges which could ~till
allow substantial conductor displacement and vibration.
This type of wedge would be practical for small appliances,
where coil forces are about 1 lb.~inch length of slot wedge,
but not for large dynamoelectrlc machines, with coil ~orces
of about 100 lb./inch length o~ slot wedge.
What is needed, i8 a strong wedge, able to prevent
conductor dlsplacement and vibration, and resist shear
stresses, shrinkage, and bowing caused by the pressure o~
the wedged conductors and heat. The wedge should, very
importantly, also provide a compresæible iron engaging
surface of considerable resiliency and ~ubricity, which
would not abrade the inner surface edges of the laminated
stator teeth during the wedge drlving operation.
SUMMARY OF THE INVENTION
The above described problems have been solved, and
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the above need met, by providing a resin impregnated,
aromatic polyamide covered~ glass cloth slot wedge, adapted
to be positioned in the teeth o~ coll slots in dynamoelec-
tric machines. A thermoset resin impregnated, aromatic
polyamide surface, on at least the two ma~or teeth contact-
ing sides, provldes outstanding lubricity, resillency,
tensile strength and thermal stabllity. It also has the
ability to notch durlng wedge insertion, rather than abrade
the edges of the stator teeth.
The aromatic polyamide is preferably in mat ~orm,
about 0.005 to about 0.025 inch thick, and forms a 70% to
95% porous matrix ~or the thermoset resin. The mat is
impregnated, between about 60 to about 80 wt.~, with a cured
thermoset resin. The glass cloth core is about 0.2 to about
0.5 inch thick, and impregnated between about 40 to about 60
wt.%, with a cured thermoset resin. This combination pro-
vides outstanding interlamlnar shear strengths of over about
2,500 lb./in. length at 100C.
J' The resin impregnated aromatlc polyamide felt mat
is placed in a suitable mold cavlty, with the resln lmpreg-
nated glass fabrlc superimposed thereon. Steam press
platens are then used to cure the resins and laminate the
, ................................................................ .- two layers, without adhesives, lnto a unitary, consolidated,
composite. The organic Aramid fiber matrix, lmpregnated
with cured thermoset resin, provides a resilient sur~ace
layer that protects the inner surface edges of the stator
,
iron during the wedging operation, and allows the use of
high strength glass core materials which in the past have
` been fo~nd abrasive when used alone. The winding bracing
system o~ this invention, control~ stator ~orces from steady
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state and short circuit conditions. It is particularly
useful in large generator stator applications.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention,
reference may be made to the preferred embodlments exemplary
of the invention, shown in the accompanying drawingæ ln
which:
Figure 1 is a cross-sectional vlew of one type o~
stator for a dynamoelectric machine, showing the teeth of a
coil slot and a slot wedge inserted therein;
Figure 2 is a cross-sectional view of one type of
slot wedge encompassed by this invention,~showing the details
of the core and wrapper arrangement;
Flgure 3(a) show~ one method of making the lam-
inate stackup for the slot wedges of this inventiol,
Figure 3(b) shows the slot wedges being formed in
a two cavity mold; and
Figure 4 shows a test apparatus used to determine
iron abrasion in the Example.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Flgure 1, metal member of a
dynamoelectric machine, such as a stator 1 is shown, wlth a
oonventional construction, consisting of coll slots 2,
contalning coil conductor windings 3, which may also contain
cooling ducts. Each coil is bounded, at the top and bottom,
by phenolic resin impregnated Kraft paper, or other suitable
separator sheet materials 4, and surrounded by insulation 5,
as is well known in the art. The insulation 5, will generally
comprise a moisture resistant, elastic comblnatlon o~ thermo-
setting resln and mica flakes. Slot wedge 6 is a brace for
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the coil windings, and is shown disposed between the top
conductor wlndings and the laminated iron stator teeth 7.
The slot wedge is lnserted between the teeth of the coil
slot, and contacts the inner surface edges 8 of the stator
teeth 7. The lnterior surface of the teeth is a notch in
the laminated stator iron components, and can have a variety
of configuratlons, such as shown at 8 or 9.
Each stator for a large dynamoelectrlc machine,
co~prlses a plurallty of low-loss silicon-steel core punch-
ings. ~or example, a large generator stator can be 10 ~eetin diameter and 20 feet long. It can comprise as many as 30
separate punchlngs per inch. Each lamination, before punch-
ing, is coated with a high temperature inorganlc lnsulatlon,
such as sodium silicate or a phosphate type insulation. The
lamination is then punched, deburred and recoated.
The punched laminations havlng the cross-section
of the stator coil are then stacked on bulldlng bolts and
flrmly clamped together by lnsulated thru-bolts and non-
magnetic finger plates, to form a stator body having coil
slots and stator teeth. The insulation between each lamln-
ated punching helps to prevent current losses~ at operatlng
temperatures, along the outside surface of the stator.
Because of the number of indi~idual laminations~ lt is
impossible to align the teeth sections to greater than a
+ 0.010 inch tolerance. Therefore, many of the teeth edge
laminations will be "sticking out", and sub~ect to bending
: or shearing by the slot wedge during slot wedge insertion.
If the teeth edge laminations are bent or sheared,
they can contact each other, causing electrical short circults,
and defeating the purpose of the interlamlnar insulation.
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There~ore, it ls essential that the slot wedge exterior be
of substantial lubricity, and of a type construction able to
be scraped by the stator teeth laminations, without bending
the laminations, while still maintaining its structural
integrlty.
When the insulated conductor windings and the
separators are inserted into place in the coil slots, then a
plurallty of slot wedges 6 are driven into place by a suit-
able drivlng means such as a block and mallet. Friction
contact occurs between the slot wedge iron engaging exterior
surface, and the stator iron laminated punchings, at teeth
edge contact points 8, on the side and bottom of the slot
wedge. In general, the slot wedge assembly has a length
equal to that of the coil slot, and usually consists of a
plurality of wedges approximately 6" in length. Therefore,
a 20-~oot long stator would contain 40 slot wedges per slot.
The slot wedges of this inventlon are easlly molded to
various conflgurations and are easily machlnable.
A preferred type of slot wedge 6 is shown in
detall in Figure 2. The slot wedge 6, consists of a glass
fiber core 20, such as glass fabric or cloth. The glass
~lber oore may be in machlned sheet form, but is pre~erably
ln spiral, i.e., wound or rolled form, as shown. A rolled
core is particularly useful, since it increases the inter-
laminar shear strength of the core by 10% to 20%. Thus,
: B exteriorf edges 21 of a rolled core can withstand a greater
outward force from the coils held in the coll slots. The
- slot wedge core is impregnated with a thermoset resin such
aæ, for example, a phenolic resin or an epoxy resin, both of
which are well known in the art. These resins can contain a
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variety of well-known curing agents 3 accelerators and
inhibitors.
The glass cloth used in the core will have a
thickness o~ about 0.003 to 0.01 inch. After overlaying or
rolllng, and curlng in the mold, the glass cloth will pro-
vide a core having a thickness of from about 0.200 to about
0.500 inch. It will be impregnated with about 40 to about
60 wt.% of a cured thermoset resin, based on resin plu5
glass cloth weight. Thicknesses below 0.200 inch and resin
loadings below 40 wt.% will allow voids to seriously impair
the core strength.
The glass fiber core is covered, on at least two
sides, by an aromatic polyamide mat, i.e., felt, facing,
which has at least a 70% porous structure~ general~y about
70% to 95% porosity, before resin impregnation. This low
density allows very high resin loading, within a tough
Aramid matrix having exceptlonal tensile strength. The
covering ls integrally lamlnated and bonded to at least the
teeth facing, iron engaging side ~urfaces 21 of the core,
and generally, for ease of application, to the top surface
22 and the iron engaging edge part of the bottom surraoe at
23 as well. This provides a slot wedge having a top sur~aoe
24, a bottom coil ~acing sur~ace 25, the iron engaglng edges
26 which will contact the teeth of the stator, and two
primary iron engaging teeth contacting sides 27.
This covering must consist of a resin lmpregnated
aromatic polyamide mat. Many other materials, such as
aromatlc polyimides are difficult to bond to the glass core
surface. The coverin~ must not be in film form, since this
type of coverlng will have a tendency to shear from the
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glass core during the wedging operation. The aromatic
polyamide mat is preferably in a single layer, non-woven
form, about 0.005 to about 0.025 inch thick after molding.
The mat provides a matrix of about 5 to 30 volume percent of
theoretical density, i.e., 70 to 95 percent porosity, ~hich
is impregnated with about 60 to about 80 wt.% of a cured
thermoset resin, based on resin plus mat weight. The
thermoset resin can be, for example, a phenolic resin or an
epoxy resin, which can contain a variety of well-knwon
curing agents, accelerators and inhibitors.
Thicknesses of the molded polyamide resin mat
below 0.005 inch, will not provide a sufficient thickness to
allow facing compression, and to allow thè rough teeth edge
surfaces to score and scrape the wedge as it is being
driven. Thicknesses below 0.005 inch will reduce the resil-
iency of the facing and cause possible rupture or telring of
the mat, and contact of the iron teeth laminations with the
abrasive glass cloth core. Resin loading below 60 wt.% wlll
seriously impair the adhesion of the covering to the core,
2~ since some of the resln used in the covering seeps into the
core during high pressure lamination, provlding outstandlng
bonding of the two comPonents of the laminate wlthout use o~
adhesives. Less than 60 wt.% resln would also decrease the
lubricity of the covering and its ability to absorb the
mechanical scraping and scoring of the teeth punchings.
An all aromatic polyamide slot wedge is not useful
for large dynamoelectric machines because of excessive creep
,
and shrinkage at operating temperatures. The preferred
thickness ratio of impregnated glass fiber core layer:impreg-
nated aromatic polyamide facing layer is between about 10:1
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to about 100:1. A ratio less than 10:1 will cause shrinkage
problems. A ratio over 100:1, i.e., very thin covering
layer, will cause possible abrasion problems.
Aromatic polyamlde, in yarn, paper~ mat and fiber
form are well kncwn in the art, and comprise aromatic rings
united by carbonamide links
.~ .
- C - NH - .
Such aromatic nylon materials have a wide range of chemical
and physical properties, and have excellent thermal stabi-
lity. They can be prepared by reacting an aromatlc diaminewith an aromatlc diacid chloride in an aqueous system. A
; complete description of their properties ànd synthesis can
be found, for example, ln U.S. Patents 3, 671, 542 and 3,240,760,
herein incorporated by reference. These Aramids are used in
this invention in the form of high molecular weight ~ilament
mats. These fibrous mats comprlse substantially round fiber
filaments havin~ an approximate average diameter of between
about 0.0001 to 0.0008 inch. The mat may also contain
fibrid binder particles. The mat has about 90% to 100%
resilienoy against compactiOn, i.e., it will absorb impact
easlly and return to its original shape. Such reslliency i~
retained to a great degree even when the mat ls loaded with
resin.
The most preferred aromatic polyamide i8 a poly
, (phenylenephthalamide) having a tenslle strength of over
about 90,000 and preferably over about 250,000 lb./sq.in.,
and a tensile modulus of over about 2.0 x 106 and pre~erably
over about 10 x 106 lb./sq.in. One example of this type of
~aterial consists essentially of recurring units of poly
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(1,4-phenyleneterephthalamide):
~ NH ~ N~ - C ~ C ~ ,`
described as Kevlar by Gan et al, in Vol. 19 o~ the Journal
0~ Applied Polymer Science, pp. 69-82 (1975). These tensile
properties will provide a reasonably close match with the
glass in the core, which has a tensile strength of approx-
imately 200,000 to 400,000 lb./sq.in., and a tensile modulus
o~ about 10 x 106 lb./sq.in.
By closely matching the values of the two com-
ponents of the laminated composite, there~wlll be lesschance of delamination under the coil pressures and temp-
eratures encountered ln large dynamoelectric machlnes, which
can be about 75 to 150 lb./inch length of ~lot wedge at
about 75C to 125C. Also, no adhesive need be used to bond
the Aramid and glass together. The aromatic polyamides,
when in porouæ mat form provide a matrix of about 5 to 30
volume percent density for the thermoset resin. The impreg-
nated, cured mat is resilient, flexible and has lubricating
properties, allowing it to absorb soraping contact with
rough surfaces.
Figure 3(a) shows the aromatic polyamide felt 31,
lmpregnated with resin and a roll of impregnated glass
~abric 32. They are placed in the mold 35 with associated
P/Q ~ens
LJ steam patternE 36, shown in Figure 3(b~.
EXAMPLE l
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; Several resin impregnated aromatic polyamide faced
glass based slot wedges were made. A style #7628 glass
cloth strip, 2-3/8" wide, and 0.010" thick, was impregnated
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with an acetQne solution of a bisphenol A epoxy res~n,
having an epoxy equivalent weight of 450 to 550, (sold
commercially by Shell Chemical Co. as EPON 1001) using
trimellitic anhydride as a catalyst. This impregnated strip
was passed through a treating tower at 140C, to evaporate
the acetone solvent. This provlded a B staged, non-tacky
strip, with about 50 to 55 wt.% resin loading, whlch was cut
to a 60" length.
A 75% porous, i.e., 25 vol.% dense strip of hlgh
modulus aromatlc polyamlde non-woven felted mat, havlng a
weight of 7 oz./sq.yd., a tensile strength of about 300,000
to 400,000 lb./sq.in., and about g5% resiliency (described
as primarily poly 1,4-phenlyleneterephthalamide, sold com-
merclally as Kevlar 29 by E.I. DuPont De Nemours & Co.)
3-1/2" wide and 0.125" thlck, was lmpregnated wIth a methanol
solution of a phenol-formaldehyde resin. This impregnated
strip was passed through a treating tower at about 140C, to
evaporate the solvent. This partly cured the resin in the
strip, and provided a dry pre-preg, with about 70 to 75 wt.%
-of phenolic resin in a 25 vol.% Aramid matrix. The strip
was then cut to 6" lengths.
The epoxy-glass strip was rolled into a 20 layer
thick tube and superimposed on the phenolic-Kevlar covering
strip, as shown in Figure 3(a) of the drawings. ~he phenolic-
glass tube was pressed flat and the ends of the phenolic-
Kevlar strips were bent over the flattened tube top. No
adhesives were used. This lay up was placed in a mold
;: - ' ' -
cavity, as shown in Figure 3(b), ~nd heat and pressure
consolidated between hot press platens at 155C for 1/2 hour
at l,OOO psi. The composite was allowed to cool, and then
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removed, to provide a consolidated, bonded, laminated slot
wedge. The molded composite had a resilient, lubricating,
aromatic polyamide facing on the short face side,the two
teeth contacting edge sides and on the edges of the bottom
side, as shown in Figure 2 of the drawings. The aromatic
polyamide covering was compressed to a thickness of about
0.015", and the aromatic polyamide matrix was loaded with
about 70 wt.% resin. The glass cloth core was about 0.361'
thick, and was loaded with about 50 wt.% resin. There
appeared to be excellent bonding of the two adhesiveless
layers .
Tests were then run on this composite for strength
and stability. The wedge was placed, face down, in a hollow
steel test fixture having a simulated stator surface. Here,
the beveled side edges rested on steel in the fixture, and a
steel pressing bar simulating conductor winding pressure in
~; a stator, was pressed against the coil bracing back of the
slot wedge. A 30 ton Amsler Universal testing machine was
used in con~unction with a Baldwin microformer unit to
measure deflection. The test assembly was operated in an
oven with a thermometer attached to the specimen. The
interlaminar wedge shear strength at 100C was measured to
be 3,510 lb./inch length of slot wedge. This iæ over 230%
above the usual 75 to 150 lb./inch length coil pressure -
found in most large dynamoelectric machines and well above
the 1,500 lb./inch length typical of phenolic resin Kraft
paper sheet slot wedges.
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A similar slot wedge was tested at 100C and 150
psi for 48 hours. This test simulated actual dynamoelectric
machine operating conditions. The % thickness shrinkage,
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and % bowing o~ the slot wedge after removal was not measu-
rable. This is a dramatic improvement over the 2% to 4%
shrinkage for phenolic resin Kraft paper sheet slot wedges,
and 5% shrinkage for an all Kevlar wedge impregnated with
phenolic resin. The observed shrinkage of ~evlar requires
its use in combination with a glass core, in order to be
useful in large dynamoelectric machines.
Abrasion tests were run using a machined, solid
Aramid slot wedge and a test fixture, shown in Figure 4 of
the drawings. The test fixture 40 comprised a 5" long stack
of laminated punchings, each insulated from each other by a
phosphate type insulation. There were 30 punchings per inch
of fixture length. The slot wedge consisted of a molded
block of sheets of phenolic resin impregnated Kevlar aromatic
polyamlde. The molded block was about 0.04" thick, 7.5"
long, and provided a 25 vol.% aromatic polyamide matrix
loaded with about 75 wt.% phenolic resin. The color of the
wedge was pale yellow. The block was machined to a length ~ -
of 0.976 + 0.015 inches with a 0.031 radius at its ends, as
shown at 40 in Figure 4. A slmllar wedge was machlned from
a 0.04" thlck molded block of epoxy resin impregnated glass
cloth. Both wedges were machined to exactly matching dimen-
sions. The distance between the deepest portion 41 of the
teeth 42 of the fixture was 1.0 inches. Bolts 43 holdlng
the laminated punchings of the test fixture together are
shown as 44.
The abrasion test was a short, mechanical push-
pull stroke, applying 150 psi force between the wedge and
the iron that moved each wedge through the punchings. New
punchings were used for each test fixture. Testlng was
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conducted at 25C. This test very closely slmulated actual
wedge insertion conditions for generator stators. Both the
phenolic-aromatic polyamide wedge and the epoxy-glass cloth
wedge were moved through their test fixtures, engaglng the
lron for 1,000 cycles. Iron deposits were found on the
contacting surfaces of the epoxy-glass cloth wedge. The
phenolic-aromatlc polyamide wedge appeared to have less
effect on the punchings and dld not have any appreciable
lron deposits on the contacting sur~aces. The phenolic-
aromatic polyamide wedge showed much more wear. Scanning
electron micrographs of the punchings of each test flxture
were examined and the punching edges in contact wlth the
phenolic-aromatic polyamide showed much less wear than the
punching edges in contact with the epoxy glass cloth wedge.
Water absorption tests were run according to standard ASTM
D-570, which involves immersing samples in 25C water for 24
hours. The results showed very good results of 1.1% water
absorption by weight for the phenolic-aromatic polyamide-
epoxy glass cloth wedge.
Phenolic-aromatic polyamide ~aced, epoxy-glass
cloth slot wedges, made as described above were tested in
approximately 6" lengths, as a stator winding wedge system,
in the slots of a stator in a large two pole steam turbine
generator 20KV, 669 Megawatt, with outstanding results.
These slot wedges were easily driven into the slots, did not
harm the iron edge laminations they contacted, insuring the
i magnetic integrity o~ the stator core assembly. The slot
wedges also maintained radial pressure on the coils, holding
`~ the pressed coils tightly in place to prevent vlbration.
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