Note: Descriptions are shown in the official language in which they were submitted.
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RD-10,158
MEANS FOR MOUNTING
OF ARMATURE CONDUCTORS
Background of the Invention
This invention relates to AC machines, and particu-
larly to such machines utilizing armature conductors mounted
in the air gap on supports attached to the stator core.
In certain large AC machines, such as those having
superconducting field coils, insulated armature conductor
bars are mounted in the air gap between the stator and the
rotor. A design requirement for such machines is a rigid
attachment in the radial and azimuthal directions. The
rigid attachment is necessary, in order for the connections
between the conductor bars and the stator core to withstand
the short circuit forces applied to the conductor bars when '
a sudden surge in armature current occurs, and to limit
vibratory mot$on of the conductor bars under ~he lnfluence
of running forces.
In operation, an axially-long electrodynamic
machine develops a heat concentration in the armature con-
ductor bars due to the current passage therethrough. The
iron stator core has a coefficient of thermal expansion
different from that of the armature conductor bars normally
made of copper. As a result, the conductor bars experience
a different axial expansion from that experienced by the
stator core. Therefore, an arrangement is required which
provides a flexible connection in the axial direction
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RD-10,158
between the armature conductor bars and the stator core.
A means of mounting armature conductors to a
stator of an AC machine is disclosed in U.S. Patent No.
3,405,297, to Madsen, issued October ~, 1968. In that
patent is disclosed a means of affixing armature conductors
to the stator core by an axial wedge-shaped tooth which holds
the insulated conductors by compression to the stator core.
This provides the necessary rigid connection in two directions,
but can accomrnodate axial thermal expansio~ only by slip-
page between the tooth and the conductors.
Another known technique for attaching armature
conductors to a statcr core is disclosed in U.S. Patent No.
3,082,337, issued March 19, 1963 to Horsley. In that patent
is disclosed a method of embedding armature conductors in
- 15 an insulating material in the air gap. The insulating mat-
erial is cast molded with the conductors located in the
casting. Again, the connection between the conductors and
the supporting rneans is rigid in all di.rections. Differen-
tial thermal expansion, therefore, results in substantial
stress at the interface between the conductors and the
insulating supports.
In prior art techniques of attaching the armature
conductors to stator core, the conductors were fitted into
slots in mounting teeth and secured by mechanical means,
such as wedges, or by adhesives. Mounting teeth were
rigidly secured to the stator iron core, e.g., by adhesives.
With either wedge or adhesive mounting of the armature
conductors, the thermal expansion of the armature conductors
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RD-10,158
due to heating by the arma~ure current had to be accommo-
dated by a relative slippage between the conductors and the
mounting teeth. Resultant relative movement between arma-
ture conductors and the mounting teeth produced abrasion
on the insulating material coating the armature conductors.
This abrasion clearly was undesirable.
Armature conductor bars in AC machines are surroun-
ded by an insulating layer having a limited mechanical
capability to tolerate shear stress. When a conductor
expands, a rigid axial mounting would cause all the stress
created by the thermal expansion to be applied to the insul- ,~
ating material. The limited stress capabilities of the
insulation require that some means be provided to allow for
differential expansion between a stator iron core and the
armature conductors, in elements other than the insulation.
The object of the present invention is to provide ~'
a mounting structure for armature conductors in AC machines
which will provide rigid attachment in the radial and
azimuthal directions, and also limit the axial shear load
on the armature! conductor insulation, due to relative motion
caused by differential thermal expansion between the arma-
ture conductors and the stator iron core, to a level within
the mechanical stress tolerance capabilities of the insulation
material.
Description of the Inventio~
The invention of the instant application provides
reinforced plastic teeth in the form of thin, wedge-shaped
sheets separated by thin, wedge-shaped spacer plates of
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RD-10,158
reinforced plastic material, having at least one discon-
tinuity which provides a spring section adjacent the discon~
tinuity on the teeth. A plurality of axially spaced stacks
of teeth and spacer plates provides a rigid attachment
between armature conductors and stator iron core in the
radial and azimuthal directions and a flexible attachment
in the axial direction.
Brief Description of the Draw ngs
The features of the invention believed to be novel
and unobvious over the prlor art are set forth with particu-
larity in the appended cLaims. The invention itself, how-
ever, as to organization, method of operation and objects
and advantages thereof, may best be understood by reference
to the following description taken in conj~mction with the
drawings wherein:
Fig. 1 is a vertical elevation view of the attach-
ment means of the invention;
Fig. 2 i8 a cro9s sectional vi.ew of Fig. 1 ~aken
along line 2-2 showing a deflected and undeflected stack of
teeth and spacers;
Fig. 3 is a view similar to Fig. 1 illustrating
an alternative embodiment: of the invention; and
Flg. 4 is a cross sectional view of Fig. 3 taken
along line 4-4 showing a deflected and undeflected stack of
teeth and spacers.
Manner and Process
of Making and Using
the Invention
The particular structure shown in Figs. 1 through 4
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RD-10,158
and described herein is merely exemplary, and the scope of
the invention is defined in applican~'s claims.
l'he mounting structure 10 illustrated herein incor-
porates a plurality of stacks 11 of teeth 12 separated by
spacers 13 attached to an iron stator core 14 in the air gap
15 separating the stator core 14 (only partially shown) from
the rotor 16 (only partially shown). In each instance a
mounting tooth 12 is disposed at the far end of each stack
11. Each spacer 13 comprises a spacer plate 17, a spacer
segment 18 and a gap 19 therebetween transverse to a radius
33 passing through the axi.s of rotation of the rotor and the
center of the conductor bars 22. The gap 19 could be arcuate
rather than straight as shown. The presence of gap 19 pro-
vides a predetermined amount of unsupported transverse area
20 in the mounting tooth (or teeth) adjacent thereto. This
msupported area 20 provides a spring section on each mounting
tooth 12 over which the tooth can be made to deflect.
As shown in Figs. 1 and 3, the mounting teeth 12
and spacer plates 17 have slots 21 in which are located
insulated armature conductor bars 22 secured by being bonded
to the slot surfaces 24 by a suitable adhesive, such as a
heat-resistant polyester adhesive. In addition to the
adhesive, a wedge member 23 may also be used to secure the
conductor bars 22 in the slots 21. If used, wedge member 23
would be made of a material having thermal expansion char-
acteristics similar to those of the armature conductor bars
22, so that no stress i9 applied to the insulation layer 25 of
the armature conductor adjacent the wedge member 23.
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RD-10,158
The conductor bars 22 could be a solid copper or
other conductive material, or a bundle of conductive wires
embedded within an insulating resin and covered by a layer 25
of insulating material. More typically, ~he conductor bars
22 comprise a stack of conductive strips embedded within an
insulating resin and coated with a layer 25 of insulating
material. The conductor bars 22 may also be configured to
provide cooling pa~sages for f~ow of a coolant fluid of any
conventional type. The support system disclosed herein will
provide the advantageous connection for each of these types
of armature conductor bar structure and any other conductor
bar internal structure. The internal bar structure is
immaterial to the invention described herein, so long as the
outer surface of the insulation layer conforms generally to
the shape o the slots 21. The conductor bars 22 may be
parallel to the longitudinal axis of the machine or may be
skewed relative to the longitudinal axi~.
In a long machine, a plurality o spaced stacks 11
of teeth 12, interleaved with spacers 13, both of fiber
reinforced plastic material, are provided with a gap 26
between the stacks 11, so that the thermal expansion of
the iron stator core 14 to which these stacks 11 are bonded
by adhesive does not apply intolerable stress to the adhesive
joint 27, Although the description herein has been limited
to a single tooth stack, the same construction is repeated
all around the inner cylindrical surface of the stator core
14, as shown in Figs. 1 and 3 by the broken section of
ad;acent teeth.
The teeth 12 are normally made of a cloth or glass
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RD-10,158
fiber reinforced plastic material with an epoxy impregnant.
The spacers 13 may be made of material identical or similar
to the tooth material. The teeth 12 and spacers 13 are
bonded by a polyester epoxy or other heat-resistant adhesive,
or, alternatively, they may be bonded by heating under pres-
sure to produce adhesion between the adjacent surfaces of
the teeth 12 and spacers 13, to form the laminated stacks 11.
The teeth 12 and spacers 13 are bonded to the stator iron
core 14 at joint 27 by a suitable adhesive such as a heat-
resistant polye~ter adhesive, e.g., a polyester epoxy.
The teeth 12 and spacers 13 may be of the same
thickness or different thicknesses. The spacers 13 must be
of adequate thickness to provide separation between the
adjacent surfaces of adjacent teeth so that at maximum
deflection the surfaces of adjacent teeth do not meet in
the unsupported transverse area 20. Contact between adjacent
teeth in the area 20 would interfere with the desired accom-
modation of thermal expansion of the armature conductor6 by
frictional resistance to relative motion.
The stacks 11 of teeth 12 and spacers 13 may be
of any appropriate width to provide adequate strength in
the azimuthal and radial directions without subjecting the
adhesive bond 27 between the stack 11 and the stator core 14
to intolerable shear stress due to thermal expansion of the
iron stator core 14. The gap 26 is provided between adjacent
stacks 11 to limit the stress on the adhesive joint 27 to
that created by the thermal expansion of the stator iron
core 14 in the axial length over which the stator core 14 is
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attached to each stack 11. ~ue to the wedge shape and
structural strength of the reinforced plastic material,
adequate rigidity and strength for support are provided in
the azimuthal and radial directions to withstand the short-
circuit forces and to limit vibratory motion under the
influence of running forces. The short-circuit forces are
the forces applied to the armature conductors when a fault
current is applied,,to the conductors in the presence of the
machine magnetic field. These forces tend to move the con-
ductors in the radial and azimuthal directions. The vibratory
motion created by running forces i,n the machine is due to the
mechanical interaction and electromagnetic effects of the
interaction between armature current and machine magnetic
field when the machine is operating.
As shown in Fig. 2, the adjacent stacks ll can
accommodate differential thermal expansion by the iron stator
core 14 and armature conductor bars 22 because of the spring
section 20 created by the transverse gap 19 between spacer
plates 17 and spacer segments 18 whereby the stacks 1l. oE
teeth 12 can deflect in the axial direction. With the instant
invention, the spring section 20 of each mounting tooth 12
allows independently-bonded sections of the armature con-
ductors 22 to move axially relative to other sections of the
conductors without applying any severe stress to the conduc-
tor bar insulation layer 25. The stacks 11 of teeth 12 and
spacers 13 are of such a width that the expansion in the
incremental axial length of a conductor bar 22 attached to
a single stack 11 does not apply a thermal stress to the
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RD-10,158
layer 25 of insulation beyond the stress tolerance limits
of the insulation material.
In order to prevent creep of the armature conduc-
tor bars 22 due to repeated expansion and contraction due to
heating and cooling caused by intermittent use, or other
operating variations, the bars 22 are usually attached at one
location with a rigi~ connection in all directions. Thereby,
no relative motion can occur between the stator core 14 and
the conductor bars 22 at the point of rigid attachment. The
disclosed mounting structure 10 providing spaced attachment
between the stator core 14 and conductor bars 22 provides
accommodation of incremental thermal expansion. By select-
ing the thickness of spacers 13, the required maximum deflect-
ion at the mounting stacks 11 farthest from the rigid attach-
ment can be accommodated.
In a set of design conditions in which it is decided
that the expansion should be from the center out, a stack 11
of teeth 12 without a spring section 20 may be affixed to
the conductor bar insulation layer 25 at the axial center
of the machine to securely locate the armature conductors 22
relative to the stator core 14. As shown in Figs. 2 and 4,
the degree of deflection for ad;acent stacks of teeth may
differ. This would generally occur ~or stacks at different
distances from the rigid attachment.
At the ends of the machine, conventional shaping
of the conductor bars 22 allows for thermal expansion of
the conductors without any mechanical interference with
other parts of the machine.
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An alternative embodiment of the invention is
illustrated in Figs. 3 and 4. In ~ig. 3 is shown a stack 11'
of mounting teeth 12' having an arcuate oblong slot 28 coin-
cident with an arcuate gap 19' between spacer plate 17' and
spacer segmen~ 18' of the spacers 13', which provides an
enhanced flexibility spring section 20' to the stacks 11' of
mounting teeth 12'. The gap 19' and the oblong slot 28 could
be straight transverse openings rather than arcuate as shown.
As Qhown in Fig. 4, the slots 28 provide for a limited cross
sectional area 29 of the fiber reinforced plastic teeth 12'
in the spring section 20'. l'he size of this area 29 is
determined by the required azimuthal and radial rigidity and
strength requirements. By using the slots 28 shown in Figs. 3
and 4, the tooth thickness may be increased to provide addit-
ional strength, along with increased flexibility.
The conductor bars 22 may be constructed to have
coolant passages and be cooled by water or other suitable
coolant circulating therethrough. The differential thermal
expansion of either a cooled or uncooled conductor bar
arrangement would be accommodated by the present invention.
~le mounting arrangement disclosed herein could be
used in a wide range of machine sizes. The preferred range
contemplated by applicant is from approximately 20 MW up to
the largest AC machine. In generators having a power rating
of 300 MW to 1200 MW the air gap 15 from rotor surface 30
to stator core surface 31 is approximately 8 to approximately
12 inches. The height of the support stacks for generator
of such ratings would be such as to allow mechanical clearance
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between the rotor surface 30 and the upper limit 32 of the
teeth of approximately 1 inch, and the height of the spring
section 20 would be from approximately one-half inch to two
inches.
S Best Mode
The best mode contemplates utilization of a straight
transverse gap 19 in the spacer 13. The best mode of the
instant invention contemplates the utilization of a mica resin
insulation system on the conductor bars of the type sold
under the trademark Micapal II, a trademark of the General
Electric Company. The teeth and spacers are made of indus-
trial laminates of the type sold under the trademark Textolite,
also a trademark of the General Electric Company, formed of ~'
fiber (e.g. of cloth or glass) reinforced plastic materlal ,
impregnated with an epoxy resin. The best mode also contem-
plates a thickness of approximately 30 to approximately 60
mils for both the teeth and spacers. The height o the sprin~
section 20 is approximately 1 inch. Also, each stack 11 oE
teeth 12 and spacers 13 is approximately one inch wide in
the axial direction. The teeth 11 are bonded to the conduc-
tor bar insulation layer 25 by a heat-resistant polyester
epoxy adhesive.
The arrangement described herein provides rigid
azimuthal and radial attachment of armature conductor bars
to the stator iron core in an electrodynamic machine, such
as an AC generator, without allowing intolerable stresses
to be applied to the insulation layer surrounding the con-
ductor bars.
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. RD-10,158
While preferred features and the best mode of
the invention have been shown, many modifications and changes
will occur to those skilled in the art. It is, therefore,
to be understood that the appended claims are intended to
cover all such modifications and changes as fall within the
true spirit of the invention.
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