Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
9~`3
20-TR-1404
INSULATED ARMATURE COIL
FOR DYNAMOELECTRIC MACHINE
Back~round of the Invention
This invention relates generally to rotating dynamoelectric
machines, and it relates more particularly to improvements in the
electrical insulation of an armature coil for the rotor of such a
machine.
In large, relatively high horsepower direct current (d-c)
dynamoelectric machines such as locomotive traction motors, the
armature comprises a rotatable, cylindrica1 core of ferromagnetic
laminations having a plurality of slots in its periphery for
receiving armature coils thet are electr;cally connected to an
external circuit via a rotating commutator and cooperating
stationary brushes. Each armature coil has multiple individual
turns. It typically is formed by covering each of a plurality of
long, thin copper bars with suitable dielectric material to
15 provide turn to-turn insulation, binding a set of eight (more or
less) of these bars in parallel and bending the set into a
generally rectilinear winding whose opposite sides are straight
and parallel, and then covering the winding with a sheath of
suitable dielectric material so as electrically to insulate the
bundle of juxtaposed bars from the exposed edges o~ the core
laminations that define the sidewalls and bottoms of the slots in
which the straight sides of the coil are placed and that are at
ground potential. There are severa1 known techniques for
applying the turn-to-ground insulating sheath on a multiple turn
armature coil. One is to wrap each of the straight sides of the
bundle of copper bars (i.e., the slot section of the coil) in
multiple layers of a thin sheet of dielectric material; see prior
art U.S. patents No. 2,675,421 and No. 21697,055. In a second
known method, each slot section is encased between a pair of
complementary, pre-formed, relatively inflexible channel-shaped
3~
20TR 1404
-- 2 --
members of dielectric material; such members are easy to
manufacture and assemble but provide relatively poor creepage to
ground~ A third method is to spiral wrap the sides of the coil
in insulating tape. The third method can be used either alone,
in combination with the first method (see U.S. patent No.
3,662,199), or in combination with the second method.
Whatever method is used, the turn-to ground insulation of an
armature coil needs to have sufficient dielectric strength,
thickness, and integrity to prevent electrical breakdown (i.e.
short circuits) from any turn in the coil to ground under all
possible environmental conditions which, for a locomotiYe
traction motor9 include constant vibration, frequent mechanical
shocks, occasional electrical overloads, a wide range of ambient
temperatures~ and an atmosphere that can be very wet and/or
dirty. And the desired insulating properties need to be
~iaintained, without appreciable deterioration, as the machine
ages and in spite of cyclic changes, due to temperature
excursions, in the length of each slot section of thP coil
relative to the longitudinal dimension of the sidewalls of the
associated slot. (As is well known, each time the average
magnitude of armature current is increased to its full-load
rating, the heating effect of this current will cause the copper
bars in the coil to expand, and the amount of such expansion
differs from that of the laminated core which initially is cooler
than the coil and which in any event has a different coefficient
of thermal expansion.)
Good heat transfer is another generally desirable
characteristic of the insulating system. This characteristic is
particularly significant in traction motors where the goal is to
obtain more output torque per unit of weight. To help attain
this goal, any one or combination of the following possible
changes to the armature of the motor is desirable: (1) increase
the cross-sectional area of the copper bars in each armature coil
for a slot of given size, thereby allowing the coil to conduct
~2~
20TR 1404
-- 3 --
more current without increasing current density; (2) increase the
current density (and consequently the heat generated) in the
bars; (3) decrease the depth of each slot so that bars of given
cross-sectional area are located closer to the surface of the
core and hence closer to the field poles of the machine. But
none of these changes can be achieved without reducing the
thickness of the turn-to-ground insulation of the armature coil.
The thinner the outer sheath of insulation on the armature coil,
the more space for the copper bars inside the sheath and the
better the transfer of heat from the bars to the rotor core. By
thus reducing the generation of heat and/or promoting its
dissipation, the armature coil can carry more current (and the
motor can therefore develop more torque) without exceeding a
given maximum safe temperature rise.
An insulating material that is particularly advantageous for
traction motor applications is known generically as Type H
polyimide film. An FEP-fluorocarbon resin coated rorm of such
film is manufactured and sold by Dupont Company under its
trademark "Kapton." Thin gauge Kapton insulation is very
flexible, has a relatively high dielectric strength (typically at
least 3,000 to 4,000 volts per mil), and remains physically and
electrically stable at elevated temperatures. The coating of
FEP-fluorocarbon resin (popularly known by the Dupont trademark
"Teflon") provides a very smooth, heat-sealable surface on the
base of the polyimide film. This also improves the chemical
resistance oF the film and reduces the rate of moisture
permeability and of oxldative decomposition. Such composite
material has been heretofore used successfully to insulate
rectangular motor magnet wire and to insulate the field coils of
locomotive traction motors (see U.S. patent 4,376,904-Horrigan).
Precision motors have heretofore used slot liners made of H film.
For more info~ation about Kapton and its typical prior uses, see
the paper by D. H. Berkebile and D. L. Stevenson titled "The Use
r~ ~3~1! 3 2 0 TR 14 0 4
-- 4 --
of 'Kapton' Polyimide Film in Aerospace Applications" published
in 1982 by the Socie~y of Auto~otive Engineers at pag2s 3562-68
of its Conference Record of an SAE meeting on October 5-8, 1981
(preprint No. 811091).
Summary of the Invention
A general objective of the present invention is to provide
an improved insulating system for the armature coils of
dynamoelectric machines.
Another objective is the provisiun of an armature coil
having a sheath of turn-to-ground insulation characteri7ed by a
relatively thin wall which has a high dielectric strength, by
good creepage to ground, and by the absence of troublesome
binding or abrasion between the inside surface of the sheath and
the coil conductors when the latter expand or contract
longitudinallY-
A rurther objective is the provision of a multiple turnarmature coil having turn-to-turn insulation that is relatively
s~all in size and optimal in location.
It is yet another object of the invention to provide an
anmature coil insulating system that effectively utilizes the
beneficial characteristics of polyimide film.
In carrying out the in~ention in one form, each armature
coil on the rotor of a dynamoelectric machine comprises a bundle
of parallel, separately insulated conductors of generally
rectangular cross section that is bent in a generally rectilinear
configuration having first and second relatively lony and
straight slot sections that are respectively adapted to be
inserted in separate slots in the periphery of a cylindrical core
of the rotor. At one end of the rotor the first and second slot
sections of the bundle of conductors are respectively joined to
first and second shorter sections which form obtuse angles
therewith and which in turn extend convergently ~o a point of
intersection where they join one another via an acutely bent
~L2 5 ~ 2 0 TR 14 0 4
loop. Turn-to-ground insulation for the coil is provided by two
pre~formed tubes of substantially non-compressible,
non-thermoplastic dielectric material. The first tube surrounds
the exterior surface of the first slot section and the adjoining
shorter section of the bundle of conductors, whereas the second
tube surrounds the exterior surface of the second slot section
and the second shorter section.
Each of the aforesaid tubes fits snuggly but slidably over
the surrounded sections of the bundle of conductors to provide
electrical insulation between the bundle and the slot walls of
the rotor core. The wall of the tube has a unitary, seamless,
watertight construction that ensures virtually the same amount of
insulation on all sides of each slot section of the coil and that
provides good creepage to ground. The wall will not cold flow
when radially inward pressure is applied to the coil during the
slot closing (weaging) step of the manufacturing process.
Furthermore, the wall is thin and flexible enough to bend in any
plane without aPpreciable los5 of either physical or dielectric
intesrity. Its thinness permits the respective conductors of the
coil to have relatively large cross sectional areas and therefore
to carry more current in a slot of given dimensions, and its
thinness also enhances the transfer of heat from the conductors
to the coreO The wall of each tube is also characterized by a
very smooth interior surface that provides a relatively slippery
interface with the surrounded conductors, whereby the
longitudinal expansion or contraction of the conductors inside
the tube in service will not abrade or wear out the insulation.
Preferably each armature coil comprises at least four
conductors which are arranged in quadrature with respect to each
other9 and there are four individual turns per bundle of
conductors. Inside the coil the four ccnductors are separated
from one another by turn-to-turn insulating means comprising a
pre-formed unitary member o-f substantially non-compressible,
SC~r3
non-thermoplastic dielectric material having a cross-shaped cross
section. This member is thin and flexible enough to bend in any
plane without appreciable 10s5 of either its physical integrity
or its electrical insulating properties, and it occupies only a
very small space inside the coil. This permits the respective
conductors of the coil to have larger cross sectional areas.
Preferably both the tubular turn-to-ground insulation and
the cross shaped turn to-turn insulation comprise multiple layers
of very thin polyimide film sealed together by fluorinated
ethylene propylene (FEP) resin. In the case of the aforesaid
tubes, the smoothness and slipperiness of the interior surface of
the wall of the tube is enhanced by a coating of FEP.
The invention will be better understood and its various
objects and advantages will be more fully appreciated from the
following description taken in conjunction with the accomPanying
drawings.
Brief D _cr1ption of the Drawings
Fig. 1 is a simplified side elevation, partly in cross
sectionl of the rotor of a rotating dynamoelectric machine such
as a d-c motor, the rotor having a plurality of peripheral slots
in which are disposed an equal plurality of armature coils
embodying the present invention;
Fig. 2 is a simplified schematic electrical diagram of one
of the armature coils of the Fig. 1 rotor, illustrating its four
individual turns in series relationship with each other;
Fig. 3 is an enlarged cross-sectional view of one of the
slots in the core of the rotor of Fig. 1, illustrating that the
first slot section of one coil is located in the bottom position
of the slot underneath a second slot section of another coil;
Fig. 4 is a plan view of a whole armature coil for the Fig.
1 rotor;
Fig. S is an enlarged cross-sectional view nf the Fig. 4
coil, taken along lines 5-5 at a bend of the bottom slot section
of the coil;
Fig. 6 is a perspective view of part of the pre-formed tube
of dielectric material that surrounds each of the slot sections
of the Fig. 4 coil in accordance with the present invention;
Fig. 7 is a perspective view of part cf the pre-formed
cross-shaped member of dielectric material that i5 disposed
inside ~he coil to separate the four turns from one another in
accordance with the present invention, and
Fig. 8 is an enlarged and fragmentary perspective view of
the armature head end of the Fig. 1 rotor, with the upper tier of
the armature coils partially broken away to better show the lower
tier and a layer o~ electrical insulation therebetween.
Description of the Pre~erred Embodiment
The rotor represented in Fig. 1 is well suited for use in a
dynamoelectric machine such as a cylindrical d-c traction motor.
- The rotor has a shaft 11 that is adapted to be supported in
suitable bearings (not sho~n) for rotation about its axis. A
conventional commutator 12 comprising a cylindrical array of
discrete electroconductive segments or bars is mounted near one
end of the shaft, and a ring-shaped armature head 13 is mounted
near the opposite end. A cylindrical core 14 of magnetizable
material is disposed on the shaft 11 between the commutator 12
and armature head 13. In practice, the core 14 actually
comprises a stack of thin ferromagnetic laminations.
The ccmmutator 12, as it i 5 i 1lustrated in Fig. 1, is a
typical ~'-ring arch-bound type comprising an outer retaining ring
15 that is bolted to a cooperating ring 16 on the shaft 11 so as
to capture the commutator segments therebetween. The inboard
ends of the respective segments extend rzdially outwardly,
thereby forming a cylindrical array of risers 17 to which the
armature coils of the rotor can be conveniently connected. The
-- 8 --
commutator segments are usually made of copper, and they are
electrically insulated from the two metallic retaining rings by
means of a pair of annular commutator cones 18 and 19 of
dielectric material that are respectively sandwiched between
Y-shaped notches at opposite ends of each segment and the
respectively opposing rings 15 and 16. Each segment has an
outwardly facing surface adapted to be slidingly contacted by a
carbon brush (not shown) as the rotor turns about the axis of its
shaft 11. A profile of one of the segments is shown at 23.
For passing cooling air in an axial direction through the
rotor, there is a ring of holes (see reference No. 27 in Fig. 1)
in the armature head 13, a similar ring of holes (28) is provided
in the retaining ring 16 of the commutator 12, and these holes
register with passageways (not shown) through the core 14.
The rotor core 14 includes a plurality of axially extending
slots 30 spaced apart from one another around its periphery.
Physically inserted in these slots and electrically connected to
selected co~mutator segments are an equal plurality of armature
coils. ~n one embodiment of the invention 46 coils are used on
~he rotor of a d-c commutator motor having a continuous output
rating in excess of 1,000 horsepower. Each armature coil
actually comprises a bundle of parallel, elongated b~rs that are
made of electroconductive material such as copper and that are
individually covered with thin layers of electrical insulation
su~h as Kapton. Each of these separately insulated bars or
conductors has a generally rectangular cross section~
In a conventional manner, the bundle of parallel conductors
is bent to form a generally rectilinear winding having two
relatively long and straight slot sections B and T (see Fig. 4).
3Q The first slot section B of each coil is located in the bottom
position of a core slot, whereas the second slot section T is
located in the top position of a separate slot. These slot
sections are interconnected at the closed end or bight of the
~ 5 ~3~
coil by means of a loop L which slightly overhangs the outboard
end of the armature head 130 The parts of each coil that adjoin
the loop L and extend over the cylindrical perimeter of the
armature head are encircled by conventional banding 31 which
5 prevents radial movement thereof due to centrifugal force when
the rotor shaft is turning at high speed.
At the open end of each coil, opposite ends of each of the
bundled conductors are connected to selected segments of the
commutator 12. More particularly, these distal ends D of the
conductors are respectively connected to the risers of a
predetPrmined set of the cor~mutator segments. The parts of each
coil that extend from the rotor core 14 to the commutator
segments are tightly secured to the perimeter of the retaining
ring 16 by a band 32 of insulating material. After all of its
parts are assembled, the whole rntor is impre~nated with
insulating varnish by a conventional vacuum-pressure technique
(VPI) and then baked at elevated temperature so as to cure the
varnish which fills any voids in the assembly9 thereby promoting
heat transfer and water resistance.
ZO In the illustrated embodiment, the armature coil is a
polycoil having four individual turns/ and the distal ends of the
bundled conductors are so interconnected that the four turns are
electrically in series with each other. This can be seen in Fig.
2 where the four turns of one coil are shown connected to a set
of five consecutive commutator segments Z1 through 25. As will
be appreciated by a person skilled in the art, there are thin
layers of dielectric material (not shown) interleaved with the
commutator segments so as to provide electrical insulation
between adjacent segments. The first tur~ of the coil has a top
half lT that is associated with the slot section T of the
illustrated coil and a bottom half lB associated with slot
section B of the same coil. The distal end of the t~p half lT is
connected to corr~utator segment 21, and the distal end of the
20 TR 1404
- 10 -
bottom half lB is connected to the next segment 22. The second
tu~n of the same coil also has top and bottom halves 2T and 2B,
respectively, with the former being connected9 in co~on with the
bottom half lB of the first turn, to the segment 22 and the
latter being connected to the third commutator seg~ent 23 of the
set. Similarly, the third turn has top and bottom halves 3T and
38 connected between adjacent segments 23 and ~4, and the fourth
turn has top and bottom halves 4T ard 4B connected between
segments 24 and 25. Fig. 1 shows that the distal ends of both
the bottom hal~ 2~ of the second turn and the top half 3T of the
third turn are connected to the riser of the same segment 23.
Inside each polycoil the four turns are physically arranged
in quadrature ~lith respect to each other, and the loop L at the
bight of the coil inverts the turns so that the top and bottcm
halves of each turn are disposed in diagonally opposite
quadrants. In practice each of the four individual ~urns shown
in Fig. 2 is preferably split into two or ~ore parallel paths
provided by at least two juxtaposed insulated conductors, the
corresponding ends of which share co~mon electrical junctures.
Z Fig. 3 shows how the first slot section B of one ar~ature
coil and the second slot section T of anotller coil fit
respectively into bottom and top positions o~ one of the slots 30
in the periphery of the rotor core 14. The cpen enu or mouth of
the slot 30 is closed by a conventional slot wedge-34 which
retains the slot sections of both coils in place. Rotors of some
maehines have more armature coils than slots, in which case at
lease one additional slot section may be placed in slot 30
between the illustrated secttons B and T. By using improved
manufacturing processes that ensure negligible dimensional
d~spartties among the various bundles of conductors, the various
wedges, and the vartous slots themselves, a tight fit is obtained
without placing any prior art filler strips of insulating
material between the wedge 34 and the top coil.
~5~ 20 TR 1404
As is indicated in Fig. 3, each coil preferably comprises 2
bundle of eight separately insulated conductors, and the distal
ends of these conductors are so interconnected that there are two
parallel conductors per turn and four serial turns per coil. In
5 accordance with the present invention, the exterior surface of
each slot section of the bundle of conductors is surrounded by a
pre-formed tube 35 of dielectric material. The significant
characteristics of this tube will soon be described in
conjunction with the description of Figs. 4 6. Optionally, the
coil is wrapped in a single, thin layer 36 of insulating tape
which helps to protect the outside of each tube 35 from
mechanical damage while the coil is being inserted into the
slots. The function of the tube 35 is to provide electrical
insulation between all of the coil's conductors and both the
sidewalls of the slot 30 (i.e., turn-to-sround insulation) and
the conductors in the adjacent slot section of the companion coil
(i.e., coil-to-coil insulation). When the rotor is operating
normally in a typical machine, its core 14 is usually at ground
potential, whereas the electrical potential of the conductors
comprising one of the armature coils can be as high as 1,400
volts with respect to ground and also with respect to the
conductors in the adjacent slot section of a different coil.
In accordance ~ith the present invention, the four turns of
each coil are separated from one another by pre-formed unitary
cross pieces 37 of dielectric material that are disposed inside
the coil. This enhanoes the turn-to-turn electrical insulation
that is provided by the insulating layers cavering the individual
conductors. In normal operation the potential difference between
the conductors of consecutive turns is typically 50 volts, and
therefore the potential of the fourth turn is approximately 150
volts diFFerent than that of the first turn of the same coil.
The construction and advantage of the cross-shaped members 37
~'~ S ~3
- 12 -
will be better understood from the later description of Figs. 5
and 7.
The generally r~ctilinear conTiguration of the armature coil
is clearly shown in Fig. 4. The first and second straight,
S parallel slot sections B and T of the coil are integrally joined
a~ their anmature head ends to first and second shorter sections
41 and 42, respectively. Th~ shorter sections 41 and 42 of the
coil extend at obtuse angles from the respective slo~ sections B
and T to a point of convergence where they are joined together by
~he acutely bent loop L. Upon forming the loop L, the bundle of
conductors is t~isted a half revolution (180 degrees) so that the
four turns of the coil are transposed at this point. As a
result, the coil turn which occupies the lower inboard quadrant
in the slot section B of the bundle of conductors ~e.g.~ the turn
whose bottom half is identified by the reference character lB in
Fig. 2) will occupy the upper outboard quadrant in the slot
section T. In the illustrated embodiment of the invention, two
diagonally opposite pairs of conductors are sheathed in flexible,
short rein-forcement sleeves 43 of insulating material (such as
woven glass fibers) in the region of the loop L
As is shown in Fig. 4, the slot sections B and T of the
armature coil are respectively joined at their commutator ends to
third and fourth shorter sections 44 and 45 which form obtuse
angles therewith, and the latter sections of the coil in turn
lead to the distal ends ~ of ~he individual conductors. In the
vicinity of their distal ends the conductors are stripped of
their insulating covers and are offset and flattened so as to be
properly aligned and conditioned for making good contact with the
risers of the set of commutator segments to which this armature
coil will be connected when assembled with the other coils on the
rotor.
In FigO 4 the optional layer 36 of insulating tape on the
outsi~e of the illustrated coil has been omitted in order to
~5~
- 13 -
reveal the disposition of the pre-formed tubes 35 of dielectric
material. A first one of the tubes 35 surrounds the exterior
surface of essentially the whole of the first slot section B of
the bundled conductors and the exterior surface of at least part
(and preferably the whole) of the adjoining shorter section 41.
A second similar tube surrounds the exterior surface of
essentially the whole of the second slot section T and the
exterior surface of at least part (and preferably the whole) of
the second shorter section 42. E~ch of these tubes fits
snuggly but slidably over the exterior surface of the surrounded
sections to provide electrical insulation between the bundle of
conductors in the coil and the walls of the slo~ 30 in the rotor
core 14.
As is best seen in Fig. 6, the wall of each pre-formed tube
35 has a generally rectangular cross section. It is rnade of a
substantially non-compressible, non-thermoplastic material having
a relatively high dielectric strength. T~,e tube wall has a
unitary, seamless construction, and it is thin and flexible
enough to bend in any plane without appreciable loss of either
its physical or its dielectrio integrity. The interior surface
of the wal, is smooth enough to permit the bundle of conductors
to move freely inside the tube as they expand and contract
longitudinally in the core slot. In the presently preferred
embodiment of the invention, these characteristics are obtained
by forming the wall of the tube 35 from multiple layers of very
thin polyimide film intimately bonded together by fluorinated
ethylene propylene (FEP) resin. Plain polyimide film (Type H)
has a dielectric constant of approximately 3.0 or higher at
temperatures below 300~ C. One brand of this material, known as
Kapton Type F, inclu~es a coating of FEP-fluorocarbon, known as
Teflon, on one or both sides.
In the preferred enlbodiment of the invention, each ~ube 35
is pre-forrned by wrapping a wide sheet of non-oriented Kapton
5 ~
~ 14 -
(coated with FEP resin on both sides) approximately eight times
around a mandrel of desired shape and length, applying pressure,
heating the mandrel until the FEP resin melts (between 350 and
400~ C), cooling +he mandrel to permit the resin to resolidify
(at approximately 220 C) which seals the adjoining layers of
Kapton to one another, and then releasing pressure and removing
the completed tube from the mandrel. Both internal and external
sides of the wall of this pre-formed tube are coated with FEP
which provides a very smooth surface that permits the tube to
slide easily over the bundle of insulated conductors. Once the
eight layers of the sheet of Kapton are cemented or fused
together in the above-described manner to form the unitary 9
seamless wall of the tube, the wall will remain infusible and
dimensionally stable when exposed to elevated temperatures during
subsequent manufacture or operation of the rotor. It will not
seize or bond to the insulated conductors inside the tube during
the tinal VPI cure of the rotor. The tube wall has a
substantially uniform thickness which is not greater than
approximately 15 mils9 and it will not cold flow or creep under
pressure. In the presently preferred embodiment of the
invention, the tube 35 is approximately two feet long, its inside
dimensions are 0.64 inch high by 0.51 inch wide, and its wall is
approximately 0.01 inch thick.
In the embodiment of the invention that is illustrated in
Fig. 4, the tubes 35 do not extend beyond the coil sections B and
T at the commutator end of the armaiure coil, and known
insulating material (not shown) is usually wrapped around the
bundle Q~ conductors along the third and fourth shorter sections
44 and 45 of the coil to provide additior.al turn-to-ground
insulation between each of these sections and the perimeter of
the commutator retaining ring 16. However, in an alternative
embodiment the pre-formed tubes 35 will be longer so that a tube
surrounds the exterior surface of the bundle of conductors along
- 15 -
part of each of the latter sections9 thereby desirably increasing
the electrical creepage distance that these tubes provide between
the commutator end of the rotor core 14 and the conductors in the
slot sections B and T of the coil.
Insulating means is disposed inside the armature coil for
separating the four pairs of parallel, separately insulated
conductors from one another at least in the vicinity of the loop
L and of the obtuse angles at opposite ends of each of the slot
sections B and T. As was described earlier in conjunction with
Fig. 3, and as is shown more clearly in Fiss. 5 and 7, this
insulating means comprises a pre-form~d unitary member 37 of
dielectric material having a cross-shaped cross section. In
accordance with the present invention, the member 37 is made of
substantial1y non-compressible, non-thermoplastic material that
has a rela~ively high dielectric strength and thAt is thin and
flexible enough to bend in any plane without appreciable loss of
either i~s physical integrity or its electrical insulating
properties. Preferably these characteristics are obtained by
forming the member 37 from two layers of very thin polyimide film
intimately bonded together by FEP resin. This can be done
conveniently by feeding tapes of relatively narrow-width Kapton
Type F film (coated with FEP resin on one side) through a die
having four intersecting slots which conform to the desired cross
section of the member 37, with each tape spanning a different
pair of mutually perpendicular slots so that each of the four
slots is filled with adjoining halves of two separate tapes
having their coated sides facing each other, heating the die to a
temperature above the melting point of the FEP resin, cooling the
tapes before they exit the die to permit the resin to resolidify
which seals the adjoining tapes to each other and thereby forms a
unitary 2-ply crosspiece, and cutting the completed piece to the
desired 1ength. Preferably the cross-shaped member 37 is long
enough to extend continuously along the loop L, along the whole
3 ~ 3 2 0 TR 14 0 4
- 16 ~
length of both of the first ar,d second shorter sections 41 and 42
of the coil~ along the whole length of both of the slot sections
B and T, and along an appreciable part of each of the third and
rourth snorter sections 44 and 45.
The vertical and horizontal partitions of the pre-formed
cross-shaped member 3, are actually only about one-fourth as
thic~ as the wall of the previously described pre-formed tube 35.
The vert-,cal partitions provide extra insul~tion between the
first and fourth turns of the coil and between the second and
1C third turns. In Fig. 5 ~he first turn comprises the conductor
pair lB in the lower inboard quadrant of the first 510t section B
of the coil, the second turn comprises the conductor pair 2B in
the upper inboard quadrant, the third turn comprises the
conductnr pair 3B in the upper outboard quadrant, and the fourth
turn comprises the cunductor pair 4B in the lower outboard
quadrant of the same slot section. The thin layer of insulaticn
tha~ covers each of the eight conductors in the coil is
represented in Fi~. 5 by the reference No. 47. Preferably the
insulating layer 47 is Kapton, and the FEP coatin~ on its
exterior surface cooperates with the F~P coating on the inside
surface of the tube 35 to facilitate lon~it!~dinal movement by the
bundle of conductors, with respect to the tube 35, when the
conductors expand and contract due to thermal cycling in service.
Note that the FEP coating also resists "wetting" by the varnish
that is applied to the rotor during the final VPI cure, and
therefore it prevents the conductors from being bonded to the
inside of the tube 35 by the varnish that penetrates into this
area from opposite ends of the tube.
The horizontal partitions of the cross-shaped membe~ 37
provide extra turn-to-turn insulation between the first and
second turns of the coils (conductor pairs lB and 2B in Fig. 5)
and between the third and fourth turns (conductor pairs 3B and
4B). This is particu7arly important at the loop L and at th~
~3~
four "corners" of the coil where the bundle of eight conductors
is bent to form the obtuse angles at opposite en~s of the
parallel slot sections B and T. As is illustrated in Fig. 5,
bending a conductor distorts its cross section, and a swelling or
"upset" tends to develop in the inboard region of the conductor.
The upset is most pronounced in the vicinity of the inside radius
of the bend. Heretofore two diagonally opposite pairs of
conductors have been wrapped in flexible reinforcement tape of
insulating material at each corner of the coil to supplement the
insulation on the individual conductors, thereby enlarging the
gap between adjacent upset regions of conductor pairs lB and 2B
(and of pairs 3B and 4B), respectivelyO The crosspiece 37 of the
present invention serves the same purpose. Being very thin,
substantially incompressible and resistant to cold flow, and
being located solely in the areas where the extra turn-to-turn
insulation is required, ~he member 37 occupies less space than
the prior art reinforcemen~ tape and thereby permits larger
conductors to be used in a core slot of given si~e. Upon bending
the bundle of conductors to for~ a corner of the coil, wrinkles
or creases are formed in the inboard horizontal partition of the
member 37. The resulting ripples or c-rinkles are shown in Fig.
5. They desirably enhance the insulation between adjacent upset
regions of the conductor pairs that occupy the two inboard
quadrants of the coil.
A conventional hydraulic/pneumatic actuated coil forming
machine is used to make the loop L and the other bends or corners
of the armature coil shown in Fig. 4. Initially the bundle of
eight parallel, separately insulated conductors is straight, and
the distal ends D are not flattened. At this poin~ in the coil
forming process, the pre-formed cross-shaped member 37 is
symmetrically positioned inside the bundle of conductors, and the
two insulating sleeves 43 are put over diasonally opposite pairs
of conductors half way between their opposite ends. The next
~5
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step of the process is to bend and twist the bundle so as to form
the loop L. Then the two pre-formed tubes 35 are put over the
respective ends of tne bundle which is still straiaht (except for
the loop L). Ordinarily, because of the smooth interior surface
S of its wall, each tube 35 slides easily over the bundle of
conductors. However, if some of the conductors are bowed, they
will be forced compactly to~ether in the process of assembling
the tubes onto the bundle. After putting the tubes 35 over
opposite ends of the bundle of conductors, each end is bent at
three separate places to form the shorter sections 41, 42, 44,
and 45 and the straight, parallel slot sections B and T of the
illustrated coil.
Fig. 8 shows how the first and second shorter sections 41
and 42 of the armature coil are securely banded to the perimeter
of the armature head 13 of the rotor. The layer 36 of insulating
tape that optionally covers the outside of each of the coils (and
that provides a surface to which varnish adheres during the final
VPI cure of the rotor) has been omitted in this figure. By
surrounding the exterior surface of essentially the whole of each
of the shorter sec~ions 41 and ~2 of each coil, the pre-formed
tubes 35 of dielectric material are e ff ective to provide
electrical insulation between the armature head 13 and the bundle
of conductors that the tubes envelop. The tubes also insulate
the bottom tier of coil sections 41 from the top tier of sections
42, and they insulate the top tier from the banding 31. In
practice the insulation provided by the tubes ~5 is supplemented
by a thin layer 51 of electrical insulating material between the
banding 31 and the top tier, by another thin layer 52 of
coil-to-coil insulation between the top and bottom tiers, and by
a thin layer 53 of coil-to-ground insulation between the b~ttom
tier and the armature head. In each instance, however, the
supplementary layer of insulation can be significantly narrower
and/or thinner than has heretofore been the case, thereby
~ ~3 ~(,3~ 2 0 TR 1 '} 0 4
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facilitating tne trans;er of heat from the conductors in the
arrnature coils to the armature head and to the stream of cooling
air. The tubes 35 ensure a very lcng creepage distance between
the slot sections of each bundle of conductors and the outboard
end of the rotor core 14.
While a preferred ernbodiment of the invention has been shown
and described by way of example, many modifications will
undoubtedly occur to persons skilled in the art. The concluding
claims are therefore intended to cover all such modifications as
fall within the true spirit and scope of the invention.
