Note: Descriptions are shown in the official language in which they were submitted.
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ELECTRICAL INDUCTIVE APPARATUS
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates in general to electrical
inductive apparatus, such as transformers, and more par-
ticularly to vapor-cooled inductive apparatus.
Description of the Prior Art:
The combination of gas/vapor medium has proven
to be a viable alternative to oil as a dielectric cooling
medium to be used in transformers, as well as other elec-
trical apparatus. The limiting factor regarding wide-
spread use has been of an economic nature, i.e., oil is
but a fraction of the cost of known vapor alternatives.
A recent advance in the transformer industry
that has helped reduce the amount of expensive liquid
dielectric necessary for a gas/vapor transformer has been
the development of powder coated insulated wire. The
development of this insulation technique has enabled the
insulation requirements of winding conductors to be re-
duced to several mils thickness thereby allowing reduction
in sizes of the windings and corresponding size reduction
of the transformer and required vapor cooling liquid
dielectric medium. However, this method of insulation
presents a problem because the highly uniform surface
covering, normally a desirable by-product oE the new
insulation techn:Lque, does not allow the liquid dielectric
to pass between adjacent turns of a windinK formed of wire
so insu:Lated.
Prior art: techniques of providing passages with
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suitable spacers between the turns of the windings, used
in oil filled transformers, are not s~litable in vapor-
cooled transformers using powder coated insulation for
several reasons. First, the difference between the di-
electric constants of a gas or vapor media and conven-
tional oil barriers greatly changes the stress grading so
that oil structures cannot be effectively used. Second,
the passages provided by solid spacers require a larger
radial build on the winding, therefore requiring a larger
amount of expensive vaporizable liquid dielectric and an
increased size in the transformer itself. Third, insert-
ing spacers between the turns of the winding reduces the
strength of the winding to withstand short circuit ~orces.
Accordingly, it would be desirable to have a
powder coated insulated coil with integral passages to
provide adequate paths for the liquid dielectric to dis-
perse over and flow between the surfaces of an induction
winding without the use of solid spacers.
SUMMARY O~ THE INVENTION
Briefly, the present invention is new and im-
proved vapor-cooled electrical inductive apparatus having
a winding with predetermined surface irregularities on the
turn surfaces of the winding to provide spaces between
certain adjacent portions of the turn sur-faces to permit a
cooling/insulating vaporizable liquid dielectric to flow
therebetween. The surface irregularities may take the
forrn of transverse grooves or bosses of insulation dis-
posed at predetermined intervals in one of the sides of an
elongated metallic conductor.
Also disclosed :in the present :invention is a
method and apparatus for forming precisely spaced grooves
and measuring the distance between the grooves so formed
in the surface of a continuously moving elongated metallic
conductor. The method includes the step of insulating the
grooved conductor to produce a homogeneous solid insulat:ed
conductor having grooves at a predetermined spacing cut
into at least one surface.
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BRI~F DESCRIPTION OF THE DRA~INGS
The invention may be better understood, and
further advantages and uses thereof more readily apparent,
when considered in view of the following detailed descrip-
tion of exemplary embodiments, taken with the accompanyingdrawings~ in which:
Figure 1 is a fragmentary elevational view of
vapor-cooled electrical apparatus which may be constructed
according to the teachings of the invention;
Figure 2 is a top view of a typical layer of a
coil of the apparatus of Figure 1;
Figure 3 is a top view of a solid insulated
grooved conductor according to the teachings of the inven-
tion;
Figure 4 is a front view of the conductor shown
in Figure 3;
Figure 5 is a cross-sectional view of the con-
ductor as shown in Figure 3 taken between arrows 5-S;
Figure 6 is a cross-sectional view of the con-
ductor as shown in Figure 3 taken between arrows 6-6;
Figure 7 is a diagrammatic view in elevation of
apparatus for forming precisely-spaced grooves in the
surface of a continuously-moving elongated metallic con-
ductor and insulating said grooved conductor according to
the teachings of the invention;
Figure 7A is a plan view of a sensing means
according to the teachings of the invention;
Figure 7B is a side view of a concave surface~
cutting bit for use in the apparatus of Figure 7A; and
Figure 8 is a diagrammatic view in elevation of
apparatus for producing bosses in a solid coating of
uniform insulation according to the teachings of the
invention.
D~SCRIPTION OF THE PREFERREI) EM~OVIMENTS
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Referring now to the drawings and Figure 1 in
particular, there is shown a diagrammatic representation
of a three-phase power transformer 10 which is of the
gas/vapor type. Transformer 10 includes a tank or casing
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12 having a magnetic core winding assembly 14 disclosed
therein, ancl liquid dielectric 16 such as C2CLl" ~8F16~,
or the like, which is vaporiæable within the normal oper-
ating temperature range of the magnetic core winding
assembly 14. The liquid dielec~ric 16 is distributed over
the magnetic core winding assembly 14 by any suitabl.e
means, such as via pump 18 and piping ~neans 20. In addi-
tion to the vapors of the liquid dielectric 16, tank 12
may include a non~condensible gas, such as SF6, to provide
insulation during start-up of the transformer 10.
Core winding assembly 14 includes magnetic core
22 and three sets of windings 24, one or each phase of
the power source (not shown) transformer 10 would be
connected to. ~indings 24 include a plurality of a~ially
adjacent layers such as layer 26. As shown in Figure 2,
each layer such as layer 26 has a plurality of radially
adjacent turns, such as turns 32 and 34 having turn sur-
faces such as turn surfaces 36, 38, llo and 42 in contact
with one another.
In the prior art, these turns were insulated by
wrapping with a cellulose paper. The wrapped paper turns
had enough irregularities between the turn surfaces to
permit the liquid diel.ectric to flow therebetween and
thereby spread a uniform film over the winding which would
evaporate and cool the winding. Recent powder coating
techniques have developed uniform solid insulation deposi-
tions of 2 to 4 mils thickness deposited on the surface of
the winding conductors, thereby enabling the coils to be
reduced in radial build. ~lowever, when the conductor was
insulated with the new powder coated solid type insu-
lation, the turn surfaces fit flush to one another such
that the liquid dielectric did not have paths to pass
through the winding.
It was essential that the cooling/insulating
liquid dielectric be able to flow uniformly throwghout the
interior of the winding depositing a film of liquid di-
electric over the turn surfaces of the coil for subsequent
vapo-rization, cooling, and insulating functions. Two
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different solutions were cons:idered to alleviat:e this
prohlern. The first was the use of solid insulating
spacers to form coolant ducts throughout the winding
similar to the oil ducts used in oil immersed trans-
formers. This solution proved unsatisfactory for several
reasons. The spacers i.ncrease the radial build of the
winding, negating the space advantage provided by the
powder coated insulation. Also, the solid spacers reduce
the high strength of the coil necessary to withstand short
circuit forces. Most important, howeverJ was that differ-
ences between the dielectric constants of the gas or vapor
media and conventional oil barriers (solid insulation
spacers) greatly change the stress grading. The dielec-
tric constant of a gas or vapor is very close to one (1)
while the dielectric constant of conventional solid :insu-
lating materials is approximately four (4) to six (6). A
high dielectric constant material which penetrates a
non-uniform or highly stressed dielectric field present in
a gaseous dielectric, can cause very low corona inception
voltages and low dielectric breakdowns, compared with no
solid spacers. Thus, certain desirable and conventional
arrangements of coil and winding supporting spacers, such
as those used in liquid filled apparatus, are denied use
in gas/vapor applications because of high dielectric
constant spacers penetrating non-uniform fields in an
insulating dielectric having a dielectric constant of near
1. .
The simplest and most desirable solution was
that of using no spacers if possible, i.e. to provide the
powder coated insulated surfaces with some type of irregu-
larities so as to provide licluid coolant c:irculation
passages throughout the winding. The p-roblem now was how
to provide irregulariL;.es in a surface that, due to the
powder coating insulating process, is characterized by its
uniformity. Two methods were employed to procluce the
irregularities in an elongated conductor having a uniform
covering of a solid homogeneous coa~ing oE electrical
insulati.on.
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The ~irst method is :illustrated in Figs. 3
through 6 wherein transverse indentations in the form of
evenly-spacccl grooves such as grooves ~l8 werc~ place(l in
the surface of the conductor prior to the powder coating
deposition of insulation. The grooves 48 have a width of
250 mils and were disposed in one of the surfaces 52 of
one of the sides of rectangular configured elongated
conductor 50 having the larger cross-sectional dimension.
Grooves 4~ were formed to a depth of 6 mils and after the
powder coating deposition of insulation step retained the
6 mil depth. The depth selected for the grooves 48 is
subject to the parameter that the ratio of the depth of
the grooves 48 to the cross sectional a-rea of the metallic
conductor S0 must be selected to provide the conductor 50
with the predetermined current capacity necessary for
operation of the contemplated winding. When the insulated
conductor 50 with the grooves so formed was wound around a
coil form to construct a winding similar to windings 24,
the liquid dielectric flowed in the passages formed by the
grooves very well. By controlling the spacing, the depth
and the angle (although Figs. 3 and 4 show grooves 48
disposed at 90~ transverse to the longitudinal length of
conductor 50, the grooves may be disposed in a surface of
the conductor at any predetermined transverse angle) of
the grooves so formed in the conductor 50, it is possible
to control the rate of flow of the liquid dielectric.
~ote that grooves 48 illustrated in Figs. 3 and
4 have an hourglass funnel configuration. Although this
configuration is not necessary in order to practice the
invention, i.e., straight grooves perform satisfactorily,
they illustrate a preferred embodiment of the invention.
The hourglass funnel-shapecl grooves 48 provide hourglass
funnel-shaped ducts between certain adjacent portions Or
the turn surfaces 52 when conductor 50 is wrapped into a
winding, thereby increasing the flow of liquid dielectric
within the hourglass funnel-shaped ducts while provicling
sufficient surface area on the surface 52 of conductor 50,
by way of the barrel-shaped spaces 56 between the hour-
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glass funnel-shaped grooves, to fully withstand compres-
sive forces due to the tight wrapping of the conductor
when it is wound into a winding. Figs 5 and 6, cross-
sectional views of the barrel-shaped spaces 56 and the
hourglass-shaped grooves 48 respectively, show in eleva-
tion the unique configuration o~ these items.
Although both the straight and hourglass grooves
have been described, the invention is not limited to any
particular shape of the groove, but rather emcompasses all
groove configurations. The shape of the groove, the angle
of the groove and the dimensions of the groove as well as
the shape and dimensions of the conductor, all may be
varied without departing from the teachings of the inven-
tion.
Apparatus for forming precisely-spaced grooves
in the surface of a continwously moving elongated metallic
conductor such as conductor 50 is shown schematically in
Fig. 7. Grooving apparatus 60 includes frame 62 support-
ing a grooving means 6~, such as the router cutter appara-
tus shown, for grooving the surface of a continuously
moving elongated metallic conductor, means 66 for changing
the depth of cut of grooving means 64 such as the depth
indexer shown, and support means 68, such as the back-up
anvil shown, for supporting the continuously moving elong-
ated metallic conductor. Grooving means 64 could also bea laser cutter, stamping apparatus or any other means for
forming a groove on the continuously moving elongated
metallic conductor. Support means 68 could also be a
horizontal support surface, series of parallel rollers, or
any other means for supporting the continuously moving
elongated metallic condwctor while it is being grooved.
Grooving apparatus 60 includes means Eor varying the fre-
~uency of operation of grooving means 64 such as drive
belt 70 and drive motor 72 in combination with a motor
speed control such as is shown generally at 74. By vary-
ing the frequency of operation, grooving means 64 can be
controlled to form the grooves at a predetermined spacing
into the sur~ace of a contin~lous].y moving elongated metal-
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Grooving apparatus 60 also includes measuring
means 76 for measuring the space between the grooves in
the surface 52 of continuously moving elongated metallic
conductor 50. Measuring means 76 includes sensing means
78, stroboscopic light 80 electrically connected and
responsive to sensing means 78, and spacing scale 82.
Stroboscopic light 80 is disposed on frame 62 on one side
of and above the moving conductor and spacing scale 82 is
disposed on the other side. Sensing means 78 senses the
forming of each groove by grooving means 64 and may con-
sist of a magnetic, electricalJ or mechanical sensing
device or any other àrrangement for sensing the forming of
each groove by grooving means 64. One arrangement for
sensing means 78 is shown schematically in Fig. 7A wherein
an eccentric cam 83 is fixedly mounted for rotation with
router cutter head 84. A set of mechanical contact points
86 are mounted such that contact point lever arm 88 is
spring biased towards eccentric cam 83 for momentary
contact with eccentric cam 83. Upon rotation of eccentric
cam 83 with router cutter head 84, mechanical contact
points 86 open and close with every revolution of router
cutter head 84 thereby momentarily completing the electri-
cal power circuit for stroboscopic light 78 causing strob-
oscopic light 78 to flash and momentarily illuminatespacing scale 80 and a predetermined portion of newly-
grooved continuously moving elongated conductor 50 when
sensing means 76 senses the forming of each groove. A
momentary stationary image of the moving conductor 50 is
produced at the location of spacing scale 80 J thereby
enabling an operator to compare the spacing between the
grooves with the spacing scale and adjust the frequency of
operation of grooving means 6~ to cause grooving means 64
to form grooves at a predetermined spacing into the sur-
ace 52 of moving elongated conductor 50.
In order to cause the grooves ~8 of surface 52of conductor 50 ~see Figures 3 and 4) to have the hour-
glass funnel shape discussed above J router cutter head 8
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incl.udes a concave surfaced cutting bit 90 as shown in
Figure 7B. The ends of concave surface 92 of cutting bit
90 contact the ends of sur:face 52 of continuously moving
conductor 50 earlier and later as well as cut deeper than
the middle of concave surface C~2 of cutting bit 90 thereby
forming hourglass funnel-shaped grooves such as grooves
48.
~eferring again now to Figure 7, in operation
the continuously moving elongated conductor, such as
conductor 50 is moved past and between the grooving means
64 and the support means 68 to cause grooves to be formed
in the surface, such as surface 52, of a continuously
moving elongated conductor, such as conductor 50. Sensing
means 78 senses the forming of each groove and completes
the electric power circuit for stroboscopic light 80
thereby flashing stroboscopic light synchronously with the
sensing of the forming of each groove to momentarily il-
luminate the spacing scale 82 and a predetermined portion
94 of the newly grooved continuously moving elongated
conductor 50 to obtain a momentary stationary image of the
predetermined portion 94 of newly grooved conductor 50.
An operator may then measure the distance between grooves
by comparing the spacing of the grooves on the momentary
image with the desired spacing on spacing scale 82 and
varying the frequency of operati.on of grooving means 6LI
such as by varying the angular velocity of router cutter
head 84 (see Fig. 7A) by adjusting the speed of motor 72
to cause the grooves to be formed in the surface 52 of the
moving conductor 50 at the desired spacing.
After forming the grooves at a predetermined
spacing in the s-urface 52, conductor S0 is then ~passecl
through an electrostatic powde-r coating means shown gener-
ally at 110 and means for hea~ing the conductor 50 to a
predetermined temperature shown generall.y at 112 to pro-
vide a uniform homogeneous coating of solid insulati.on.
Apparatus and the manner of electrostatic powder coating
the periphery of a continuously moving elongated conductor
with a rectangular cross-sectional configuration such as
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conductor 50 with a uniform layer of solid heat-fused,
cured solventless finely divided resinous polymeric powder
is disclosed in U.S. Patent 4,051,809 assigned to the same
assignee as the present application. Basically a uniform
layer of heat fused, solventless, finally divided resinous
polymeric powder such as the epoxy resin powder formula-
tion is electrostatically powder coated on the periphery
of grooved conductor 50 by electrostatic powder coating
means 110 and the uniformly coated grooved conductor 50
is heated to a predetermined temperature in heating means
112. For the epoxy resin formulation disclosed in the
hereinbefore mentioned co-pending application, a temperature
of approximately 500C is suitable to fuse the powdered
particles o insulation into a uniform, homogeneous coating
of solid insulation. The grooved conductor 50 so
insulated is characterized by its uniform homogeneous
coating of insulation, i.e , the insulation thickness in
the grooves is the same as the insulation thickness on
the balance of the periphery of the conductor 50.
The second method employed to produce the irreg-
ularities in a surface of an elongated conductor such as
conductor 50 having a uniform covering of a solid homo-
geneous coating of the electrical insulation hereinbefore
described was to provide bosses or protuberances in the
insulating material itself at a predetermined spacing.
Apparatus for doing this is shown in Fig. 8 wherein a
stick of compressed insulation powder 120 is continuously
fed into means for shearing small pieces of compressed
insulation 122 and dropping the pieces along the surface
52 of continuously moving elongated conductor 50 and then
passing conductor 50 through an electrostatic powder
coater and heater as described above. In this manner, the
small pieces of compressed powdered insulation and the
uniform coating oE powdered particles of the same insulat-
ing powder fuse into a uniform homogeneous coating of
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solid insulation having bosses or protuberances of the
insulating material at predetermined xpaces in order to
provide irregularities in the surface of the insulated
conductor.
In conclusion, the invention discloses an im-
proved vapor-cooled electrical induction apparatus having
a winding formed with an elongated metallic conductor
having surface irregularities to provide spaces between
certain a~jacent por~ions of the turn surfaces to permit a
vaporizable dielectric liquid to flow through the winding.
Although the invention was developed i.n order to solve
problems relative to the transformer industry, it will be
appreciated that the invention is not limited to transform
applications but rather is applicable to any vapor cooled
inductive apparatus wherein the uniform finish of a powder
coated insulated conductor is desired to be combined with
surface irregularities in the insulated turn surfaces of
induction windings to provide spaces to permit a vaporiz-
able liquid dielectric to flow through the windings.
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