CA1180073A

CA1180073A - Vapor cooled electrical inductive apparatus

Info

Publication number: CA1180073A
Application number: CA000376900A
Authority: CA
Inventors: Richard D. Gibbs; Roger C. Johnson
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1980-05-28
Filing date: 1981-05-05
Publication date: 1984-12-27
Also published as: KR840002387B1; JPS609648B2; NO811767L; JPS5710913A; KR830006784A; FR2483678A1

Abstract

48,334 ABSTRACT OF THE DISCLOSURE
Vapor cooled induction apparatus having a wind-ing with predetermined surface irregularities on the turn surfaces of the winding to provide spaces to permit a cooling/insulating vaporizable liquid dielectric to flow between the turn surfaces of the winding to enable a film of the insulating cooling dielectric to be deposited on the surface area of the winding. The surface irregularities may be transverse grooves disposed at predetermined inter-vals in at least one surface of an elongated metallic conductor used to form the winding or they may be bosses of insulation disposed on a predetermined spacing on at least one surface of the elongated metallic conductor.
Also disclosed are a method and apparatus for forming precisely spaced grooves in the surface of a continuously moving elongated conductor and thereafter insulating the grooved conductor with a uniform, solid, homogeneous coating of electrical insulation.

Description

` ~.8V~'~3 1 48,339 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 ~' .

2 ~8,339 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.

3 ~8,339 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
_ .. . .. ~ . ... .
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 .
'

4 ~8,339 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 ~, . .

5 ~8~9 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.

6 48,339 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-b ~~0 73

7 ~,339 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-~' . ';

~ ~800 ~

8 48,339lic conductor such as conductor 50.
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 ~r~

`J'~

9 48,339 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 1 ~8V~ ~3 1~ 48,339 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 , ,-, ij .~ . .. .

.

11 4~,3~9 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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Claims

12 48,339 CLAIMS:

1. Electrical inductive apparatus, comprising:
an enclosure;
a winding including at least two adjacent turns of an electrical conductor having homogeneously solid insulated turn surfaces in contact with one another dis-posed in said enclosure and producing heat during normal operation;
a liquid dielectric having a predetermined viscosity disposed in said enclosure to a predetermined level said liquid dielectric being vaporizable within the normal operating temperature range of said winding; and means for distributing said liquid dielectric over said winding;
at least one of said turn surfaces having prede-termined surface irregularities therein to provide spaces between certain adjacent portions of said turn surfaces to permit said liquid dielectric to flow therebetween.

2. The electrical inductive apparatus of claim 1 wherein the winding includes a plurality of axially adjacent layers, each of said layers having a plurality of radially adjacent turns having homogeneously solid insu-lated turn surfaces in contact with one another,

3. The electrical inductive apparatus of claim 1 wherein the surface irregularities include a plurality of transverse indentations at predetermined intervals along the longitudinal length of the homogeneously solid insulated turn surface.

4. The electrical inductive apparatus of claim 13 48,339 3 wherein the indentations include grooves of a predeter-mined width and depth disposed in the homogeneously solid insulated turn surface at a predetermined angle transverse to the longitudinal length of the turn surface.

5. The electrical inductive apparatus of claim 1 wherein the electrical conductor is an elongated metal-lic conductor having a substantially rectangular cross-sectional configuration wherein one of the rectangular cross-sectional dimensions of the metallic conductor is larger than the other dimension, and the surface irregu-larities include grooves of a predetermined width and depth disposed at predetermined intervals in at least one of the sides of said elongated metallic conductor having the larger cross-sectional dimension at a predetermined angle transverse to the longitudinal length of said elong-ated metallic conductor.

6. The electrical inductive apparatus of claim 5 wherein the predetermined angle is 90°.

7. The electrical inductive apparatus of claim 5 wherein the ratio of the depth of the grooves to the cross-sectional area of the metallic conductor is selected to provide the metallic conductor with a predetermined current capacity.

8. The electrical inductive apparatus of claim 5 wherein the grooves have an hourglass funnel shape.

9. The electrical inductive apparatus of claim 5 wherein the electrical conductor is uniformly covered with a solid homogeneous coating of electrical insulating material.

10. The electrical inductive apparatus of claim 9 wherein the solid homogeneous coating of electrical insulating material is formed of a heat-fused, cured, solventless, finely divided resinous polymeric powder.

11. The electrical inductive apparatus of claim 10 wherein the polymeric powder is an epoxy resin.

12. The electrical inductive apparatus of claim 1 wherein the electrical conductor is covered with a solid homogeneous coating of electrical insulating material and 14 48,339 the surface irregularities are bosses of said insulating material.

13. The electrical induction apparatus of claim 12 wherein the solid homogeneous coating of electrical insulating material is formed of a heat-fused, cured, solventless, finely divided resinous polymeric powder.

14. The electrical inductive apparatus of claim 13 wherein the polymeric powder is an epoxy resin.

15. A homogeneously solid insulated conductor for use in a vapor cooled induction winding comprising:
an elongated metallic conductor having a uniform coating of a solid homogeneous electrical insulating material, said insulated conductor having at least one surface having predetermined surface irregularities.

16. The conductor of claim 15 wherein the solid homogeneous coating of an electrical insulating material is formed of a heat-fused, cured, solventless, finally divides resinous polymeric powder.

17. The conductor of claim 16 wherein the polyrneric powder is an epoxy resin.

18. The conductor of claim 15 wherein the sur-face irregularities are bosses of said insulating material.

19, The conductor of claim 15 wherein the sur-face irregularities include a plurality of transverse indentations at predetermined intervals along the longi-tudinal length of the at least one surface.

20. The conductor of claim 19 wherein the ratio of the depth of the indentations to the cross-sectional area of the metallic conductor is selected to provide the metallic conductor with a predetermined current capacity.

21, The conductor of claim 19 wherein the in-dentations include grooves of a predetermined width and depth disposed in the at least one surface at a predeter-mined angle transverse to the longitudinal length of the at least one surface.

48,339

22. The conductor of claim 15 wherein the elon-gated metallic conductor has a substantially cross-sectional configuration wherein one of the cross-sectional dimensions is larger than the other dimension and the at least one surface is located on a side of the elongated metallic conductor having the larger cross-sectional dimension.