NZ200399A

NZ200399A - Forming paperless electric coils:winding conductor on gelled insulation coating

Info

Publication number: NZ200399A
Application number: NZ200399A
Authority: NZ
Inventors: R D Buckley; E L Boyd; B J Palmer; D C Westervelt
Original assignee: Westinghouse Electric Corp
Priority date: 1981-05-15
Filing date: 1982-04-26
Publication date: 1985-12-13
Also published as: MX151864A; ES512215A0; BR8202781A; KR880002128B1; CA1202697A; EP0065147B1; DE3268236D1; ES8400631A1; NO821528L; AU559725B2; EP0065147A1; NO158598C; AU8315982A; NO158598B; KR840000053A

Description

<div class="application article clearfix" id="description"> 20039 Priority Date(s): Q~.~AQ.~. . ohJ.Q. Complete Specification Filed: h.'&Q Class: //. P.lF.44 U&/75/QR/..Q6 Publication Date: ... .it 5 .Q£.Q J9ft§ .... P.O. Journal, No: .j&m N. Z. No. HEW ZEALflKD Jf jjf |ftin ... Patents Act 1953 | 26 APR 1982 K" fiECEJVSD 1 COMPLETE SPECIFICATION h'' .jeaMescgeft&rnraj^ELiJELEr- in amegitte-eetcs Cfcuuutuo$£-^/?ee -ffc/W5>o/etteft Coik/UD MzlkoO. We WESTINGHOUSE ELECTRIC CORPORATION, Westinghouse Building, Gateway Center, Pittsburgh, Pennsylvania 1522 2, United States of America, a corporation organized and existing under the laws of the • Commonwealth of Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- -1- (followed by Page 1A) METHOD OF PROVIDING INSULATION SUPPORT FOR ELECTRICAL CONDUCTORS, ESPECIALLY IN ELECTRIC COILS This invention relates generally to the art of providing insulation support for electrical conductors, and, more particularly, to a method of making electric coils. In many conventional coils, such as transformer coils, the various conductor or winding layers are supported and insulated from each other by means of cellu-losic insulation, such as oil-paper or cardboard, for example. Other conventional coil structures employ non-cellulosic insulating material, such as cast-resin, to provide conductor support and insulation, and these cellulose-free coils have certain advantages over the others insofar as they are more resistant to short circuits, moisture degradation, mechanical vibration, and fire, and less susceptible of out-gassing and thermal aging. Unfortunately, cellulose-free coils of conventional design also have certain drawbacks, chief among them relatively high cost in terms of both manufacture and loadability, and a difficulty of ridding them of shrinkage voids. It is the principal object of the invention to provide a method which will alleviate these problems heretofore encountered with cellulose-free structures, and the invention, from a broad aspect thereof, accordingly resides in a method of providing insulating support for an 2003 9 electrical conductor, characterized by the steps of applying a liquid coating of an electrical insulating material upon a substrate, gelling the liquid coating to a firmness sufficient to support an electrical conductor, and apply-5 ing a conductor upon the gelled insulation. The above-stated sequence of steps can be repeated as often as required to provide a desired number of conductor layers, in which event a mandrel, an insulated supporting member or a first conductor layer applied upon 10 the insulated supporting member will form the substrate for the first liquid coating of insulating material to be applied and gelled, and each subsequent conductor layer supported by such gelled insulation coating will form the substrate for the next liquid coating of insulation to be 15 applied and gelled. The term "gelling", as used herein in context with the invention, is intended to mean partially polymerizing to an extent rendering the liquid insulation sufficiently consistent to provide mechanical support for the 20 conductor applied thereupon, but leaving it plastic enough for the conductor to somewhat nest in it and thereby to be held against sliding. Moreover, as liquid insulation coating is applied upon conductor layer and conductor layer is applied upon gelled insulation coating, the 25 conductor layers as well as all conductor portions in each layer become completely insulation-bound and any polymerization shrinkage is accommodated as the insulated structure is being formed, all of which contributes to producing a coil the insulation of which is a homogeneous and 30 essentially void-free mass in intimate physical contact with essentially all surfaces of the winding or windings embedded therein. The liquid insulating material preferably is gelled through irradiation from a suitable source, such as 35 an infrared or ultraviolet radiation unit or an electron beam unit. At present, ultraviolet radiation is believed to be the most practical and, accordingly, is preferred. 20039 The insulating material may be any suitable cross-linkable liquid resin, such as acrylic epoxy, and preferably is a substantially unfilled resin capable of being instantly gelled through irradiation. 5 Depending upon such factors as the viscosity of the liquid insulation before gelling, the desired thickness of each finished coating, and the like, the insulation coating upon each substrate (i.e. mandrel, insulating support member or previously applied conductor layer) may 10 be applied as a single-layer coating or it may be formed by applying several thin layers of liquid insulation one upon the other and gelling each such layer before the next one is applied. The viscosity of the liquid insulation should be- as low as possible in order to minimize the 15 chance for pockets or voids to develop as the coating is being formed, but it also should be sufficient to minimize undesirable flow of the applied liquid insulation before gelling. In addition to offering the advantages mentioned 20 hereinbefore, as well as others still to become apparent as the description proceeds, the method according to the invention lends itself admirably well to being applied to the art of coil forming since it permits layer insulation to be formed in situ while the coil structure being built 25 is on a mandrel or coil former and the latter is rotating at commercial winding speeds. When so employed, the method preferably comprises the step of forming an insulating coating upon the rotating mandrel or coil former by applying thereon liquid 30 insulation in one or several layers and instantly gelling each layer thus applied, and it includes further the steps of winding upon the above-mentioned insulating coating an electric conductor layer, forming upon the latter another gelled insulation coating in the manner set forth above, 35 winding thereon another conductor layer, and so forth until the coil forming operation is completed. After completion of the coil forming operation, the finished product, is subjected to a suitable curing process causing the gelled insulation to set. If desired, provision for cooling ducts can be made during the coil forming operation by introducing, in the liquid insulation, strips of a 5 material which can be subsequently removed from the finished coil, such as polyethylene, for example, which can be melted out with heat suitably applied. It will be appreciated that a coil formed in accordance with the invention will have a much better 10 conductor space factor than a conventional paper-wound coil, for example. Moreover, the novel coil winding method makes possible a reduction of the conductor mean turn and of the overall coil dimensions (determining the size of the core needed for the coil), it does away with. 15 costly coil bonding and drying operations, and it obviates oil impregnation problems since, contrary to conventional insulation systems employing cellulosic material, such as paper, a coil formed in accordance with the invention needs no oil for insulation purposes, all of which tends 20 to lower cost significantly with respect to coil structures of the prior art. Still another significant advantage derived from the invention in connection with, coil winding has to do with insulation grading. It is known that when an elec-25 trical. winding is formed from wire wound helically about the coil axis alternately back and forth between the opposite coil ends so as to form consecutive layers of conductor turns, the dielectric stress from layer to layer is relatively low at the mutually connected ends of any 30 two adjacent turns layers and gradually increases toward the mutually non-connected ends of such turns layers. With conventional coil structures having winding or turns layers spaced apart uniformly for the whole length, i.e. axial dimension, of the coil, the overall coil size is 35 determined by the thickness which the insulation between turns layers must have in order to withstand the highest dielectric stress therebetween, that is, it is determined 5 200399 by the thickness of insulation needed at the non-connected ends of the turns layers. According to a broad aspect of the invention there is provided a method of forming an electric coil structure, characterized by the steps of applying a liquid coating of electrical insulation upon a substrate, gelling the liquid coating to a firmness sufficient to support a conductor, and winding a conductor upon the gelled coating, in which said gelled coating is formed by winding and gelling a plurality of thin liquid l^ers of insulation one upon the other. The method according to the invention allows the total volume of the insulation and, hence, the total coil size to be considerably reduced in a facile manner by grading the insulation during coil winding, that is, by varying the thickness of insulation between adjacent winding layers in accordance with the changing dielectric stress therebetween. In a preferred embodiment of the invention, such graded insulating coating is formed upon a conductor-turns layer, or winding portion, of the coil structure by applying and instantly gelling, as the coil structure is being rotated, layer upon layer of liquid insulation in a manner such that the width of the various layers, as measured across the underlying winding portion from the end thereof which will be the high-stress end with respect to the conductor-turns layer or winding portion to be formed next, changes incrementally from insulation layer to successive insulation layer so that the resulting insulating coating will have a wedge-like or tapered cross-section, that is, will be graded, its thickness being maximal at the high-stress end and decreasing gradually toward the low-stress end of the underlying winding- portion thus coated. The incremental change in the width of successively applied insulation layers is achieved through axial relative displacement effected between the insulation applicator and the coil structure as the latter is being rotated. Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: 200390 e Figure -1 is a cross-sectional partial view of an electric coil made in accordance with the prior art; Figure 2 is an isometric view schematically illustrating a manner of making an electric coil in accordance with a preferred embodiment of the invention; Figure 3 is a sectional view taken along line II-XI of Figure 4; Figure 4 is an isometric view of the nearly finished coil; Figure 5 is a cross-sectional partial view of an electric coil having graded insulation formed in accordance with the invention; Figure 6 is an isometric view schematically illustrating one manner of forming layer insulation in a coil such as shown in Figure 5; Figure 7 is an enlarged, fragmentary sectional view illustrating in greater detail how insulation grading is achieved by the method of Figure 6; and Figure 8 is a cross-sectional partial view similar to Figure 5 and showing an electric coil with graded insulation. 7 200399 Referring now to Figure 1 of the drawings, it shows part of a conventional transformer coil, still in a coil forming mandrel 4, in which layers 3a, 3b and 3c of conductor turns, forming part of a winding of the coil, are supported and insulated from each other by cellulosic insulation in the form of paper wraps or cardboard tubes 2a, 2b and 2c. Typically, such coil is formed in successive steps by applying the first wrap or tube of cellulosic insulation 2a upon the mandrel 4, then winding thereon the first layer 3a of turns from one end of the coil to the other, as indicated by the lowermost arrow in Figure 1, thereafter applying the second wrap or tube 2b of insulation upon the turns layer 3a, then winding thereon the second layer 3b of turns in the opposite direction, and so forth until the coil is finished. As distinct therefrom, Figure 2 schematically illustrates a method of making a cellulose-free coil, such as shown in Figures 3 and 4, in accordance with the invention. In Figure 2, reference numeral 4 again designates a mandrel, numeral 5 refers to an applicator, such as a paint roller, numeral 6 designates a winding station, numeral 7 indicates a conductor, such as enamelled copper wire, numeral 9 designates a gelling station, numeral 10 indicates the direction in which the mandrel 4 with the coil structure thereon is rotated during a coil forming operation, and numeral 17 indicates an insulating coating applied by means of the applicator 5. As mentioned here- 8 2003 9 inbefore, the gelling station 9 may comprise any suitable radiation source, such as an infra-red or ultraviolet or electron beam unit, but preferably comprises an ultraviolet radiation source. 5 Fig. 2 shows the coil forming operation at an advanced stage. From Fig. 3 it is seen that the whole coil forming operation of this embodiment comprises the steps of providing an insulating substrate 13 upon the mandrel 4; forming upon the substrate 13 a first, e.g. 10 low-voltage, winding by applying, as the mandrel is turning, several layers 15 of insulated, e.g. enamelled, conductor strip first upon the insulating substrate 13 and then one upon the other; forming a gelled insulating coating 17 upon the- winding 15; helically winding, as 15 shown in Fig. 2, preferably insulated, e.g. enamelled, conductor wire 7 upon the gelled coating 17 from one coil end to the other so as to form a layer of conductor turns 19 as part of a second, e.g. high-voltage, winding; forming a gelled insulating coating 21 upon this turns layer 20 19; helically winding upon the. coating 21 a layer of turns 23 from the same wire as above but proceeding in the opposite axial direction; and covering the turns layer 23 with an insulating coating 25, preferably likewise gelled. The insulating coatings. 17, 21 and 25 are shown in Fig. 3 25 as forming overlaps 17', 21' and 25', respectively, which cover the edges of the respective underlying winding 15 and winding layers 19, 23 at both ends of the coil so as to provide maximum protection from arc-overs between the edges of adjacent windings or winding portions. 30 The substrate 13 on the mandrel 4 may be a tubular member preformed from a suitable resinous material and slipped onto the mandrel or it may be an insulating coating formed in the same manner as the coatings 17 and 21 and, preferably, also the coating 25, namely by apply-35 ing the insulating material as a viscous liquid by means of the applicator 5 (Fig. 2), and instantly gelling the applied liquid insulation through irradiation received as 2003 9 it is being carried past the gelling station 9 by the mandrel 4 rotating in the direction of the arrow 10. The thickness of each insulation coating 13, 17, 21 or 25 may vary, depending upon such parameters as the 5 required insulating or dielectric strength of the coating, its mechanical strength, and the like; and the various coatings may be formed as single-layer coatings or as multi-layer coatings, depending upon overall coating thickness desired, the viscosity of the liquid insulation 10 to be applied, coil winding speed, and the like. A multi-layer coating is formed, as the mandrel 4 is turning, by applying several relatively thin layers of liquid insulation one upon the other by means of the applicator 5, and instantly gelling them at the gelling 15 station 9, one such liquid layer of insulation being applied and gelled during each revolution of the mandrel. For instance, there may be 5 to 10 liquid layers, each about 40 mils (1.0 mm) thick, wound upon each other and resulting in a coating having a thickness of about from 20 0.2 to 0.4 inch (5.0 to 10.0 mm), or there may be 30 to 50 liquid layers, each about 4 mils (0.1 mm) thick, wound upon each other and resulting in a. coating having a thickness of from 0.1 to 0.2 inch (3.0 to 5.0 mm) . Building up such insulating coating from thin 25 layers of liquid insulation each wound upon the other and instantly gelled offers a significant advantage insofar as the liquid insulation thus applied in thin layers will readily flow into and thus eliminate any spaces between adjacent conductor portions, and any holes and voids, and 30 will completely cover and effectively isolate small contaminants such as might be present and as would reduce the breakdown strength of the finished coating. Of course, even though the insulation is applied layer upon layer, it will be understood that applying it as a liquid and just 35 gelling, instead of curing, the latter before the next layer is applied will yield a coating that is not strati--fied but is dense and homogeneous. Thus, the term "multi- 20039 10 layer" used herein as part of the expression "multi-layer coating" is to be construed as referring to the manner of applying the coating and not to the structure of the finished coating. 5 If desired, extra insulation can be provided between the conductor-strip layers 15 of the first winding by applying to the pre—insulated conductor strip, as it is being wound in place, a liquid layer of insulation by means of the applicator 5 (Fig. 2), and instantly gelling 10 the liquid layer, thus applied, through irradiation received at the gelling station 9. It should be. noted also that even though the first winding is shown in the embodiment of Fig. 3 as wound spirally, i.e., as layer-wound, from conductor 15 strip, it could be formed from a conductor wire wound helically in a similar manner as shown in Fig. 2; and that, furthermore, the second winding, although shown herein as helically wound from wire, could be formed from conductive strip material layer-wound in a similar manner 20 as the first winding 15 of the illustrated embodiment. Of course, the particular number of conductor layers 15 and turns layers 19, 23 employed, in this embodiment likewise-must not be considered as limiting, having regard to the scope of the invention. 25 The insulation overlaps 17', 21' and 25' may be formed independently of the respective coatings 17, 21, 25 by applying insulation to the opposite edges of the winding 15 and each turns layer 19 or 23 as the winding or turns layer is formed, and instantly gelling the applied 30 edge insulation in a similar manner as explained in connection with the insulating coatings. As an alternative which may be preferred, the overlaps, such as 17', 21' and 25' can be formed concurrently with the respective insulating coatings 17, 21 and 35 25, simply by applying an excess of insulation beyond the opposite edges of the associated winding or turns layer and lapping it, the overlaps thus formed being gelled, of course, together with the remaining part of the coating. 200399 As seen from Figs. 3 and 4, provision for cooling ducts can be readily made by winding into the outer insulating coating 25 a strip or strips 35 of a suitable material which can be removed when the coil structure is 5 complete. Thus, with the coating 25 formed to part of its desired thickness, the strips 35 are put in place thereon at the desired locations and then are covered with more insulation as the mandrel 11 continues to rotate. When the coil winding operation is finished and the coil struc-10 ture is complete, the strips 35 are removed to leave ducts for cooling liquid, such as transformer-oil, to pass therethrough. A suitable material of which the strips 35 may be made is polyethylene which can be melted out, subsequently, e.g., by electrically energizing the fin-15 ished coil prior to immersing it in a coolant. Referring now to Figs. 5, 6 and 7 of the drawings which are partial views of an electric coil formed with graded insulation in accordance with the invention, Fig. 5 shows the coil, mounted on a mandrel 4, as compris-20 ing conductor turns layers 29a, 29b and 29c forming portions of an electric winding, an insulating substrate or base coating 27a on the mandrel, graded insulating coatings 27b and 27c, and an insulating coating 34. The conductor-turns layers 29a-c, wound from a single conduc-25 tor 7 (Fig. 6), such as copper wire, are interconnected at the thinner ends of the graded insulating coatings 27b and 27c therebetween to form a complete winding. It will be appreciated., of course, that the invention is not limited to the three winding portions and four insulating coatings 30 shown in this embodiment, the number of windings and winding portions, and consequently the number of insulating coatings, depending in each case upon the kind of coil desired. Fig. 6 illustrates a method of forming a coil 35 such as shown in Fig. 5. Except for the step of insulation grading, this method is similar to the one previously described herein in connection with forming insulation 2003 99 12 coatings from several gelled liquid layers of insulation applied one upon the other, and the same reference numerals are used in Fig. 6 as in Fig. 2 to indicate similar elements performing corresponding functions, such as the 5 coil former or mandrel 4, the insulation applicator 5, and the gelling station 9. The inner and outer insulating coatings 27a and 34 of the coil shown in Fig. 5 are of substantially uniform thickness throughout, and they can be formed in the same manner as hereinbefore set forth in 10 connection with the previously described embodiment. The following description will be limited to the manner of forming graded insulation coatings, such as the coatings 27b and 27c. Referring in this context to Fig. 6 which shows 15 the coil forming operation at a stage where the turns layer 29a is wound in place upon the insulating coating 27a and the insulating coating 27b is applied upon the turns layer 29a, it will be seen therefrom that provision is made in this embodiment for axial relative displacement 20 to occur between the insulation applicator 5 and the coil structure as the liquid insulation is being applied. More-specifically, the applicator 5 is seen as advancing in the same axial direction as the conductor-turns winding operation, with the result that, during each revolution of the 25 coil former 4, the applicator 5 applies a liquid layer of insulation (instantly gelled at 9) to cover the whole of the previously applied and gelled layer and, in addition, at least one still exposed conductor turn of the turns layer 29a. This procedure is graphically illustrated in 30 Fig. 7 wherein the lines, such as lines 27b^ and represent the various layers of liquid insulation applied and gelled individually, albeit preferably in one continuous operation. Of course, it will be appreciated that, even though the width of the successively applied layers 35 in this embodiment is shown as incrementally increasing (because the applicator 5 is assumed to advance from left to right, as viewed in Figs. 6 and 7), it would incremen 13 tally decrease if the applicator 5 first applied liquid insulation to cover the whole width of the underlying conductor-turns layer, and then advanced toward the left. Upon the insulating coating 27b thus formed, the 5 wire 7 is wound, starting at the thin end and proceeding towards the thick end of the coating, to form the turns layer 29b, upon which the graded insulating coating 27c then is formed in the same manner as described with "respect to the coating 27b, but with the axial relative 10 motion between the applicator 5 and the coil structure reversed in order to form the coating 27c with a reverse taper, having regard to the previously formed coating 27b. Next, the conductor-turns layer 29c is wound in place upon the gelled coating 27c, and then the insulating 15 coating 34 is formed on the turns layer 29c, preferably by means of the same applicator 5, however arrested in its axial movement and applying several layers of liquid insulation one upon the other and all of them over the full width of the coil, as the latter is turning. 20 It will be appreciated that alternate insulating coatings, such as coatings 27a-c and 34, and conductor-turns layers, such as layers 29a-c, can be formed, according to the invention, in one substantially continuous winding operation. Furthermore, it will be clear from the 25 above that the volume of insulation in a coil formed as described above will be only about half the volume of a similarly rated coil formed in accordance with conventional practice, such as shown in Fig. 1, and in which the insulating layers between conductor-turns layers are of 30 uniform thickness determined by the region of maximum dielectric stress. Turning now to the next embodiment of the invention, Fig. 8 shows, as mounted on a mandrel or coil former 4 having end flanges 60 and 62, a coil structure which is 35 similar to the one of Fig. 5 in that it, too, comprises conductor-turns layers 44a, 44b, 44c, an insulating base coating or substrate 42a, an insulating outer coating 50, 14 200399 and graded insulating coatings 42b and 42c which are relatively thick at one end, such as at 68 or 76, respectively, and relatively thin at the other end, such as at 70 or 78, respectively. The coil structure of Figure 8 differs from the one of Figure 5 by the manner In which its insulating coatings are formed or, rather, the kind of applicator employed in applying them. </div>

Claims

<div class="application article clearfix printTableText" id="claims"> 15 200399 WHAT WE CLAIM IS:

1. A method of forming an electric coil structure, characterized by the steps of applying a liquid coating of electrical insulation upon a substrate, gelling the liquid coating to a firmness sufficient to support a conductor, and winding a conductor upon the gelled coating, in which said gelled coating is formed by winding and gelling a plurality of thin liquidlayers of insulation one upon the other.

2. A method according to claim 1, characterized in that said conductor is a pre-insulated strip-like conductor wound spirally upon said gelled coating.

3. A method according to claim 1 characterized in that said conductor is a strip-like conductor, and that the liquid coating of insulation is applied to the strip-like conductor, and is instantly gelled, as the conductor is being wound spirally in place.

4. A method according to claim 1, characterized in that said conductor is a wire wound helically upon said gelled coating.

5. A method according to claim 4, characterized in that said steps are reiterated, in the sequence stated, in such manner that the steps of applying and gelling each liquid coating, except a final one, are followed by a step of helically winding a layer of turns from said wire upon the gelled coating, and each step of winding such layer of turns is followed by the steps of applying upon the latter, and of instantly gelling, a liquid coating of insulation.

6. A method according to claim 5, characterized in that successive layers of turns are alternately wound axially in opposite directions such that each turns layer intermediate two other turns layers is directly connected at one end to the preceding turns layer and, at its opposite end, is connected to the next-following turns layer, the gelled liquid coating of insulation between each pair of adjacent tur J.6 200399 being applied in such manner as to have a thickness which gradually increases from the directly connected ends of said adjacent turns layers toward the separated ends thereof.

7. A method according to claim 6, characterized in that the gelled coating between each pair of adjacent turns layers is formed by applying and instantly gelling liquid layer of insulation upon liquid layer in a manner such as to cause the width of the individual insulation layers, as measured from the separated ends of the adjacent turns layers towards the connected ends thereof, to change incrementally from insulation layer to successive insulation layer.

8. A method according to claim 7, characterized in that said liquid layers are applied by means of applicator, and are instantly gelled, simultaneously with rotating the coil and with effecting axial relative movement between the latter and the applicator.

9. A method according to any one of the claims 1 to 8, characterized in that liquid overlaps of said insulation are formed and instantly gelled upon the axially outer edges of each winding formed from the conductor.

10. A method according to any one of the claims 1 to 9, characterized by the steps of introducing, in the applied insulation, strips of a material capable of being subsequently removed, and of removing said strips upon completion of the coil structure to form cooling ducts in the insulation.

11. A method according to claim 10, characterized in that said material is polyethylene, and that said strips are melted out of the insulation through the application of heat.

12. A method according to any one of the claims 1 to 11, characterized in that the liquid insulation is applied and isntantly gelled, and the conductor is wound in place, in a substantially continuous winding operation during which the coil structure is repeatedly rotated sequentially past an 17 200399 insulation applicator, a gelling station, and a conductor winding station.

13. A method according to any one of the preceding claims, characterized in that said insulation is a cross-linkable liquid resin.

14. A method according to claim 13, characterized in that said liquid resin is an unfilled resin and is instantly gelled through irradiation.

15. A method according to any one of the preceding claims, characterized in that the liquid insulation is applied having a viscosity just high enough to prevent undesirable flow of the applied liquid insulation before gelling.

16. An electric coil structure, constructed and adapted for use substantially as hereinbefore described and r FT<ajs a. -tes illustrated with reference to I the accompanying drawings. WESTINGHOUSE ELECTRIC CORPORATION By their attorneys HENRY HUGHES LIMITED BY : </div>