US3633140A

US3633140A - Dry insulated transformer

Info

Publication number: US3633140A
Application number: US67288A
Authority: US
Inventors: Glen W Lake; Myron D Coeper
Original assignee: Chemetron Corp
Current assignee: Chemetron Corp; Alloy Rods Global Inc; Citicorp North America Inc
Priority date: 1970-08-26
Filing date: 1970-08-26
Publication date: 1972-01-04
Anticipated expiration: 1989-01-04

Abstract

This disclosure includes a high-voltage dry-insulated transformer and to the method of constructing the transformer. The primary coil is a multiple-turn, multiple-layer winding constructed by alternately winding a coil layer and then insulation sheets or tape on a winding form. The insulation sheet is a nonwoven glass filament cloth which is impregnated with a semicured epoxy resin. A plurality of insulating cloth layers are wrapped about the primary coil to define the necessary intercoil insulation. The secondary coil is then similarly formed. The interlayer and intercoil insulating cloth extends beyond the axial end faces of the coils and the space is filled by wrapping of a corresponding tape between the two extended layers. The cloth is applied under tension and heat and the exterior of each layer is rolled to exclude air and cause the resin to flow into the voids and crevices. The exterior is wrapped with a shrinktype Mylar and the ends of the assembly are capped to confine the insulating resin during the curing and processing cycle, the Mylar acts as a positive force during curing to cause the resin to flow into all voids in the coil. The Mylar is removed after the coil has been cured.

Description

United States Patent 3,297,970 1/1967 J0nes..;

Continuation of application Ser. No. 780,335, Dec. 2, 1968, now abandoned. This application Aug. 26, 1970, Ser. No. 67,288

, DRY INSULATED TRANSFORMER 7 Claims, 7 Drawing Figs.

US. (I 336/182, 29/605, 264/272, 336/96, 336/205, 336/206 Int. Cl H01] 27/32 Field of Search 338/205,

References Cited UNITED STATES PATENTS Primary ExaminerE. A. Goldberg ABSTRACT: This disclosure includes a high-voltage dry-insulated transformer and to the method of constructing the transformer. The primary coil is a multiple-tum, multiple-layer winding constructed by alternately winding a coil layer and then insulation sheets or tape on a winding form. The insulation sheet is a nonwoven glass filament cloth which is impregnated with a semicured epoxy resin. A plurality of insulating cloth layers are wrapped about the primary coil to define the necessary intercoil insulation. The secondary coil is then similarly formed. The interlayer and intercoil insulating cloth extends beyond the axial end faces of the coils and the space is filled by wrapping of a corresponding tape between the two extended layers. The cloth is applied under tension and heat and the exterior of each layer is rolled to exclude air and cause the resin to flow into the voids and crevices. Theexterior is wrapped with a shrink-type Mylar and the ends of the assembly are capped to confine the insulating resin during the curing and processing cycle, the Mylar acts as a positive force during curing to cause the resin to flow into all voids in the coil. The Mylar is removed after the coil has been cured.

, l DRYJINSULATED TRANSFORMER 'This case is a continuation ofSer. No. 780,335, filed Dec. 2,

'-l,968,'now abandoned.

BACKGROUND OFTHE INVENTION Thisir'iventionrelates to, an inductivecoil and the method of making the'coil and more particularly to a high-voltage dry-insulated inductive coil unitof a high-voltage transformer.

I-Iigh-ivOItageJcoiIs'and transfonners require special insulating techniquesbecause of the detrimental effects arising in the presenceof air, -moisture,.as well as other foreign and contaminating 'materialin the operating environment. Although oil -immersed coils provide-certain operating advantages, dryinsulated 'and encapsulated'transformer and other inductive coils-havesubstantiabadvantages from the standpoint of handling and-the like. However, dry-type-insulation must be specially formed andspecialconsiderations taken to avoid the adverse effects associated withCorona. Void orforeign material in thecoil insulationtraps air within the insulation which is subject ,toa voltage difference; If thevoltage gradient is sufficiently high, actual ionizationof the air and sparkover may occur. This' results in rapid deterioration of the insulating characteristic of the insulationand eventually results in a disruption'or breakdown thereof. Some high-voltage transformers and other inductive coils of the-dry-type insulation have been formed by encapsulating or potting of the coil with a suitable resinafter the coil iswound. Such coils, however,

have been found to have severe limitations both aste the physical size and theuvoltage applications because of entrapment of air within the insulation.

SUMMARY The present invention isp articularly directed to an encapsulated high-voltage induction'coil provided with an encapsulating dry insulation and to the method of making such coil prac- .are disposed in'superimposed relationship such as in a trans- .former to form'thenecessary intercoil relationship. Free resin may be applied .to the-insulating material during winding if a larger-'amountofiresin is required for a particular application. The interlayer and intercoil; insulating cloth preferably extends beyond the axialend faces of the coil to the desired end insulating depth. Thespace at eachend between insulating layers is filled with a corresponding layer insulation by continuous wrapping between the two layers. The various insulating cloth sheetsarepreferably applied under tension and the exterior of each layer preferablyrolled or otherwise worked to excludeair. The insulatingcloth is also warmed slightly during the winding and workingto cause the resin on the insulation material to more readily flow into the voids and crevices between the coil turns. After the formation of the coil with the interposed insulation, it is subjected to a curing and processing cycle including the heating under pressure and vacuum to cure the resin and remove all air.

In a preferred and novel construction after the winding of a coil with insulation material as described above, the exterior is preferably wrapped with a heat shrink type material such as a shrink-type Mylar. The endfaces of the coil are capped to confine the insulating resin during the curing and processing cycle.

The heat shrink outer layer contracts during the curing process and establishes a positive force causing the resin to flow into all of the voids arid crevices and more surely excludes air from the insulation whereby a void and air free solid insulation about the windings is obtained. After the curing the Mylar wrapping is removed.

1 teaching of the present invention;

In the formation of a transformer the stepspreferably include the sequential forming, of the in'nei windingv including the curing and processing of the insulation. The'major intercoil insulation is then applied, [cured and processed,

Thereafter, the outer winding is wound with thedesired. insulation in a corresponding manner and is then curedyand processed in the same-procedure to set the insulating material of the second winding and complete the transformer, If the transformer is not too .lar geathe iseveralwindings'and .the

major intercoil insulation may be wound in a single sequence with the curing the processing simultaneously provided for the a completed coil.

BRIEF DESCRIPTION OF THE; DRAWINGS FIG. 1 is a plan view of a transformer withparts-broken away to show details of:constructiori; 1 w

FIG. 2 is a side elevational view of the transformer shownjin.

FIG. 5 is a diagrammatic illustration of a preferred method for applying the windings and the insulation in theformation of a coil;

FIG. 6 is a side elevational view ot1FIG. 5; and I FIG. 7 is a diagrammatic illustration-showing the coil placed inacuring oven. 7 t

DESCRIPTIONOFA PREFERRED s reoomiem Referringto the drawings and-particularly to FIG. 1,: the present invention is illustrated in connection with an ahnularr or 'doughnut-shaped transformer having'an inner primary winding I wound on a tubular winding-form 2, The primary winding 1 is a multipledayer and multiple-tum winding having a plurality of primarytaps and end connectors 3. Superim posed in axially stacked relation about the primarywinding .l' is a delta secondary winding 4'anda wye secondary winding" The connectors 6 for winding 4 ;project laterally or'radially from the periphery of the transformer and similar connectors 7 project radially from the lower-portion'of the coil.- The pri-j mary winding 1 is separated fromtliesecondary windings 4.

and S by a relatively heavy layerot major insulation 8."The

ends of the transformer 1 and the secondary windings 4 and 5 are separated by aheavy layer of insulation 9 iand 'l0. Additionally, the individual layers ofcoil tums-are separated from each other by interlayer insulation 11 of a varying "thickness and the periphery is sealed by a layer of insulation 12 The insulation 8 through 12 is fused to form a solid; integral mass which completely encapsulates the coils or windings.

Referringparticularly to FIG. 4, the diagrammatic illustration of the winding layout is shown for purposes of illustrating the winding construction of the transformer and the method of forming such transformer. I

The several windings or coils are wound about the centra tubular winding form 2 which corresponds in length to the completed transformer. One or morelayers of an'=insulatit1g;

sheet 13 is wound about the form 2, The insulating sheet 13, and all the subsequent tapes and sheets" of insulating described, are a nonwoven cloth which is pr'eimpregnated with a semicured epoxy resin. The resin content was approximately 40 percent by weight. Such an insulating tape istrianufa'ctured and sold under the trademark ScotchplyVb'y MinnesotaMining and Mariufacturing Company. In an actual construction, a single layer of insulating tape'l3 corresponding to the heights of the form 2 and of a 20mill thickness was employed. The first primary coil layer 14 is wound upon the tape covered form 2 as a plurality of immediatelyadjacent convolutions.

Referring particularly to FIG. 2 in an actual construction, each turn was fonned of a pair of immediately adjacent square portion .of the: transformer.

conductors and 16 for convenience and ease of winding. The conductors 15 and 16 are disposed in immediately adjacent axial side by side relationship and spirally wound upon the tape 13; to form the multiple-turn layer 14. The initial turn is spaced downwardly from the upper end of the coil form 2, shown to'the left in FIG. 4, and the last turn is correspondingly spaced from the lower end of the coil form 2.

The coil turns of layer 14 may be individually wrapped with insulation, not shown, with the total length dimension generally corresponding to all of the other layers as hereinafter described After the winding of the first multiple layer 14 is completed, the end spaces adjacent the opposite end coil turns of the first coil 14 are filled with an insulating tape 17. For example, in an actual construction, the coil form 2 extended approximately 1 inch beyond the end turns of the coil layer 14. The space was filled with a suitable tape wrapped around both ends.

Two superimposed sheets or layers 18 of insulating cloth are then applied over the first coil layer 14. As previously described with respect to FIGS. 1 and 2, the first coil layer 14 of the primary is tapped to provide the several primary tap connections 3. In the illustrated embodiment of the invention, the insulating sheets 18 include appropriate axially spaced openings 19 in alignment with the proper coil turn to produce the desired voltage tap. The several openings 19 are also circumferentially spaced to permit interconnection of the several taps 3. The taps 3 are shown superimposed in FIG. 4 in accordance with the usual convention.

The connectors 3 may be in any desired manner such as a flat contact strip extending downwardly adjacent the outer surface of the insulating sheets 18, with the intermost end brazed or otherwise connected to the adjacent coil turns of layer 14. The connections 3 are preferably wound with a plurality of layers of an insulating tape.

A second layer including a pair of insulating sheets 24, generally corresponding to sheets 18, is wrapped about the coil and tapped connections. The second coil layer is then reverse wound on the first coil layer 14, that is from the lower end of the coil, shown to the right in FIG. 4, upwardly with the uppermost turn terminating in alignment with the uppermost turn of the first coil layer 14. The winding turns may be formed from an integral conductor with the interconnection 26 extending through a suitable edge slot and openings 27 provided in the insulating sheets. In the transformer constructed, the first coil layer included turns with the turns gapped to extend the winding over 22 inches of the 24-inch length of tube form 2. Generally, the wrapping of the individual turn of layer 14 with insulation 15 accounted for the additional space of such turns. The second coil layer 25 and all subsequent coil layers were wound with coil turns, such that they constituted essentially a solid copper conductor throughout the 22 winding inches.

After the winding of the second coil layer 25, the end spaces are filled with the suitable size insulating tape to extend the insulation outwardly to the end face of the form 2. The second coil layer 25 is covered with insulating sheets 28 similar to that for layer 14. Additional coil layers 29 and a final coil layer 30 are successively similarly applied and wrapped with insulating sheets with the outer end spaces being filled with the filler insulating tape. In the illustrated embodiment of the invention, a total of six layers are shown with the outermost layer having its end terminating in the upper plane of the transformer and having the lead 3 extend outwardly to define the opposite end of the coil connection.

In preferred construction, the last five turns of the primary coil layer 30 are individually wrapped with a tape similar to the wrapping-of the initial turns of the first coil layer 14.

Although the winding of the coil turns and the applying of the insulating tape and sheets may be in any suitable manner, a preferred method is diagrammatically shown in FIGS. 5 and 6. Each insulating sheet is applied through a suitable tension means 31 to securely wrap each layer of insulation upon the adjacentcoil layer. Additionally, a heat source 32, such as a suitable heat lamp, is applied to soften the resin in the insulating tape and sheets and thereby transform the resin into a 'flowable state such that the resin will tend to flow into and fill the voids and crevices. Additionally, each layer of insulation is rolled or worked onto the adjacent coil layer as by a roller 33 as it is applied to remove all significant amount of air from between the layers and the adjacent member.

After the winding of the final coil layer 30, the assembly is removed from the winding apparatus and one or more layers of a heat shrink tape or sheet 34 such as Mylar is wrapped about the outer peripheral surface, as shown in FIG. 7.

The Mylar may be a 2-mill film type commercially available under the trademark Scotch-lite.

End caps 35 and 36 are secured to the opposite end faces of the primary winding or coil in clamping engagement with the end faces of the coil to confine the insulating resin within the coil. The Mylar-wrapped and capped assembly is disposed within a suitable curing apparatus 37 and subjected to an appropriate curing cycle including heat, pressure and vacuum in accordance with well-known procedure. The heating of the assembly causes the heat shrink Mylar to contract and thereby forces the resin to flow into all voids and crevices, resulting in a solid, void-free insulating mass. After completion of the curing process the end caps 35 and 36 and the Mylar cover 34 are removed.

The cured insulated primary coil 1 is reassembled with the wrapping apparatus.

Major intercoil insulation 8 is then applied to the outer periphery of the cured primary. In the practical construction, 25 layers of 20-mill Scotchply cloth sheet 38 wrapped about the primary to define approximately 56-inch thick major insulation.

The several layers 38 are wrapped onto each other as diagrammatically shown in FIGS. 5 and 6 to maintain tension on the individual layers while they are simultaneously subjected to heat of source 32 and a roller working of roll 33 to remove air and the like.

The assembly is then again removed and placed in the curing apparatus 37 and the insulation layers 38 subjected to the same curing process to define a solid mass of major insulation 8 which in turn blends and bonds to the outer periphery of the primary coil 1.

The cured assembly is then again applied to the wrapping apparatus to receive the secondary windings 4 and 5, the coil turns of which are disposed in stacked relation as shown in FIGS. 2 and 4. I

The delta winding 4 is started at the top with the initial turn generally aligned with the top turns of the several coil layers of the primary winding or coil 1. Each coil turn is formed from a pair of conductors generally similar to the primary winding 1. The first and last three turns of the delta winding are preferably individually wrapped with insulating tape which may be similar to the individual wrapping of the individual turns of the first primary coil layer 14. A single layer of tape was applied between each of the coil layers.

The delta winding 4 of the transformer constructed spanned 50 percent of the depth of the transformer. Each coil layer 39 was wound with l6 turns and six coil layers 39 were provided. Each coil layer 39 was concentrically wound with the opposite end turns spaced respectively from the outer end or top face of the finished transformer and from the center of the transformer and thus from the wye winding 5. The coil layers 39 were separated by a sheet of insulation 40 and the end spaces to the opposite ends of the coil turns were similarly filled with suitable insulation tape 41, as shown in FIGS. 2 and 3 and more specifically described with respect to the primary.

The delta winding spanned approximately 9% inches and was spaced inwardly from the outer face approximately 1%- inch and from the center of the assembly approximately onehalf inch. A lie-inch 20-mill Scotchply tape 41 was applied to the outboard end of the delta winding and a 178 -inch 20-mill Scotchply tape 41 was applied to the inboard end of the winding to fill the adjacent space and maintain a continuous insulating tape filler to the opposite end of the winding.

The wye secondary winding 5 is similarly applied to the.

lower half of the transformer. The wye winding includes three coil layers 42. The diagrammatic illustration of FIG. 4 shows a substantial void between the outermost layer and the outer surface of the transformer. In fact, each coil layer includes a double radial layer of conductors 43, as shown in FIGS. 2 and 3, such that each coil turn includes four conductors arranged in four quadrants to define a square multiconductor for each turn. Each coil layer 42 will generally correspond to two of the coil layers of the delta winding and the radially extension will correspond to that of the deltawinding.

Additionally, the coil layers 42 of the wye winding 5 are separated by a double layer of insulation 44. In the actual transformer'construction, the winding was spaced from the center of the assembly by approximately one-half inch and spanned approximately inches thereby spacing the lowermost turns from the outer face by approximately l'z-inch. The end spaces were filled by ye-inch by -mill tape and a 1%- inch by 20-mill tape 46, similar to the delta winding.

After the formation of the delta winding 4 and the wye winding 5 a double layer of insulating sheets 47 of a full depth is applied about the secondary winding.

Stress cone insulation 49, as shown in FIG. 2, may be applied to the top and bottom by wrapping a plurality of layers of insulating tape 8 about the upper and lowermost ends of the coil. For example, the upper and lower 5 inches of the peripheral surface of the 24-inch high transformer which has been described herein was formed with a stress cone. The stress cone was formed by 2-inch by 20-mill tape with an overlap wrapped to define the thickness to the outermost ends.

Three layers of heat shrink Mylar are then applied about the completed windings with the connecting end of the several windings extending outwardly through the tape insulation and the heat shrink Mylar. The assembly is removed from the winding apparatus and end caps 35 applied to again confine the insulating resin.

The assembly is placed in the curing apparatus 37 and is subjected to the heat, pressure and vacuum in accordance with known procedures to completely cure the resin. Once again, the shrinking of the outer Mylar tape causes the resin to flow into all the voids and crevices and thereby insures a solid and continuous insulation. The stress cone areas are then ground to a suitable radius to complete the transformer.

The several primary taps 3 and

secondary connectors

6 and 7 may be wrapped with a suitable tape or other insulating material 51 to define integral stress cones for removing the high-voltage stress from the point of termination and thereby minimizing or eliminating corona on the external surface.

The transformer constructed in accordance with the present invention has been found to provide a highly reliable and ef' fective high-voltage insulation.

Although the curing step for'the primary and secondary windings as well as the major insulation has been described as individual sequential steps, they may be simultaneously provided if the construction and the curing apparatus permit.

A transformer constructed in accordance with the illustrated embodiment of the invention has advantageously been employed in a high-voltage direct current power supply for a plasma arc process. A three-phase transformer was employed with each of the phases provided by a transformer as shown in the drawings.

The particular embodiment of the invention set forth above including the particulars of the number of turns, spacing of coils, insulating layers and the like are for the purpose of clearly explaining one structure. Such detail as spacing,

I. An inductive coil means to be formed into a totally encapsulated coil comprising, a plurality of spaced coil layers, insulation disposed between said layers and including at least one layer of a cloth material impregnated with an uncured resin, said cloth material projecting axially substantially of said coil layers, and means responsive to heat for compressing said coil layers by shrinking into tight engagement therewith to cause the resin in the insulation to flow into the voids and crevices of the coil thereby forming a solid insulating mass.

2. The inductive coil means of claim 1 wherein said insulation is totally of a nonwoven cloth material impregnated with an uncured resin and includes a layer of cloth material between each coil layer, said cloth material projecting axially outwardly of said coil layers, and a plurality of superimposed layers of said cloth material filling the end spaces aligned with said coil layers. 1

3. The inductive coil means of claim 1 including a spaced multilayer secondary winding having a plurality of spaced coil layers, and an interlayer of cloth material impregnated with an uncured resin being disposed between each layer of said secondary winding, means responsive to heat for compressing said secondary winding by shrinking into tight engagement therewith to cause the resin to flow into the voids and crevices forming a solid insulating mass, and a plurality of layers of a cloth material disposed between said windings to form an intercoil insulation, and means responsive to heat for compressing said intercoil insulation by shrinking into tight engagement therewith to cause the resin in the intercoil insulation to flow into the voids and crevices forming a solid insulating mass.

4. The inductive coil means of claim 3, wherein the interlayer and intercoil cloth material of said secondary winding projects axially outward to define end insulation, and a plurality of layers of cloth material impregnated with an uncured resin concentrically wrapped between said projecting cloth material to complete the end insulation.

5. The inductive coil means of claim 1 having outwardly extending terminal means and integral stress cones extending outwardly about said terminals from the outermost layers of insulation to reduce dielectric stress concentration.

6. An inductive coil means to be formed into a totally encapsulated coil comprising, a plurality of spaced coil layers, and insulation disposed between said layers including a layer of a cloth material impregnated with an uncured resin between each coil layer, and a heat-shrinkable cover responsive to the flow temperature of the resin covering said coil layers and insulation whereby heating of said coil shrinks said cover and forces the resin to flow into the voids and crevices in the coil layers to create a solid and continuous insulation.

7. The inductive coil means of claim 1 wherein said insulation is totally of a nonwoven cloth material impregnated with an uncured resin and includes a layer of said cloth material between each coil layer.

Claims

1. An inductive coil means to be formed into a totally encapsulated coil comprising, a plurality of spaced coil layers, insulation disposed between said layers and including at least one layer of a cloth material impregnated with an uncured resin, said cloth material projecting axially substantially of said coil layers, and means responsive to heat for compressing said coil layers by shrinking into tight engagement therewith to cause the resin in the insulation to flow into the voids and crevices of the coil thereby forming a solid insulating mass.

2. The inductive coil means of claim 1 wherein said insulation is totally of a nonwoven cloth material impregnated with an uncured resin and includes a layer of cloth material between each coil layer, said cloth material projecting axially outwardly of said coil layers, and a plurality of superimposed layers of said cloth material filling the end spaces aligned with said coil layers.