US3740685A

US3740685A - Transformer with connector and method of assembly

Info

Publication number: US3740685A
Application number: US00195748A
Authority: US
Inventors: J Fisher
Original assignee: Kuhlman Corp
Current assignee: Kuhlman Corp
Priority date: 1971-11-04
Filing date: 1971-11-04
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19

Abstract

A connector assembly for the low voltage, aluminum, output conductors of a transformer which includes a copper stud forming the through connection from the interior of a transformer casing to the external connector. The low voltage leads from the transformer assembly are preferably formed of aluminum and are attached to the copper stud by means of a concentrically grooved brass washer which is forced into the face of dead-soft aluminum strip by means of a compression nut. The electrical path for the connector assembly includes the dead-soft aluminum strip, the concentrically grooved brass washer, the brass compression nuts and the copper stud.

Description

United States Patent [1 1 Mallet 336/58 Fisher June 19, 1973 UN TRANSFORMER WITH CONNECTOR AND METHOD OF ASSEMBLY Primary Examiner-E. A. Goldberg Attorney-J. King Harness, Paul F. Seibold, Cyrus [75] Inventor. John L. Fisher, Lexington, Ky. G- Minkler [73] Assignee: Kuhlman Corporation, Troy, Mich. H i V 22 Filed: Nov. 4, 1971 [57] ABSTRACT A connector assembly for the low voltage, aluminum, [21] l95748 output conductors of a transformer which includes a copper stud forming the through connection from the i [52] US. Cl. 336/192, 29/602, 336/58, interior of a transformer casing to the external connec- 339/595 A tor. The low voltage leads from the transformer assem- [51] Int. Cl. H0lf 15/10 bly are preferably formed of aluminum and are at- [58] Field of Search 336/192, 58; tached to the copper stud by means of a concentrically 339/95 A; 29/602 grooved brass washer which is forced into the face of dead-soft aluminum strip by means of a compression [56] References Cited nut. The electrical path for the connector assembly in- UNTTED STATES PATENTS cludes the dead-soft aluminum strip, the concentrically 728 092 5 1903 Edwards ...Q.'. 339 95 A brass wash, the brass i l 2,990,528 6 1961 Zimsky 336/58 the copper 3,314,030 4/1967 22 Claims, 8 Drawing Figures TRANSFORMER-WITH CONNECTOR AND METHOD OF ASSEMBLY BACKGROUND AND SUMMARY OF THE DEVELOPMENT This invention relates generally to a connector assembly for connecting aluminum strip conductors to a stud and more particularly to a connector assembly which includes a concentrically grooved washer made of material which is sufficiently hard relative to the aluminum conductor that the aluminum conductor will flow into the voids created by the concentric grooves thereby eliminating poor connections inherent in thermally cycled connectors for aluminum strips.

In the past, copper was the common material utilized for transformer secondary coil leads or busses, the copper being typically formed in a relatively flat strip. However, with the unusual increase in cost of copper, other materials have been sought which have the proper electrical and mechanical characteristics for use in connection with the leads of the secondary winding of a transformer.

One material which hasbeen found to have the desirable electrical characteristics is aluminum. Typically, electrical grade aluminum is extremely soft and attains its highest conductivity in the dead-soft, annealed state. However, certain problems have arisen in the use of aluminum for the secondary strip lead, these problems having been present form some period of time.

For-example, one problem which has existed with the use of dead-soft aluminum is the tendency for the aluminum to cold flow out of the connector assembly when any compressive force is applied. This problem particularly arises when it is desired to clamp the aluminum strip to a connector assembly for providing either a termination of the electrical conductor or the connection of the conductor to an external connector outside of the transformer casing.

The problem becomes particularly acute when the phenomenon of thermal cycling occurs wherein the thermal expansion of the various components of the connector assembly are different, thus creating an extremely high compressive force on the strip aluminum.

cled.

For example, aluminum expands at a rate which is approximately 1.3 to 1.5 times the rate of expansion of copper. This causes the aluminum to cold flow out of the joint or 'connectorthereby decreasing the crosssectional area of the conductor strip. Also, the cooling down of the conductor due to a reduced current flow or due to the reduction of the environmental temperature causes the aluminum to retract from the connector thereby increasing the electrical resistance of the connection. Once the joint has loosened as a result of cold flow, surface contact resistance between the various components of the electricaljoint increases both due to a laclt of joint pressure and formation of nonconductive oxides, the oxides developing on the aluminum as a result of the relatively loose fit of the joints or connector assembly. This increased electrical resistance increases the contact heating during subsequent electrical loading and the thermal cycling becomes more destructive until a thermal runaway condition occurs. When this runaway condition occurs the connection fails. I

Another phenomenon occurs with certain connections heretofore used in connection with the termination of secondary conductors of a transformer, this With the connector assembly of the present invention, all of the problems described above are substantially reduced plus adding other desirable features to the connection of an aluminum terminal strip of the secondary transformer to an external connector. The assembly of the present invention includes the provision of a concentrically grooved washer, either grooved on one or both faces, the washer being extremely flat relative to its diameter, and a clamping mechanism is provided for initially slightly deforming or cold flowing the aluminum by forcing the. concentrically grooved face of the washer slightly into the surface of the aluminum buss bar strip. In this way, any aluminum oxide crust that may be present on the face of the aluminum buss bar is broken thereby providing intimate contact between the exposed clean surfaces of the aluminum and the sharp ridges of the washer face. Also, the aluminum is slightly cold flowed into the grooves of the concentrically grooved washer leaving small voids or spaces at the apex of the void area formed by the grooves in the washer. Thus, when the joint is thermally cycled, the aluminum tends to flow into the voids formed by the concentric grooves rather than out of the joint to substantially limit clamping pressures on the aluminum buss strip. Further, when the joint cools, and the aluminum shrinks at a rate greater than other components in the system, the aluminum is restricted to movement along the angular faces of the grooves of the concentrically grooved washer effectively maintaining intimate contact of clean electrically conductive surfaces of the aluminum and the washer and also essentially maintaining clamping pressure on the joint. Thus, a good electrical connection is maintained and the formation of additional aluminum oxide is precluded.

Accordingly, it is one object of the present invention to provide an improved connector assembly for use in connecting low voltage aluminum strip conductors to the through connection in a transformer.

It is another object of the present invention to provide an improved connector assembly for a transformer which has improved thermal cycling characteristics.

It is a further object of the present invention to provide an improved connector assembly for a transformer which precludes oxides from forming in the strip buss connector joint which would be detrimental to the performance of the connection.

It is still a further object of the present invention to provide an improved connector assembly which enables the effective use of aluminum strip conductors in the secondary circuit of a transformer.

It is still a further object of the present invention to provide an improved connector assembly for the secondary circuit of a transformer which minimizes the resistance of the of the connection throughout the life of the transformer.

It is still a further object of the present invention to provide an improved connector assembly which is particularly adaptable for use in connection with interconnecting the secondary winding of a transformer with the transformer tank exterior conductor.

It is still a further object of the present invention to provide an improved connector assembly for use in conjunction with interconnecting conductors fabricated of materials which have widely varied thermal expansion characteristics.

It is a further object of the present invention to provide improved connector assembly for a transformer which is inexpensive to manufacture, reliable in use and substantially reduces problems heretofore encountered in connector assemblies of this type.

Further objects, features and advantages of this invention will become more apparent from a consideration of the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a sectional view of a transformer assembly, illustrating the primary and secondary windings in symbolic form, and particularly illustrating the connector assembly of the present invention;

FIG. 2 is a plan view of a grooved washer of the present invention;

FIG. 3ais a cross-sectional view of the washer of FIG. 2 taken along lines Zia-3a thereof;

FIG. 3b is a cross-sectional view of a modified form of washer of FIGS. 2 and 3a and particularly illustrating grooving on both faces of the washer;

FIG. 4 is a detail view of a connector assembly of the present invention and particularly illustrating two single faced grooved washers on either side of a buss bar;

FIG. 5 is a perspective view of a laminated buss bar and particularly illustrating the edge welding thereof;

FIG. 6 is aside view of the connector assembly of FIG. 4 and particularly illustrating the use thereof in connection with the laminated buss bar of FIG. 5; and

FIG. 7 is a side view of a modified connector assembly and particularly illustrating the use of two single face groove washers on the outboard sides oflaminated buss bars and further including adouble faced grooved washer between selected laminations of the buss bars or between two laminated buss bars terminating to one threaded stud connection assembly.-

Referring now to the drawings, and particularly to FIG. 1 thereof, there is illustrated a transformer assembly 10 which is formed generally of an outer casing 12 and a cover member 14, as is typical in the art. The primary conductors of the transformer are fed a high voltage by means of an input conductor assembly 16 which includes an insulating member 18 to insure that the high voltage is isolated from the tank. The high voltage is fed to the primary winding, symbolically illustrated at 20, by means of conductors 22,24 and the primary is magnetically coupled with a secondary winding, symbolically illustrated at 26.

The interior of the transformer tank 12 is filled with oil generally to a level indicated at 28 to provide a cooling and insulating fluid for the transformer windings 20,26. The cover member 14 is joined to the main tank at a lip section, a lip being formed on both the tank and the cover at 30,32, respectively. The two lips are joined by means of a clip 34 or other similar type of fastening member commonly used in transformers of this type.

The secondary winding 26 includes a pair of output conductors, one of which is symbolically illustrated at 36, and the other of which is illustrated as a strip or bar conductor assembly 38. It is to be understood that both the output conductors 36,38 are identical. The conductor 38 is fed through the transformer tank wall 12 by means of a connector assembly 40, forming at least a portion of the subject matter of the present invention.

The connector assembly 40 includes means for hermetically sealing the interior of the connector assembly 40 such that the oil 28 does not leak to the exterior of the tank 12. Typically, a pair of cup elements 42,44 form this sea] and the connection is made through the interior of the cup members 42,44. In the case of the present invention, the buss element 38 is connected to a stud member 46 by meansof a plurality of locknuts and washers to be more fully explained in conjunction with the description of FIGS. 2 through 7. The stud member 46 extends through the interior of the cup elements 42,44 to an exterior connector 50 to which the service conductors are connected.

As was stated above, it has been found that aluminum conductors, formed as is conductor 38, may be effectively used in conjunction with the secondary windings of a transformer if the problems of oxidation and thermal cycling at the lead terminations are solved. It has been found that both of these problems may be substantially reduced by the use of a concentrically grooved washer interposed between the strip conductor and a fastening member, as for example a nut. Such a washer element is illustrated at 54 in FIG. 2. The washer element includes a centrally located aperture 56 and a plurality of grooves 58 formed therein. It has been found that the grooves may be easily formed in the washer 54 by mounting the washer on a mandrel and rotating the washer in a position adjacent a sharp. cutting tool thereby cutting the grooves in the washer rather than applying the grooves by means of a stamping process. It has been found that the grooves could best be applied by the use of a tap tool, the tap being positioned with the axis of the tool parallel to the face of the washer, for simultaneous cutting of plural grooves. The operating edge of the flute of the tap actually inachines the grooves.

FIGS. 3a and 3b illustrate a cross-sectional view of washers which may be typically used in connection with connector assemblies incorporating features of the present invention. Particularly, FIG. 3a is a crosssectional view of a washer having a grooved area on a single face such as that illustrated in FIG. 2. FIG. 3b is a modified form of a washer 60 having the identical inner aperture62 as was described in conjunction with FIGS. 2 and 3a and a plurality of grooves 64 on one face of the washer 60. Additionally, the washer 60 is provided with a second set of concentric grooves 66 on the opposite face of the washer 60. Thus, the washer 60 may be utilized in conjunction with two aluminum conductor strips, the washer being positioned between the two strips such as will be described in conjunction with FIG. 7.

Referring now to FIG. 4, there is illustrated a typical connector assembly utilizing the principles of the present invention. Particularly, the connector assembly is associated with a transformer tank 12 including the cup member 42 described in conjunction with FIG. 1. A buss bar assembly is illustrated at 38 and includes an insulating tube and central conductor 70. The buss strip 70 is inserted on the stud 46 after a nut 78 and a single faced washer 54 is inserted on the stud 46.

Thereafter, a second single faced concentric washer 54 is applied with the grooves in the case of both washers facing the buss conductor 70. Finally, a compression nut 80 and a locknut 82 are applied, the compression nut 80 compressing the assembly, including the washers 54 and conductor 70, to cause the aluminum conductor 70 to cold-flow so that aluminum is forced into the grooves 58 to a certain extent. However, the grooves are not completely filled and a void is provided. The nut 82 is then applied to lock the assembly in the position shown.

Referring now to FIGS. 5 and 6, there is illustrated a modified form of the conductor 70, the modified form being fabricated as a laminated buss assembly 86. The conductor 86 of FIG. 6 is fabricated as illustrated in FIG. 5. Particularly, the conductor 86 is fabricated of aluminumstrips which are'placed in face abutting relation and tig welded, as at 88, to insure that all the individual conductors are provided with a good electrically conductive path to the faces of the concentric grooved washer connectors. The weld 88 is made close to an aperture 90 to reduce the electrical path. The aperture 90 is utilized to permit insertion of the stud member 46. The assembly of. FIG. 6 is seen to be sub stantially identical to that described in conjunction with FIG. 4 with the exception of the type of conductor 86 being connected to the stud .46. As was the case above, the connector assembly includes a nut 78, a single face grooved washer 54, a second single face grooved washer 54, a compression nut 80 and a locknut 82. The connector assembly is put together identically to that described in conjunction with FIG. 4.

Referring now to FIG. 7, there is illustrated a further modified form of conductor assembly 92, this assembly being formed of afirst and second

laminated conductor assemblies

94,96, each

laminated conductor

94,96 being tig welded as wasthe case with conductor 86. Again, theexterior assembly of the conductor assemblies92 is identical to that described in conjunction with FIGS. 4 and 6 and includes a nut 78, a pair of sin gle face grooved washers 54, a compression nut 80 and a locknut 82 to fasten the entire assembly on a stud46. However, a space is provided between

conductor assemblies

94,96 into which is inserted a double face grooved washer 60 such as was described in conjunction with the description of FIG. 3b. The washer 60 includes the two grooved faces into which the aluminum of the

conductors

94,96 are cold-flowed as a result of the turning of the compression nut 80. The washer 60 is provided to increase the electrical contact between

conductors

94,96, and thus maintain good electrical conductivity between

conductor assemblies

94 and 96.

Accordingly, when any of the connections illustrated in FIGS. 4, 6 or 7 are thermally cycled, the difference in expansion and contraction of the various materials used in the connector assembly, for example copper, brass and aluminum, will cause a differential expansion and an increase in the compressive force on the washer and conductor assembly. This will cause the aluminum to flow into the grooves or the voids created by the grooves and subsequent reduction in temperature will permit the aluminum to remain in contact with the grooved faces of the washer thereby maintaining the electrical contact. It is preferable to fabricate the washers such that the grooved washer faces will have quite sharp ridges to allow ready penetration into the aluminum strip surface. It has been found that the thermal cycling characteristics are improved with a sharper washer. I

While it will be apparent that the preferred embodi ments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper material, and means for maintaining the electrical resistance of the connector assembly after the connector assembly has been thermally cycled including a washer having a plurality of concentric grooves formed on at least one fact thereof, said washer being positioned on the stud adjacent the said soft material between two compression elements with the said grooves being con-- tiguous with the soft material, the compression elements being operated toforce soft material at least partially into said grooves. I

2. The improvement of claim 1 wherein said at least one of the windings is the secondary winding and said ends are fabricated of aluminum, said grooves being formed with sharp ridges and are continuous.

3. The improvement of claim 2 wherein the circuit to the exterior of the transformer tank includes said aluminum ends, said washer, said compression element and the stud.

'4. In the transformer assembly of claim 2 further including cooling fluid contained within the tank, the improvement further comprising said connector assembly having at least a portion thereof within the tank and below the level of said cooling fluid and further including means for providing afluid-tightseal with the tank.

5. The improvement of claim 3 wherein said ends are fabricated of a plurality of aluminum strips, said aluminum strips including an aperture formed adjacent one end thereof.

6. The improvement of claim 5 wherein said aluminum strips are positioned in face to face abutting relation and a weld is provided at the edges of said strips closely adjacent said aperture to maintain the electrical resistance characteristics of said welded strips.

7. The improvement of claim 6 wherein said connector assembly includes a second washer having a concentrically grooved face, said second washer being positioned adjacent said aluminum strips with said grooved face contiguous with said aluminum strips.

8 The improvement of claim 7 wherein said compression element operates to force soft material at least partially into the said grooves of said second washer.

9. The improvement of claim 8 wherein said weld is discontinuous across the edges of said aluminum strips, at least two of said strips being spaced at said discontinuity to provide a space between said strips.

10. The improvement of claim 9 .wherein said connector assembly further includes a third washer positioned in said space between said strips, said third washer having concentrically grooved faces on opposite sides of said washer, said compression element operating to force soft material at least partially into said grooves of said third washer.

11. The method of forming a transformer assembly comprising the steps of assembling a primary winding and a secondary winding in a tank, assembling a connector assembly including a stud associated with at least one of said windings, the ends of the at least one of the windings being fabricated of a soft, cold-flowable material, and maintaining the electrical resistance of the connector assembly after the assembly has been thermally cycled including assembling a washer with a plurality of concentric grooves on at least one face of said washer, positioning at least two compression elements and the said washer on the stud adjacent the soft material, said washer being between the two compression elements with said groove being positioned contiguous with said soft material, and operating at least one compression element to force said soft material at least partially into said grooves.

12. In the transformer assembly of claim 11 wherein at least one of the said windings is the secondary winding and said ends are fabricated of aluminum.

13. In the transformer assembly of claim 12 wherein the circuit to the exteriorof the transformer tank includes said aluminum ends, said washer, said compression elements andthe stud.

14. In the transformer assembly of claim 12 further including cooling fluid contained within the tank, the

into said grooves of said third washer.

one end thereof.

16. The method of claim 15 further including positioning said strips in face to face abutting relation and welding the edges of said strips closely adjacent said aperture to maintain the electrical resistance characteristics of said welded strips.

17. The method of claim 16 further including providing a second washer having a concentrically grooved face, and positioning said second washer adjacent said aluminum strips with said grooved face contiguous with said aluminum strips.

18. The method of claim 17 further including operating said compression element to force soft material at least partially into the said grooves of said second washer.

' 19. The method of claim 18 further including providing a discontinuity across the edges of said aluminum strips, and spacing at least two of said strips at said discontinuity to provide a space therebetween.

20. The method of claim 19 further including providing a third washer in said space between said strips, said third washer having concentrically grooved faces on opposite sides of said washer and operating said compression element to force soft material at least partially 21. The improvement of claim 11 wherein at least two of said washer, stud and compression elements are of differing coefficients of thermal expansion.

22. The method of claim 11 wherein said washer is formed by steps including mounting blank washer stock on a mandrel, mounting a cutting tool adjacenta face of the washer stock, rotating one of said stock and tool relative to the other, and advancing one of said stock and tool relative to the other.

Claims

2. The improvement of claim 1 wherein said at least one of the windings is the secondary winding and said ends are fabricated of aluminum, said grooves being formed with sharp ridges and are continuous.
3. The improvement of claim 2 wherein the circuit to the Exterior of the transformer tank includes said aluminum ends, said washer, said compression element and the stud.
4. In the transformer assembly of claim 2 further including cooling fluid contained within the tank, the improvement further comprising said connector assembly having at least a portion thereof within the tank and below the level of said cooling fluid and further including means for providing a fluid-tight seal with the tank.
5. The improvement of claim 3 wherein said ends are fabricated of a plurality of aluminum strips, said aluminum strips including an aperture formed adjacent one end thereof.
6. The improvement of claim 5 wherein said aluminum strips are positioned in face to face abutting relation and a weld is provided at the edges of said strips closely adjacent said aperture to maintain the electrical resistance characteristics of said welded strips.
7. The improvement of claim 6 wherein said connector assembly includes a second washer having a concentrically grooved face, said second washer being positioned adjacent said aluminum strips with said grooved face contiguous with said aluminum strips. 8 The improvement of claim 7 wherein said compression element operates to force soft material at least partially into the said grooves of said second washer.
9. The improvement of claim 8 wherein said weld is discontinuous across the edges of said aluminum strips, at least two of said strips being spaced at said discontinuity to provide a space between said strips.
10. The improvement of claim 9 wherein said connector assembly further includes a third washer positioned in said space between said strips, said third washer having concentrically grooved faces on opposite sides of said washer, said compression element operating to force soft material at least partially into said grooves of said third washer.
11. The method of forming a transformer assembly comprising the steps of assembling a primary winding and a secondary winding in a tank, assembling a connector assembly including a stud associated with at least one of said windings, the ends of the at least one of the windings being fabricated of a soft, cold-flowable material, and maintaining the electrical resistance of the connector assembly after the assembly has been thermally cycled including assembling a washer with a plurality of concentric grooves on at least one face of said washer, positioning at least two compression elements and the said washer on the stud adjacent the soft material, said washer being between the two compression elements with said groove being positioned contiguous with said soft material, and operating at least one compression element to force said soft material at least partially into said grooves.
12. In the transformer assembly of claim 11 wherein at least one of the said windings is the secondary winding and said ends are fabricated of aluminum.
13. In the transformer assembly of claim 12 wherein the circuit to the exterior of the transformer tank includes said aluminum ends, said washer, said compression elements and the stud.
14. In the transformer assembly of claim 12 further including cooling fluid contained within the tank, the method further comprising said connector assembly having at least a portion thereof within the tank and below the level of said cooling fluid and further providing a fluid-tight seal with the tank.
15. The method of claim 13 further including fabricating said ends of a plurality of aluminum strips, and forming an aperture in said aluminum strips adjacent one end thereof.
16. The method of claim 15 further including positioning said strips in face to face abutting relation and welding the edges of said strips closely adjacent said aperture to maintain the electrical resistance characteristics of said welded strips.
17. The method of claim 16 further including providing a second washer having a concentrically grooved face, and positioning said second washer adjacent said aluminum strips with said grooved face Contiguous with said aluminum strips.
18. The method of claim 17 further including operating said compression element to force soft material at least partially into the said grooves of said second washer.
19. The method of claim 18 further including providing a discontinuity across the edges of said aluminum strips, and spacing at least two of said strips at said discontinuity to provide a space therebetween.
20. The method of claim 19 further including providing a third washer in said space between said strips, said third washer having concentrically grooved faces on opposite sides of said washer and operating said compression element to force soft material at least partially into said grooves of said third washer.
21. The improvement of claim 11 wherein at least two of said washer, stud and compression elements are of differing coefficients of thermal expansion.
22. The method of claim 11 wherein said washer is formed by steps including mounting blank washer stock on a mandrel, mounting a cutting tool adjacent a face of the washer stock, rotating one of said stock and tool relative to the other, and advancing one of said stock and tool relative to the other.