AN INSULATED CONDUCTOR AND PROCESS FOR MAKING AN INSULATED CONDUCTOR

Abstract: A process for making an insulated conductor in accordance with the present invention includes extruding an insulative material onto a conductor and subsequently rolling the insulative material on the conductor to a prescribed thickness. The extruding step comprises extruding the insulative material to a thickness of about 0.0025 inch to about 0.0035 inch, and the rolling step comprises rolling the insulative material to a thickness of about 0.00125 to about 0.00315 inch.

Description: AN INSULATED CONDUCTOR AND PROCESS FOR MAKING AN INSULATED CONDUCTOR FIELD OF THE INVENTION The present invention relates generally to an insulated conductor and processes for making an insulated conductor, and more particularly to processes for making a high voltage insulated electrical conductor for use in electrical transformers. Still more particularly, the invention relates to an insulated conductor and a process for making an electrical conductor having an insulation coating disposed thereon of thickness of about 0.00125 to about 0.00315 inch. BACKGROUND OF THE INVENTION Rectangular conductors with high dielectric strength insulation, such as polyphenylsulfone, are coated using thermoplastic extruders equipped with crossheads tooled to coat rectangular conductors. Typically, the extruded insulation coating thickness range is about 0.0025 inch (the minimum obtainable) to about 0.0035 inch (easily obtainable) . One of the shortcomings of the extrusion crosshead is that the coating thickness cannot be controlled to thin coatings of less than 0.0025 inch. Accordingly, a goal of the present invention is to provide a process for making electrical conductors in which the thickness of the extruded coating can be reduced by about 10% to about 50% to provide a reduced insulation thickness range of about 0.00125 inch to about 0.00315 inch depending on the extruded starting thickness and the percent reduction utilized. The process in accordance with the invention provides a coating of insulative material which can have a prescribed thickness less than that produced by the presently available extrusion process (es) . SUMMARY OF THE INVENTION An insulated conductor is provided comprising an electrical conductor and an insulative coating disposed on the conductor. In accordance with the invention, the coating has a thickness of about 0.00125 inch to about 0.00315 inch, and preferably about 0.00125 to about 0.00175 inch. A process for making an insulated conductor in accordance with the present invention includes extruding an insulative material onto a conductor and subsequently roll reducing the coated conductor so that the insulative material on the conductor is reduced by about 10% to about 50% to a prescribed thickness and the conductor assumes a prescribed thickness and width. The extruding step preferably comprising extruding the insulative material to a thickness of about 0.0025 inch to about 0.0035 inch and more preferably to a thickness of at least about 0.0025 inch, and the rolling step preferably comprises rolling the insulative material to a thickness of about 0.00125 to 0.00315 inch and preferably to a thickness of about 0.00125 to 0.00175 inch. In a preferred embodiment of the invention, the insulative material is a thermoplastic polymer, such as polyphenylsulfone. Furthermore, in preferred embodiments of the invention, the conductor is generally rectangular in cross-section. The preferred embodiment of the invention also includes rolling the conductor to a reduced thickness and increased surface area, i.e., the rolling step includes rolling the insulative material to a prescribed thickness and at the same time rolling the conductor to a reduced thickness. Thus, both the coating thickness and the shape of the coated product are altered in the rolling step. Other features of the invention are disclosed below. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 schematically depicts an extruder and the process of extruding an insulative material onto the surface of a rectangular conductor. The product of the extrusion process is a conductor 10 comprising an electrical conductor 12 and an insulative coating 14. Fig. 2 schematically depicts the rolling step in accordance with the present invention, wherein up to four rolls 16a-16d are employed to roll the insulative coating to a desired thickness, and at same time alter the shape (thickness or surface area) of the electrical conductor 12. Fig. 3 illustrates one form of transformer; a transformer 20 comprising a pair of coils 10' (i.e., coils composed of an insulated conductor in accordance with the present invention) and a core 18. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention employs developed sizes of conductor that can be reduced to the desired dimensions with the desired thickness of insulation. Presently preferred embodiments of the invention employ reducing rolls. This invention, when applied in conjunction with the thermoplastic extruder, allows rectangular conductors (e.g., aluminum or copper) to be produced with the desired dimensions of conductor and insulation thickness. This invention can be employed to control the insulation thickness of either of the two opposing sides of the conductor, or of all four sides, depending on the roller configuration. As mentioned, the extrusion of thermoplastic coatings onto rectangular conductors is limited generally to a minimum thickness of 0.0025 inch. This is an inherent limitation due to the way presently available extruder crossheads, and their associated die components, apply the melted polymer to the conductor. This extrusion process is represented by the block bearing the same name in Fig. 1. A product of this process is a conductor 10 comprising the electrical conductor 12 and its associated insulative coating 14, wherein the coating has a minimum thickness of 0.0025 inch. As indicated above, the extruded insulation coating thickness can range from about 0.0025 inch (the minimum obtainable) to about 0.0035 inch (easily obtainable) . The polymers applicable to high voltage conductors used in transformers 20 (Fig. 3) must have performance characteristics that ensure functional life performance for up to 25 years. These polymers have dielectric strengths that allow them to be used with coating thicknesses of less than 0.0025 inch, i.e., in the range of about 0.00125 to about 0.00315 inch and preferably in the range of about 0.00125 to about 0.00175 inch. The product of the inventive process disclosed herein is a rectangular conductor 10' (see Fig. 2) having an insulation of a thickness which meets the dielectric needs of the transformer but does not exceed such need by an excessive amount. Excessive insulation is costly from not only a materials cost standpoint but also from a space factor standpoint, which is a detriment to maintaining a small core/coil assembly 18, 10' (see Fig. 3) . The core/coil assembly size equates to the cost of the transformer 20, not only in materials used but also in electrical losses prevented. According to the present invention, a set of reducing rolls is employed to reduce the insulation thickness. The reducing rolls can be configured in different ways, such as two flat rolls with parallel axes or one flat roll in combination with a slightly tapered, grooved roll, or four flat rolls (one on each side of the conductor 12) or four flat rolls as is configured in what is commonly known as a "Turks" head. These various configurations are represented generally in Fig. 2, which depicts four flat rolls 16a-16d. The final size of the conductor product (i.e., the conductor and insulative coating) with its desired thickness of insulation is produced by developing a starting size of conductor with an extrudable thickness of insulation that when rolled yields a conductor of the desired or predetermined dimensions with the desired or predetermined thickness of insulation. For the particular transformer application for which the process/insulated conductor in accordance with the invention was developed, the conductor typically has a width no more than about ten times its thickness and the thickness of the insulation is about 0.00125 to 0.00175 inch. However, depending upon required performance characteristics, functional life performance periods, polymer utilized, dielectric strengths, etc., even lesser coating thicknesses are possible in accordance with the process of the present invention. For example, coating thickness less than 0.00125 inch may be utilized for certain applications, as will be understood to those skilled in the art, and such reduced coating thicknesses may be obtained by the inventive process disclosed herein. The process involves the extrusion of a larger cross-section conductor than the desired final size. This conductor is then extrusion coated with thermoplastic insulation. The thickness of the coating, for example, can be approximately 0.0025 inch, which is the minimum thickness possible by currently available extruders. The coated conductor is then rolled into a final desired cross- sectional thickness and width. During the rolling step, the ratio of the conductor surface to the volume of the conductor increases as the conductor cross-section changes from one rectangular shape to a different rectangular shape, i.e., as the thickness of the conductor is reduced. This means that the insulation thickness is reduced to below the original 0.0025 inch, resulting in a more efficient conductor. Typical dimensions, in inches, of a conductor reduced in a two-way roll are: - starting base conductor size = 0.1140 thickness x 0.1620 width. - starting coated conductor size = 0.1190 thickness x 0.1670 width. - rolled bare conductor size = 0.0725 thickness x 0.2090 width. - rolled coated conductor size = 0.0760 thickness x 0.2120 width. In sum, the present invention employs one or more roll means or apparatus to alter the shape of the coated conductor to achieve a desired or predetermined thickness of insulation. The above description of preferred embodiments is not intended to limit the scope of protection of the following claims. Thus, for example, except where they are expressly so limited, the following claims are not limited to processes employing any particular number, configuration, or shape of roll or means or apparatus.

Claims: We claim: 1. A process for making an insulated conductor, comprising: (a) extruding an insulative material onto a conductor; and (b) rolling said insulative material on said conductor to a predetermined thickness . 2. A process as recited in claim 1, wherein step (a) comprises extruding said insulative material to a thickness of about 0.0025 to about 0.0035 inch. 3. A process as recited in claim 2, wherein step (b) comprises rolling said insulative material to a thickness of about 0.00125 to about 0.00315 inch. 4. A process as recited in claim 1, wherein step (a) comprises extruding said insulative material to a thickness of at least 0.0025 inch. 5. A process as recited in claim 4, wherein step (b) comprises rolling said insulative material to a thickness of less than 0.0025 inch. 6. A process as recited in claim 4, wherein step (b) comprises rolling said insulative material to a thickness of about 0.00125 to about 0.00175 inch. 7. A process as recited in claim 1, wherein said insulative material is a thermoplastic polymer. 8. A process as recited in claim 7, wherein thermoplastic polymer comprises polyphenylsulfone. 9. A process as recited in claim 1, wherein said conductor is generally rectangular. 10. A process as recited in claim 1, wherein step (b) comprises rolling said conductor to a reduced thickness. 11. A process as recited in claim 1, wherein step (b) comprises rolling said conductor to an increased surface area. 12. A process as recited in claim 1, wherein step (b) comprises employing at least two flat rolls. 13. A process as recited in claim 1, wherein step (b) comprises employing at least one tapered, grooved roll. 14. A process as recited in claim 1, wherein step (a) comprises extruding said insulative material to a thickness of at least 0.0025 inch; said conductor is generally rectangular; and step (b) comprises rolling said insulative material to a thickness of about 0.00125 to about 0.00175 inch, and rolling said conductor to a reduced thickness and increased surface area. 15. An insulated conductor comprising: a) an electrical conductor; and b) an insulative coating disposed on said electrical conductor, said insulative coating having a thickness of about 0.00125 to about 0.00315 inch. 16. An insulated conductor as defined in claim 15 wherein said electrical conductor is aluminum. 17. An insulated conductor as defined in claim 15 wherein said electrical conductor is copper. 18. An insulated conductor as defined in claim 15 wherein said insulative material is a thermoplastic polymer. 19. An insulated conductor comprising: a) an electrical conductor; and b) an extruded insulative coating disposed on said electrical conductor, said extruded insulative coating having a thickness of about 0.00125 to about 0.00175 inch. 20. An insulated conductor as defined in claim 19 wherein said electrical conductor is aluminum. 21. An insulated conductor as defined in claim 19 wherein said electrical conductor is copper. 22. An insulated conductor as defined in claim 19 wherein said insulative material is a thermoplastic polymer. 23. A transformer coil comprising an insulated conductor comprising: a) an electrical conductor; and b) an insulative coating disposed on said electrical conductor, said insulative coating having a thickness of 0.00175 inch or less. 24. A transformer coil as defined in claim 23 wherein said electrical conductor is aluminum. 25. A transformer coil as defined in claim 23 wherein said electrical conductor is copper. 26. A transformer coil as defined in claim 23 wherein said insulative material is a thermoplastic polymer. 27. A transformer comprising a core and a coil, said coil comprising an insulated conductor comprising: a) an electrical conductor; and, b) an insulative coating disposed on said electrical conductor, said insulative coating having a thickness of 0.00175 inch or less. 28. A transformer as defined in claim 27 wherein said electrical conductor is aluminum. 29. A transformer as defined in claim 27 wherein said electrical conductor is copper. 30. A transformer as defined in claim 27 wherein said insulative material is a thermoplastic polymer. 31. A process for making an insulated conductor comprising: a) extruding a thermoplastic polymer onto a conductor to form a conductor having an insulated coating thereon; b) rolling said insulated coating and conductor to produce a conductor of predetermined width and thickness and a coating of predetermined thickness. 32. A process as recited in claim 31, wherein step (a) comprises extruding said polymer to a thickness of about 0.0025 inch. 33. A process as recited in claim 32 wherein step (b) comprises rolling said thermoplastic polymer to a thickness of about 0.00125 to about 0.0175 inch and said conductor to a width no more than ten times its thickness. 34. A transformer coil comprising an insulated conductor comprising: a) an electrical conductor; and b) an extruded thermoplastic polymer insulative coating disposed on said electrical conductor; said coating having a thickness of about 0.00125 to about 0.0175 inch and said electrical conductor having a width no more than ten times its thickness. 35. A transformer comprising a core and a coil, said coil comprising an insulated conductor comprising: a) an electrical conductor; and b) an extruded thermoplastic polymer insulative coating disposed on said electrical conductor; said coating having a thickness of about 0.00125 to about 0.0175 inch and said electrical conductor having a width no more than ten times its thickness. 36. A transformer comprising a core and a coil, said coil comprising an insulated conductor comprising: a) an electrical conductor; and b) an extruded thermoplastic polymer insulative coating disposed on said electrical conductor; said coating having a thickness of about 0.00125 to about 0.00315 inch and said electrical conductor having a width no more than ten times its thickness. 37. A process for making an insulated conductor comprising: a) extruding an insulative material onto a conductor to a predetermined thickness; and b) rolling said insulative material to reduce the thickness thereof by about 10% to about 50% to provide a reduced insulative material thickness from about 0.00125 to about 0.00315 inch. 38. A process as recited in claim 37, wherein step (b) includes rolling said conductor to produce a conductor of predetermined width and thickness. 39. A process as recited in claim 38, wherein step (b) comprises rolling said insulative material to a thickness of about 0.00125 to about 0.0175 inch and said conductor to a width no more than ten times its thickness.

Inventors: HILL NORRIS L, LINSENBARDT THOMAS L, HILL, NORRIS, L., LINSENBARDT, THOMAS, L.
Applicants: ABB POWER T & D CO, ABB POWER T & D COMPANY INC.
Application year: 1996
Main classification: H01B7
IPC codes: H01B13, H01F27