Patent Application
20050275496
Transformer coils used in high-voltage and other applications are formed by winding a conductor and casting and curing a thermosetting resin composition around the conductor windings to form a resin body covering the coil. The resin body provides dielectric properties to the transformer coil assembly, as well as holding the conductor windings in place. The resin also provides protection and more uniform thermal properties to the coil assembly. Without some form of support structure for the coil assembly, the resin may develop cracks during casting or during use when the assembly is subjected to external conditions, such as high temperature, high humidity, moisture penetration and the like, or due to internal factors, such as heat generation or stress due to high current flow, electrical fault conditions, and the like.
The resin body is subjected to thermal forces from coil temperatures well above ambient during operation due to I2R losses in the conductors, from eddy currents, from hysteresis losses in the core, and from stray flux impinging the axial ends of the windings. Further, the resin body may be subject to vibratory forces during operation. The resin body should satisfactorily restrain, resist, and withstand all of these forces over long term operation.
A transformer coil assembly is disclosed that includes a first layer having a plurality of fibers interconnected to form a fabric and a plurality of spacers. Each spacer is affixed on a first side of the spacer to the fabric and protruding from a first surface of the fabric. A second layer has a conductor in contact with at least one of the plurality of spacers on a second side of each spacer that opposes the first side. The first and second layers are covered by resin.
A method of forming a transformer coil assembly is disclosed that includes providing a first fabric layer having a plurality of fibers interconnected and a plurality of protruding spacers affixed to a surface of the fabric. A conductor layer is applied to the first fabric layer in contact with at least one of the plurality of protruding spacers. A resin is applied to cover at least the first fabric layer and the conductor layer.
A transformer coil assembly is disclosed that includes means for establishing a support structure for the transformer coil assembly, the support structure having a first thickness along a first dimension. Spacer means are affixed to the support structure and have a second thickness along the first dimension, the second thickness being greater than the first thickness. The spacer means are formed of a material having a lower compressibility than material used to form the support structure. Conductor means are in contact with the spacer means. Dielectric means cover the support structure means, the spacer means, and the conductor means.
A fibrous material for reinforcing a resin cast transformer coil assembly is disclosed that includes a plurality of fibers interconnected to form a fabric. A plurality of spacers is affixed to the fabric and protrudes from a surface of the fabric. The spacers are arranged in a plurality of rows, where each row is segmented such that superimposing rows onto each other provides an unsegmented row of spacers.
Objects and advantages will become apparent to those skilled in the art upon reading this description in conjunction with the accompanying drawings, in which like reference numerals have been used to designate like elements, and in which:
The means for establishing a support structure 310 can include multiple fibers interconnected to form a fabric. The fabric can include glass fibers and can include electrical grade glass. The fabric can include any of a variety of fibers that are known in this art to be suitable for transformer cast applications, such as polyphenylene sulfide (PPS), polyamides (nylon), polyvinyl chloride (PVC), flouropolymers (PTFE), and the like.
The first layer 130 of the transformer coil assembly 100 also includes spacer means 330, affixed to the support structure means 310. The spacer means 330 can include multiple spacers and is preferably formed of a less compressive material than fabric, such as resin or epoxy. The spacer means 330 are affixed to a surface of the support structure means 310. Here, the term “affixed” means that the spacers can be secured adjacent to a surface of the support structure means 310, by adhesives or other known means, or can be partially embedded in the support structure means 310. The spacer means 330 protrude from the support structure means 310 by a distance, i.e., height, 335. It should be appreciated that although the spacer means 330 are shown affixed to only one surface of the support structure means 310, the spacer means 330 can also be attached to both opposing surfaces of the support structure means 310.
The second layer 140 includes a conductor means 145 in contact with at least one of the spacers of the spacer means 330 on a second side 332 of each spacer that opposes the first side 331. The conductor means 145 can be a single conductor that is wound continuously to form a single transformer coil winding, or can be multiple conductors, depending on the type of transformer coil assembly 100. The conductor means 145 can include tabs 160 for accessing the conductor means 145 by other electrical components outside the transformer coil assembly 100.
The transformer coil assembly 100 includes a dielectric means for covering the support structure means 310, the spacer means 330, and the conductor means 145. The dielectric means can be a resin body 110 covering the layers of the transformer coil assembly 100. Although the dielectric means will be described hereinafter as a resin body 110, or simply resin 110, one of skill in this art will recognize that a number of dielectric materials may be used that are suitable for use in a transformer cast. The thickness of the resin body should be uniform to provide dielectric properties that are uniform throughout the transformer coil assembly. Here, the term uniform means substantially the same throughout with some tolerance. A dielectric with favorable properties will resist breakdown under high voltages, does not itself draw appreciable power from the circuit, is physically stable, and has characteristics that do not vary much over a fairly wide temperature range.
The transformer coil assembly 100 can optionally include a third layer 150 having support structure means 315 and spacer means 335. The third layer 150 can be made of the same materials as the first layer, although this is not a requirement. When the optional third layer 150 is employed, the dielectric means, such as a resin body 110, can cover the first, second, and third layers 130, 140, 150, providing an overall thickness 160.
The means for establishing support structure 310 provides reinforcing support to the resin body 110 to prevent the development of cracks during casting or during use when the assembly is subjected to external conditions, such as high temperature, high humidity, moisture penetration and the like, or due to internal factors, such as high coil temperatures or vibratory forces during operation.
The spacer means 330 protrude from the support structure means 310 by a distance 335. The protrusion of the spacer means 330 creates a space 320 between conductor means 145 and the support structure means 310, where the resin 110 can more easily flow during the casting process. That is, without the spacers, the resin would have to “wick” into the support structure, which takes additional time and may produce uneven dispersion of the resin 110. Uneven dispersion produces a resin body 110 that does not have uniform dielectric properties. The spacer means 330 provides a more even resin body 110 having more uniform dielectric properties than using, for example, a support structure 310 only.
Moreover, the height 335 of the spacer means 330 can be selected to provide a desired overall thickness 120 of the first layer 130 using less support structure means 310, such as fabric. That is, to achieve the same thickness 120 of the first layer 130, and therefore the same dielectric properties, without the spacer means 330, many layers of fabric would typically be required. The layers of fabric would not only cause uneven dispersing of the resin 110, as described above, but would be subject to compression by the conductor means 145 as the conductor means 145 is applied, e.g., wound, over the fabric layers. Compression is typically uneven and results in a non-uniform thickness of the first layer, causing non-uniform dielectric properties. The spacer means 330 therefore preferably is less compressive, i.e., is less subject to changes in volume when a force is applied, than the support structure means 310. For example, epoxy spacers are less compressive than layers of electrical grade glass.
The spacers 230 can be arranged in a plurality of rows 240A, 240B. The rows 240A, 240B can be segmented as shown.
As can be appreciated from
It is, however, preferable to use segmented rows of spacers. The segmenting allows better flow of the resin around the spacers. In addition, longer spacers are more likely to conduct electricity from one area of the conductor to another, or create a voltage potential between spacers.
It will be appreciated by those of ordinary skill in the art that the invention can be embodied in various specific forms without departing from its essential characteristics. The disclosed embodiments are considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims, rather than the foregoing description, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced thereby.
It should be emphasized that the terms “comprises”, “comprising”, “includes” and “including” when used in this description and claims, are taken to specify the presence of stated features, steps, or components, but the use of these terms does not preclude the presence or addition of one or more other features, steps, components, or groups thereof.
