FIELD OF THE INVENTION

[0001] The present invention generally relates to electrical insulators. More particularly, the present invention pertains to use of binder materials in electrical insulators.

BACKGROUND OF THE INVENTION

[0002] Electrical insulators, or dielectrics, are utilized in a variety of items to separate electrical conductors. Insulators can be dry type or fluid-filled. Fluid filled insulators insulate conductors by using a fluid such as oil. Fluid filled insulators are best suited for high heat applications, such as large industrial complexes. However, fluid filled insulators are costly to manufacture and costly to maintain. Dry type insulators are better suited for ranges of temperatures that are more moderate such as for example, homes and small businesses, and they require less maintenance.

[0003] Typical dry type insulators incorporate staple fibers such as aramid or mica. In order to form a matrix of these fibers, a varnish is used. The fibers and varnish are blended together to form the matrix which is then formed into the insulator. This creates more processing steps and does not yield ideal mechanical properties because the varnish does not add strength to the fibers. Further, the additional processing steps add to the cost of manufacturing.

[0004] Accordingly, it is desirable to provide a dry type insulator capable of providing insulation in higher temperature ranges, having better mechanical properties, while also reducing or removing additional processing steps that result in overall reduction in cost.

SUMMARY OF THE INVENTION

[0005] The foregoing needs are met, to a great extent, by the present invention, wherein a dry type electrical insulator is formed that can operate at high temperatures, has strong mechanical properties, has fewer processing steps and entails less cost. [0006] In one embodiment, a dry type electrical insulation is provided that includes a base fiber having an outer surface and a first melting point and a binder material, coated onto the outer surface of the base fiber, having a second melting point. In this embodiment, the second melting point is lower than the first melting point.

[0007] In another embodiment, a dry type insulation matrix is provided that includes a plurality of composite fibers having a base fiber having a first melting point and a binder material co-extruded therewith, having a second melting point. In this embodiment, the second melting point is lower than the first.

[0008] There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.

[0009] In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.

[0010] As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[001 1] FIG. 1 is a perspective view of components for dry type electrical insulation in accordance with an embodiment of the present invention. [0012] FIG. 2 is a perspective view of components for dry type electrical insulation in accordance with another embodiment of the present invention.

[0013] FIG. 3 is a perspective view of components for dry type electrical insulation in accordance with yet another embodiment of the present invention.

[0014] FIG. 4 is a perspective view of a matrix formed using any of the embodiments as shown in FIGS. 1, 2 and/or 3.

[0015] FIG. 5 is a cross sectional view of a first step in forming a laminate in accordance still another embodiment of the present invention.

[0016] FIG. 6 is a cross sectional view of a second step in forming the laminate of

FIG. 4.

[0017] FIG. 7 is a flow diagram of a method for fabricating the dry type insulation according to embodiments of the present invention.

DETAILED DESCRIPTION

[0018] Embodiments of the present invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. FIG. 1 is a perspective view of components for dry type electrical insulation in accordance with an embodiment of the present invention. In particular, FIG. 1 shows two composite fibers 10, where the composite fiber 10 includes a base fiber 12 having an outer surface 14. The outer surface 14 is coated with a sheath of a binder material 16.

[0019] The base fiber 12 can be made from a staple fiber such as wool, hemp, raw cotton, flax, aramid, mica or other natural material. The base fiber 12 can also be made from a thermoplastic such as polyethylene terephthalate (PET), polyphenylene sulphide (PPS), polyetherimide (PEI), polyethylene napthalate (PEN), polyethersulfone (PES) or polybutylene terephthalate (PBT) and/or combinations thereof. Generally, the base fiber 12 is formed of a material having a high melting point.

[0020] The binder material 16 is preferably an amorphous or crystalline thermoplastic material. More particularly, the binder material 16 can be formed from at least one of a copolymer of polyethylene terephthalate (CoPET), polybutylene terephthalate (PBT), or undrawn polyphenylene sulphide (PPS) and/or combinations thereof. The melting point of the binder material 16 is lower than the melting point of the base fiber 12. At typical processing temperatures of about 220-240°C, or about 20°C above the melting point of the binder material 16, the binder material 16 melts and adheres to other composite fibers 10, forming a strong matrix with better mechanical properties than conventional dry type insulation materials. Alternately, the binder material 16 can be any material suitable for the operating temperature and mechanical strength requirement based on the device to be insulated.

[0021] For instance, if the binder material melts at 220°C a suitable base fiber 12 would be one that would not melt until at least 250°C. The operating temperature of the insulation would be lower than the melting point of either the binder material or the base fibers so that the matrix does not melt during operation, for example, in the range of 150- 200°C. Such a material could be suitable for an application in a device that has approximately 200°C continuous operation. Dry type insulation of the prior art has not been able to accommodate such a high temperature range. Thus, embodiments of the present invention allow for dry type insulation to be utilized at a higher temperature range than would otherwise be possible.

[0022] Preferably, the binder material 16 can be compressible to a high density material on the order of about 0.50 to about 1.10 g/cc, and have the ability to bond the base fibers 12, while maintaining good dielectric properties. Additionally, within this range, the mechanical properties are strong enough for most applications within the dry type electrical apparatus. Embodiments of this invention will also allow the binder material 16 to be chosen such that the processing temperature will be above the anticipated operating temperature. Because the binder material 16 is incorporated directly on the surface of the base fiber 12 and is co-extruded with the base fiber 12, there is no requirement for impregnation with a varnish system.

[0023] In an embodiment of the present invention, it is possible to vary the amount of base fibers 12 that include the binder material 16. For example, at 100% loading, all of the base fibers 12 are co-extruded with the binder material 16. During processing, the binder material 16 melts and adheres to other composite fibers 10 to form a matrix. When 100% of the fibers in the matrix include the binder material 16, (or there is a 100% loading, referring to the percentage of base fibers 12 that are coated with the binder material 16), a very strong, rigid matrix is formed. However, this can be very costly. Further, some applications do not require such rigidity and strength. It has also been found that at 100% loading, the porosity of the completed matrix is reduced, which can be undesirable in certain applications.

[0024] As another example, it may be desirable to incorporate only 50% of base fibers that are co-extruded with binder material 16. The other 50% of the base fibers 12 would be left bare. In this instance, raising the processing temperatures above the melting point of the binder material 16 ensures that the binder material 16 melts and binds the base fibers 12 of the coated and uncoated base fibers 12. The binder material 16 on half of the base fibers 12 will allow all of the fibers to adhere to each other, acting as binder for the entire matrix. Thus, a 50% loading, referring to the percentage of the coated base fibers 12, still yields strength but lowers costs. There is also some amount of porosity.

[0025] Therefore, the load of the base fibers, or the percentage of the base fibers 12 coated with binder material 16, can be varied, depending on the mechanical strengths and costs, as desired. In embodiments of the present invention, 50 - 100% loading is preferable. Some instances have shown that 70-80% loading is acceptable for most normal applications, including ranges and limits there between. Consideration on the percentage of loading is also based on the type of base fiber 12 that is used. A traditionally weaker base fiber may require greater loading, whereas a stronger base fiber may require less loading.

[0026] FIG. 2 illustrates a perspective view of components for dry type electrical insulation in accordance with another embodiment of the present invention. As shown in FIG. 2, a composite fiber 18 includes numerous base fibers 20 having outer surfaces 22. The outer surfaces 22 are all covered with a single coating of a binder material 24. The binder material 24 can be co-extruded over the outer surfaces 22 of the base fibers 20 forming a multiple core structure of base fibers 20. These two composite fibers 18 can then be bonded together using heat and pressure to form a matrix of the dry type insulation. The number of base fibers 20 that are co-extruded together with the binder material 24 can be varied as desired. [0027] FIG. 3 is a perspective view of components for dry type electrical insulation in accordance with yet another embodiment of the present invention. The composite structure 26 of FIG. 3 includes base fibers 28 having outer surfaces 30. Particles of binder material 32, in the form of a powder are incorporated during processing. The base fibers 28 and the binder material powder 32 are air blended and heated to a temperature above the melting point of the binder material 32, allowing the binder material 32 to melt and adhere to the base fibers 28. This embodiment allows for a high amount of porosity.

[0028] FIG. 4 is a perspective view of a matrix 34 formed using any of the embodiments as shown in FIGS. 1, 2 and/or 3. The diameter of each base fiber is typically on the order of microns and the length of each base fiber is typically on the order of millimeters or centimeters. As such, thousands or even millions of such composite fibers 10 are bound together to form the dry type electrical insulation matrix 34 described herein.

[0029] FIGS. 5 and 6 illustrate processing steps during formation of a laminate 36 of an insulator and a conductor. As shown in FIG. 5, sheets of conductor material 38 can be layered with dry type insulation 40. The insulation 40 is formed as discussed with respect to FIGS. 1, 2, and/or 3. Heat and pressure are applied to press the conductor 38 to the insulation 40 to form the finished laminate 36. FIG. 6 illustrates such a formed laminate 36 after heat and pressure are applied, bonding the insulation 40 to the conductor 38. Alternately, the material can be formed or bonded in place in the device to be insulated or pre-formed and wrapped around or placed in the device to be insulated.

[0030] For example, the layers can be placed in the device to be insulated and then heat can be applied, melting the layers together. In an embodiment of the present invention, the layers of insulation 40 are longer than the layers of the conductor 38. This allows for the insulation 40 to prevent contact of the layers of conductor 38 so that the laminate 36 does not short out. The longer length of the layers of insulation 40 also form a cap over the laminate 36. The sizes, lengths, widths, of the composite fibers, the particulates and the laminates can all be varied as desired.

[0031] FIG. 7 is a flow diagram of a method for fabricating the dry type insulation according to an embodiment of the present invention. Step 42 includes forming a composite fiber by co-extruding a base fiber with binder material. The base fiber can have a first melting point and the binder material can have a second melting point which is lower than the first melting point. Step 44 includes heating the composite fibers to a temperature above the second melting point, but below the first melting point. Step 46 includes forming a matrix of the composite fibers by compression. As discussed previously, the percentage of the base fibers that include the binder material may be varied as desired.

[0032] Additionally, the method can include layering the base fiber and binder material between layers of a sheet conductor to form a laminate of the sheet conductor. The compressing and heating steps 44 and 46 can further include compressing and heating such that the resulting dry type electrical insulation has a density of between approximately 0.5 g/cm ³ and approximately 1.10 g/cm ³ .

[0033] Further, the method of FIG. 7 can include forming the dry type insulation in place around the device to be insulated. The method can include co-extruding the binder material over the first outer surface of the base fiber, or alternately, co-extruding the binder material over the outer surface of multiple base fibers such that multiple base fibers form a multi-fiber core. The method can also include dispersing small particles of the binder material between the multiple base fibers.

[0034] The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.