CORONA SHIELD, ELECTRIC MACHINE, AND METHOD FOR MANUFACTURING THE CORONA SHIELD

Abstract

A corona shield for an electric machine, has a varnish that contains a first polymer resin, first electrically conductive particles that are dispersed in the first polymer resin, and microcapsules which are dispersed in the first polymer resin and include a second polymer resin in their interior.

Claims

1. A corona shield for an electrical machine, comprising: a varnish including a first polymer resin, first electrically conductive particles dispersed in the first polymer resin and microcapsules dispersed in the first polymer resin, a second polymer resin being included within said microcapsules, wherein the varnish includes second electrically conductive particles disposed within the microcapsules.

2. The corona shield as claimed in claim 1, wherein the first electrically conductive particles and/or the second electrically conductive particles include graphite and/or carbon black.

3. The corona shield as claimed in claim 1, wherein the sum total of the proportions by weight of the microcapsules and the first electrically conductive particles, based on the varnish, is from 5% to 90%.

4. The corona shield as claimed in claim 1, wherein the weight ratio of the microcapsules to the first electrically conductive particles is from 1 to 10, especially from 1 to 2.

5. The corona shield as claimed in claim 1, wherein the first polymer resin and/or second polymer resin is a copolymer.

6. The corona shield as claimed in claim 5, wherein a portion of the microcapsules includes only one of the monomers of the copolymer and another portion of the microcapsules only another of the monomers of the copolymer.

7. The corona shield as claimed in claim 1, wherein electrically nonconductive inorganic nanoparticles are included within the microcapsules.

8. The corona shield as claimed in claim 1, wherein a solvent is included within the microcapsules.

9. The corona shield as claimed in claim 1, wherein the wall material of the microcapsules includes wax, polyurea-formaldehyde and/or polyurethane.

10. The corona shield as claimed in claim 1, wherein the microcapsules have an average diameter of 10 m to 1500 m.

11. The corona shield as claimed in claim 1, wherein the corona shield has a porous, electrically nonconductive tape impregnated by the varnish.

12. An electrical machine comprising: an electrical conductor, a main insulation that encases the electrical conductor, and a corona shield as claimed in claim 1 applied to the outside of the main insulation.

13. A process for producing a corona shield as claimed claim 1, comprising: applying a varnish including a first polymer resin, first electrically conductive particles dispersed in the first polymer resin and microcapsules dispersed in the first polymer resin, a second polymer resin being included within said microcapsules, to a main insulation that encases an electrical conductor; and curing the first polymer resin.

14. The process as claimed in claim 13, wherein the varnish includes a solvent outside and within the microcapsules and the polymer resin is cured by evaporating the solvent present outside the microcapsules.

15. The corona shield as claimed in claim 4, wherein the weight ratio of the microcapsules to the first electrically conductive particles is from 1 to 2.

16. The corona shield as claimed in claim 5, wherein the copolymer is a polymer based on polyacrylate, acrylic ester, acrylonitrile, and/or polystyrene, and wherein the first polymer resin and the second polymer resin are the same.

17. The corona shield as claimed in claim 7, wherein the nanoparticles include TiO.sub.2, SiO.sub.2, Al.sub.2O.sub.3 and/or MgO.

18. The corona shield as claimed in claim 8, wherein the solvent included within the microcapsules comprises ethanol, n-propanol, isopropanol, ethyl acetate, an alkane, n-pentane, n-hexane, and/or n-heptane.

19. The corona shield as claimed in claim 10, wherein the microcapsules have a wall thickness of 50 nm to 3500 nm.

20. The corona shield as claimed in claim 11, wherein the tape includes a weave and/or a nonwoven, and wherein the weave and/or the nonwoven includes polyethylene terephthalate, polyester, glass, polyimide, polyaramid, polyamide, polypropylene, and/or PTFE.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] There follows a detailed elucidation of the invention with reference to the schematic drawings appended. The figures show:

[0020] FIG. 1 a corona shield of the invention prior to damage,

[0021] FIG. 2 the corona shield after damage and

[0022] FIGS. 3 and 4 the process of healing the damage.

DETAILED DESCRIPTION OF INVENTION

[0023] As apparent from FIGS. 1 to 4, a corona shield 1, for example an outer corona shield and/or an end corona shield, for an electrical machine includes a varnish 4. The varnish 4 includes a first polymer resin, first electrically conductive particles 6 dispersed in the first polymer resin and microcapsules 5 dispersed in the first polymer resin. A second polymer resin is included within the microcapsules 5. It is conceivable that the varnish includes an inorganic and electrically nonconductive filler, for example in the form of nanoparticles, where the filler is dispersed in the first polymer resin and/or second polymer resin. The filler allows the resistance of the corona shield 1 to partial discharges to be increased.

[0024] The microcapsules 5 may be produced, for example, in a dropletization process or by emulsion polymerization. The wall material of the microcapsules 5 may include wax, polyurea-formaldehyde and/or polyurethane. The microcapsules 5 may have an average diameter of 10 m to 1500 m. The microcapsules 5 may have a wall thickness of 50 nm to 3500 nm.

[0025] The varnish 4 may include second electrically conductive particles disposed within the microcapsules 5. The second electrically conductive particles may be the same as the first electrically conductive particles 6 in terms of their chemical composition and their size. It is also conceivable that the second electrically conductive particles are the same as the first electrically conductive particles 6 in terms of their chemical composition, but have a smaller average diameter than the first electrically conductive particles 6. It is thus possible for the second electrically conductive particles to be more easily accommodated in the microcapsules 5. For example, the first electrically conductive particles and/or the second electrically conductive particles may include graphite, carbon black and/or inorganic particles having an electrically conductive coating. It is conceivable that the electrical conductivity of the second particles is higher than the electrical conductivity of the first particles. This can achieve the effect that the electrical conductivity of the cured damaged regions, in spite of a lower particle concentration, is just as high as before the damage.

[0026] The sum total of the proportions by weight of the microcapsules 5 and the first semiconductor particles 6 based on the varnish 4 is, for example, from 10% to 50%. The weight ratio of the microcapsules 5 to the first electrically conductive particles is, for example, from 1 to 10, especially from 1 to 2.

[0027] For example, the first polymer resin and/or the second polymer resin are a copolymer. The copolymer may, for example, be a polymer based on polyacrylate, especially acrylic ester and/or acrylonitrile, and/or polystyrene. It is conceivable that a portion of the microcapsules 5 includes only one of the monomers of the copolymer and another portion of the microcapsules 5 only another of the monomers of the copolymer. This achieves the effect that the two monomers come into contact only in the event of bursting of the microcapsules 5, and the second polymer resin can cure.

[0028] In another example, the second polymer resin may include a monomer disposed only within a portion of the microcapsules 5. A polymerization initiator may be disposed within another portion of the microcapsules 5. The polymerization initiator may be dissolved in a solvent. This achieves the effect that the polymerization initiator and the monomer come into contact only in the event of bursting of the microcapsules 5, and hence the second polymer resin cures.

[0029] The varnish 4 may include a reactive diluent, for example 3-ethyloxetane-3-methanol or cycloaliphatic epoxides. The reactive diluents may have been mixed with the first polymer resin and/or with the second polymer resin.

[0030] Electrically nonconductive inorganic nanoparticles may additionally be included within the microcapsules 5. For example, the nanoparticles may include TiO.sub.2, SiO.sub.2, Al.sub.2O.sub.3 and/or MgO or consist of the aforementioned substances. A solvent may also be included within the microcapsules 5, especially ethanol, n-propanol, isopropanol, ethyl acetate and/or an alkane, especially n-pentane, n-hexane and/or n-heptane.

[0031] It is conceivable that the corona shield 1 includes a porous, electrically nonconductive tape impregnated by the varnish 4. The tape may include a weave and/or a nonwoven. The weave and/or the nonwoven may include hollow fibres. The weave and/or the nonwoven may include polyethylene terephthalate (PET), polyester, glass, polyimide, polyaramid, polyamide, polypropylene and/or PTFE.

[0032] FIGS. 1 to 4 show how the corona shield of the invention in the electrical machine self-heals. The electrical machine includes an electrical conductor, a main insulation that encases the electrical conductor, and the corona shield 1. The corona shield 1 has a radial outer face 2 and a radial inner face 3. The corona shield 1 has been applied to the radial outer face of the main insulation, such that the radial inner face 3 adjoins the radial outer face of the main insulation. The radial outer face 2 of the corona shield 1 is in touch contact with a laminated core of the electrical machine and can be damaged by this touch contact, by outside action and/or by partial discharges, which gives rise, as shown in FIG. 2, to a damaged region 7.

[0033] The damage results in bursting of the microcapsules 5 and flow of the second polymer resin present within them into the damaged region 7, as illustrated by the arrows 8 in FIG. 3. After the second polymer resin has cured, the damaged region 7 is filled and hence healed, as shown by the reference numeral 9 in FIG. 4.

[0034] Even though the invention has been illustrated in detail and described by the preferred working examples, the invention is not restricted by the examples disclosed, and other variations may be inferred therefrom by the person skilled in the art without leaving the scope of protection of the invention.