CORONA SHIELDING SYSTEM FOR A HIGH-VOLTAGE MACHINE, REPAIR LACQUER, AND METHOD FOR PRODUCTION

Abstract

A corona shielding system for a high voltage machine including a sleeve for a live conductor of the high voltage machine, wherein the sleeve has an electrically conductive lacquer, wherein a filler is added to the conductive lacquer, the filler at least partially including a thermoexpanding filler, is provided. A repair lacquer and a method for production is further provided.

Claims

1. A corona shielding system for a high-voltage machine comprising: a covering for a current-carrying conductor of the high-voltage machine, wherein the covering has an electrically conductive lacquer; wherein a filler is added to the conductive lacquer, wherein the filler at least partially comprises a thermally expanding filler.

2. The corona shielding system for a high-voltage machine as claimed in claim 1, wherein the filler is electrically conductive.

3. The corona shielding system as claimed in claim 1, wherein the filler consists entirely of thermally expanding filler.

4. The corona shielding system as claimed in claim 1, wherein the thermally expanding filler at least partially comprises a plurality of microscopic hollow spheres of which an envelope consists of polymers.

5. The corona shielding system as claimed in claim 4, wherein various inorganic coatings, which have a positive effect on mechanical strength, erosion resistance, thermal or electrical conductivity, are applied to or deposited on the envelope.

6. The corona shielding system as claimed in claim 4, wherein the plurality of hollow spheres contain gas and/or boiling liquid, wherein, under the action of heat, the envelope of the plurality of hollow spheres softens and the gas and/or boiling liquid contained in the plurality of hollow spheres causes an expansion.

7. The corona shielding system as claimed in claim 1, wherein nanoscale and/or microscale inorganic erosion-inhibiting particles are added to the lacquer.

8. The corona shielding system as claimed in claim 1, wherein the lacquer is elastic or semi-elastic.

9. The corona shielding system as claimed in claim 1, wherein an expansion temperature of the thermally expanding filler is above a gelation temperature and/or a curing temperature of the lacquer.

10. The corona shielding system as claimed in claim 1, wherein the lacquer with the thermally expanding filler is pre-gelled.

11. The corona shielding system as claimed in claim 1, wherein the lacquer with the thermally expanding filler has different degrees of crosslinking on application.

12. The corona shielding system as claimed in claim 1, the corona shielding system is an external corona shielding.

13. The corona shielding system as claimed in claim 1, wherein the corona shielding system contains an overhang corona shielding.

14. A repair lacquer for repairing a covering for a high-voltage machine, comprising: an electrically conductive lacquer, wherein a filler is added to the conductive lacquer, wherein the filler at least partially comprises a thermally expanding filler.

15. The repair lacquer for repairing a covering for a high-voltage machine as claimed in claim 14, wherein the thermally expanding filler at least partially comprises a plurality of microscopic hollow spheres of which an envelope consists of polymers.

16. The repair lacquer for repairing a covering as claimed in claim 15, wherein various inorganic coatings, which have a positive effect on mechanical strength, erosion resistance, thermal or electrical conductivity, are applied to or deposited on the envelope.

17. The repair lacquer for repairing a covering as claimed claim 14, wherein nanoscale and/or microscale inorganic erosion-inhibiting particles are added to the lacquer.

18. The repair lacquer for repairing a covering as claimed in claim 14, wherein the lacquer is elastic or semi-elastic.

19. The repair lacquer for repairing a covering as claimed claim 14, wherein an expansion temperature of the thermally expanding filler is above a gelation temperature and/or a curing temperature of the lacquer.

20. The repair lacquer for repairing a covering as claimed in claim 14, wherein the lacquer with the thermally expanding filler is pre-gelled.

21. The repair lacquer for repairing a covering as claimed in claim 14, wherein the lacquer with the thermally expanding filler has different degrees of crosslinking on application.

22. The repair lacquer as claimed in claim 14 for repairing a covering.

23. A method for producing a corona shielding system for a high-voltage machine, including a conductive covering for a current-carrying conductor of the high-voltage machine, wherein the covering is at least partially eroded, comprising the following steps: providing a conductive lacquer, wherein a thermally expanding filler is added to the conductive lacquer; applying the conductive lacquer, with the added thermally expanding filler, at least to an erosion location; flowing in of the conductive lacquer, with the added thermally expanding filler, at least partially into the erosion location; pre-drying and/or pre-gelling of the conductive lacquer with the added thermally expanding filler; and expanding the conductive lacquer, with the added thermally expanding filler, wherein, as a consequence of the expanding, the erosion location and the hard-to-reach regions thereof are essentially completely filled.

24. The method for producing a corona shielding system as claimed in claim 23, wherein the expansion is effected by heating with hot air and/or in operation by operating heat, in particular by operating heat of a generator, or by a special heating procedure/generator heat cycle.

25. The method for producing a corona shielding system as claimed in claim 23, the thermally expanding filler at least partially comprises a plurality of microscopic hollow spheres of which the envelope consists of polymers, wherein the expansion of the plurality of hollow spheres is limited by the lacquer or temperature.

26. The method for producing a corona shielding system as claimed in claim 23, wherein the degree of expansion of the plurality of hollow spheres at a given temperature, and the reversibility or one-off nature of the expansion are set by determining the sphere shell material and the filler.

Description

BRIEF DESCRIPTION

[0041] Some of the embodiments will be described in detailk, with reference to the following figures, wherein like designations denote like members, wherein:

[0042] FIG. 1 shows a longitudinal section through the stator of a turbogenerator, having an embodiments of the corona shielding system;

[0043] FIG. 2 shows an embodiment of a repair lacquer; and

[0044] FIG. 3 shows an embodiment of the method with reference to the repair of a hard-to-reach location.

DETAILED DESCRIPTION

[0045] As shown in the figure, a turbogenerator stator 1 has a stator laminated core 2, out of which a generator winding bar 3 projects. The generator winding bar 3 is surrounded by a main insulation 4, wherein the winding bar 3 is arranged with its main insulation 4 and with one of its ends also outside the stator laminated core 2. The figure shows, in the region of the point at which the winding bar 3 emerges from the stator laminated core 2, an external corona shielding 5 which surrounds the main insulation 4 and is grounded via the laminated core by a grounding means 6. An inner potential grading 7 is also provided between the generator winding bar 3 and the main insulation 4. The overhang corona shielding 8 encloses the main insulation 4 over a partial length starting from that end of the external corona shielding 5 which is oriented away from the stator laminated core 2. The corona shielding system can comprise the external corona shielding 5 and the overhang corona shielding 8, wherein the overhang corona shielding is electrically connected to the external corona shielding at its end oriented toward the laminated core. The elements 3, 4, 5, 7 pass through the slot (not depicted) of the laminated core and also have, at the other end of the laminated core, the arrangement corresponding to FIG. 1 with an overhang corona shielding 8.

[0046] The possible erosion locations affect in principle the entire length of the external corona shielding, wherein, depending on the manufacturer and construction of the generator, either the external corona shielding inside the laminated core or the external corona shielding outside the laminated core is affected to a greater degree. The erosion progressing in the axial direction disrupts the electrical connection between the overhang corona shielding and the laminated core. In the radial direction, there are on one hand partial discharges, and on the other hand the bars are loosened and thus, in extreme cases, subject to severe vibration. Of course, the erosion can also or additionally affect the overhang corona shielding 8.

[0047] Repair and/or manufacture therefore requires a conductive substance which can bridge the existing or developing gaps, and will ensure conductive wetting of the exposed surface of the main insulation.

[0048] Adding thermally expandable filler to the conductive lacquer 10 (hereinbelow also termed matrix in parallel) (FIG. 2) can produce a thermally expandable repair lacquer 14 (FIG. 2).

[0049] FIG. 2 shows such a repair lacquer 14. A repair lacquer 14 of this type (FIG. 2) will, in a liquid state, fill the gaps as much as possible, will then gel or pre-dry (e.g. in the case of a matrix that crosslinks at room temperature) under ambient conditions, and will then expand under the influence of heat.

[0050] The pre-gelling/pre-drying inside the repair lacquer 14 prevents excessive expansion, and as a result the filler can expand only as much as permitted by the intermolecular bonds in the lacquer 10.

[0051] It is thus possible in particular for the gaps on eroded corona shielding regions to be better and more reliably filled, in comparison with the unfilled, shrinking lacquer of the prior art. The thermally expandable filler used can be microscopic hollow spheres 13 of which the envelope 11 consists of polymers. Various organic or inorganic coatings, which have a positive effect on mechanical strength, erosion resistance, and thermal or electrical conductivity, can be applied to or deposited on the envelope 11. Under the action of heat, the envelope 11 of the hollow spheres 13 softens and the gas 12 and/or the boiling liquid 12 contained in the hollow spheres 13 leads to an expansion. Thus, heat causes the resulting thermally expandable repair lacquer 14 to take up more volume and, respectively, to be able to fill the available volume.

[0052] Of advantage for use as conductive lacquer is the fact that the surface of such hollow spheres 13 is wetted with the lacquer 10, due to the viscosity of the lacquer, and therefore the cavities inside the hollow spheres are electrically shielded. It is thus also possible to use hollow spheres 13 having no conductive coating.

[0053] For polymeric sphere shell materials, the temperature range for expansion of the hollow spheres 13 is in the range of 60-220 C. The degree of possible expansion of the hollow spheres 13 at a given temperature, and the reversibility or one-off nature of the expansion can be set by means of a suitable choice for the sphere shell material and the filler. In that context, possible sphere diameters are: 10-40 m unexpanded, up to 200 m expanded. The wall thickness can in this case range from several tens of m (unexpanded) to several m or less (expanded).

[0054] Crucial to the material properties of the thermally expandable material are essentially the degree of filling with hollow spheres 13 and the size of these, and the properties of the lacquer 10 containing and enclosing the micro hollow spheres 13. It is also possible for the expansion of the hollow spheres 13 to be limited by the lacquer 10 or the temperature. Thus, the expansion of the overall material is limited.

[0055] During repair, the expansion can be effected by heating with hot air or in operation by operating heat, e.g. of the generator, or by a higher temperature action still, in the context of a special generator heat cycle. In addition, if the expansion temperature of the filler is above the gelation temperature and/or the curing temperature of the lacquer 10, it is also possible to use a heat-curing lacquer system 10. This enables short repair times.

[0056] Another possibility offers the choice of an elastic or semi-elastic lacquer 10 or matrix. Thus, a repair lacquer or a lacquer for use in the context of generator manufacture 14 is also conceivable, which lacquer can expand, in the event of erosion, by operating heat or by a special heating procedure/generator heat cycle. If part of the lacquer 14 is eroded, the eroded volume can be at least partially filled by expansion of the remaining regions. This reduces the rate of erosion.

[0057] In order to increase the erosion resistance of the repair lacquer 14, it is also possible for nanoscale or microscale inorganic erosion-inhibiting particles (not shown) to be added to the lacquer 10. This significantly reduces the rate of erosion in the event of partial discharges.

[0058] In addition, different degrees of crosslinking in the repair lacquer 14 allow expansion in the axial direction into the otherwise very hard-to-reach gaps. This is described with reference to FIG. 3:

FIG. 3 shows the repair of a hard-to-reach erosion location 16 in the cooling channel 15 of the laminated core. The crosslinked lacquer skin 17 and the differently crosslinked internal regions 18 within the repair lacquer 14 produce a barrier at the surface which can block the expansion of the lacquer in the radial direction (upward in FIG. 3) and can promote expansion in the axial direction (left and right in FIG. 3). The differences in partial crosslinking of the repair lacquer 14 are a result of the differing degree of exposure, for example as a consequence of the layer thickness, to curing catalysts such as air, heat, UV light, etc.

[0059] In addition to expansion of the filler particles, the temperature effect also causes final crosslinking of the repair lacquer 14 such that the repair lacquer 14 solidifies sufficiently. Depending on the lacquer material, it is however possible to achieve a targeted residual elasticity which is necessary to compensate for any thermomechanical load cycles.

[0060] Embodiments of the invention permit a more rapid, more reliable and more durable repair of the corona shielding using the repair lacquer. It also provides an improved corona shielding system. If part of the lacquer according to embodiments of the invention is eroded, the eroded volume can namely be at least partially filled by expansion of the remaining regions. This reduces the rate of erosion. It is in principle possible to avoid having to create a new winding.

[0061] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0062] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.