REDUCING AGEING OF AN INSULATION MATERIAL OF A WINDING, IN PARTICULAR OF AN OIL-IMPREGNATED HIGH-VOLTAGE DEVICE

Abstract

An assembly includes at least one winding and a housing in which the winding is disposed. The winding has at least one electrical conductor and a cellulosic or cellulose-containing insulation material at least partially surrounds the winding and/or the electrical conductor thereof. The housing is filled with a liquid coolant during operation so that the winding is located in a liquid coolant during operation. In addition to existing cellulose-containing insulation material which encloses the winding and/or the electrical conductor thereof for insulation purposes, the housing and/or a coolant circuit for the coolant contains at least one composition containing chemical compounds for reducing the aging of cellulose-containing insulation material. A method of reducing the aging of cellulosic insulation material of a winding is also provided.

Claims

1-19. (canceled)

20. An assembly, comprising: a housing filled with a liquid coolant during operation; a cooling circuit for the coolant; at least one winding disposed in said housing and disposed within the liquid coolant during operation, said at least one winding including at least one electrical conductor; a cellulosic insulation material at least partly surrounding at least one of said at least one winding or said electrical conductor of said at least one winding, for insulation purposes; and at least one composition in addition to said cellulosic insulation material at least partly surrounding at least one of said at least one winding or said electrical conductor of said at least one winding for insulation purposes; said at least one composition disposed in at least one of said housing or said cooling circuit; and said at least one composition containing chemical compounds for reducing aging of said cellulosic insulation material.

21. The assembly according to claim 20, wherein said at least one composition includes an additional cellulosic insulation material provided with chemical compounds for reducing the aging of cellulosic insulation material.

22. The assembly according to claim 21, wherein said at least one composition is a thermally upgraded paper.

23. The assembly according to claim 20, wherein said at least one composition is mounted at a position within said housing containing a region of the coolant being hotter than other regions of the coolant during operation.

24. The assembly according to claim 23, wherein said housing has a lid, and said at least one composition is disposed in a region of said lid.

25. The assembly according to claim 20, which further comprises a holder holding said at least one composition, said holder being releasably secured within at least one of said housing or said cooling circuit.

26. The assembly according to claim 20, which further comprises: a cooling element or radiator disposed outside said housing; said cooling circuit including a pipeline connecting said housing to said cooling element or radiator for supplying said cooling element or radiator with heated coolant; and said at least one composition disposed in said pipeline.

27. The assembly according to claim 20, wherein said at least one composition is mounted in said housing on at least one part, or between two parts, of said cellulosic insulation material at least partly surrounding at least one of said at least one winding or said electrical conductor of said at least one winding for insulation purposes.

28. The assembly according to claim 20, wherein said chemical compounds for reducing the aging of said cellulosic insulation material include at least one of dicyandiamide, melamine, or polyacrylamide.

29. A method of reducing aging of cellulosic insulation material of a winding, the method comprising: providing a winding including at least one electrical conductor; at least partly surrounding at least one of the winding or the electrical conductor of the winding with a cellulosic insulation material for insulation purposes; placing the winding within a liquid coolant during operation; adding at least one composition to at least one of the liquid coolant or existing cellulosic insulation material, in addition to the cellulosic insulation material at least partly surrounding at least one of the winding or the electrical conductor of the winding for insulation purposes; and providing the at least one composition with chemical compounds for reducing aging of cellulosic insulation material.

30. The method according to claim 29, which further comprises adding the at least one composition in liquid form.

31. The method according to claim 29, which further comprises providing the composition with an additional cellulosic insulation material having been provided with chemical compounds for reducing the aging of cellulosic insulation material.

32. The method according to claim 31, which further comprises providing the composition as a thermally upgraded paper.

33. The method according to claim 29, which further comprises adding the composition at a position containing a region of the coolant being hotter than other regions of the coolant during operation.

34. The method according to claim 29, which further comprises adding the composition to existing cellulosic insulation material during production of the winding.

35. The method according to claim 34, which further comprises applying the composition, prior to any process of drying the winding, to at least one part, or between two parts, of the cellulosic insulation material at least partly surrounding at least one of the winding or the electrical conductor of the winding for insulation purposes.

36. The method according to claim 34, which further comprises adding the composition to a heat carrier for drying, during a process of drying the winding.

37. The method according to claim 34, which further comprises adding the composition to air guided into a drying system, after a process of drying the winding.

38. The method according to claim 29, which further comprises selecting the chemical compounds for reducing the aging of the cellulosic insulation material as at least one of dicyandiamide, melamine, or polyacrylamide.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0038] For further elucidation of the invention, the part of the description that follows makes reference to the figures, from which further advantageous details and possible fields of use of the invention can be inferred. The figures should be considered by way of example and should set out the character of the invention but in no way restrict it or even describe it in a confining manner. The figures show:

[0039] FIG. 1 a schematic diagram of a transformer,

[0040] FIG. 2 experimental results for the aging of cellulosic insulation material.

WAYS OF EXECUTING THE INVENTION

[0041] FIG. 1 shows a schematic diagram of a transformer 1. The transformer 1 of the invention has multiple transformer windings, of which only one transformer winding 2 is shown here, which is wound around a core 10. This arrangement corresponds to the core-type design. There is also a shell-type design which has a very similar pattern of behavior and to which the invention can likewise be applied. In addition, the transformer 1 has a housing 3 filled with a liquid coolant 4. The upper part of the housing 3 is formed by a lid region, called lid 13 for short hereinafter. There are usually flanges mounted in the lid 13 in order to have local access to the interior of the housing for servicing activities for example.

[0042] For accommodation of the coolant 4 at high temperatures, an expansion vessel 11 is provided here, which is connected to the housing 3 via a pipeline 12. A cooling circuit 5 is disposed between the expansion vessel 11 and housing 3. As well as the expansion vessel 11, said cooling circuit 5 comprises pipelines 12, 14, one or more cooling elements 6 (radiators here), and a pump 7 (not obligatory). The pipeline 12 that leads from the lid 13 of the housing 3 to a cooling element 6 introduces the hot coolant 4 into the cooling element 6. The cooled coolant 4, optionally via a pump 7, is conveyed from the cooling element 6 back into the housing 3, generally close to the bottom.

[0043] The conductor 8 of the transformer winding 2 is wrapped with paper, for example thermally upgraded paper. Spacers made of pressboard material are often present between the coils of each winding 2; there are also cylinders and other parts made of pressboard material that serve for electrical insulation in, around and between the windings 2 and the core 10 etc., and enable access of the coolant 4 to voltage-bearing parts. The accompanying press device that compresses the transformer winding 2 in vertical direction is not shown in FIG. 1; all that are shown are cellulosic pressboards 9. In addition to the paper that may already have been thermally upgraded, with which the conductor 8 has been wrapped, an additional composition 16 containing chemical compounds for reducing the aging of cellulosic insulation material, for example thermally upgraded paper, is disposed in the housing 3, specifically in the region of the lid 13, for example on the underside thereof, such that the composition 16 can be introduced and removed again in a simple manner from the top, for instance by opening a device in the lid 13. The composition 16 is best mounted close to the pipeline 12 in the lid 13 because there is an appropriate flow rate of the coolant 4 there. On opening of the device in the lid 13, it should be ensured that the pipeline 12 to the expansion vessel 11 is closed, in order to prevent outflow of the coolant through the device in the lid 13. But it would also be possible for the composition 15—alternatively or additionally—to be mounted directly in the pipeline 12 that leads to the radiator 6. The thermally upgrading substances present in the composition 15, 16 are introduced into liquid coolant and find their way to all liquid-wetted parts through the circulation of the coolant, i.e. including all insulation parts made of cellulose.

[0044] The chemical compounds for reducing the aging of cellulosic insulation material can then diffuse both into the thermally upgraded paper with which the conductor 8 has been wrapped and into the pressboard 9 and all other cellulosic parts. This firstly replaces the compounds that have already been degraded in the thermally upgraded paper of the conductor 8. Secondly, these compounds are deposited for the first time in the pressboard material of the pressboard 9, and hence reduce aging of the pressboard material.

[0045] FIG. 2 shows the results of aging experiments with different insulation materials. Plotted on the horizontal axis is the time in weeks, and on the vertical axis the level of polymerization of the cellulose in the respective materials. The level of polymerization of the cellulose is a measure of fiber strength and hence of the tensile strength of the material. The level of polymerization can be measured.

[0046] The uppermost curve shows the progression of the level of polymerization of a thermally upgraded paper (TU) over time, which has merely been placed into an oil bath at 140° C., the oil corresponding to the coolant of a transformer. The lowermost curve shows the progression of the polymerization level of a paper that has not been thermally upgraded (n-TU) over time, which has merely been placed into an oil bath at 140° C. It can be seen that the untreated paper ages much more quickly over a prolonged period than the treated, i.e. thermally upgraded, paper.

[0047] If both thermally upgraded paper and paper that has not been thermally upgraded are placed together into the oil bath at 140° C. (TU+n-TU), the thermally upgraded paper according to the second curve from the top—considered at week 16—shows a reduced level of polymerization compared to the thermally upgraded paper placed in on its own (uppermost curve). For the paper that has not been thermally upgraded, by contrast, according to the second curve from the bottom—considered at week 16—the resultant level of polymerization is elevated compared to the paper that has not been thermally upgraded and is placed in on its own (lowermost curve). The thermally upgraded paper thus loses the chemical compounds that reduce aging when the two are placed in together, whereas these compounds accumulate in the paper that had not been thermally upgraded beforehand. The balancing is thus effected by the transfer of the coolant, i.e. usually the insulation oil, since the solid parts are in direct contact only to a limited degree, if at all.

LIST OF REFERENCE NUMERALS

[0048] 1 transformer [0049] 2 (transformer) winding [0050] 3 housing [0051] 4 liquid coolant [0052] 5 cooling circuit [0053] 6 cooling element (radiator) [0054] 7 pump [0055] 8 conductor of the transformer winding [0056] 9 pressboard [0057] 10 core [0058] 11 expansion vessel [0059] 12 pipeline [0060] 13 lid of the housing 3 [0061] 14 return tube [0062] 15 composition comprising chemical compounds for reducing the aging of cellulosic insulation material (thermally upgraded paper) [0063] 16 composition comprising chemical compounds for reducing the aging of cellulosic insulation material (thermally upgraded paper)