METHOD FOR DRYING A TRANSFORMER HAVING A MULTISTAGE COOLING SYSTEM, AND COOLING DEVICE CONTROLLER FOR SUCH A TRANSFORMER

Abstract

A method for drying a transformer which has a multistage cooling system, in particular a power transformer or a choke, has at least one transformer winding and at least one insulator for electrical insulation. Individual cooling stages of the cooling system are respectively associated with a loading state range of the transformer and are activated when the respective loading state range of the transformer is reached. The loading state range is a function which depends at least on a temperature of the transformer. The drying method is carried out during the operation of the transformer. An upper cooling stage, which lies above the lowest cooling stage, is or remains deactivated and the cooling stage which is situated directly below the upper cooling stage is or remains activated while the transformer is in the loading state range which is associated with the upper cooling stage.

Claims

1-11. (canceled)

12. A method for drying a transformer with a multistage cooling system, the transformer having at least one transformer winding and at least one insulator for electrical insulation; the cooling system having cooling stages with a lowest cooling stage and a highest cooling stage, wherein individual said cooling stages are respectively associated with one loading state range of the transformer and are activated when the respective loading state range of the transformer is reached, and wherein the loading state range is a function that depends at least on a temperature of the transformer; the method for drying the transformer, to be carried out during an operation of the transformer, comprising: while the transformer is operating in a loading state range that is associated with a given upper cooling stage which lies above the lowest cooling stage, deactivating, or maintaining in a deactivated state, the given upper cooling stage, and activating, or maintaining in an activated state, a cooling stage which lies directly below the given upper cooling stage.

13. The method according to claim 12, wherein the transformer is a power transformer or a choking coil.

14. The method according to claim 12, wherein the loading state range also depends on a current load of the transformer, and the method comprises: only deactivating, or maintaining in the deactivated state, the given upper cooling stage, and only activating, or maintaining in the activated state, the cooling stage lying directly below the given upper cooling stage, when the current load has dropped below or does not exceed a threshold value, the threshold value lying below a maximum value of the current load of the transformer within the loading state range associated with the given upper cooling stage and within the loading state range.

15. The method according to claim 14, which comprises defining the threshold value at no more than 80% of a maximum value of the current load of the transformer in the loading state range associated with the given upper cooling stage.

16. The method according to claim 15, which comprises defining the threshold value at no more than 70% of the maximum value of the current load of the transformer in the loading state range associated with the given upper cooling stage.

17. The method according to claim 16, which comprises defining the threshold value at no more than 60% of the maximum value of the current load of the transformer in the loading state range associated with the given upper cooling stage.

18. The method according to claim 12, wherein the given upper cooling stage is the highest cooling stage.

19. A cooling device controller for a transformer having a multistage cooling system, having at least one transformer winding and at least one insulator for electrical insulation, the cooling device controller being configured for carrying out the method according to claim 12.

20. The cooling device controller according to claim 19, configured for a power transformer or a choking coil.

21. A transformer, comprising: at least one transformer winding and at least one insulator for electrical insulation; a multistage cooling system with a plurality of cooling stages; and cooling device controller configured for carrying out the method according to claim 12.

22. The transformer according to claim 21, wherein the transformer is a power transformer or a choking coil.

23. The transformer according to claim 21, wherein said plurality of cooling stages comprises at least three cooling stages.

24. The transformer according to claim 21, wherein said at least one insulator is an insulating liquid.

25. The transformer according to claim 24, wherein said at least one insulator is an insulating oil.

26. The transformer according to claim 21, wherein said at least one insulator comprises a solid-material insulation.

27. The transformer according to claim 26, wherein said solid-material insulation comprises cellulose or aramid.

28. The transformer according to claim 21, wherein said cooling stages are selected from the group consisting of Oil Natural Air Natural (ONAN), Oil Directed Air Forced (ODAF), Oil Directed Air Natural (ODAN), Coolant Natural Air Natural (KNAN), Coolant Directed Air Forced (KDAF), and Coolant Directed Air Natural (KDAN), wherein “O” is oil, “A” is air, and “K” is a coolant of a higher heat classification than oil, and wherein the following cooling stages are provided in ascending order: ONAN, ONAF; or KNAN, KNAF; or ODAF1, ODAF2; or KDAF1, KDAF2; or OFAF1, OFAF2; or KFAF1, KFAF2; or ONAN, OFAN; or KNAN, KFAN; or ONAN, ODAN, ODAF; or KNAN, KDAN, KDAF; or ONAN, ONAF1, ONAF2; or KNAN, KNAF1, KNAF2.

29. A computer program product, comprising non-transitory computer program code with instructions which, when loaded into a cooling device controller, are configured to carry out the method according to claim 12.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0042] The invention will now be explained in more detail by means of an exemplary embodiment. The drawing is exemplary and is indeed intended to visualize the concept of the invention but not to restrict the latter or even reflect the latter in an exhaustive manner. In the drawing:

[0043] FIG. 1 shows a schematic illustration of a transformer according to the invention.

WAYS OF IMPLEMENTING THE INVENTION

[0044] FIG. 1 shows a schematic illustration of a transformer 1 according to the invention which possesses a transformer winding 3 which is wound about a transformer core 10. The transformer winding 3 is composed at least of a low-voltage winding as well as a high-voltage winding which are not illustrated in more detail. Furthermore, the transformer winding 3, more specifically the electric conductor thereof, for electrical insulation is wrapped with cellulosic paper (not specifically illustrated).

[0045] The transformer winding 3 and the transformer core 10 are disposed in a housing 2 of the transformer 1, said housing 2 being filled with a transformer oil 7. The transformer oil 7 can be, for example, mineral oil. The transformer oil 7 likewise serves for electrical insulation, on the one hand. That is to say that insulating means of the transformer 1 comprise the transformer oil 7 and the cellulosic paper, wherein the latter is accordingly impregnated with transformer oil 7.

[0046] On the other hand, the transformer oil 7 serves for cooling because the transformer winding 3 during the operation of the transformer 1 generates heat which intensifies as the electrical load, or the current load, respectively, of the transformer 1 increases. The transformer oil 7 here can circulate in a cooling circuit 4 which comprises the housing 2. The circulation of the transformer oil 7 can take place by natural convection and/or be forced by means of a pump 11. Furthermore, at least one radiator 5 for enabling an exchange of heat between the transformer oil 7 and the ambient air is provided in the cooling circuit 4. The radiator 5 here is cooled by the ambient air, wherein the ambient air absorbs heat from the radiator 5. Cooler ambient air can be supplied to the radiator 5 by way of natural convection and/or by means of at least one ventilator 6. When the cooling of the radiator 5 takes place by means of the ventilator 6, ambient air is suctioned by the ventilator 6 and, at an outlet side 9 of the ventilator 6 that faces the radiator 5, blown onto the radiator 5.

[0047] In the exemplary embodiment illustrated, the transformer oil 7, the pump 11, the radiator 5 and the ventilator 6 of the latter are in particular used for implementing three cooling stages—a lowest cooling stage, a medium cooling stage, and a highest cooling stage—of the transformer 1.

[0048] These cooling stages are associated with respective loading state ranges, that is to say that each of the cooling stages is assigned to a loading state range, wherein each loading state range comprises a range of loading states which cause aging of the transformer 1. The loading state, or the loading state range, respectively, here depends at least on the temperature of the transformer 1. In the exemplary embodiment illustrated, the loading state, or the loading state range, respectively, moreover depends explicitly on the electrical load, or the current load, respectively, of the transformer 1.

[0049] As the loading state range increases, ever higher cooling stages are successively activated by means of a cooling device controller 8, and the higher cooling stages are successively deactivated as the loading state range decreases. That is to say that the lowest cooling stage is associated with a low loading state range, the medium cooling stage is associated with a medium loading state range, and the highest cooling stage is associated with a high loading state range.

[0050] Dotted lines in FIG. 1 indicate that the cooling device controller 8 is operatively connected to the pump 11 and the ventilator 6 in order for said pump 11 and said ventilator 6 to be selectively switched on or off. The chain-dotted line in FIG. 1 indicates that the cooling device controller 8 processes items of information pertaining to the current loading state, or loading state range, respectively, of the transformer 1. These items of information can be made available by way of means known per se, in particular sensors for the temperature of the transformer 1 as well as for the electrical power consumption or for the current flowing on the secondary side of the transformer 1.

[0051] The highest cooling stage in the exemplary embodiment illustrated is ODAF (“Oil Directed Air Forced”), that is to say that the transformer oil 7 is pumped by the pump 11 in a directed manner through the cooling circuit 4, and the ventilator 6 is activated such that a maximum cooling output is implemented.

[0052] By switching off the ventilator 6, ODAN (“Oil Directed Air Natural”) as the medium cooling stage in the exemplary embodiment illustrated is implemented, in which medium cooling stage only the circulation of air by virtue of natural convection remains such that the cooling output in the medium cooling stage is reduced in relation to the highest cooling stage. It is to be noted that it would alternatively also be conceivable for the medium cooling stage to be implemented by switching off the pump 11 and permitting the ventilator 6 to run, which would be described as ONAF (“Oil Natural Air Forced”).

[0053] When the pump 11 in the exemplary embodiment illustrated is now also switched off, the transformer oil 7 can still circulate only by virtue of the natural convection, as a result of which the cooling output in the lowest cooling stage is reduced yet again in relation to the medium cooling stage. That is to say that the lowest cooling stage in the exemplary embodiment illustrated is ONAN (“Oil Natural Air Natural”).

[0054] The cooling device controller 8 is moreover specified for carrying out a method according to the invention for drying, that is to say for actuating in particular the pump 11 and the ventilator 6 depending on the loading state range of the transformer 1 such that the method according to the invention is carried out as follows during the operation of the transformer 1: An upper cooling stage which lies above the lowest cooling stage is deactivated or remains deactivated, and the cooling stage lying directly below the upper cooling stage is activated or remains activated, while the transformer 1 is situated in the loading state range associated with the upper cooling stage. In the exemplary embodiment illustrated here, the upper cooling stage is only deactivated or remains deactivated, and the cooling stage lying directly below the upper cooling stage is only activated or remains activated, when the current load has dropped below a threshold value and/or does not exceed the threshold value, wherein the threshold value lies below a maximum value of the current load of the transformer 1 in the loading state range associated with the upper cooling stage and within this loading state range.

[0055] The upper cooling stage is preferably the highest cooling stage.

[0056] The threshold value in relation to the maximum value of the current load of the transformer 1 in the loading state range associated with the upper cooling stage can be reduced, for example, by at least 20%, preferably by at least 30%, particularly preferably by at least 40%.

[0057] Further illustration of the method according to the invention:

[0058] The following table A provides an example for conventional triple-stage cooling of the transformer 1 illustrated in FIG. 1. The stated typical load current is stated as a percentage of the nominal current, or the maximum load current, respectively. The stated load current here typically depends on the ambient temperature and the dynamics of the system, and at high ambient temperatures is thus correspondingly displaced toward smaller percentage values, and at low ambient temperatures conversely displaced toward higher percentage values. To this extent, a high ambient temperature is advantageous when applying the drying mode, or the method according to the invention, respectively, for drying, in order to achieve efficient drying even in the case of comparatively small load currents.

[0059] The loading state range which is in each case associated with the cooling stages is a function of both the temperature of the transformer 1, wherein the temperature can in particular be a hot oil temperature, as well as of the load current.

TABLE-US-00001 TABLE A CONVENTIONAL TRIPLE-STAGE COOLING Cooling stage 1 2 3 Type ONAN ONAF ODAF Switched-on ancillary — Fan Pumps + apparatuses Fan Threshold temperature “On” 60 70 [° C.] Threshold temperature “Off” 50 60 [° C.] Occurring temperatures [° C.] <60    50-70    >60    Typical load current <60% 60-80%  >80%

[0060] An embodiment of the drying method according to the invention is illustrated in contrast in the following Table B. It goes without saying that it also applies to the method according to Table B that the loading state range which is in each case associated with the cooling stages is a function of both the temperature of the transformer 1, wherein the temperature can in particular be a hot oil temperature, as well as of the load current.

TABLE-US-00002 TABLE B EMBODIMENT OF THE METHOD ACCORDING TO THE INVENTION Cooling stage 1 2 3 Type ONAN ODAN ODAF Switched-on ancillary — Pumps Pumps + apparatuses Fan Load current <70% Threshold temperature “On” [° C.] 70 80 Threshold temperature “Off” [° C.] 65 76 Occurring temperatures [° C.] <70 65-80 >75 Drying mode: >60° C. Load current ≥70% Threshold temperature “On” [° C.] 68 70 Threshold temperature “Off” [° C.] 60 66 Occurring temperatures [° C.] <68 60-70 >65 Drying mode: >60° C.

[0061] Two cases are illustrated in Table B, specifically one for a load current of <70% of the nominal current, and one for a load current of ≥70% of the nominal current. Efficient drying here takes place in each case at more than 60° C.

[0062] It is to be noted that it is derived from Table B that the medium cooling stage ODAN is chosen instead of ONAF, for which no structural modification has to be performed on the transformer 1. The corresponding types of cooling are simply set by way of the cooling device controller 8.

[0063] In comparison to the conventional cooling according to Table A, in the embodiment of the method according to the invention illustrated in Table B the second cooling stage is used especially in loading state ranges which are associated with the highest cooling stage according to Table A. Accordingly, the temperatures occurring in the operation of the second cooling stage in Table B are significantly higher than in Table A, this enabling efficient drying during the operation of the transformer 1.

LIST OF REFERENCE SIGNS

[0064] 1 Transformer [0065] 2 Housing of the transformer [0066] 3 Transformer winding, having cellulosic paper wrapped around the conductor [0067] 4 Cooling circuit [0068] 5 Radiator [0069] 6 Ventilator [0070] 7 Transformer oil [0071] 8 Cooling device controller [0072] 9 Outlet side of the ventilator [0073] 10 Transformer core [0074] 11 Pump