EP3726547A1 - Method for drying a transformer comprising a multi-stage cooling system and cooling system control for such a transformer - Google Patents

Abstract

Method for drying a transformer (1) having a multi-stage cooling system, in particular a power transformer or a choke, with at least one transformer winding (3) and at least one insulating means (7) for electrical insulation, the cooling stages comprising a lowest cooling stage and a highest cooling stage, with the individual cooling stages are each associated with a load condition range of the transformer (1) and are activated when the respective load condition range of the transformer (1) is reached, the load condition range being a function which at least depends on a temperature of the transformer (1), and where the Method for drying during operation of the transformer (1) is carried out. It is proposed that an upper cooling level, which is above the lowest cooling level, is or remains deactivated and the cooling level immediately below the upper cooling level is or remains activated while the transformer (1) is in the load condition range belonging to the upper cooling level.

Description

FIELD OF THE INVENTION

The present invention relates to a method for drying a transformer having a multi-stage cooling system, in particular a power transformer or a choke, with at least one transformer winding and at least one insulating means for electrical insulation, the cooling stages comprising a lowest cooling stage and a highest cooling stage, the individual cooling stages each are associated with a load condition range of the transformer and are activated when the respective load condition range of the transformer is reached, wherein the load condition range is a function which depends at least on a temperature of the transformer, and wherein the method for drying is carried out during operation of the transformer.

The present invention further relates to a cooler control for a transformer having a multi-stage cooling system, in particular a power transformer or a choke, with at least one transformer winding and at least one insulating means for electrical insulation.

STATE OF THE ART

Power transformers represent capital goods with relatively high costs and a desirable long service life. To achieve the latter property, the material of the transformer is subject to in particular transformer insulation, which is used primarily for electrical insulation of the transformer windings and comprises, for example, a combination of oil and cellulose paper, a drying process in the manufacture of a transformer, since moisture accelerates aging during operation. During operation, however, there is an increase in the moisture content, which is why transformers, in particular the transformer insulation material, could be dried from time to time in order to increase the life of the transformers.

For this purpose, it is known from the prior art to dry the active parts of transformers in a vapor phase drying system, cf. e.g. https://de.wikipedia.org/wiki/Vapour-Phase-Trocknung. Since the respective transformer to be dried has to be brought into a drying oven for this purpose, this drying clearly does not take place during operation of the transformer and causes corresponding downtimes.

Furthermore, attempts for drying during operation are known from the prior art, in which filter cartridges are used in order to continuously absorb or extract moisture from the transformer oil or from the insulating liquid. The drying process in the solid insulation continues through the drying of the insulating liquid. The disadvantage here is the extremely long process duration in practice, especially for the solid insulation, which can even exceed a year. This can lead to a further disadvantage, namely when assessing a transformer, since - depending on the drying process, especially with extraction processes with vacuum - not only the dissolved moisture, but also other dissolved components such as fault gases are removed from the insulating liquid. During the drying process, the usual oil analysis (see e.g. https://de.wikipedia.org/wiki/Leistungstransformator#Ölanalys e) the condition of the insulation system is no longer monitored.

OBJECT OF THE INVENTION

It is therefore the object of the present invention to provide a possibility for rapid drying of transformers during operation.

DISCLOSURE OF THE INVENTION

In order to achieve the stated object, a method for drying a transformer having a multi-stage cooling system, in particular a power transformer or a choke, with at least one transformer winding and at least one insulating means for electrical insulation, the cooling stages comprising a lowest cooling stage and a highest cooling stage, wherein the individual cooling stages are each associated with a load condition range of the transformer and are activated when the respective load condition range of the transformer is reached, the load condition range being a function that depends at least on a temperature of the transformer, and wherein the drying method is carried out during operation of the transformer it is provided according to the invention that an upper cooling level, which is above the lowest cooling level, is or remains deactivated and the cooling level immediately below the upper cooling level ak is or remains activated while the transformer is in the load condition range associated with the upper cooling stage.

A load condition in the load condition range causes aging of the transformer and is explicitly dependent at least on the temperature of the transformer.

The transformer is thus set to a higher temperature, which is also referred to below as "increased temperature", than without this measure at the specific operating point.

“Area” in the term load condition area indicates, on the one hand, that it is not a mathematical point with which the cooling stage is associated, but that the cooling stage is associated with a range of load conditions that inevitably occurs in practice. For example, in practice it makes no difference whether the temperature is X ° C or a slightly different one, e.g. X ° C + 0.1 ° C, although mathematically, strictly speaking, there is a quantitatively slightly different load condition. On the other hand, a certain temperature range and thus a certain range of load conditions can be associated with the respective cooling stage.

In the method according to the invention, a temperature increase to an elevated temperature is brought about by means of a suitably selected reduction in the cooling capacity - thus without additional heating means. If the at least one insulating means comprises a solid insulation, which solid insulation contains in particular hygroscopic material such as cellulose (for example in solid material, so-called pressboard or "press board", or wrapping paper), this increased temperature is high enough to prevent moisture diffusion from the solid insulation to promote. If the at least one insulating means comprises a liquid insulation, in particular oil such as mineral oil, the increased temperature increases the absorption capacity of the liquid insulation for the moisture, the moisture being increased in a manner known per se - for example by means of filter cartridges, which are in turn cellulose or may contain other suitable materials - from which the liquid can be removed. This results in significantly faster and more efficient drying conditions, with drying during the ongoing operations and typically only takes a few weeks.

It should be noted that the “temperature of the transformer” can in principle be understood to mean different measured variables, for example a hot oil temperature or the temperature at a certain particularly hot point (“hotspot”) of the fixed insulation or of the transformer. The hot oil temperature is typically measured in the area of a cover of an oil-filled housing of the transformer, the transformer winding and the transformer core being arranged in the housing. The temperature of the hot spot in the solid material is usually above the hot oil temperature. This value can either be estimated on the basis of the hot oil temperature taking into account the load current, or the hotspot temperature can be measured directly with high-voltage-resistant sensors, in particular by means of fiber optic sensors.

As already stated, the at least one insulating means can contain both solid and liquid insulation, in particular cellulose paper and / or oil. The at least one insulating means is used, in particular, to electrically isolate the at least one transformer winding or its metallic conductors.

The general rule is that the cooling capacity is increased with increasing load or with higher load condition ranges and vice versa. The change in the cooling capacity can take place in stages, whereby cooling stages are automatically defined. The cooling output can, however, also take place essentially continuously, for example by continuously controlling a speed, although cooling stages can of course also be defined in this case, for example as certain speed ranges. In this case, one could also speak of virtual cooling levels. Such cooling stages or virtual cooling stages form the cooling system.

The load condition areas associated with the cooling stages can be defined or predeterminable.

It goes without saying that the method according to the invention can also be provided as a computer-implemented method.

In principle, it is conceivable that the temperature of the transformer is influenced by different factors, which thus implicitly also influence the load condition or the load condition range. Of course, it is also possible that the load condition range or the load condition explicitly depends on further variables, for example on the electrical load or the current load on the transformer and / or the ambient temperature. In preferred embodiments of the method according to the invention, these variables can also be taken into account. Accordingly, it is provided in a preferred embodiment of the method according to the invention that the load state range also depends on the current load on the transformer and that the upper cooling stage is or remains deactivated and the cooling stage immediately below the upper cooling stage is or remains activated only then, when the current load has fallen below a threshold value and / or does not exceed the threshold value, the threshold value being below a maximum value of the current load on the transformer in the load state range belonging to the upper cooling stage and within this load state range.

That is to say, achieving the increased temperature is coupled in this case with a current load or electrical load on the transformer that is reduced compared to the maximum value. This has the additional advantage that the temperature distribution actually present in the transformer is nowhere near as inhomogeneous as it is with high temperatures Operating currents or electrical loads. High electrical transformer loads are usually coupled with a pronounced inhomogeneity of the temperature distribution, so that on the one hand the hot spots already mentioned appear prominently, while on the other hand the more humid parts of the insulation only have a rather moderate temperature level. Most of the moisture then accumulates in the cooler areas. The approach according to the invention makes use of a state in which the hot spots are only moderately pronounced and cooler areas are also warmed better or dried more quickly. There is practically no risk of pronounced local hot spots with extreme aging. With the method according to the invention, even the worst case can be excluded, namely a gas bubble formation in the insulation system, which in the high-voltage area can lead to immediate damage by explosion and thus to transformer failure - with the risk of fire and great restoration effort.

Specifically, for example, hot oil temperatures can be achieved which are in the range of e.g. maximum 80 ° C. The temperature distribution in the transformer at these hot oil temperatures is then typically such that only slight hot spots below 95 ° C. occur in the solid insulation. It should be noted that these figures, which are only given as examples, also depend on the thermal class of the materials used.

Since only minor hot spots are generated, the drying process practically does not lead to any relevant increased aging of the at least one insulating means.

The means provided for measuring the corresponding characteristic value, in particular corresponding current or power sensors, are known per se.

In a particularly preferred embodiment of the method according to the invention, it is provided that the threshold value is at most 80%, preferably at most 70%, particularly preferably at most 60%, of the maximum value of the load on the transformer in the load state range associated with the upper cooling stage. Inhomogeneous temperature distributions with harmful hot spots can be significantly reduced in this way, with the increased temperature also minimizing the disadvantage of cooler areas with poor drying properties, so that the overall insulation or all the insulating means receive or maintain a temperature that is advantageous for drying.

In a preferred embodiment of the method according to the invention it is provided that the upper cooling stage is the highest cooling stage. In this way, the load condition range associated with the highest cooling level ensures that the increased temperature that is established for the drying is particularly high, as a result of which particularly rapid drying can be achieved.

Cooler controls of transformers used today can be set up to take into account aspects that go beyond pure cooling - at least to a certain extent - by controlling the cooling accordingly. For example, such cooler controls can control a reduction in overall losses, an increase in the overload capacity and / or an equalization of the wear and tear on the cooling units. Such cooler controls can advantageously be used to carry out the method according to the invention, in particular by adapting the software of the respective cooler control accordingly. It is therefore according to the invention in a cooler control for a transformer having a multistage cooling system, in particular a power transformer or a choke, with at least one transformer winding and at least one insulating means for electrical insulation it is provided that the cooler control is set up to carry out a method according to the invention. That is to say, the cooler control can control suitable means, in particular the cooling system, in such a way that the method according to the invention is carried out with the aid of these means.

As already mentioned, the cooler control can have or use corresponding software for this purpose, which is loaded into a memory of the cooler control, for example. It is also conceivable that this software can also be transmitted over a network or distributed on a data carrier. Therefore, a computer program product is provided according to the invention, comprising commands which cause the cooler control according to the invention to carry out the method according to the invention.

Analogously, a transformer, in particular a power transformer or choke, with at least one transformer winding and at least one insulating means for electrical insulation, comprising a multi-stage cooling system and the cooler control according to the invention, is provided according to the invention.

In a preferred embodiment of the transformer according to the invention it is provided that at least three cooling stages are provided. This favors the achievement of sufficiently high elevated temperatures for rapid drying and, at the same time, the most homogeneous temperature distribution possible, since the cooling stage immediately below the upper cooling stage does not have to be the lowest cooling stage.

For optimum insulation on the one hand and good cooling on the other hand, it is provided in a preferred embodiment of the transformer according to the invention that the at least one insulating medium comprises insulating liquid, in particular oil, and preferably solid insulation comprising cellulose. The insulating liquid or the oil acts simultaneously as an insulator and as Coolant. This can for example be mineral oil, vegetable oil or synthetic liquids such as silicone oil. In addition, insulating liquids with increased flash points are conceivable.

Furthermore, for optimal insulation on the one hand and good cooling on the other hand, in a preferred embodiment of the transformer according to the invention it is provided that the at least one insulating means comprises solid insulation, which preferably comprises cellulose or aramid. As a hygroscopic material such as cellulose as solid insulation, which typically surrounds the at least one transformer winding or its turns, e.g. Cellulose paper or pressboard or "pressboard" material can be provided. Aramid, in turn, has advantageous properties especially at very high temperatures, aramid also absorbing moisture, although it can be impregnated to a certain extent.

In particularly preferred embodiments of the transformer according to the invention, for optimal cooling using insulating liquid or oil, 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.

In these particularly preferred exemplary embodiments, both two-stage and three-stage cooling systems are provided.

The names given are common terms in cooling technology, cf. https://de.wikipedia.org/wiki/K%C3%BChlung. "O" stands for "Oil", "K" for an insulating liquid with a higher insulating liquid than oil Thermal class or increased flash point, "N" for "Natural" (here the respective medium or fluid is only moved due to naturally occurring convection), "F" for "Forced" (pumps are used here to move the medium or fluid) , "D" for "Directed" (here the windings are pumped in a targeted or directional manner), "A" for "Air". The numbers indicate, in ascending order, an increased number of the corresponding coolants for moving the respective cooling medium / fluid, ie AF1 stands for a certain number of fans, whereas AF2 stands for a comparatively higher number of fans.

It should be noted that both radiators and coolers can be used, with coolers necessarily requiring fans and pumps, whereas natural convection of the cooling media / fluids can also be provided for radiators.

In general, it should also be noted that, in addition to air, another cooling fluid could also be used, for example another gas or a liquid such as e.g. Water.

For the exemplary embodiments ONAN, ODAN, ODAF and KNAN, KDAN, KDAF:
ODAF stands for "Oil Directed Air Forced", ie the oil is pumped in a directional manner by means of at least one oil pump and at least one fan is switched on, which means that the highest cooling level is achieved with the strongest cooling. The oil circulates in a cooling circuit that includes at least one radiator for heat exchange with the environment and at least one fan or fan, preferably at least one axial fan, in which the axis of rotation of an impeller runs parallel or axially to an air flow. The at least one fan can - compared to cooling with natural convection - significantly higher cooling of the at least one radiator or a significantly higher heat exchange with the ambient air can be achieved.

KDAF refers to a cooling stage analogous to ODAF, whereby instead of oil, an insulating liquid with a higher temperature class or higher flash point is used.

By switching off the at least one fan, only the air circulation remains due to natural convection, so that the cooling performance in the middle cooling level is lower than in the highest cooling level. Accordingly, ODAN stands for "Oil Directed Air Natural".

KDAN denotes a cooling stage analogous to ODAN, whereby instead of oil, the insulating liquid with a higher temperature class or higher flash point is used.

If the at least one pump is now also switched off, the oil can only circulate due to natural convection, which further reduces the cooling capacity in the lowest cooling level compared to the medium cooling level. Accordingly, ONAN stands for "Oil Natural Air Natural".

KNAN denotes a cooling stage analogous to ONAN, whereby instead of oil, the insulating liquid with a higher temperature class or higher flash point is used.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

eine schematische Darstellung eines erfindungsgemäßen Transformators

The invention will now be explained in more detail using an exemplary embodiment. The drawing is exemplary and is intended to explain the concept of the invention, but in no way restrict it or reproduce it conclusively. It shows:

Fig. 1

a schematic representation of a transformer according to the invention

WAYS OF CARRYING OUT THE INVENTION

Fig. 1 shows a schematic representation of a transformer 1 according to the invention, which has a transformer winding 3 which is wound around a transformer core 10. The transformer winding 3 consists of at least one low-voltage and high-voltage winding, not shown in any further figurative form. Furthermore, the transformer winding 3, more precisely its electrical conductor, is wrapped with cellulose paper (not shown separately) for electrical insulation.

The transformer winding 3 and the transformer core 10 are arranged in a housing 2 of the transformer 1 which is filled with a transformer oil 7. The transformer oil 7 can e.g. be mineral oil. The transformer oil 7 is also used for electrical insulation on the one hand. I.e. Insulating means of the transformer 1 comprise the transformer oil 7 and the cellulose paper, the latter being impregnated with transformer oil 7 accordingly.

On the other hand, the transformer oil 7 is used for cooling, since the transformer winding 3 generates heat during operation of the transformer 1, which heat increases with the electrical load or the current load on the transformer 1. The transformer oil 7 can circulate in a cooling circuit 4 that encompasses the housing 2. The circulation of the transformer oil 7 can take place by natural convection and / or can be forced by means of a pump 11. At least one radiator 5 is also provided in the cooling circuit 4 in order to enable heat exchange between the transformer oil 7 and the ambient air. Here, the radiator 5 is cooled by the ambient air, the ambient air absorbing heat from the radiator 5. Cooler ambient air can be supplied to the radiator 5 via natural convection and / or by means of at least one fan 6. If the If the radiator 5 is cooled by means of the fan 6, ambient air is sucked in by the fan 6 and blown onto the radiator 5 at an outlet side 9 of the fan 6 facing the radiator 5.

In the exemplary embodiment shown, in particular the transformer oil 7, the pump 11, the radiator 5 and the fan 6 are used to implement three cooling stages - a lowest cooling stage, a medium cooling stage and a highest cooling stage - of the transformer 1.

These cooling stages are associated with associated load condition areas, i. Each of the cooling stages is assigned to a load condition area, each load condition area comprising a range of load conditions which cause the transformer 1 to age. The load condition or the load condition range is at least dependent on the temperature of the transformer 1. In the exemplary embodiment shown, the load condition or the load condition range is also explicitly dependent on the electrical load or the current load on the transformer 1.

By means of a cooler control 8, as the load condition range increases, successively higher and higher cooling levels are activated, and as the load condition range decreases, the higher cooling levels are successively deactivated. I.e. the lowest cooling level is associated with a low load condition area, the medium cooling level with a medium load condition area and the highest cooling level with a high load condition area.

In Fig. 1 Dotted lines indicate that the cooler control 8 is operatively connected to the pump 11 and the fan 6 in order to switch them on or off as desired. The dash-dotted line in Fig. 1 indicates that the cooler control 8 information about the current Load condition or load condition range of the transformer 1 processed. This information can be made available via means known per se, in particular sensors for the temperature of the transformer 1 and for the electrical power consumption or for the current flowing on the secondary side of the transformer 1.

The highest cooling level in the illustrated embodiment is ODAF ("Oil Directed Air Forced"), i.e. the transformer oil 7 is pumped through the cooling circuit 4 in a directed manner with the pump 11 and the fan 6 is activated so that a maximum cooling capacity is achieved.

By switching off the fan 6, ODAN ("Oil Directed Air Natural") is implemented as the middle cooling stage in the illustrated embodiment, in which only the air circulation remains due to natural convection, so that the cooling performance in the middle cooling stage is lower than in the highest cooling stage. It should be noted that it would alternatively also be conceivable to realize the middle cooling stage by switching off the pump 11 and running the fan 6, which would be referred to as ONAF ("Oil Natural Air Forced").

If, in the illustrated embodiment, the pump 11 is now also switched off, the transformer oil 7 can only circulate due to natural convection, whereby the cooling capacity in the lowest cooling level is further reduced compared to the middle cooling level. I.e. the lowest cooling level in the illustrated embodiment is ONAN ("Oil Natural Air Natural").

The cooler control 8 is also set up to carry out a method according to the invention for drying, ie in particular to control the pump 11 and the fan 6 depending on the load condition range of the transformer 1 so that the method according to the invention during of the operation of the transformer 1 is carried out as follows: An upper cooling level, which is above the lowest cooling level, is deactivated or remains deactivated and the cooling level immediately below the upper cooling level is activated or remains activated, while transformer 1 belongs to the upper cooling level Stress condition area is located. In the illustrated embodiment, the upper cooling stage is only deactivated or remains deactivated and the cooling stage immediately below the upper cooling stage is only activated or remains activated when the current load has fallen below a threshold value and / or does not exceed the threshold value, with the The threshold value is below a maximum value of the current-wise load on the transformer 1 in the load state range belonging to the upper cooling stage and within this load state range.

The upper cooling stage is preferably the highest cooling stage.

The threshold value can be reduced by at least 20%, preferably by at least 30%, particularly preferably by at least 40%, for example by at least 20%, preferably by at least 30%, particularly preferably by at least 40%, compared to the maximum value of the current load on the transformer 1 in the load state range belonging to the upper cooling stage.

Further illustration of the method according to the invention:
The following table A gives an example of a conventional three-stage cooling of the in Fig. 1 shown transformer 1. The specified typical load current is given as a percentage of the nominal current or maximum load current. The specified load current is typically dependent on the ambient temperature and the dynamics of the system and shifts accordingly to lower percentages at high ambient temperatures and, conversely, to higher percentages at low ambient temperatures Percentages. In this respect, when using the drying mode or the method according to the invention for drying, a high ambient temperature is advantageous in order to achieve efficient drying even with smaller load currents.

The load condition range that is associated with the cooling stages is a function of both the temperature of the transformer 1, the temperature in particular being a hot oil temperature, and of the load current. TABLE A - CONVENTIONAL THREE STAGE COOLING Cooling level 1 2 3 Type ONAN ONAF ODAF Switched on additional units - Fan Pumps + fans Threshold temperature "On" [° C] 60 70 Threshold temperature "Off" [° C] 50 60 Occurring temperatures [° C] <60 50-70 > 60 Typical load current <60% 60-80% > 80%

In contrast, one embodiment of the drying process according to the invention is illustrated in Table B below. Clearly, it also applies to the method according to Table B that the load condition range associated with the cooling stages is a function of both the temperature of the transformer 1, the temperature in particular being a hot oil temperature, and of the load current. TABLE B - EMBODIMENT OF THE METHOD OF THE INVENTION Cooling level 1 2 3 Type ONAN ODAN ODAF Switched on additional units - pump Pumps + fans 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

Table B shows two cases, namely once for a load current <70% of the rated current and once for a load current ≥ 70% of the rated current. Efficient drying takes place at more than 60 ° C.

It should be noted that it can be seen from Table B that the medium cooling stage ODAN is selected instead of ONAF, for which no structural change has to be made to the transformer 1. The corresponding types of cooling are simply set via the cooler control 8.

Compared 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 load condition areas that belong to the highest cooling stage according to Table A. Correspondingly, the temperatures occurring during operation of the second cooling stage in Table B are significantly higher than in Table A, which enables efficient drying during the operation of the transformer 1.

List of reference symbols:

1

transformer

2

Housing of the transformer

3

Transformer winding, with cellulose paper wrapped around the conductor

4th

Cooling circuit

5

radiator

6th

fan

7th

Transformer oil

8th

Cooler control

9

Outlet side of the fan

10

Transformer core

11

pump

Claims (11)

Method for drying a transformer (1) having a multi-stage cooling system, in particular a power transformer or a choke, with at least one transformer winding (3) and at least one insulating means (7) for electrical insulation,
wherein the cooling stages include a lowest cooling stage and a highest cooling stage, the individual cooling stages are each associated with a load condition range of the transformer (1) and are activated when the respective load condition range of the transformer (1) is reached, the load condition range being a function that at least depends on a temperature of the transformer (1),
and wherein the method for drying is carried out during the operation of the transformer (1), characterized in that an upper cooling stage which is above the lowest cooling stage is or remains deactivated and the cooling stage immediately below the upper cooling stage is or remains activated, while the transformer (1) is in the load condition area belonging to the upper cooling stage. Method according to claim 1, characterized in that the load condition range also depends on the current load on the transformer (1) and that the upper cooling stage is or remains deactivated and the cooling stage immediately below the upper cooling stage is only activated or remains when the current load has fallen below a threshold value and / or does not exceed the threshold value, the threshold value being below a maximum value of the current load on the transformer (1) in the load state range belonging to the upper cooling stage and within this Load condition area. Method according to Claim 2, characterized in that the threshold value is at most 80%, preferably at most 70%, particularly preferably at most 60%, of the maximum value of the current load on the transformer (1) in the load condition range associated with the upper cooling stage. Method according to one of Claims 1 to 3, characterized in that the upper cooling stage is the highest cooling stage. Cooler control (8) for a transformer (1) having a multi-stage cooling system, in particular a power transformer or a choke, with at least one transformer winding (3) and at least one insulating means (7) for electrical insulation, characterized in that the cooler control (8) carries out of a method according to one of claims 1 to 4 is set up. Transformer (1), in particular power transformer or choke, with at least one transformer winding (3) and at least one insulating means (7) for electrical insulation, comprising a multi-stage cooling system and the cooler control (8) according to Claim 5. Transformer (1) according to Claim 6, characterized in that at least three cooling stages are provided. Transformer (1) according to one of Claims 6 to 7, characterized in that the at least one insulating means comprises insulating liquid, in particular oil (7). Transformer (1) according to one of Claims 6 to 8, characterized in that the at least one insulating means comprises solid insulation, which preferably comprises cellulose or aramid. Transformer (1) according to Claim 7 and Claim 8, characterized in that 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. Computer program product, comprising instructions which cause the cooler control (8) according to claim 5 to carry out the method according to any one of claims 1 to 4.

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