Transformer with temperature-dependent cooling function

Abstract

An electric device has a housing and an active part in the housing that can be supplied with a high voltage and that generates heat when operated. The housing is filled with an insulating liquid for cooling. A cooling system for cooling the insulating liquid has at least one cooling element which is connected to the external atmosphere in a heat-conductive manner and via which the insulating liquid is conducted. Temperature fluctuations of the electric device are limited or even prevented in an inexpensive manner. The cooling system has a rising section which is connected to the housing, is provided with rising branches, and is connected to a cooling element at each rising branch. The volume of the rising section is selected on the basis of a thermal expansion coefficient of the insulating liquid such that the fill state reaches a different number of rising branches at specific temperatures.

Claims

1. An electrical device, comprising: a housing; an active part disposed in said housing, said active part being subject to high voltage and generating heat when operated; an insulating liquid for cooling filled in said housing; and a cooling system for cooling said insulating liquid, said cooling system having a rising section connected to said housing for carrying said insulating liquid, said rising section being formed with a plurality of rising branches and having a respective cooling element connected at each said rising branch, said cooling elements being thermally conductively connected to an ambient atmosphere; wherein a volume of said rising section is selected in dependence on a coefficient of thermal expansion of said insulating liquid such that a filling level reaches a different number of said rising branches at prespecified temperatures.

2. The electrical device according to claim 1, wherein said rising section has at least one inclined section which runs in an inclined manner in relation to a side wall of said housing, and wherein said rising branches are arranged in said inclined section.

3. The electrical device according to claim 2, wherein each said cooling element is a radiator which has a plurality of inner cooling channels.

4. The electrical device according to claim 2, wherein each rising branch is connected to a separate cooling pipe.

5. The electrical device according to claim 1, wherein said rising section has a vertical pipe section that extends said housing in a direction of a side that is averted from a base wall, and wherein said rising branches are arranged in said vertical pipe section.

6. The electrical device according to claim 5, wherein said cooling element is a pipe cooling means having an output connected to a base region of said housing, and wherein each said rising branch is connected to an input of said tubular pipe cooling means.

7. The electrical device according to claim 6, comprising a heat exchanger having an output connected to a base region of said housing, and wherein at least one rising branch is connected to an input of a pipeline which leads to said heat exchanger.

8. The electrical device according to claim 7, wherein said rising branch of said pipeline which leads to the input of said heat exchanger is arranged beneath at least one further rising branch for a further said cooling element.

9. The electrical device according to claim 1, wherein said housing, the cooling elements and said rising section form a pressure-resistant, hermetically sealed unit, and a space above the filling level of said insulating liquid is filled with a compressible inert gas.

10. The electrical device according to claim 1, wherein said rising section is formed with an opening above a maximum filling level of said insulating liquid, wherein a gas exchange with a surrounding area or further vessels is possible through said opening in an event of changes in volume which are caused by changes in a temperature of said insulating liquid, and wherein an interior of said cooling elements entirely or partially absorbs the fluctuations in the volume of said insulating liquid.

11. The electrical device according to claim 1, wherein a rising branch is connected to a heat pipe.

12. The electrical device according to claim 1, further comprising a fan for intensifying a cooling effect of said cooling system.

13. The electrical device according to claim 12, further comprising a filling level sensor, wherein said fan has a regulating device which is connected to said filling level sensor.

14. The electrical device according to claim 1, wherein said cooling elements are arranged with a vertical offset from one another.

15. The electrical device according to claim 1, wherein said electrical device is a transformer or an inductor coil.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIGS. 1 to 6 each show a schematic illustration of an exemplary embodiment of the electrical device according to the invention.

DESCRIPTION OF THE INVENTION

(2) FIG. 1 shows a first exemplary embodiment of the device according to the invention which is a transformer 1 here. The transformer 1 has an active part 2 which, for its part, comprises a winding arrangement 4 which is wound around a magnetic core 3. The winding arrangement 4 comprises a low- and high-voltage winding, not illustrated further in the figures. Furthermore, the transformer 1 has a housing 6 which is filled with an insulating liquid 20. An oil expansion tank 26 which is connected to the housing 6 of the transformer 1 by means of a pipeline 15 is provided for accommodating insulating liquid at high temperatures. A cooling system 8 is arranged between the oil expansion tank 26 and the housing 6. The cooling system 8 has a rising pipe 15 as a rising section which has an inclined section 15.1. A return pipe 16 is further provided. The inclined section 15.1 of the pipeline 15 contains rising branches 9 which are connected to the upper input of radiators 10. Each radiator 10 is, for its part, equipped with a plurality of cooling channels which run parallel in relation to one another and which are connected to the return pipe 16 by means of an output. In FIG. 1, filling levels of the insulating liquid are further indicated by dashed lines. The filling level 21.3 corresponds to the minimum filling level of the insulating liquid which is established when the transformer 1 is not in operation. A filling level which is provided with reference numeral 21.1 is established during normal operation. The filling level 21.5 corresponds to a maximum filling level.

(3) On account of the partially inclined profile of the pipeline 15, the radiators or, in other words, cooling elements 10 are arranged in a staggered manner in respect of height. This staggering in respect of height has an advantageous effect on the circulation rate of the insulating liquid 20 through the cooling system 8. The radiators are further hydraulically connected to the transformer 1 by the return line 16. An increasing temperature results in a rising filling level in the radiators 10 and also the pipeline 15 and, in particular, in the inclined section 15.1 owing to the expansion of the insulating liquid 20. The radiators 10 can come into effect only when the insulating liquid passes through said radiators or circulates in said radiators. To this end, the insulating liquid level in the inclined section 15.1 has to reach the rising branch 9 which is respectively associated with the radiator 10. The arrangement of the cooling elements 10 is selected in such a way that, depending on the desired cooling rate, a number of radiators which corresponds to the filling level of the insulating liquid is incorporated in the flow of the insulating liquid 20. Since, according to the invention, the cooling system 8 takes on the task of absorbing the thermally induced fluctuations in the volume of the insulating liquid, the expansion tank 26 can be configured to be more compact and, in an exemplary embodiment which differs from this, can be entirely dispensed with.

(4) FIG. 2 shows an exemplary embodiment, which differs from FIG. 1, of the electrical device 1 according to the invention which is likewise in the form of a transformer 1 here. According to this exemplary embodiment, the housing 6 and the cooling system 8 are dimensioned such that the bottom edge of the cover of the transformer is arranged below the surface of the insulating liquid 20 at all temperatures of the insulating liquid 20. Therefore, the lower parts of a high-voltage bushing, not illustrated in the figures, are always completely surrounded by the insulating liquid 20. The pipeline 15 also has an inclined section 15.1 according to the exemplary embodiment illustrated in FIG. 2. However, the rising branches 3 of the inclined section 15.1 are each connected to the input of a separate cooling pipe 10. The cooling pipes 10 likewise act as cooling elements and, depending on the filling level of the insulating liquid 20, can be incorporated in the circulation of the insulating liquid 20, so that the cooling power increases to such an extent that an equilibrium is established between the supplied lost heat of the transformer 1 and the heat of the cooling system 8 which has been given off. If the filling level is so high that virtually all of the cooling pipes 10 are incorporated in the cooling operation, this is detected by a sensor 34 which is arranged in a tubular projection which protrudes in a perpendicular manner from the pipeline 15. The output signal of the sensor 34 is transferred to a regulating device, not shown in the figures, which then switches on a fan 12 which provides additional cooling. The actuation of the fan 12 is therefore combined with the hydraulic cooling.

(5) In the exemplary embodiment shown in FIG. 2, the upper manifold pipe of the cooling system 8, that is to say the pipeline 15, is provided with a venting line 18. As the insulating liquid level rises, air is displaced out of the cooling system 8 and carried away by means of the venting means 18 and to a dehumidifying device 28 which is arranged at the outer end of the venting line 18 in order to avoid humidification of the insulating liquid when the system cools down and the filling level of the insulating liquid consequently drops.

(6) FIG. 3 shows a further exemplary embodiment of the transformer 1 according to the invention which, here, has means for thermal insulation 39 which are realized by insulating plates in the example shown. The thermally insulating plates 39 are fitted to the outside of the housing 6 of the transformer 1. Therefore, it is, for example, possible to run an alternating load operation even given arctic external temperatures since the idling losses now lead to heating up of the transformer, in the case of which the viscosity of the insulating liquid drops to values which allow circulation of said insulating liquid. The formation of dangerous local hotspots in the winding in the event of changes in load is avoided in this way. This is advantageous particularly in the case of transformers of which the housing 6 is filled with an insulating liquid 20 based on natural or synthetic esters since the viscosity of these fluids is considerably higher than in the case of insulating liquids 20 based on mineral oil. The rising branch 9 in the rising pipe 15 is arranged in such a way that circulation of the insulating liquid 20 of the device in the cooling element begins only when a temperature of the insulating liquid 20 which ensures reliable operation of the electrical device is reached.

(7) Furthermore, a circuit for utilizing the lost heat of the transformer is illustrated in FIG. 3. Said circuit comprises a heat exchanger 17.1 which feeds a heating circuit for waste heat utilization 17.5. The inlet of the insulating liquid 20 is provided at a level which corresponds to a temperature at which meaningful utilization of the waste heat is possible. Furthermore, in an embodiment with waste heat utilization, the further cooling elements, by way of their upper fluid inlet, are arranged above the rising branch 9 for the cooling circuit with waste heat utilization. Therefore, effective utilization of the waste heat is possible without fittings which can be adjusted by motor since the circuit for waste heat utilization is preferably automatically supplied with warm cooling liquid. If the lost heat of the transformer 1 exceeds the quantity of heat required by the system for lost heat utilization or the waste heat utilization means is not in operation, this results in further heating of the insulating liquid and therefore in an increase in volume. Therefore, the insulating liquid 20 rises, so that further cooling elements are incorporated in the cooling operation. By virtue of suitably setting the diameter of the rising pipe 15 for supplying the cooling system 8, the temperature differences which lead to the incorporation of further cooling elements 10 can be precisely controlled. Therefore, a degree of control accuracy of less than 1 K is possible for the insulating liquid 20 given a correspondingly small diameter of the rising pipe 25.

(8) Within the scope of the invention, the housing of the electrical device and the cooling system are filled with so much insulating liquid 20 that, at all temperatures in the temperature range already known, the housing is filled with the insulating liquid up to the bottom edge of a cover which closes the housing at the top and therefore the windings 4 and the lower parts of the bushings 7 are always surrounded by the insulating liquid.

(9) The diameter of the rising pipe 15 is advantageously increased in size above the topmost rising branch, so that, in the event of a further rise in temperature, the cooling power no longer increases as the cooling area increases, but rather only as a function of the temperature difference in relation to the ambient temperature. This increase in size of the cross section of the rising pipe further serves to absorb a further increase in the volume of the insulating liquid which is caused by heating, since all of the cooling elements are already incorporated in the cooling circuit on account of the corresponding filling level of the insulating liquid being reached.

(10) FIG. 4 shows an exemplary embodiment of the invention in which conventional radiators 10.1, 10.2, 10.3 are arranged on the transformer 1 in such a way that their upper manifold pipes 10.8 are arranged with a vertical offset. The transformer 1 has an expansion tank 26 of considerably reduced volume. Venting of the cooling system 8 is performed by means of pipelines to the expansion tank 26 which are arranged above a Buchholz relay 31.

(11) In a further embodiment of the invention, at least some of the cooling elements 10 are arranged at the same height and are connected to the transformer 1 by means of a rising pipe 15 which is equipped with rising branches. The cooling elements 10 which are not filled with insulating liquid 20 at the respective filling level and also the supply line to the cooling system are compressible gas volumes and, given a corresponding design, can serve as burst-prevention means in the case of an inner short circuit of the transformer.

(12) FIG. 5 shows a further exemplary embodiment in which matching of the cooling area to the temperature of the transformer 1 is achieved by inclined positioning of commercially available plates or pipe radiator 10. The inclined section 15.1 of the rising pipe 15 is provided with a venting connection at the upper end, situated opposite the input in the exemplary embodiment. The air which is displaced as the filling level rises is carried away by means of the pipeline 18 via this connection. The radiator 10 therefore both has a cooling effect and furthermore serves as an expansion tank of the transformer 1. The technical solution can be executed both as a breathing transformer 1 and also as a hermetically sealed transformer 1. In the case of the hermetic design, a gas compression chamber 29, which is illustrated in dashed lines in FIG. 5, is connected to the pipeline 18 instead of the air dehumidifying device 28. The space above the insulating liquid 20 is filled with an inert gas, preferably nitrogen.

(13) In the exemplary embodiment according to FIG. 6, the transformer 1 is additionally equipped with heat pipes 14. Said heat pipes are arranged in such a way that they deploy their cooling effect only when a specific filling level of the insulating liquid 20 is reached. The heat pipes 14 are designed for relatively high operating temperatures and lead to a considerable increase in the lost power which can be carried away. The heat pipes are, for example, a heat pipe or a thermosiphon which are known as such and manage without pumps or the like. In the exemplary embodiment, the heat pipes are configured as thermosiphon 14. In this case, a condensation section of the thermosiphon 14 is provided with additional cooling areas. In a special refinement, it is possible for air to additionally be blown onto the condensation section of the heat pipe 14 by a fan 12.5. Furthermore, the transformer 1 in the exemplary embodiment is of hermetically sealed design. To this end, the rising pipe 15 is enhanced with a gas compression chamber 29 above the maximum filling level 24.

LIST OF REFERENCE SYMBOLS

(14) 1 Electrical device 2 Active part 3 Core 4 Winding 6 Housing 7 High-voltage bushing 8 Cooling system 9 Rising branch 10 Cooling element 10.1 . . . 10.5 Cooling elements 1, 2, 3, 4, 5 10.8 Upper manifold pipe of the cooling device (in the case of a radiator) 12 Fan 14 Heat pipe 15 Rising tube 16 Return line 17.1 Heat exchange system 17.2 Pump 17.5 Heating circuit for waste heat utilization 18 Pipeline 19 Pipeline 20 Insulating liquid 21 Insulating liquid level 21.1 Insulating liquid level during normal operation 21.3 Minimum insulating liquid level 21.5 Maximum insulating liquid level 24 Region above the insulating liquid level 26 Oil expansion tank 28 Air dehumidifying device 29 Pressure compensation vessel 31 Buchholz relay 33 Temperature sensor 34 Filling level sensor 36 Pressure sensor 39 Thermally insulating plates