Cooling device and method for cooling at least one oil-to-air external heat exchanger - Patents.com

Abstract

A cooling device (20) for cooling at least one OAEHE in a transformer. The cooling device (20) comprises at least one impeller-motor device (10), at least one fluid pipe (11), and at least one fluid discharge device (12). The at least one impeller-motor device (10) is adapted to supply fluid to an inlet of the at least one fluid discharge device (12) via the at least one fluid pipe (11), to cause the fluid to flow through the at least one fluid discharge device (12), and to cause the fluid to discharge through at least one fluid outlet of the at least one fluid discharge device (12). The cooling device (20) further comprises a funnel (15). The at least one impeller-motor device (10) is disposed in the housing (16) at a distance of at least 3 meters from the at least one fluid discharge device (12).

Description

[Technical field]

[0001] FIELD OF THEINVENTION The present invention relates to the field of transformers, in particular to a cooling device for cooling at least one oil-to-air external heat exchanger (OAEHE) in a transformer. [Background technology]

[0002] background A power transformer is a device used in the transmission grid of an electric power system to convert voltage and current for the transportation and distribution of electrical energy.

[0003] Power transformers require high current and hence generation of heat is inevitable. This heat propagates in the oil inside the transformer tank. For normal operation of the transformer, it is important to dissipate this heat to the surroundings. An important part of oil cooling is performed by installing external devices such as radiators, coolers, through which the transformer oil is circulated and cooled. State of the art air cooling for transformers is performed using conventional fans i.e. bladed fans, or natural convection. For high power rated transformers, natural convection is not sufficient and hence forced cooling is required for this operation. When water is available, water cooling may be used. Around 10% of power transformers utilize coolers and around 5% require fans. The utilization of water cooling and air cooling using fans is only 1%. Around 90% of power transformers may utilize radiators. In large power transformers, fans may also be required to handle over-rating situations. In conclusion, approximately 95% of power transformers may incorporate fans for cooling into their design.

[0004] Due to the heating of power transformers and the installation of external cooling equipment, ambient air may be brought in to cool these devices, which work on the natural or forced convection principle. This air must be at the required speed and volume, i.e. high air flow rate. The external cooling equipment should preferably not disturb the environment or surroundings, for example by noise or vibration. It should also be able to operate in harsh environments, for example from -40°C to +60°C.

[0005] Currently, standard fans are the state-of-the-art solution for cooling power transformers. The main reason behind this is that it is a well-known technology. Similar techniques are used for air conditioning for homes and large buildings, as well as cooling for industrial facilities and data centers.

[0006] However, implementing standard fans for external cooling of power transformers introduces several problems:

[0007] - Complexity: The fan motor is attached to the blades, both inside a metal cage, plus many electrical cables are needed to power the motor.

[0008] -It is difficult to increase the cooling air flow rate due to the fan characteristic performance curve. -Poor scalability: Increasing blade size increases the moment of inertia as a squared order.

[0009] - Complicated access to the blades and / or motors makes maintenance difficult, time-consuming and expensive.

[0010] - Fans are noisy, e.g. around 70dB, and mitigation can be costly and raise legal issues.

[0011] -The fans are quite heavy, on the order of 5kg each. -High security risk as cooling fans are easy to sabotage.

[0012] - They are vulnerable to weather conditions, for example if they are located near the coast. The present disclosure presents an improved and viable solution for a cooling device. Summary of the Invention [Problem to be solved by the invention]

[0013] overview An objective of the embodiments herein is to provide enhanced cooling of an OAEHE in a transformer, or at least an alternative to known solutions in the art. [Means for solving the problem]

[0014] According to one aspect, the object is achieved by providing a cooling device for cooling at least one OAEHE in a transformer. The cooling device comprises at least one impeller-motor device, at least one fluid conduit, and at least one fluid discharge device. The at least one fluid discharge device comprises a fluid inlet for receiving fluid from the at least one fluid conduit and at least one fluid outlet arranged to direct a fluid flow towards the at least one OAEHE. The at least one impeller-motor device is adapted to supply fluid to the inlet of the at least one fluid discharge device via the at least one fluid conduit, to cause the fluid to flow through the at least one fluid discharge device, and to cause the fluid to discharge through the at least one fluid outlet of the at least one fluid discharge device. The cooling device further comprises a funnel. The at least one impeller-motor device is disposed in the housing at a distance of at least 3 meters from the at least one fluid discharge device.

[0015] According to another aspect, the above-mentioned object is also achieved by providing a method performed by a cooling device for cooling at least one OAEHE in a transformer. The cooling device comprises at least one impeller-motor device, at least one fluid pipe, and at least one fluid discharge device. The at least one fluid discharge device comprises a fluid inlet for receiving fluid from the at least one fluid pipe, and at least one fluid outlet. The cooling device supplies a fluid flow to the at least one fluid pipe using the at least one impeller-motor device. The cooling device further transports the fluid flow along the at least one fluid pipe to the inlet of the at least one fluid discharge device. The cooling device further causes the fluid to flow through the at least one fluid discharge device. The cooling device then further discharges the fluid flow through the at least one fluid outlet in the direction of the at least one OAEHE. The cooling device further comprises a funnel. The at least one impeller is disposed in the housing at a distance of at least 3 meters from the at least one fluid discharge device.

[0016] The embodiments herein are based on the realization that by providing a cooling device comprising at least one fluid ejection device, at least one fluid pipe, at least one funnel, and at least one impeller-motor device disposed in a housing at a distance of at least 3 meters from the at least one fluid ejection device, the cooling device can utilize the surrounding fluid to increase the fluid flow transported to the fluid ejection device, thereby effectively providing a strong and enhanced fluid flow to the at least one OAEHE of the transformer.

[0017] Brief explanation of the figure Further technical features of the present invention will become apparent through the following description of one or several exemplary embodiments given with reference to the accompanying drawings. [Brief description of the drawings]

[0018] [Figure 1]1 is a schematic diagram depicting a cooling device based on the Bernoulli principle, according to an embodiment herein. [Diagram 2] 1 is a schematic diagram depicting a cooling device according to an embodiment herein. [Diagram 3] 1 is a schematic diagram depicting a cross-section of a fluid ejection device. [Figure 4] 1 is a schematic diagram depicting a fluid ejection device having a hose, according to some embodiments. [Diagram 5] 1 is a flowchart depicting a method performed by a cooling device, according to an embodiment herein. [Figure 6a] FIG. 1 is a schematic diagram depicting a cooling device applied to a radiator or cooling group external to the tank of a large power transformer according to some embodiments. [Figure 6b] FIG. 1 is a schematic diagram depicting a cooling device applied to a radiator or cooling group external to the tank of a large power transformer according to some embodiments. [Figure 6c] FIG. 1 is a schematic diagram depicting a cooling device applied to a radiator or cooling group external to the tank of a large power transformer according to some embodiments. [Figure 6d] FIG. 1 is a schematic diagram depicting a cooling device applied to a radiator or cooling group external to the tank of a large power transformer according to some embodiments. [Figure 6e] FIG. 1 is a schematic diagram depicting a cooling device applied to a radiator or cooling group external to the tank of a large power transformer according to some embodiments. [Figure 6f] FIG. 1 is a schematic diagram depicting a cooling device applied to a radiator or cooling group external to the tank of a large power transformer according to some embodiments. [Figure 7] FIG. 1 depicts an example of outlet volumetric flow rate as a function of inlet volumetric flow rate for various fluid ejection device diameters. [Figure 8] FIG. 2 is a schematic diagram depicting a fluid ejection device having different fluid flow rates A, B, and C. [Figure 9a] 1 shows a schematic diagram according to some embodiments. [Figure 9b] 1 shows a schematic diagram according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] It should be noted that the drawings are not necessarily drawn to scale and that dimensions of certain elements may be exaggerated for clarity.

[0020] Detailed Description A portion of a cooling device 20 according to some embodiments is shown in FIG. 1. The cooling device 20 is based on Bernoulli's principle and includes that a fluid flow, e.g. an air flow, destined for a fluid ejector 12, e.g. an emitter ring, is generated in a generation chamber, e.g. a chamber or housing, which may be sound-insulated. The fluid flow is then transported to the fluid ejector 12. The fluid flow leaves the fluid ejector 12 by an outlet, which may be a narrow slit, at a high velocity resulting in low pressure. This increases the initial fluid flow by 10 to 50 times, depending on the geometry and dimensions of the fluid ejector 12, due to induction and entrainment, i.e. the Bernoulli effect, which attracts air from the surroundings. The fluid ejector 12 has no electrical connections and the fluid flow is generated in the generation chamber. FIG. 1 also shows a funnel 15, e.g. a funnel duct with a Coanda boundary, for enhancing the fluid flow. The OAEHE is shown in FIG. 1 in the form of a radiator.

[0021] An integrated description and operation of a cooling device 20 according to an embodiment herein is shown in FIG. 2. The cooling device 20 comprises at least one impeller-motor device 10, at least one fluid conduit 11, and at least one fluid ejector 12. The at least one fluid ejector 12 may be hollow and comprises a fluid inlet for receiving fluid from the at least one fluid conduit 11, and at least one fluid outlet positioned to direct the fluid flow towards the at least one OAEHE. The cooling device 20 further comprises a funnel 15. Operation of the cooling device 20 includes:

[0022] 1. The generated fluid stream may be delivered to the impeller-motor device 10. The fluid stream may be filtered through a filter before being delivered to the impeller-motor device 10.

[0023] 2. The impeller-motor device 10 then supplies, e.g. accelerates, the fluid flow to the fluid conduit 11. The fluid conduit 11 may include an insulating material. The impeller-motor device 10 is disposed in a housing 16 at a distance from the at least one fluid ejector 12. This distance between the impeller-motor device 10 and the at least one fluid ejector 12 may be at least 1 meter, 3 meters, 5 meters, or more. This distance between the impeller-motor device 10 and the at least one fluid ejector 12 is advantageous because, for example, sound from the impeller-motor device is generated far away from the transformer, allowing for sound mitigation procedures such as, for example, a sound-insulating housing 16 and a volume-reducing fluid conduit 11. By relocating the source of the sound to the sound-insulating housing, the operation of the fluid ejector 12 may be 20-40 dB lower in sound compared to a conventional bladed fan. The housing 16 may be sound-insulated, insulated, may include an insulating material, may be humidity-controlled, and may be dust-proof and / or sound-absorbing. The housing 16 and the at least one fluid conduit 11 may be located underground or covered by a solid structure, thereby reducing the risk of vandalism and deliberate attacks on the transformer plant. According to some embodiments, the cooling device 20 may comprise a plurality of fluid conduits 11 adapted to supply fluid to a plurality of fluid discharge devices 12.

[0024] 3. The fluid flow is transported along the tube 11 towards the inlet of the fluid ejector 12 with minimal pressure drop. The fluid ejector 12 may be disposed, e.g. fixed, in a funnel 15. The funnel 15 may be provided with a rounded smooth boundary 18 at the inlet of the funnel 15 to promote the Coanda effect, which mitigates edge turbulence and reduces the pressure drop at the inlet of the funnel 15. The inlet of the funnel 15 may be provided with a filter grid 17. The filter grid 17 is used to prevent undesired objects from entering the OAEHE.

[0025] 4. The fluid flow may be forced to disperse at high pressures inside the fluid ejector 12 . 5. The high velocity fluid is then ejected, e.g., discharged, through an outlet of the fluid ejector 12. According to some embodiments, the fluid ejector 12 comprises at least one slit, and the fluid may be ejected through a slit that may be narrow, e.g., a slit designed to direct flow towards the OAEHE.

[0026] 6. Due to the high velocity of the fluid, the fluid behind the fluid ejector 12 is induced into the central region of the fluid ejector 12. Also, near the exit of the fluid ejector 12, the fluid is entrained. The induction and entrainment, i.e., the Bernoulli effect, can increase the initial fluid flow M by 10-50 times depending on the geometry and dimensions of the fluid ejector 12.

[0027] 7. The aerodynamic shape of the toroidal surface of the fluid ejector 12 and the Coanda effect allow the fluid flow to be directed towards the OAEHE.

[0028] 8. The additional fluid flow may be added to the axial region of the fluid ejection device 12 using a hose 21 or a second fluid ejection device that is smaller than the fluid ejection device 12. That is, the maximum cross-sectional dimension of the second fluid ejection device is smaller than the maximum cross-sectional dimension of the first fluid ejection device 12 to intensify and homogenize the ejected, e.g., emitted, fluid flow.

[0029] 9. The obtained fluid flow may be increased to meet the requirements for cooling at least one OAEHE in the transformer. A set of parameters may provide such a dedicated design. These parameters may include: a. Impeller-motor unit power b. The diameter and / or size of the fluid ejection device c. Slit thickness d. The toroidal shape of the fluid ejector 12 and the cross-sectional dimensions of the fluid ejector 12 The fluid ejector 12 may have a cross section that is circular, elliptical, rectangular, or any other polygonal shape. The fluid outlet of the ejector 12 follows the outer periphery of the ejector 12.

[0030] 10. The high velocity fluid passes through the OAEHE, and the geometry of the OAEHE creates a pressure drop. The remaining fluid flow may be utilized to cool a second or more OAEHEs.

[0031] The result of operation of the cooling device 20 is typically an increase in inlet fluid flow of 10 to 50 times. The technology of the cooling device 20 utilizes the surrounding fluid to amplify the fluid flow that is transported to the fluid exhaust device 12. It is concluded that the cooling device 20 effectively provides a stronger and enhanced fluid flow to at least one OAEHE of the transformer.

[0032] Figure 3 shows a cross section of the fluid ejector 12. The velocity of the fluid flow, e.g., the air flow shown in Figure 3, at the outlet c of the fluid ejector 12 is very high, e.g., >15 m / s. The relationship of the dimensions a, b, and θ may be arranged to attempt to obtain a minimum homogenous fluid flow H for the OAEHE.

[0033] 4 shows the fluid ejector 12 with an additional hose 21 according to some embodiments herein. The hose 21 can homogenize the fluid flow towards the OAEHE. The end of the funnel 15 may be bent and have a smooth boundary 18 that is rounded rather than sharp to guide and enhance the fluid flow and promote the Coanda effect, which mitigates turbulence at the end and reduces the pressure drop at the inlet of the funnel 15. FIG. 4 further shows a cross section X of the fluid ejector 12.

[0034] Method operations performed by the cooling device 20 for cooling at least one OAEHE in a transformer according to embodiments herein will now be described with reference to the flowchart depicted in FIG. 5. The operations do not have to be performed in the order described below and may be performed in any suitable order. Operations performed in some embodiments are marked with dashed boxes. The cooling device 20 comprises at least one impeller-motor device 10, at least one fluid conduit 11, and at least one fluid discharge device 12. The fluid discharge device 12 comprises a fluid inlet for receiving fluid from the at least one fluid conduit 11 and at least one fluid outlet.

[0035] Behavior 501. The cooling device 20 can generate a filtered fluid flow to the at least one impeller-motor device 10. The filter is to avoid having dust and / or particles in the at least one impeller-motor device 10 through the at least one fluid pipe 11 and the at least one fluid ejector 12. The at least one impeller-motor device 10 is located in the housing 16 at a distance of at least 3 meters from the at least one fluid ejector 12. This separation can shift the source of sound to the sound-insulating housing, and thus the operation of the fluid ejector 12 is sound 20-40 dB lower compared to a conventional bladed fan. The housing 16 can be one or more of sound-insulated, insulated, includes a thermal insulating material, humidity-controlled, dust-proof and / or sound-absorbing.

[0036] Operation 502. The cooling device 20 uses at least one impeller-motor device 10 to supply a fluid flow to at least one fluid conduit 11. The at least one fluid conduit 11 may include a thermal insulating material. The cooling device 20 may comprise a plurality of fluid conduits 11 adapted to supply fluid to a plurality of fluid ejection devices 12.

[0037] Operation 503. The cooling device 20 transports a fluid flow along at least one fluid pipe 11 to the inlet of at least one fluid ejector 12. The at least one fluid ejector 12 has a circular, elliptical, rectangular or any other polygonal cross section. The fluid outlet of the ejector 12 follows the outer periphery of the ejector 12. The cooling device 20 comprises a funnel 15. The at least one fluid ejector 12 may be disposed within the funnel 15. The funnel 15 may have a rounded smooth boundary 18 at the inlet of the funnel 15 to promote the Coanda effect, which mitigates edge turbulence and reduces the pressure drop at the inlet of the funnel 15.

[0038] Operation 504. The cooling system 20 directs the fluid through at least one fluid ejector 12 .

[0039] Operation 505. The cooling device 20 discharges, e.g., ejects, the fluid flow through at least one fluid outlet in the direction of the at least one OAEHE. The fluid ejection device 12 may include at least one slit designed to be narrow enough to change the recited physical properties of the fluid flow by the recited amounts due to the Bernoulli effect, and the cooling device 20 may eject the fluid through the slit in the direction of the at least one OAEHE to cool the OAEHE.

[0040] Operation 506. The cooling device 20 may add an additional fluid flow to the axial area of ​​the fluid ejection device 12 by means of a hose 21 or a second fluid ejection device to intensify and / or homogenize the supplied fluid flow. The second fluid ejection device may be smaller than the fluid ejection device 12. That is, the maximum cross-sectional dimension of the second fluid ejection device may be smaller than the maximum cross-sectional dimension of the fluid ejection device 12.

[0041] According to some embodiments, the cooling device may be equipped with a visual device to verify the functionality of the at least one fluid ejection device 12. The visual device may be useful, for example, if the fluid ejection device 12 becomes clogged.

[0042] As a result, the embodiments herein thus provide a cooling device 20 comprising at least one connected impeller-motor device 10, a fluid tube 11 and a fluid ejector 12 that emits a powerful fluid flow. The impeller-motor device 10 is placed inside a housing 16 that may be protected and sound-proofed and / or may be a thermally insulated, humidity-controlled, dust-proof and sound-absorbing chamber. The fluid tube 11 may be made from a robust and thermally insulating material. An example of a robust and thermally insulating material is a polymer composite material that may include reinforcement such as carbon fiber. For robustness, the fluid tube 11 may also be made from a metal covered by concrete. The fluid ejector 12 has a circular, elliptical, rectangular or any other polygonal cross section. The fluid outlet of the ejector 12 follows the outer periphery of the ejector 12. The outlet of the fluid ejector 12 may comprise a narrow slit through which the fluid exits and heads towards the device to be cooled.

[0043] Table 1. Cooling device 20 solves the problems posed by the application of state-of-the-art solutions.

[0044] [Table 1]

[0045] The embodiments herein provide external cooling to large power transformers. State-of-the-art methods using standard fans generate high noise, have complex structures, are heavy and difficult to maintain. The proposed cooling device 20 is simple, lightweight and easy to maintain. It is also quiet as it has no moving parts at the cooling site. The latter is possible due to the separation of the fluid ejector 12 from the impeller motor device 10, which is confined within a housing that can be sound insulated. The embodiments herein are based on the Bernoulli principle, which allows for an order of magnitude increase in the inlet fluid flow rate provided by the impeller-motor device 10.

[0046] Figures 6a-6f show schematic diagrams according to some embodiments, illustrating various possible embodiments when applying the cooling device 20 to an OAEHE, e.g. a radiator or cooling group, outside the tank of a large power transformer. Figure 6a shows a radiator on a battery with a horizontal cooling device 20. Figure 6b shows a radiator on a battery with a vertical cooling device 20. Figure 6c shows a radiator on a header with a horizontal cooling device 20. Figure 6d shows a radiator on a header with a vertical cooling device 20. Figure 6e shows a radiator on a tank with a horizontal cooling device 20. Figure 6f shows a radiator on a tank with a vertical cooling device 20.

[0047] 7 shows a diagram according to some embodiments of the outlet volumetric flow rate as a function of the inlet volumetric flow rate for various sizes of fluid ejectors 12. A higher number on the vertical axis indicates that a larger fluid ejector 12 provides a significantly better cooling flow rate.

[0048] FIG. 8 shows a schematic diagram according to some embodiments, showing three cooling fluid ejectors 12 with different air flow rates A, B, C. Since the top of the OAEHE is hotter than the bottom, it is possible to design the fluid conduit 11 to provide more fluid flow to the top fluid ejector 12, e.g., the top ring. According to some embodiments, it may be possible to use three interconnected fluid ejectors 12. To avoid high pressure drops, the transition of the fluid conduit 11 may be smooth.

[0049] Figure 9a shows a schematic diagram according to some embodiments, where one way to compensate for the fluid flow in the center region is to share and split the incoming fluid flow with the center hose (bottom left). This has been experimentally verified as shown in the comparative graph in Figure 9b.

[0050] Advantages and benefits of the embodiments herein are as follows: · The size of the fluid ejector 12 is proportional to the fluid flow rate (flexible: can be resized when increased cooling is required).

[0051] · The size of the impeller-motor unit 10 is proportional to the fluid flow rate (flexibility: increased cooling can be utilized when required).

[0052] An additional hose 21 along the axis of the fluid ejection device 12 can increase the fluid flow rate and flow homogeneity.

[0053] The power required for the cooling device 20 is small compared to a conventional bladed fan because the multiplication factor accounts for the flow rate required to cool the OAEHE.

[0054] In temporary over-rating situations, extended cooling fluid flow ranges can be effectively generated as required.

[0055] The cooling system 20 is highly efficient in outdoor environments. The impeller-motor device 10 can be separated from the fluid ejection device 12, making it possible to achieve beneficial operations such as sound insulation resulting from the impeller-motor device 10.

[0056] Noise is reduced by at least 25dB compared to conventional fans (approximately 70dB). Noise is a significant issue for transformers. Reducing noise makes it possible to install transformers closer to residential areas.

[0057] Separating the impeller-motor arrangement 10 and the fluid ejection arrangement 12 also makes it possible to protect the moving parts, e.g. the impeller-motor arrangement 10, from harsh environmental conditions such as snow, rain, lightning, storms, etc.

[0058] · Flexibility in the choice of materials, e.g. metals and / or composites. Robust construction of the cooling unit 20 with no moving parts.

[0059] Because the cooling device has no components that can split or wear, it is more reliable and can therefore be expected to have a much longer lifespan than bladed fans.

[0060] The cooling device 20 does not have dust deposits that cause cleaning difficulties. The cooling device 20 can operate in a wide range of climatic temperatures (-40°C to +60°C).

[0061] The cooling device 20 can be replaced with a standard fan without significant modification.

[0062] For OAEHEs such as radiators, the cooling device 20 does not block the vertical fluid flow (natural convection). The cooling device 20 can be installed under an existing OAEHE to increase the cooling range (forced convection), which allows the power rating of an existing transformer to be increased. By applying the cooling device 20 under the OAEHE to achieve forced convection, the radiators ONAN and OFAN can be turned into ONAF and OFAF, respectively.

[0063] The impeller-motor arrangement 10 is separated from the fluid discharge arrangement 12 and located away from the transformer, so that a constant supply of fresh fluid circulates, thus preventing heating of the fluid around the transformer.

[0064] The cooling device 20 can enable new designs of OAEHEs with reduced footprints.

[0065] · Two cooling devices 20 (one large, one small) facing each other in a sandwich-like configuration for efficient cooling allows higher and more homogenous flow distribution.

[0066] · Multiple cooling devices 20 can be fed from a single powerful impeller-motor device 10 via a fluid duct branching system.

[0067] If necessary, a funnel 15 or flow director can be connected as a flow guide, ensuring that all fluid passes through the OAEHE.

[0068] Improved cooling efficiency reduces the external OAEHE size, thereby reducing the overall weight of the transformer.

[0069] Due to better external cooling efficiency, less oil is required to cool the transformer.

[0070] Simple and easy manufacturing. Reduced maintenance as most components are encapsulated, eliminating risk to personnel during maintenance tasks.

[0071] · Safe for humans and / or animals. It should be noted that any feature of any aspect may be applied to any other aspect, whenever appropriate, and likewise any advantage of any aspect may be applied to any other aspect.

[0072] In general, all terms used in the claims should be interpreted according to their ordinary meaning in the art unless otherwise expressly defined herein. All references to "elements, apparatus, components, means, steps, etc." should be openly interpreted as referring to at least one example of an element, apparatus, component, means, step, etc., unless otherwise specified. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless otherwise specified. The use of "first," "second," etc., for different features / components of the present disclosure is intended only to distinguish that feature / component from other similar features / components, and does not impose any order or hierarchy on that feature / component.

[0073] It will be appreciated that the foregoing description and accompanying drawings represent non-limiting examples of the methods taught herein. As such, the techniques taught herein are not limited by the foregoing description and accompanying drawings. Instead, embodiments herein are limited only by the following claims and their legal equivalents.

Claims

1. A cooling device (20) for cooling at least one oil-to-air external heat exchanger (OAEHE) within a transformer, the cooling device (20) comprising: at least one impeller-motor device (10); at least one fluid pipe (11); at least one fluid discharge device (12) having a fluid inlet for receiving fluid from the at least one fluid pipe (11) and at least one fluid outlet arranged to produce a fluid flow that is uniformly distributed towards the OAEHE; the at least one impeller-motor device (10) being adapted to supply fluid to an inlet of the at least one fluid discharge device (12) via the at least one fluid pipe (11) and to cause the fluid to flow through the at least one fluid discharge device (12), the at least one impeller-motor device (10) being arranged within a housing (16) at a distance of at least one meter from the at least one fluid discharge device (12), the cooling device (20).

2. The cooling device (20) according to claim 1, comprising a plurality of fluid pipes (11) adapted to supply fluid to a plurality of fluid discharge devices (12).

3. The cooling device (20) according to claim 1 or 2, wherein the fluid discharge device (12) comprises at least one slit designed to narrow so as to change the enumerated physical properties of the fluid flow by the enumerated amount due to the Bernoulli effect.

4. The cooling device (20) according to claim 1, wherein the at least one fluid discharge device (12) has a circular, elliptical, rectangular, or any other polygonal cross-section.

5. The cooling device (20) according to claim 1, wherein the at least one fluid discharge device (12) is arranged within a funnel (15).

6. The cooling device (20) according to claim 5, wherein the funnel (15) has a rounded smooth boundary (18) at an inlet of the funnel (15) to promote the Coanda effect, the Coanda effect mitigating end turbulence and reducing the pressure drop at the inlet of the funnel (15).

7. The cooling device (20) according to claim 1, wherein the housing (16) is sound-insulated, heat-insulated, contains heat-insulating material, humidity-controlled, and is one or more of dust-proof and / or sound-absorbing.

8. The cooling device (20) according to claim 1, wherein the at least one fluid pipe (11) contains a heat insulating material.

9. The cooling device (20) according to claim 1, further comprising a hose (21) arranged to intensify and / or homogenize the supplied fluid and / or a second fluid discharge device.

10. The cooling device (20) according to claim 9, wherein the maximum cross-sectional dimension of the second fluid discharge device is smaller than the maximum cross-sectional dimension of the fluid discharge device (12).

11. The cooling device (20) according to claim 1, further comprising a visual device for verifying the function of the at least one fluid discharge device (12).

12. A method performed by a cooling device (20) for cooling at least one oil-to-air external heat exchanger (OAEHE) in a transformer, the cooling device (20) comprising at least one impeller-motor device (10), at least one fluid pipe (11), and at least one fluid discharge device (12) having a fluid inlet for receiving fluid from the at least one fluid pipe (11) and at least one fluid outlet, the method comprising: Supplying a fluid flow to the at least one fluid pipe (11) using the at least one impeller-motor device (10) (502); Transporting the fluid flow to the inlet of the at least one fluid discharge device (12) along the at least one fluid pipe (11) (503); Flowing the fluid through the at least one fluid discharge device (12) (504); Discharging the fluid flow through the at least one fluid outlet in the direction of the at least one OAEHE (505), wherein the at least one impeller-motor device (10) is arranged within a housing (16) at a distance of at least one meter from the at least one fluid discharge device (12).

13. The method according to claim 12, further comprising generating a filtered fluid flow to the at least one impeller-motor device (10) (501).

14. The method according to claim 12 or 13, further comprising adding a further fluid flow to the axial region of the fluid discharge device (12) using a hose (21) or a second fluid discharge device to intensify and / or homogenize the supplied fluid flow (506).

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