Non-liquid immersed transformer

Abstract

A non-liquid-immersed transformer is provided. The transformer includes a magnetic core and a coil winding forming a plurality of winding turns around the magnetic core, as well as a cooling system. The cooling system includes a heat exchanger, a main feed tube and a main return tube, and a cooling pipe for the flow of cooling fluid. The cooling pipe extends at least partially along the coil winding between a first point adjacent to one end of the coil winding and a second point adjacent to the other end of the coil winding. The cooling pipe also includes a plurality of windings to extend the path of the cooling fluid between one end of the winding and one of the main feed tube and the main return tube.

Description

Technical Field

[0001] The present disclosure relates to transformers, and more particularly, to non-liquid immersed transformers including a fluid cooling system. Background Art

[0002] To cool down the transformer, some systems use a gas (e.g., air) to refrigerate its windings or coils. This air cooling can be forced or natural. In the case of forced air cooling, a blowing device (e.g., a fan) can be positioned to blow an air stream to the windings. However, the cooling capacity of this air stream may not be sufficient to dissipate the heat.

[0003] It is also known to cool non-liquid immersed transformers using water coolers, which consist of passing forced air through tubes with a circulating cooling fluid (e.g. water) in order to cool the air flow, and then directing this cold air flow to the coils of the transformer to increase its cooling capacity. This solution presents several drawbacks, such as the necessity of using a housing, which increases the footprint and cost of the transformer.

[0004] Alternative solutions consist in using hollow conductors or metal tubes (for example made of copper or aluminum) as the conducting turns of the transformer windings and also for the circulation of the cooling fluid. The use of these metal tubes involves several drawbacks: such hollow conductor tubes require additional space in order to accommodate the conduits, that is, in order to allow sufficient cooling fluid to flow, and therefore the size, that is, the floor space, not only of the coil windings but also of the entire transformer increases significantly. Moreover, such special winding tubes are difficult and expensive to manufacture. In addition, the relatively large size of these hollow conductors leads to a significant increase in additional losses due to eddy currents in the conductors.

[0005] Another alternative is to use cooling tubes around or inside the transformer coil windings with a dielectric fluid (such as oil, natural ester or synthetic ester fluid) circulating therein. K3 fluids, i.e. dielectric fluids with a flash point above 300°C, can also be used, but they are flammable fluids. In addition, some dielectric fluids can be harmful to the environment in the event of a leak or fire outbreak.

[0006] On the other hand, the use of non-dielectric fluids involves other drawbacks or technical difficulties due to the presence of electric fields inside the transformer and the risk of discharges or other electrical phenomena.

[0007] In summary, it is desirable to provide a cooling solution for non-liquid immersed transformers that is environmentally friendly, has high cooling capacity, is safe in operation, reduces the risk of transformer faults and / or failures, and is cost-effective. Summary of the invention

[0008] A non-liquid immersed transformer is provided. The transformer includes a magnetic core, a coil winding forming a plurality of winding turns around the magnetic core, and a cooling system. The cooling system includes a heat exchanger, a main feed pipe and a main return pipe, and a cooling pipe for the flow of a cooling fluid. The cooling pipe extends at least partially along the coil winding between a first point adjacent to an end of the coil winding and a second point adjacent to the other end of the coil winding. The cooling pipe also includes a plurality of windings to extend the path of the cooling fluid between one end of the winding and one of the main feed pipe and the main return pipe.

[0009] The use of multiple windings provides a longer connecting pipe which extends the path of the cooling fluid, that is, the length travelled by the cooling fluid before reaching the beginning of the winding and / or after leaving the end of the winding, for example between the main feed and / or return pipe and the beginning and / or end of the winding. The longer path increases the resistance of the cooling fluid, which enables the cooling system to work with cooling fluids with low electrical conductivity (such as water), because even if a conductive fluid is used, multiple windings increase the resistivity of such a cooling fluid, thereby reducing the current flow therein. The flow of electric current in the cooling fluid may negatively affect the function of the transformer. The flow of electric current may heat the cooling fluid, and thus the cooling capacity of the fluid is reduced. In addition, the electric current may create additional problems, such as electrolysis, ions and / or the generation of gases.

[0010] Therefore, the cooling system can use water as cooling fluid. Water is cheap, environmentally friendly and non-flammable, which results in a cost-effective, environmentally safe and robust transformer.

[0011] In an example, the plurality of windings may include at least one of a spiral or a serpentine, thereby minimizing the footprint, ie, the overall volume or size, of the transformer. That is, by using a spiral or serpentine-shaped winding, the manufacture of a bulky transformer is avoided.

[0012] In an example, the winding coil may include a cover made of insulating material, which may include entry and exit points for the cooling tubes, wherein the entry and exit points of the housing are the points at which the cooling tubes pass through the housing.

[0013] In an example, the cooling fluid may have a -4 S / m, which further increases the resistivity to prevent current flow within the cooling fluid.

[0014] In an example, the cooling fluid may be water (e.g., distilled and / or deionized water) that also includes additives to mitigate corrosion and increase the temperature range of use while maintaining low conductivity. Additionally, using water in the cooling system provides a cost-effective, environmentally friendly transformer that is safe in operation.

[0015] For example, by using water as a cooling fluid instead of a flammable cooling fluid such as K3 fluid, an environmentally friendly cooling system is provided that is cost effective and includes increased cooling capacity. In addition, because water is not flammable, the risk of fire outbreaks is avoided. Moreover, the use of additives such as antifreeze and / or anti-corrosive substances can further enhance transformer maintenance by preventing premature failures.

[0016] In an example, the transformer may include a first conductive connector arranged at one of the winding turns to electrically connect the inner side of the cooling tube with the turns of the coil winding. In an example, the transformer may include a second conductive connector, such that the first conductive connector may be arranged at one winding turn and the second conductive connector may be arranged at another winding turn.

[0017] The combination of a cooling tube comprising a plurality of windings and at least a first conductive connector enhances performance and improves efficiency of the transformer. The use of a plurality of windings also improves the function of the transformer, including first and second conductive connectors. In an example, the transformer may be a high voltage transformer, i.e., generating voltages from 0.4 kV up to 72 kV and power ratings from 50 kVA to 100 MVA. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Specific embodiments of the present device will now be described by way of non-limiting example with reference to the accompanying drawings, in which:

[0019] Figure 1 schematically illustrates a simplified cross section of a transformer and cooling system according to an example; and

[0020] Figure 2 Schematically shown is a simplified cross section of a transformer and a cooling system according to another example. DETAILED DESCRIPTION

[0021] Figure 1 A dry transformer 1 is depicted, comprising a magnetic core 100 comprising at least one coil winding 300 around a Y-axis, and a cooling system 200 .

[0022] The coil winding 300 may form a plurality of turns (shown as striped lines) around the magnetic core 100: a first turn 301, i.e., the beginning of the winding; a plurality of intermediate turns 302 and a last turn 303, i.e., the end of the winding. Thus, the coil winding 300 may include two ends, i.e., portions of the winding that respectively include the first turn and the last turn of the coil winding.

[0023] The coil winding 300 can be made of a conductive material (e.g., copper or aluminum), which can be covered or coated with an insulating dielectric material (such as polyester or epoxy), except for the ends of a portion of the winding that may need to be accessible (e.g., the ends of a connecting cable to output the generated voltage).

[0024] Despite Figure 1 A single-phase core is depicted in FIG, but in an example, the transformer 1 may be a three-phase core comprising three legs, each leg comprising at least a coil winding according to any disclosed example. In such an example, the windings of the transformer may be connected in a triangle, zigzag or star connection.

[0025] The coil winding 300 may have a cover 400 made of an insulating material, such as epoxy, to protect the active part of the transformer, i.e. the winding turns. The cover 400 may also include a plurality of input / output connections, such as for cooling pipes, for voltage bushings to output the generated voltage, etc. In the example (see Figure 1 ), the cover 400 may include an entry point 401 and an exit point 402.

[0026] Figure 1 Also shown is a cooling system 200, which may include a heat exchanger 210, to which a feed pipe 230 for inputting cold water to the windings of the transformer and a return pipe 240 for outputting heated water from the windings of the transformer are connected. In an example, the feed pipe 230 and the return pipe 240 may be made of a metallic material and / or may be grounded.

[0027] The cooling system 200 may also include a cooling tube 220, which is made of a dielectric material and which may be coupled to the main feed tube 230 and the main return tube 240 at coupling points 221, 222 at its two ends, respectively. The cooling tube 220 may extend at least partially along the coil winding 300 between the first point and the second point, and wherein the cooling tube 220 may form a loop around the axis Y, thereby reducing the footprint, i.e. the volume occupied by the cooling tube. "Extended along the coil winding" means that the cooling tube 220 (or its loop) may be alternatively arranged between adjacent or subsequent winding turns, around the coil winding, in a central vacant space inside the coil winding, or in any combination thereof, such as partially around the coil and partially arranged between adjacent winding turns. By extending the cooling tube 220 along the coil winding, the cooling capacity of the cooling system is improved, because the heat generated at the winding can be more effectively dissipated due to the increased efficiency of the heat transfer solution.

[0028] The cooling tube may include a first point 250 adjacent to the end of the coil winding (i.e. adjacent to the first turn) and a second point 260 adjacent to the other end (i.e. adjacent to the last turn of the coil winding). "End of winding" refers to the part of the winding containing the first turn or the last turn of the coil winding.

[0029] A cooling circuit for the cooling fluid flow can thus be formed, i.e. the cooled cooling fluid can flow from the heat exchanger to a main feed pipe and a cooling pipe (which extends along the coil winding) and finally to a main return pipe which guides the fluid back to the heat exchanger.

[0030] The cooling tube 220 can be made of an insulating material (e.g., plastic), and to accommodate the limitations of each situation (e.g., necessary connections, specific distances or lengths, etc.), the cooling tube 220 can include different parts or tubes joined together (e.g., threaded, bonded, or by any other suitable method) to form the entire cooling tube 220.

[0031] The cooling system 200 may also include a pump 270 to force the cooling fluid through the entire cooling circuit, i.e., from the output of the heat exchanger through the entire cooling circuit and back to the input of the heat exchanger. In an example, the flow of the cooling fluid may be clockwise (see Figure 1 ), i.e. the second point 260 of the cooling tube will be considered as the entry point of the cooling fluid. In another example, the cooling fluid flow may be counterclockwise, i.e. the first point 250 will be the cooling fluid entry point.

[0032] The cooling tube 220 may further include a plurality of windings 281 , 282 , 283 , 284 to extend the path of the cooling fluid between one end of the winding and one of the main feed tube 230 and the main return tube 240 .

[0033] Furthermore, a plurality of windings extending the cooling fluid path may be arranged inside the cover 400, i.e., between the ends of the windings and the entry / exit points 401, 402 of the cover, or outside the cover, i.e., between the entry / exit points of the transformer cover 400 and one of the main pipes. In other words, the windings may be arranged inside or outside the cover 400.

[0034] In an example, multiple windings can be arranged between the main feed duct 230 and the entry point 401; between the entry point 401 and the second point 260 (i.e., the terminal end of the winding); between the first point 250 and the exit point 402 or between the exit point 402 and the main return duct 240.

[0035] In another example, there may be several multiple windings in different locations of the cooling fluid path, such as multiple windings extending the cooling fluid path between each end of the winding and the main feed and return pipes, respectively.

[0036] For example, Figure 1 A cooling tube 220 is shown comprising a plurality of windings 281, 282 arranged outside of a cover 400. A first plurality of windings 281 may be arranged between the main feed tube 230 and an entry point 401;

[0037] Figure 2 A cooling tube 220 is shown comprising a plurality of windings 283, 284 arranged inside a cover 400. A first plurality of winding structures 283 may be arranged between the entry point 401 and the second point 260, and an additional plurality of winding structures 284 may be arranged between the first point 250 and the exit point 402.

[0038] In an example (not shown), the transformer may include at least a first plurality of windings inside the cover and at least another plurality of windings outside the cover, for example, two pluralities of windings inside the cover and two pluralities of windings outside the cover.

[0039] Due to the path of the cooling fluid and because the length of the cooling tube will be extended, a larger volume is required to accommodate the additional length of the cooling tube. In an example, the cooling tube 220 can be coiled around the axis Y, Y1, Y2 to form multiple windings. In an example, the multiple windings can form a spiral. In an example, the multiple windings can form a serpentine.

[0040] By using a plurality of windings having a spiral or serpentine shape, the additional space required (ie due to the extension of the cooling tubes) can thus be minimized. The footprint (ie the overall volume) of the transformer is thus not unnecessarily enlarged.

[0041] In an example, in order to prevent the generation of a high electric field, for example, greater than 1 kV / mm, the ends of the plurality of windings may not be arranged close to each other.

[0042] In an example, the cooling fluid to be introduced into the cooling tube 220 may be water. In an example, the cooling fluid may be distilled and / or deionized water that may additionally include, for example, a coagulant and / or additive to prevent corrosion of the cooling tube and / or increase in the temperature range of use. In an example, the cooling fluid may be a water having a relative humidity of less than 5·10 -4S / m, which substantially mitigates the generation of electric current flow in the fluid, thus avoiding several problems such as heating of the cooling fluid, electrolysis, generation of ions and / or gases.

[0043] In an example (not shown), the transformer 1 may further include a first conductive connector arranged at the cooling tube to electrically connect the inner side of the cooling tube with the turns of the coil winding.

[0044] The conductive connector allows to balance the voltage of the cooling fluid circulating inside the cooling tube and the voltage of the winding turns. The cooling fluid will be in contact with the inside of the cooling tube and thus the cooling fluid will be electrically connected to the coil winding. That is, the voltage of the cooling fluid will be the same as the voltage of the winding turn it is connected to and similar to the voltage of the surrounding turns.

[0045] This substantially prevents high voltage gradients between two (close) points (i.e. the cooling tube and the turns of the coil winding), thereby preventing the generation of large electric fields that could lead to partial discharges or direct flashovers in the interior of the transformer. Partial discharges can severely affect the function of the transformer and can also damage the insulation, leading to premature dielectric aging of the insulation, which will lead to failure. If the insulation cannot withstand the large electric fields, direct flashovers may occur.

[0046] In an example, the transformer may include a second conductive connector such that the first conductive connector may be arranged at a winding turn and the second conductive connector may be arranged at another winding turn. The use of the second conductive connector may be particularly suitable depending on the electrical connection of the transformer core, for example when the transformer has no ground terminal, such as a transformer with a star connection in which the neutral point is grounded.

[0047] The combination of at least the first conductive connector and the cooling tube comprising a plurality of windings enhances the performance and improves the efficiency of the transformer. In the case of comprising the first conductive connector and the second conductive connector, the use of a plurality of windings also improves the function of the transformer.

[0048] Although only a number of specific embodiments and examples are disclosed herein, those skilled in the art will appreciate that other alternative embodiments and / or uses of the disclosed innovations and their obvious modifications and equivalents are possible. In addition, the present disclosure covers all possible combinations of the specific embodiments described. The scope of the present disclosure should not be limited by the specific embodiments, but should only be determined by a fair reading of the appended claims.

Claims

1. A non-liquid immersed transformer, comprising: a magnetic core and a coil winding, the coil winding forming a plurality of winding turns around the magnetic core; A cooling system, the cooling system comprising: Heat exchangers, The main feed and return pipes, and a cooling tube for cooling a fluid flow, the cooling tube extending at least partially along the coil winding between a first point adjacent to one end of the coil winding and a second point adjacent to another end of the coil winding, and wherein The cooling tube includes a plurality of windings to extend a path of the cooling fluid between one end of the winding and one of the main feed tube and the main return tube.

2. The transformer of claim 1, wherein the plurality of windings comprises at least one spiral or serpentine.

3. The transformer according to claim 1 or 2, comprising at least two groups of plural windings extending the path of the cooling fluid between each end of the winding and the main feed duct and the main return duct, respectively.

4. The transformer of claim 1 or 2, wherein the coil winding comprises a cover made of insulating material, the cover comprising entry and exit points for the cooling tubes.

5. The transformer of claim 4, wherein the winding member extends the path between the end of the winding and an entry point and / or an exit point of the coil cover.

6. The transformer according to claim 1 or 2, wherein the cooling tube is made of insulating material.

7. The transformer according to claim 1 or 2, wherein the cooling fluid has a relative humidity of less than 5.10 -4 Conductivity in S / m.

8. The transformer according to claim 1 or 2, wherein the cooling fluid is water.

9. The transformer according to claim 1 or 2, further comprising a first conductive connector arranged at one of the winding turns to electrically connect the inner side of the cooling tube with the turn of the coil winding.

10. The transformer of claim 8, further comprising a second conductive connector, such that the first conductive connector is arranged at one winding turn and the second conductive connector is arranged at another winding turn.

11. The transformer according to claim 1 or 2, wherein the transformer is a high voltage transformer.

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