This application claims the benefit of priority to United Kingdom Patent Application No. 2011332.0 filed on Jul. 22, 2020 and is a Continuation Application of PCT Application No. PCT/GB2021/051870 filed on Jul. 21, 2021. The entire contents of each application are hereby incorporated herein by reference.
The present invention relates to a winding assembly of a transformer, a transformer device including the winding assembly, and thermal management of the transformer windings.
In cast resin transformers, the windings are encased in a cast resin dielectric material. Cast resin is often used in the case of high voltage transformers where the isolation requirement between the input and the output circuits is high. The isolation requirements of such transformers usually range from several tens of kV to several hundreds of kV.
Cast resin transformers have many benefits over alternative systems such a liquid cooled transformers. Encasing the windings physically protects them, as well as removing the need for a coolant circulation system and the associated expense and complexity.
However, cast resin cannot typically be used to maintain the isolation requirement in high and medium frequency transformer windings. In such transformers, the loss densities are considerably high, which results in heat generation. The thick layers of cast resin material required to maintain the isolation requirement would create a barrier preventing heat flow from the windings. This would result in unacceptable build-up of heat in the windings, which could cause damage and ultimately failure of the transformer. Therefore, the cast resin method is usually only suitable for transformers with reasonably low winding loss densities, generating low levels of heat.
Instead, in high and medium frequency transformers, conventional paper insulation is typically used to maintain the isolation requirements. This has limited the level of isolation that can be achieved in high power high frequency (HPHF) transformers.
It is desirable to provide an improved thermal management system for transformer windings which allows use of a cast resin dielectric in high and medium frequency transformers, thus eliminating current limitations in the industry.
According to a first preferred embodiment of the present invention, a winding assembly for a transformer is provided. The winding assembly includes a first coil and a second coil, each including a plurality of sets of turns, wherein each set of turns includes one or more individual turns. The winding assembly further includes a first set and a second set of thermally conductive plates, and a resin dielectric material. The plurality of sets of turns of the first coil are interleaved with the plurality of sets of turns of the second coil. The first set of thermally conductive plates is interleaved with the sets of turns of the first coil, with each plate disposed adjacent to one of the sets of turns of the first coil, to transfer heat away from the first coil. The second set of thermally conductive plates is interleaved with the sets of turns of the second coil, with each plate disposed adjacent to one of the sets of turns of the second coil, to transfer heat away from the second coil. The first coil, the second coil, and the first and second sets of thermally conductive plates are encased in the cast resin dielectric material, to electrically insulate first coil and the second coil.
The preferred embodiments of the present invention facilitate efficient removal of heat generated in the windings without degrading the dielectric isolation strength between the input and output windings. This opens up the possibility of achieving very high isolation levels between the windings of high frequency transformers. The preferred embodiments of the present invention allow cast resin to be used to provide the insolation requirements in transformers where cast resin cannot typically be used due to thermal considerations. The thermally conductive plates allow heat to be removed from the windings while they are encased in the cast resin, preventing damage or failure due to overheating. Use of cast resin physically protects the windings, as well as removing the expense and complexity of a coolant circulation system.
In further preferred embodiments, the plates of the first set of thermally conductive plates may be disposed closer to the first coil than to the second coil along a coil winding axis, and the plates of the second set of thermally conductive plates may be disposed closer to the second coil than to the first coil along a coil winding axis.
The plates of each set of thermally conductive plates are positioned close to one of the coils in order to maximize removal of heat from the windings. The separation between each plate and the other winding provides space for the cast resin to fill in order to provide the required electrical isolation. Ensuring each plate is only positioned in direct proximity with one winding helps prevent the possibility of a short between the two windings through the thermally conductive plate.
Each plate of the first set of thermally conductive plates may include one or more elongate portions that are arranged to follow the turns of the first coil and may include one or more gap portions such that the plate does not form a complete turn. Each plate of the second set of thermally conductive plates may include one or more elongate portions that are arranged to follow the turns of the second coil and may include one or more gap portions such that the plate does not form a complete turn.
The elongate potions follow the turns of the coils in order to maximize the area of thermal contact between the thermally conductive plates and the respective coil in order to maximize extraction of heat from the windings. The one or more gap portions in the thermally conductive plates prevent each plate from forming a complete turn, which could lead to electrical shorting and cause failure of the device.
Each plate of the first and second sets of thermally conductive plates may be split into two sections electrically isolated from each other, with the gap portions separating the two sections. Again, this prevents the thermally conductive plates from acting like a shorted turn, which could damage the device due to high currents flowing in the thermally conductive plates.
The two electrically isolated sections of the thermally conductive plates may be symmetrical when viewed along the winding axis of the coil to which that thermally conductive plate is adjacent, and may each be arranged to follow a half turn of the coil. This is beneficial as each thermally conductive plate will transfer an equal share of the generated heat, preventing unnecessarily large thermal gradients.
The thermally conductive plate may be formed as a layer including one or more thermally conductive strip-like portions.
The first and second coils may be formed as a plurality of layers including one or more electrically conductive strip-like portions. The thermally conductive strip-like portions of the thermally conductive plates may at least partially overlap the electrically conductive strip-like portions of the first and second coils.
The strip like portions follow the path of the windings, in order to maximize the area of thermal contact between the plates and the respective coil, while minimizing proximity to other components, such as the other coil, which could lead to electrical shorting.
The thermally conductive strip-like portions may be arranged such that the thermally conductive plate is C-shaped or U-shaped.
The thermally conductive plate may be U-shaped or may include two U-shaped sections in the case of square windings. C-shaped thermally conductive plates may be used in the case of circular windings. The shape of the thermally conductive plates is such that they follow the turns of the windings, to maximize heat transfer from the windings to the thermally conductive plates.
The number of thermally conductive plates in the first set of thermally conductive plates may be equal to the number of sets of turns in the first coil, and each of the sets of turns in the first coil may have one adjacently disposed thermally conductive plate. The number of thermally conductive plates in the second set of thermally conductive plates may be equal to the number of sets of turns in the second coil, and each of the sets of turns in the second coil may have one adjacently disposed thermally conductive plate.
A one-to-one mapping between the thermally conductive plates and the sets of turns of the first and second coils means heat can be removed from each set of turns of each coil, preventing any given set of turns from overheating.
Each plate of the first and second sets of thermally conductive plates may be thermally connected to a cooling structure. The plates of the first set of thermally conductive plates may be thermally connected to a different cooling structure than the plates of the second set of thermally conductive plates, to prevent electrical contact between the two sets of thermally conductive plates.
The cooling structure aids removal of heat from the windings. Having a different cooling structure for each set of thermally conductive plates means that the first and second set of thermally conductive plates are not in electrical contact with each other via the cooling structure, reducing the risk of an electrical short between the two coils via the thermally conductive plates and cooling structure.
Each plate of the first and second sets of thermally conductive plates may be thermally connected to a cooling structure. The plates of the first set of thermally conductive plates may be thermally connected to a different cooling structure than the plates of the second set of thermally conductive plates to prevent electrical contact between the two sets of thermally conductive plates. The two sections of each thermally conductive plate may be thermally connected to different cooling structures to prevent electrical connection between the two sections of a given thermally conductive plate.
Having a different cooling structure for each set of thermally conductive plates and a different cooling structure for each of the two sections of each thermally conductive plate, in other words, a minimum of four cooling structure, reduces the risk of electrical shorting. This arrangement means that electrical contact via the cooling structure is prevented between the two sets of thermally conductive plates, reducing the risk of shorting between the two coils via the thermally conductive plates and cooling structure. Furthermore, electrical contact via the cooling structure between the two sections of a given thermally conductive plate is prevented, preventing the two sections of a thermally conductive plate being connected to form a complete turn.
The cooling structure may be radiating elements that are located outside of the resin dielectric material, and may be attached to the thermally conductive plates via connection portions which extend outside the encasing resin dielectric material.
Radiating elements mounted on the outside of the cast resin dielectric material allow the heat transferred to the thermally conductive plates from the windings to be removed via radiation and convention. Thus, a cast resin dielectric can be used to provide the isolation requirements without causing overheating in devices with high loss densities. The preferred embodiments of the present invention allow the required distance of insulation to be maintained all the way out to the radiation surfaces. Therefore, it is possible to extract the heat out of the windings without degrading the isolation properties of the transformer. An airflow over the radiating elements could be used to increase removal of heat.
The plurality of sets of turns of both the first and second coil may have first and second diameters. The first diameter may be larger than the second diameter. Each of the first set of thermally conductive plates may be disposed adjacent to the sets of turns of the first coil which have the first diameter, and each of the second set of thermally conductive plates may be disposed adjacent to the sets of turns of the second coil which have the first diameter.
Such winding arrangements may be used to mitigate high frequency losses due to the proximity effect. Murata Manufacturing Corporation's ‘pdqb’ type windings are one such arrangement, as detailed in UK patent publication GB2574481, the entire contents of which are incorporated herein by reference.
The sets of turns of the first coil may alternate between having the first diameter and the second diameter, and the sets of turns of the second coil may alternate between having the second diameter and the first diameter.
This winding arrangement provides high mitigation of high frequency losses due to the proximity effect.
The number of thermally conductive plates in the first set of thermally conductive plates may be equal to the number of sets of turns in the first coil with the first diameter, and each of the sets of turns in the first coil with the first diameter may have one adjacently disposed thermally conductive plate. The number of thermally conductive plates in the second set of thermally conductive plates may be equal to the number of sets of turns in the second coil with the first diameter, and each of the sets of turns in the second coil with the first diameter may have one adjacently disposed thermally conductive plate.
A one-to-one mapping between the thermally conductive plates and the sets of turns of the first and second coils with the larger diameter means heat can be removed from each set of turns of each coil, preventing any given set of turns from overheating.
The interconnections in the first coil between the sets of turns with the first diameter and the sets of turns with the second diameter may fit around the thermally conductive plates, and the interconnections in the second coil between the sets of turns with the first diameter and the sets of turns with the second diameter may fit around the thermally conductive plates.
The plurality of sets of turns of the first and second coils may be square shaped, and each thermally conductive plate of the first and second sets of thermally conductive plates may be U-shaped so as to follow the turns of the respective coil.
Square shaped coils allow the device to be more compact. The U-shaped thermally conductive plates follow the turns of the square shaped coils to maximize the area of thermal contact between the thermally conductive plates and the windings.
The first coil, the second coil, and the first and the second sets of thermally conductive plates may be stacked in a laminar configuration. The first and the second coils may share a common winding axis. The laminar configuration allows the device to be more compact and easier to manufacture.
The first set of thermally conductive plates and the second set of thermally conductive plates may be electrically isolated from each other. This can reduce the risk of electrical shorting between the two coils via the two sets of thermally conductive plates.
The first and second coils each include input and output terminals which may extend out of the resin dielectric material so that an electrical can be input and output from the device.
At least one of the thermally conductive plates may be made of aluminium or copper. Such materials have high thermal conductivities to increase the heat removed from the windings, while also being non-magnetic so as to not disrupt the magnetic properties of the device.
According to a second preferred embodiment of the present invention, a transformer device is provided. The transformer device includes a transformer core and the winding assembly of the first preferred embodiment of the present invention.
The preferred embodiments of the present invention can be applied to any transformer windings where both the input and output windings are in a single cast resin unit, with the cast resin providing isolation between the windings. This includes, but is not limited to, HPHF transformers and Murata Corporation's pdqb type transformer windings.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
This application relates to thermal management of transformer windings. In particular, a winding assembly for a transformer device is disclosed. The winding assembly includes first and second coils with a plurality of windings, and a first set and a second set of thermally conductive plates. The first and second coils include a plurality of interleaved sets of turns. The plates of the first and second sets of the thermally conductive plates are interleaved with the sets of turns of the first and second coils respectively, and are disposed adjacent to one of the sets of turns of the first and second coils, respectively, to transfer heat away from the first and the second coils. The first and second coils and the first and second sets of thermally conductive plates are encased in the resin dielectric material.
The transformer core 102 of
In the preferred embodiment of
As can be seen in
The windings pictured in
For example, the windings could include a first and second coil with any number of inner and outer sets of turns. The windings could switch between the inner and outer sets any number of times. For example, in one preferred embodiment each of the first and second coil 302, 304 may each include only one inner set of turns and one outer set of turns. Alternatively, a plurality of inner sets of turns and outer sets of turns could be used in each coil, with multiple switches between the inner sets of turns and outer sets of turns as each of the coils is traversed.
The windings may also differ in shape. For example, a circular arrangement could be used for the first and second coils 302, 304, rather than the square arrangement of
Alternatively, winding arrangements other than pdqb windings could be used. For example, a winding arrangement with helical first and second coils could be used. The helical first and second coils may each include a plurality of sets of turns, containing one or more individual turns. The sets of turns of the first and second coils can be interleaved in a double helix type structure, with interconnections between each of the sets of turns in a given coil. Such a preferred embodiment would not include an inner set of turns. Instead, the sets of turns of the helical coils would take the place of each of the outer set of turns.
Various other winding arrangements could be conceived. Any winding arrangement with interleaved first and second coils that are isolated from each other via cast resin could be used. The first coil and second coil of the winding assembly may be stacked in a laminar configuration. A laminar configuration allows the device to be more compact and easier to manufacture. Whichever winding arrangement is used, each coil may include just one of the sets of thermally conductive plates disposed adjacent to it, as will be discussed below.
The wires in the windings may be a metallic wire such as a copper wire. The wires may be round wire windings or flat wire windings. The wires are insulated to prevent any electrical signal flowing into or through the thermally conductive plates. This can be achieved through various structures or arrangements such as coating the wires, Kapton® tape, or the like.
Returning to
In the preferred embodiment of
In the preferred embodiment of
In this preferred embodiment, each plate of the first and second sets of thermally conductive plates is split into two sections electrically isolated from each other, with gap portions separating the two sections. Each plate of the first set of thermally conductive plates 306a, 306b is partitioned into a first section 306a and a second section 306b. Each plate of the second set of thermally conductive plates 306c, 306d is similarly partitioned into a first section 306c and a second section 306d. In this preferred embodiment, the two sections of each thermally conductive plate are symmetrical about the windings axis of the coil to which that thermally conductive plate is adjacent. The first and second sections of each plate are electrically isolated from each other due to the gap portions, as will be discussed further with respect to
The first and second sections of each thermally conductive plate may be positioned on opposing sides of the outer set of turns 302″, 304″ of the first or second coil 302, 304. For example, when the winding arrangement shown in
In the preferred embodiment of
In the present preferred embodiment, square shaped coils are used, and therefore the strip-like portions of the thermally conductive plates 306 have a U-shaped construction so as to follow the turns of the respective coil and overlap the coil when viewed along the coil winding axis. If a circular winding arrangement was used with circular first and second coils, the thermally conductive plates 306 would have a C-shaped construction in order to overlap with the coil. The strip like portions follow the path of the windings so as to maximize the area of thermal contact between the plates and the respective coil, while minimizing proximity to other components, such as the other coil, which could lead to electrical shorting.
Ensuring that each of the first set 306a, 306b and second set 306c,306d of thermally conductive plates are electrically isolated from each other helps prevent any electrical shorting from occurring between the first coil and the second coil. Each radiating element is only connected to thermally conductive plates in either the first set or the second set of thermally conductive plates, corresponding to only one of either the first coil or the second coil. Therefore, the separation of the first and second sets of thermally conductive plates is maintained all the way out to the radiating surfaces, as shown by the shading in
Furthermore, in the present preferred embodiment, each thermally conductive plate is separated by the gap portions 702 into two sections, labelled by numerals 306a to 306d in
Such an arrangement, along with the gaps 702 between each of the sections of a given thermally conductive plate, means that the sections of the thermally conductive plates are not electrically connected. If the sections of the thermally conductive plates were electrically connected so as to form a complete turn around the winding assembly, the thermally conductive plates would act like a shorted turn. In other words, a high current would flow through them which could cause a failure of the primary function of the device. The gaps 702 are made large enough to prevent a low resistance electrical path from being formed, but not so large as to unnecessarily reduce the thermal contact area between the thermally conductive plates and the set of turns in each of the coils. For example, in some preferred embodiments the gaps may be at least about 10 mm wide within manufacturing and/or measurement tolerances.
The above described arrangement of thermally conductive plates may be used with each of the winding variants discussed in relation to
For example, in a preferred embodiment where each thermally conductive plate is separated into two sections, the sections may be symmetrical about the winding axis of the respective coil, as is the case in the preferred embodiment of
The described preferred embodiment includes each thermally conductive plate being partitioned into two sections. However, in some preferred embodiments, each thermally conductive plate could be partitioned into more than two different sections, with each section attached to a different radiating element to facilitate heat removal. Alternatively, in some preferred embodiments each thermally conductive plate could include only one section. In this case the single section thermally conductive plates could all be arranged on one side of the device, or instead arranged with the thermally conductive plates corresponding to each coil on opposite sides of the device. Various other arrangements are possible, as would be understood by the skilled person.
In the case of the thermally conductive plates including a single section only, the thermally conductive plate may extend further round the outer sets of turns than the U-shaped sections of
In the preferred embodiment of
Although in the preferred embodiment of
Returning to the preferred embodiment of
When fully constructed, the first coil 302, the second coil 304, and the first and second sets of thermally conductive plates 306 are encased in the resin dielectric material. The first set of thermally conductive plates 306a, 306b are spatially separated from the second coil 304 such that, when the winding assembly is encased in the cast resin, a thick layer of resin dielectric material will fill the space between the first set of thermally conductive plates and the second coil to fulfil the isolation requirements between the first and second coils. Similarly, the second set of thermally conductive plates 306c, 306d are spatially separated from the first coil 302 such that, when the winding unit is encased in the cast resin, a thick layer of resin dielectric material will fill the space between the second set of thermally conductive plates and the first coil to fulfil the isolation requirements between the first and second coils. The resin layer between the first and second coils is typically a minimum of about 3 mm thick within manufacturing and/or measurement tolerances.
The plates of each set of thermally conductive plates are positioned close to one of the coils in order to maximize removal of heat from the windings. The resin material between each plate and the other winding provides the required electrical isolation between the first coil 302 and the second coil 304. Ensuring each plate is only positioned in direct proximity with one winding helps prevent the possibility of a short between the two windings through the thermally conductive plate.
As discussed above, high isolation requirements are desired in transformers such as HPHF transformers. Here, the cast resin provides the dielectric insulation between the windings. Each of the thermally conductive plates are positioned close to one of the coils to remove heat from that coil, and the cast resin between each of the thermally conductive plates and the other coil provides the desired isolation strength. In the case of a winding arrangement with inner and outer sets of turns, the cast resin will also provide insulation between the inner sets of turns.
Once the cast resin process is complete the winding assembly of this preferred embodiment will look as shown in
Other known cooling structures could be used in place of the radiating elements 106. For example, other examples of radiating elements could be used, or the thermally conductive plates could instead be attached to a cooling plate or the like to remove the heat extracted from the interior of the winding assembly 104.
The input and output terminals of the first and second coils (not shown in
A number of variations to the described preferred embodiments could be made, as would be understood by the skilled person. For example, various winding arrangements could be used, provided each electrical circuit formed by the thermally conductive plates and corresponding radiating elements is in close proximity with only one of the coils, and is isolated from the other coil by a gap filed with cast resin material. Possible winding arrangements include Murata's pdqb type windings with one or more inner and outer sets of turns, or a double helix type arrangement with a first and second coil. In one preferred embodiment, each of the thermally conductive plates may be placed against a single turn of one of the coils, rather than against sets of turns of each coil.
Other variations include the use of alternative coil shapes, such as circular coils instead of square coils. The shape of the thermally conductive plates can be altered so as to follow to the paths of the windings. Also, round wire windings could be used instead of flat wire windings. In this case, the thermally conductive plates could have a concave, half-cylinder shape so as to increase the contact area with the round wire windings.
The winding axes of the first and second coils are typically the same to make the device more compact and simplify the construction of the device. However, preferred embodiments of the invention are not limited to such an arrangement. The concept can be extended to any winding arrangement where both the input and output windings are encased in cast resin as a single unit, with the cast resin providing isolation between the windings. Winding arrangements where both the input and output windings are cast a single unit, for example, Murata's pdqb windings, are used to maintain the minimum separation between the windings in order to mitigate high frequency losses due to the proximity effect.
The preferred embodiments of the claimed invention allow cast resin to be used to provide the isolation requirements in transformers where cast resin cannot typically be used due to thermal considerations. The thermally conductive plates allow heat to be removed from the windings while they are encased in the cast resin, preventing damage or failure due to overheating. Use of cast resin physically protects the windings, as well as removing the expense and complexity of a coolant circulation system. The preferred embodiments of the claimed invention facilitate efficient removal of heat generated in the windings in without degrading the dielectric isolation strength between the input and output windings. This opens up the possibility of achieving very high isolation levels between the windings of high frequency transformers.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
Number | Date | Country | Kind |
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2011332.0 | Jul 2020 | GB | national |
Number | Date | Country | |
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Parent | PCT/GB2021/051870 | Jul 2021 | US |
Child | 18119731 | US |