WO2025008492A1

WO2025008492A1 - Transformer arrangement having an air duct element, air duct element, and cooling system for cooling a transformer

Info

Publication number: WO2025008492A1
Application number: PCT/EP2024/068952
Authority: WO
Inventors: Alfredo DE LA VEGA-HAZAS ALVAREZ-BARON; Antonio Nogues Barrieras; Carlos Manuel ROY MARTIN; Lorena Cebrian Lles; Juan MAORAD VIDEGAIN; Rafael MURILLO JASO; Fernando MUNOZ ARRIBAS; Vito MURGIDA; Dario Martin DIAZ MEZA
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2023-07-04
Filing date: 2024-07-04
Publication date: 2025-01-09
Anticipated expiration: 2026-01-04
Also published as: EP4489038A1

Abstract

The invention relates to an air duct element which is configured to be attached to a fan air outlet of a fan for cooling a dry-type transformer. The air duct element is configured to divide an airflow generated by the fan and delivered through the fan air outlet into at least a first airflow portion and a second airflow portion. The air duct element is configured to direct the first airflow portion and the second airflow portion to different individual parts of the transformer. The air duct element comprises a first airflow portion opening for outlet of the first airflow portion. The first airflow portion opening has two opposing edge regions which are at least partially curved in an identical direction. The invention further relates to a cooling system comprising an air duct element, and to a dry-type transformer.

Description

TRANSFORMER ARRANGEMENT HAVING AN AIR DUCT ELEMENT, AIR DUCT ELEMENT, AND COOLING SYSTEM FOR COOLING A TRANSFORMER

BACKGROUND

The present disclosure relates to a transformer arrangement comprising an air duct element for cooling a coil assembly and/or a core of the transformer arrangement, a respective air duct element, and a cooling system comprising such an air duct element.

Transformers are used to convert electricity from a first voltage level to an electricity at a second voltage level which is either higher or a lower than the first voltage level. A typical transformer comprises two sets of insulated wire coils - herein also referred to as "windings" for short - around a ferromagnetic core of the transformer, namely a high voltage (HV) winding and low voltage (LV) winding. The LV winding often constitutes an inner winding, and the HV winding an outer winding. When electrical power is applied to one winding that draws power from a source of voltage, it is then magnetically transferred to another winding that delivers power to a load at a transformed voltage. The ratio of turns in one winding to the turns in another winding is the same as the ratio of the voltage of the source to the voltage of the load.

In a dry-type transformer, typically used for power distribution networks, no dielectric liquid is used for insulating the windings. A dry-type transformer performance is principally highly limited by temperature rise during operation due to losses and heat dissipation.

Presently, centrifugal fans with very high air-flow rate are typically used for air-forced cooling of a dry-type transformer. Fig. 1 schematically shows a centrifugal fan 200 positioned in a lower region of a transformer. The transformer comprises a core 500, an inner winding 600, and an outer winding 700. Heat-producing parts of the transformer are primarily its windings and the core. The centrifugal fan 200 generates an airflow 800 directed at the windings 600, 700 and the core 500.

However, a problem here is that much of the air expelled by the centrifugal fan 200 does not specifically reach those parts of the transformer whose cooling is particularly important. This results in an airflow waste and a reduced cooling efficiency. It is also known to use a fan and an air duct coupled to the fan to direct cooling air to a dry-type transformer. However, also here only limited efficiency can be achieved with the known solutions.

Therefore, there is a need for a technology providing improved cooling of a transformer, particularly a dry-type transformer.

SUMMARY

According to the present invention, a transformer arrangement - also referred to here as a transformer for short - is provided which comprises a transformer core, defining a longitudinal axis, a coil assembly wound around the core, the coil assembly comprising a winding, and an air duct element configured and arranged to direct an airflow portion to a bottom end of the winding and/or along an inner or outer surface area of the winding and/or to at least one cooling gap provided in the transformer arrangement for cooling the coil assembly and/or the core. The longitudinal axis may coincide with a main axis of the coil assembly.

A distance between the air duct element and the bottom end of the winding may be less than 50 mm.

The air duct element allows for directing the airflow portion in a particular effective way to the bottom end of the winding and/or along the inner or outer surface area of the winding and/or at least one cooling gap for cooling the coil assembly and/or the core, i.e. to parts of the transformer arrangement whose cooling during operation of the transformer is of particular importance. In this way, an airflow waste or loss can be significantly reduced. The air duct element is particularly suited to be adapted or configured to deliver the airflow portion in a particularly precise manner to respective areas or parts of the transformer arrangement. Air can be substantially prevented from flowing to regions where it is not needed for the desired cooling effect. Moreover, the air duct element can be easily configured such that generation of turbulences is significantly reduced.

Various embodiments may implement one or more of the following features:

The air duct element may comprise a first flow channel inlet opening, a first flow channel outlet opening, a first flow channel extending from the first flow channel inlet opening to the first flow channel outlet opening, thereby defining a first longitudinal extension line. The air duct element may further comprise a second flow channel inlet opening, a second flow channel outlet opening, a second flow channel extending from the second flow channel inlet opening to the second flow channel outlet opening, thereby defining a second longitudinal extension line. The thickness or width of the first flow channel and/or the thickness or width of the second flow channel may change continuously at least along the majority of the length of the respective extension line.

The air duct element may, alternatively or additionally, comprise a first flow channel inlet opening, a first flow channel outlet opening, a first flow channel extending from the first flow channel inlet opening to the first flow channel outlet opening, thereby defining a first longitudinal centerline. The air duct element may further comprise a second flow channel inlet opening, a second flow channel outlet opening, a second flow channel extending from the second flow channel inlet opening to the second flow channel outlet opening, thereby defining a second longitudinal centerline. The cross-sectional areas of the first flow channel normal to the first centerline and/or the cross-sectional areas of the second flow channel normal to the second centerline may change continuously at least along the majority of the length of the respective flow channel or centerline.

The air duct element may, alternatively or additionally, comprise a first flow channel inlet opening, a first flow channel outlet opening, and a first flow channel extending from the first flow channel inlet opening to the first flow channel outlet opening. The air duct element may further comprise a second flow channel inlet opening, a second flow channel outlet opening, and a second flow channel extending from the second flow channel inlet opening to the second flow channel outlet opening. The cross-sectional areas of the first flow channel normal to the longitudinal transformer axis and/or the cross-sectional areas of the second flow channel normal to the longitudinal transformer axis may change continuously at least along the majority of the total length of the respective flow channel. The respective length of the flow channel may be defined in this connection as the length along the longitudinal transformer axis.

This design of the air duct element with its flow channels may allow intensities of the airflow portions, which in use of the transformer emerge from the flow channels and are directed towards the aforementioned parts of the transformer, to be preset or pre-adjusted with particular precision. In particular, air speed may be increased and/or the air flow may be directed toward specific areas, e.g., of the windings.. In other words, the partitioning of the airflow portions between the flow channels may be controlled particularly effectively and/or precisely. Moreover, the direction and speed of the airflow may be adjusted with particular precision.

The extension line may be understood as being defined by the direction of flow of a medium through the channel (e. g., assuming a laminar flow). The extension line may coincide with the channels' longitudinal centerline, extending from the channel's inlet to the channel's outlet. The extension line and centerline may be seen in a radial cross-section along the channel length. The radial cross section refers to the air duct element being in a mounted position in a transformer. Here, radial may refer to a cross section laying in a radial plane with respect to the transformer axis. As discussed above, the transformer axis is defined by the transformer core. Preferably, extension lines and centerlines are present in several different respective radial cross-sections along the channel length.

Thickness - also referred to here as width - of the channel may be understood as being defined by the shortest distance between two opposition sidewalls, preferable when seen in an above mentioned radial cross section. It may be defined, as known in the art, by the sphere method or ray method.

Each channel has a channel inlet opening, which may define an inlet opening plane, the starting point of the respective extension line or centerline laying in said inlet opening plane. Analogously, each channel has an outlet opening, which may define an outlet opening plane, the ending point of the extension line or centerline laying in said outlet opening plane. The length of each flow channel may be defined as the length of its extension line or centerline, i. e. the length between its starting point and its ending point.

Each flow channel inlet opening may have an edge, at least a major portion of which lies in a plane, this plane being referred to here as a respective flow channel inlet opening plane. The starting point of a respective centerline may be defined as a midpoint of the inlet opening, preferably seen in said radial cross-section. . Analogously, each flow channel outlet opening may have an edge, at least a major portion of which lies in a plane, this plane being referred to here as a respective flow channel outlet opening plane. The ending point of a respective centerline may be defined as a midpoint of the outlet opening, preferably seen in said radial cross-section.

The flow channel inlet opening plane and the flow channel outlet opening plane may be parallel, but do not have to be. The cross-sectional areas of the flow channel normal to the centerline may be defined as the circumferentially closed cross-sectional areas of the flow channel normal to the extension or centerline.

The first flow channel inlet opening plane may be identical or parallel to the second flow channel inlet opening plane. Generally speaking, a channel's inlet opening plane may be identical or parallel to another channel's inlet opening plane.

The flow channel inlet opening plane may be normal to the longitudinal axis of the transformer assembly. The flow channel outlet opening plane may be normal to the longitudinal axis of the transformer assembly.

The majority of the length of the flow channel along which the width of the flow channel changes continuously, may be at least 55% of the total length of the first flow channel, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98%.

The majority of the length of the flow channel along which the cross-sectional areas of the flow channel normal to the longitudinal transformer axis change continuously, may be at least 55% of the length of the flow channel, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98% of the flow channel.

The flow channel outlet opening may have a width which differs by at least 3% from the width of the flow channel inlet opening. The flow channel outlet opening may have a width which differs by at most 100% from the width of the first flow channel inlet opening.

The majority of the length of the flow channel or centerline along which the cross- sectional areas of the flow channel change continuously, may be at least 55% of the total length of the flow channel, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98%.

The flow channel outlet opening may have a cross-sectional area normal to the centerline which differs by at least 3% from the cross-sectional area of the flow channel inlet opening. The flow channel outlet opening may have a cross-sectional area normal to the centerline which differs by at most 100% from the cross-sectional area of the flow channel inlet opening.

The width of the flow channel may change when advancing along the extension or centerline, for example, in such a way that it changes by a maximum of 5% or 3% when advancing along the extension or centerline by 1 mm. The width of the flow channel may change when advancing along the extension or centerline, for example, in such a way that it changes by a minimum of 0.01% when advancing along the first extension or centerline by 1 mm.

The cross-sectional areas of the flow channel may change when advancing along the extension or centerline, for example, in such a way that it changes by a maximum of 5% or 3% when advancing along the extension or centerline by 1 mm. The cross-sectional areas of the flow channel may change when advancing along the extension or centerline, for example, in such a way that it changes by a minimum of 0.01% when advancing along the first extension or centerline by 1 mm.

The extension and/or centerline may comprise a curved section.

The curved section may extend over more than 50% of the total length of the respective extension and/or centerline, preferably over more than 60%, preferably over more than 70%, preferably over more than 80%, preferably over more than 90%.

The above specifications may apply with respect to any flow channel of the air duct element.

The first flow channel inlet opening and the second flow channel inlet opening and, if applicable each further flow channel inlet opening may constitute parts of an inlet opening of the air duct element. The air duct element may comprise a housing, wherein the first flow channel inlet opening and the second flow channel inlet opening and, if applicable each further flow channel inlet opening may constitute parts of an inlet opening of the housing of the air duct element. Preferably, the air duct element does not have a common manifold chamber connecting two mor more of the air flow channel inlet openings.

The first flow channel outlet opening and the second flow channel outlet opening and, if applicable each further flow channel outlet opening may constitute outlet openings of the air duct element. The air duct element may comprise a housing, wherein the first flow channel outlet opening and the second flow channel outlet opening and, if applicable each further flow channel outlet opening may constitute outlet openings of the housing of the air duct element.

The flow channel inlet openings of the air duct element may be directly adjacent to each other, separated by a common flow channel wall portion. This may enlarge the overall inlet opening area and improve air flow and thus cooling of a transformer. This may also or alternatively enable a particularly suitable connection to a fan. Preferably, the inlet flow channel openings take more than 80%, preferably more than 90%, even more preferably more than 95% of the air duct element's inlet opening side.

The flow channel outlet openings of the air duct element may be spaced apart from each other. This may enable particularly precise and effective control of the airflow portions leaving the flow channel outlet openings of the air duct element.

The design of the flow channel may be such that the function - or graph of the function - showing the width of the flow channel-in dependence on its location along the extension line does not show a point of discontinuity.

The design of the flow channel may, alternatively or additionally, be such that the function - or graph of the function - showing the cross-sectional areas of the flow channel normal to the centerline in dependence on their location along the centerline does not show a point of discontinuity. This may apply with respect to any flow channel of the air duct element. In other words, it may be said that the flow channel has a smooth inner surface, e.g., without discontinuities or steps.

Similarly, the design of the flow channel may, alternatively or additionally, be such that the function - or graph of the function - showing the cross-sectional areas of the flow channel normal to the longitudinal axis of the transformer assembly in dependence their the location along the longitudinal axis does not show a point of discontinuity.

The air duct element may further comprise a third flow channel inlet opening, a third flow channel outlet opening, a third flow channel extending from the third flow channel inlet opening to the third flow channel outlet opening, thereby defining a third longitudinal extension line. The thickness or width of the third flow channel may change continuously at least along the majority of the total length of the third extension line.

The air duct element may further comprise a third flow channel inlet opening, a third flow channel outlet opening, a third flow channel extending from the third flow channel inlet opening to the third flow channel outlet opening, thereby defining a third longitudinal centerline. The cross-sectional areas of the third flow channel normal to the third centerline may change continuously at least along the majority of the length of the third flow channel or centerline.

The corresponding applies to any further flow channel, if applicable, i. e. for example to a fourth flow channel, a fifth flow channel and so on. The above specifications regarding the first flow channel - including its inlet opening and outlet opening - apply analogously with respect to the second flow channel and each further flow channel of the air duct element where applicable.

The transformer arrangement may comprise a dry-type transformer. The coil assembly may comprise two or more windings. The windings may comprise at least one low- voltage winding and at least one high-voltage winding. The low-voltage winding may be an inner winding and the high-voltage winding may be an outer winding.

The bottom end of the winding may be the downward facing end of the winding when the transformer is set up in an operating position.

The distance is the smallest distance between two parts, e.g., the air duct element and the bottom end of the winding.

The distance may be less than 40 mm, less than 30 mm, less than 20 mm, less than 10 mm, or less than 5 mm. Generally, the smaller the distance, the better the guidance of the airflow. However, a minimum distance is necessary in order not to generate electrical problems between a fan, which may be provided for generating and delivering an airflow into the airduct element, and the winding of the transformer arrangement. This is naturally even more critical in the case of a high-voltage winding than in the case of a low-voltage winding. Thus, minimum distances may differ for high-voltage and low-voltage windings. The minimum distance is also dependent on the power of the transformer arrangement.

The airduct element may be made from a dielectrical material and/or a non- conductive material. This is advantageous because it reduces the risk of undesirable electrical effects being triggered by the airduct element. The airduct element may thus serve as an electric isolation between the transformer and its windings and the fan or other air guiding parts.

The air duct element may be manufactured by additive manufacturing. This particularly allows for a cheap, easy and fast manufacturing option of the airduct element and its particularly suitable geometries.

The air duct element may comprise an airflow portion opening as an outlet of an airflow portion, wherein the shape of the airflow portion opening matches the shape of an outer or inner edge of the bottom end of the winding and/or the inner or outer surface area of the winding, and/or at least one cooling gap provided in the transformer arrangement. In this way, a particularly precise guidance of the airflow portion is further supported. High losses of airflow may further be avoided by such matching shape. Reference to matching shape may be understood as referring to shapes which are aligned to a high degree as regards their geometry, extension and position. For example, the shape of the airflow portion opening may, at the side adjacent the outside or inside of a winding, correspond to the or part of the winding's bottom end's outside or inside geometry. This may, for example, refer to the two- dimensional shape of said winding, e.g., when seen at its footprint.

The airflow portion opening may be at least one of the first flow channel outlet opening, the second flow channel outlet opening, or any further flow channel outlet opening where applicable.

The airflow portion opening may just cover or be aligned with a segment of the bottom end of the winding and/or along an inner or outer surface area of the winding and/or to at least one cooling gap provided in the transformer arrangement for cooling the coil assembly and/or the core. It may thus extend within a spatial area defined or limited by two angular legs of an angle a whose angular vertex coincides with the longitudinal axis, wherein a is between 5° and 350°, preferably between 10° and 270°, preferably between 20° and 180°, preferably between 25° and 100°. Preferably, the angle a lies in a plane perpendicular to the longitudinal axis. For example, the edge of the airflow portion opening may extend in a plane perpendicular to the longitudinal axis, wherein the angle a lies the same plane as the edge of the airflow portion opening.

The airflow portion opening may match the shape of the inner or outer edge of the bottom end of the winding and/or the inner or outer surface area of the winding to such a degree that at least 80% of the airflow exiting the airflow portion opening, preferably at least 90% of the airflow, preferably at least 95% of the airflow, even more preferably at least 98% of the airflow reaches and flows along the inner or outer surface area of the winding and/or at least one cooling gap provided in the transformer arrangement.

The transformer arrangement may further comprise a fan having a fan air outlet, wherein the fan is configured and arranged to generate an airflow and to deliver the airflow through the fan air outlet to an air inlet opening of the air duct element. Inner surfaces of the air duct element for guiding the airflow from the air inlet opening to the airflow portion opening are preferably smooth and without steps or sharp edges. This further reduces generation of turbulences in the airflow and contributes to an efficient cooling. According to a further aspect of the invention, an air duct element is provided which is configured to direct an airflow portion to an outer or inner edge of a bottom end of a winding of a coil assembly of a transformer and/or along an inner or outer surface area of a winding of a coil assembly of a transformer and/or to at least one cooling gap provided in the transformer arrangement.

The air duct element may, alternatively or additionally, comprise a first flow channel inlet opening, a first flow channel outlet opening, a first flow channel extending from the first flow channel inlet opening to the first flow channel outlet opening, thereby defining a first longitudinal centerline, a second flow channel inlet opening, a second flow channel outlet opening, a second flow channel extending from the second flow channel inlet opening to the second flow channel outlet opening, thereby defining a second longitudinal centerline. The cross-sectional areas of the first flow channel normal to the first centerline and/or the cross- sectional areas of the second flow channel normal to the second centerline may change continuously at least along the majority of the length of the respective flow channel.

The extension line and/or center line referred to above is seen in a cross-section of the air duct element, particularly a radial cross-section laying in a radial plane including the longitudinal axis of a transformer to which the air duct element is mounted so as to be in an operative state.

The air duct element may comprise, alternatively or additionally, a first flow channel inlet opening, a first flow channel outlet opening, a first flow channel extending from the first flow channel inlet opening to the first flow channel outlet opening, a second flow channel inlet opening, a second flow channel outlet opening, a second flow channel extending from the second flow channel inlet opening to the second flow channel outlet opening. The cross- sectional areas of the first flow channel normal to a longitudinal axis of the transformer, seen in the air duct element's intended operational state, and/or the cross-sectional areas of the second flow channel normal to the longitudinal axis of the transformer, seen in the air duct element's intended operational state, may change continuously at least along the majority of the length of the respective flow channel. The longitudinal axis of the transformer may coincide with a main axis of the coil assembly of the transformer.

The above specifications with respect to the air duct element as part of a transformer arrangement apply here accordingly. For example, the extension line and the centerline of a flow channel are preferably those seen in a radial cross-section along the channel length, the radial cross-section taken through the longitudinal axis of the core of a respective transformer when the air duct element were in a position relative to the transformer as intended for the installed state.

At least one of the first flow channel outlet opening and the second flow channel outlet opening may match the shape of an outer or inner edge of the bottom end of the winding and/or the inner or outer surface area of the winding, and/or at least one cooling gap provided in the transformer arrangement.

At least one of the first flow channel outlet opening and the second flow channel outlet opening may have a circumferentially closed form extending around the longitudinal axis.

The majority of the length of the respective extension line may be at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98% of the length of the respective extension line.

The majority of the length of the respective flow channel or centerline may be at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98% of the length of the respective flow channel or centerline.

The first flow channel outlet opening may have a width which differs by at least 3% from the width of the first flow channel inlet opening.

The second flow channel outlet opening may have a width which differs by at least 3% from the width of the second flow channel inlet opening. The first flow channel outlet opening may have a cross-sectional area normal to the first centerline which differs by at least 3% from a cross-sectional area of the first flow channel inlet opening normal to the first centerline.

The second flow channel outlet opening may have a cross-sectional area normal to the second centerline which differs by at least 3% from a cross-sectional area of the second flow channel inlet opening normal to the second centerline.

The first flow channel outlet opening may have a width which differs by at most 100% from the width of the first flow channel inlet opening.

The second flow channel outlet opening may have a width which differs by at most 100% from the width of the second flow channel inlet opening.

The first flow channel outlet opening may have a cross-sectional area normal to the first centerline which differs by at most 100% from a cross-sectional area of the first flow channel inlet opening normal to the first centerline.

The second flow channel outlet opening may have a cross-sectional area normal to the second centerline which differs by at most 100% from a cross-sectional area of the second flow channel inlet opening normal to the second centerline.

The first centerline and/or the first extension line and/or the second centerline and/or the second extension line may comprise a curved section.

The curved section may extend over more than 50% of the total length of the respective centerline, preferably over more than 60%, preferably over more than 70%, preferably over more than 80%, preferably over more than 90%.

The first flow channel inlet opening and the second flow channel inlet opening may constitute parts of an inlet opening of the air duct element.

The first flow channel outlet opening and the second flow channel outlet opening may constitute outlet openings of the air duct element.

The design may be such that the function - or the graph of the function - showing the width of the first flow channel in dependence on its location along the first centerline does not show a point of discontinuity. The design may be such that the function - or the graph of the function - showing the width of the second flow channel in dependence on its location along the second centerline does not show a point of discontinuity.

The design may be such that the function - or the graph of the function - showing the cross-sectional areas of the first flow channel normal to the first centerline in dependence on their location along the first centerline does not show a point of discontinuity. The design may be such that the function - or the graph of the function - showing the cross-sectional areas of the second flow channel normal to the second centerline in dependence on their location along the second centerline does not show a point of discontinuity.

The air duct element may further comprise a third flow channel inlet opening, a third flow channel outlet opening, a third flow channel extending from the third flow channel inlet opening to the third flow channel outlet opening, thereby defining a third longitudinal extension line. The thickness or width of the third flow channel may change continuously at least along the majority of the length of the third extension line.

The air duct element may comprise an airflow portion opening for outlet of the airflow portion, for example in the form of the first flow channel outlet opening, the second flow channel outlet opening or any further flow channel outlet opening, where applicable. Preferably, the shape of the airflow portion opening matches the shape of an outer or inner edge of the bottom end of the winding and/or the inner or outer surface area of the winding, and/or at least one cooling gap provided in the transformer arrangement.

The airflow portion opening may have a circumferentially closed form extending around the longitudinal axis. This allows for a particular effective cooling.

According to a further aspect of the present disclosure an air duct element is provided which is configured to be attached to a fan air outlet of a fan for cooling a dry-type transformer, for example an air duct element as described above. The air duct element is configured to divide an airflow generated by the fan and delivered through the fan air outlet into at least a first airflow portion and a second airflow portion. The air duct element is configured to direct the first airflow portion and the second airflow portion to different individual parts of the transformer. Preferably, the air duct element comprises a first airflow portion opening for outlet of the first airflow portion. The first airflow portion opening has two opposing edge regions which are at least partially curved in an identical direction. Preferably, the air duct element is configured to divide the airflow generated by the fan and delivered through the fan air outlet in a controlled manner into at least a first airflow portion and a second airflow portion.

By dividing the airflow in a first airflow portion and a second airflow portion, it is possible to guide cooling air to different specific or individual parts or portions of the transformer. Since the parts of the transformer that generate particularly much heat during operation of the transformer, such as the windings and the core, typically have curved or substantially curved surface areas, the curved opposing edge regions of the first airflow portion opening allow the cooling air to be directed in a particularly targeted manner to the areas to be cooled. In this way, a significantly increased cooling efficiency can be achieved. Moreover, providing the first airflow portion opening with two opposing edge regions which are at least partially curved in an identical direction makes it possible to adapt the first airflow portion opening particularly well to the shape of an area to be cooled, which particularly reduces formation of turbulences in the airflow within the air duct element. This also contributes to the increase in efficiency.

The achievable increase in cooling efficiency allows an increase in transformer power performance to be achieved. For example, a performance increase of about 10 % can be achieved.

Further, the increase in cooling efficiency may allow to reduce the number of airgaps in a winding, e. g. in an LV winding, and/or to reduce the size of such airgaps.

Accordingly, also a reduction of the transformer size and weight can be achieved.

The air duct element is particularly suited for applications where a maximum airflow is set, such as for example in case of wind turbines.

The individual parts of the transformer may be selected from a winding of the transformer, an outer surface area of a winding of the transformer, an inner surface area of a winding of the transformer, a gap area between two windings or within a winding of the transformer, and an outer surface area of a core of the transformer. The winding may be a high voltage winding or a low voltage winding. The low voltage winding may be an inner winding and the high voltage winding may be an outer winding.

For example, the air duct element may be configured to direct the first airflow portion to an outer surface area of an outer winding, and to direct the second airflow portion to an inner surface area of the outer winding or to a gap area between the outer winding an inner winding.

The transformer may have a rated power of for example between 0.5 MVA and 40 MVA.

The air duct element may be made from a dielectrical material and/or a non- conductive material. In this way, unwanted electrical interference of the air duct element with the electrical function of the transformer can be prevented.

The air duct element may be manufactured by additive manufacturing, for example by 3D-printing. This enables particularly cost-effective production of the air duct element. Particularly, in this way, the air duct element can be produced quickly and easily at low cost.

The air duct element may be configured to be reversibly connectable to the fan air outlet.

The first airflow portion opening may comprise an edge extending in a first airflow portion opening plane.

The air duct element may comprise an air inlet opening for receiving the airflow generated by the fan. The air inlet opening may comprise an edge extending in an air inlet opening plane. The edge of the first airflow portion opening may have a length that is greater than the distance between the air inlet opening and the first airflow portion opening. In this way, the distance that the air travels between the air inlet opening and the first airflow portion opening can be kept comparatively short. In this way flow losses within the air duct element can be kept particularly low.

The first airflow portion opening plane and the air inlet opening plane may be parallel. The edge of the first airflow portion opening may have a length that is greater than the distance between the first airflow portion opening plane and the air inlet opening plane.

Alternatively, the first airflow portion opening plane and the air inlet opening plane may include an angle which is greater than 0°. This is generally advantageous with regard to an effective and space-saving arrangement of the fan. The angle may be less than 25°, preferably less than 20°.

At least a segment of the first airflow portion opening may extend along an arc of a first circle. This is a particularly advantageous design because the above-mentioned individual parts of the transformer are typically shaped at least partially circular-cylindrical. However, this is as well advantageous, for example, if a winding to be cooled is shaped so that it has a normal cross-section that is in the form of a square with "rounded corner areas", since the configuration of the first airflow portion opening may be such that the first circle matches the shape of one of the corner areas.

The arc of the first circle may be defined by an angle a of at least 30°, preferably at least 60°, preferably at least 90°. The first airflow portion opening may have a circumferential closed form. For example, the angle a may be 360°.

The first airflow portion opening may have an arcual length S measured along the first circle and a radial thickness Ar measured perpendicular to the first circle, wherein the relation S/Ar fulfills 1.2 < S/Ar < 200, preferably 1.5 < S/Ar < 150, preferably 2 < S/Ar < 100, preferably 2 < S/Ar < 50.

In principle, it is not mandatory that the first airflow portion opening is shaped so that it extends along an arc. In such a case, the first airflow portion opening may extend along a line which is at least partially curved and/or at least partially straight. In this case, the above relations may apply analogously, wherein the "arcual length S" is replaced by the "extension of the first airflow portion opening measured along the line" and the radial thickness Ar is replaced by a thickness perpendicular to the line. This length may also be briefly referred to as the "edge length" of the first airflow portion opening.

The arcual length S or the edge length of the first airflow portion opening may be larger than the distance between the air inlet opening and the first airflow portion opening.

Inner walls of the air duct element forguiding the first airflow portion and the second airflow portion may be shaped stepless. This substantially contributes to reducing formation of turbulences.

The air duct element may further comprise a second airflow portion opening for outlet of the second airflow portion.

The first airflow portion opening and the second airflow portion opening may extend in one plane. Specifically, the edge of the first airflow portion opening and the edge of the second airflow portion opening may extend in one plane. This allows for example the two openings to be positioned particularly close to an outer surface area and an inner surface area of a winding.

The second airflow portion opening may have two opposing edge regions being at least partially curved in an identical direction.

The two opposing edge regions of the first flow portion opening and the two opposing edge regions of the second airflow portion opening may be curved in the identical direction. This allows to fit particularly well to corresponding parts pf the transformer.

At least a segment of the second airflow portion opening may extend along a second circle. The second circle may have a smaller radius than the first circle. The first circle and the second circle may be formed so that they share a same center point.

The second airflow portion opening may be configured analogous to the first airflow portion opening.

The second airflow portion opening may have a circumferential closed form.

The arc of the second circle may be defined by an angle a2 of at least 30°, preferably at least 60°, preferably at least 90°.

The second airflow portion opening may have an arcual length S2 measured along the second circle and a radial thickness Ar2 measured perpendicular to the second circle, wherein the relation S2/Ar2 fulfills 1.2 < S2/Ar2 < 200, preferably 1.5 < S2/Ar2 < 150, preferably 2 < S2/Ar2 < 100, preferably 2 < S2/Ar2 < 50. In the case of a non-circular extension of the second airflow portion opening, the above relationships apply again analogously.

The shape of the first airflow portion opening may be a transformation of the shape of the second airflow portion opening in form of a centric stretching with respect to a center.

The air duct element may be further configured to divide the airflow into a third airflow portion, wherein the air duct element further comprises a third airflow portion opening for outlet of the third airflow portion.

The air duct element may be further configured to divide the airflow into a fourth airflow portion, wherein the air duct element further comprises a fourth airflow portion opening for outlet of the fourth airflow portion. A fifth, sixth, seventh, etc. airflow portion opening may be provided in a corresponding manner.

The first airflow portion opening and the third airflow portion opening may extend in different planes. Specifically, the edge of the first airflow portion opening may extend in a first plane and the edge of the third airflow portion opening may extend in a second plane, wherein the second plane differs from the first plane. The first and the second plane may be parallel. In this way, the first airflow portion opening can be positioned particularly suitably close to a first winding of the transformer and the third airflow portion opening particularly close to a second winding of the transformer extending further down than the first winding. For example, the first airflow portion opening can be positioned particularly suitably close to an outer surface of an outer winding of the transformer and the third airflow portion opening particularly close to, for example below an inner winding of the transformer. The outer winding may be a high voltage winding, and the inner winding may be a low voltage winding. The inner winding may have at least one internal gap. Alternatively, the inner winding may have no internal gap.

The third airflow portion opening may have two opposing edge regions being at least partially curved in an identical direction.

The two opposing edge regions of the first airflow portion opening and the two opposing edge regions of the third airflow portion opening may be curved in the identical direction.

At least a segment of the third airflow portion opening may extend along a third circle. The third circle may have a smaller radius than the second circle. The third circle and the first circle may be formed so that they share a same center point. The arc of the third circle may be defined by an angle a3 of at least 30°, preferably at least 60°, preferably at least 90°.

The third airflow portion opening may be configured analogous to the first airflow portion opening.

The third airflow portion opening may have a circumferential closed form.

The third airflow portion opening may have an arcual length S3 measured along the third circle and a radial thickness Ar3 measured perpendicular to the third circle, wherein the relation S3/Ar3 fulfills 1.2 < S3/Ar3 < 200, preferably 1.5 < S3/Ar3 < 150, preferably 2 < S3/Ar3 < 100, preferably 2 < S3/Ar3 < 50. In the case of a non-circular extension of the third airflow portion opening, the above relationships apply again analogously.

The air duct element may further comprise an additional component configured to direct an airflow portion leaving one of the flow channel outlet openings between the respective flow channel outlet opening and the respective winding and/or cooling gap of the transformer arrangement.

The additional component may be a separate component, configured to be connected to the remaining part of the air duct element.

The additional component may comprise an inlet opening configured to receive the airflow portion leaving the respective one of the flow channel outlet openings, the inlet opening of the additional component being connected to the respective flow channel outlet opening, and at least one outlet opening configured to direct the airflow portion received via the respective flow channel outlet opening further to a respective transformer part. The inlet opening of the additional component may be connected in a fluid-tight way to the respective flow channel outlet opening.

The additional component may comprise at least two outlet openings. For example, the first outlet opening of the additional component may be configured to direct cooling air to an outer surface of a low voltage winding, and/or the second outlet opening of the additional component may be configured to direct cooling air to an inner surface of the low voltage winding.

The at least one outlet opening of the additional component may extend within a spatial area defined by two angular legs of an angle whose angular vertex coincides with the longitudinal axis of the transformer. The at least one outlet opening of the additional component may extend along an arc of a circle, preferably along an arc of the circle having its center on the longitudinal axis of the transformer.

The at least one outlet opening of the additional component - when regarded with respect to the longitudinal axis of the transformer - may extend over a first angular range, and a further one of the flow channel outlet openings of the air duct element, which is not connected to the additional component, may extend over a second angular range, which differs from the first angular range.

For example, the air duct element may comprise a first one of the flow channel outlet openings and a second one of the flow channel outlet openings, with the second one of the flow channel outlet openings being radially closer to the longitudinal axis of the transformer arrangement, and with the additional component being connected to the second one of the flow channel outlet openings, wherein the first one of the flow channel outlet openings extends over a first angular range and the at least one outlet opening of the additional component extends over a second angular range which is larger than the first angular range.

The first angular range may be smaller than 160°, preferably smaller than 150°, preferably smaller than 140°. The difference between the second angular range and the first angular range may be at least 10°, preferably at least 20°, preferably at least 30°, preferably at least 40°.

In a transformer arrangement, the additional component may provide air flow to a low voltage winding. The additional component, with its inlet opening and its at least two outlet openings defines at least first and second flow channels therebetween. The additional components' flow channels may have corresponding geometrical features as discussed further herein above or below with regard to the flow channels of the air duct element. This particularly relates to the discussion of features of cross-sections and/or width with regard to the channels' extension lines and/or longitudinal centerlines.

The additional component may be manufactured by additive manufacturing, made from a di-electrical material and/or a non-conductive material.

The additional component is suitable to be used independently from the air duct element and/or transformer. The present disclosure therefore also relates to an additional component as described herein, without the remaining part of the air duct element as well as to combinations of an additional component and air duct elements as well as to a transformer arrangement with an air duct element and an additional component.

According to a further aspect of the invention, a cooling system for cooling a dry-type transformer is provided which comprises a fan and an air duct element according to the present disclosure. The fan has a fan air outlet and is configured to generate an airflow and to deliver the airflow through the fan air outlet. The air duct element is attached to the fan air outlet.

The air duct element may be directly attached to the fan. The air duct element may comprise an air inlet opening for receiving the airflow generated by the fan. The air inlet opening may be attached particularly in an air-tight manner to the fan air outlet.

The cooling system may comprise an intermediate piece disposed between the fan and the air duct element. The intermediate piece may be coupled directly, particularly in an air-tight manner to the fan air outlet and to the air inlet opening.

According to a further aspect of the invention, a dry-type transformer is provided which comprises a core, a coil assembly wound around the core, and a cooling system according to the present disclosure or an air duct element according to the present disclosure. The coil assembly comprises an outermost winding and an innermost winding.

The outermost winding may be a high-voltage winding. The innermost winding may be a low-voltage winding.

The core may comprise a linear core segment, where the outermost winding and the innermost winding are wound around the linear core segment. The linear core segment may be oriented vertically.

The first airflow portion opening of the air duct element may be configured and arranged to direct the first airflow portion along an outer surface area of the outermost winding.

The second airflow portion opening of the air duct element may be configured and arranged to direct the second airflow portion into a gap area formed by the coil assembly between the outermost winding and the innermost winding or to an inner surface area of the outermost winding.

The third airflow portion opening of the air duct element may be configured and arranged to direct the third airflow portion partially along an outer surface area of the innermost winding and/or partially along an inner surface area of the innermost coil.

The distance between the coil assembly and the air duct element may be less than 10 cm, preferably less than 5 cm.

In particular, the present disclosure comprises the following aspects:

1. A transformer arrangement, comprising a transformer core (50), defining a longitudinal axis (L), a coil assembly wound around the core (50), the coil assembly comprising a winding (60, 70), and an air duct element (2) configured and arranged to direct an airflow portion (62, 64, 66) to a bottom end (69, 79) of the winding (60, 70) and/or along an inner or outer surface area (72, 74; 65, 67) of the winding (60, 70) for cooling the coil assembly and/or the core (50).

2. The arrangement of aspect 1, wherein the air duct element (2) comprises a first flow channel inlet opening (110), a first flow channel outlet opening (10), a first flow channel (210) extending from the first flow channel inlet opening (110) to the first flow channel outlet opening (10), thereby defining a first longitudinal extension line, a second flow channel inlet opening (120), a second flow channel outlet opening (20), a second flow channel (220) extending from the second flow channel inlet opening (120) to the second flow channel outlet opening (20), thereby defining a second longitudinal extension line, wherein the thickness or width of the first flow channel (210) and/or the thickness or width of the second flow channel (220) change continuously at least along the majority of the length of the respective extension line.

2a. The arrangement of aspect 1, preferably the arrangement according to aspect 2, wherein the air duct element (2) comprises a first flow channel inlet opening (110), a first flow channel outlet opening (10), a first flow channel (210) extending from the first flow channel inlet opening (110) to the first flow channel outlet opening (10), thereby defining a first longitudinal centerline (Cl), a second flow channel inlet opening (120), a second flow channel outlet opening (20), a second flow channel (220) extending from the second flow channel inlet opening (120) to the second flow channel outlet opening (20), thereby defining a second longitudinal centerline (C2), wherein the cross-sectional areas of the first flow channel (210) normal to the first centerline (Cl) and/or the cross-sectional areas of the second flow channel (220) normal to the second centerline (C2) change continuously at least along the majority of the length of the respective flow channel (210, 220) or centerline (Cl, C2).

2b. The arrangement of aspect 1, wherein the air duct element (2) comprises a first flow channel inlet opening (110), a first flow channel outlet opening (10), a first flow channel (210) extending from the first flow channel inlet opening (110) to the first flow channel outlet opening (10), a second flow channel inlet opening (120), a second flow channel outlet opening (20), a second flow channel (220) extending from the second flow channel inlet opening (120) to the second flow channel outlet opening (20), wherein the cross-sectional areas of the first flow channel (210) normal to the longitudinal axis (L) and/or the cross-sectional areas of the second flow channel (220) normal to the longitudinal axis (L) change continuously at least along the majority of the total length of the respective flow channel.

2c. The arrangement of any of the preceding aspects, wherein the extension line and/or center line is seen in a cross-section of the air duct element (2), particularly a radial crosssection laying in a plane including the longitudinal axis (L) of the transformer.

3. The arrangement of any of the preceding aspects, wherein a distance (6) between the air duct element (2) and the bottom end (69, 79) of the winding (60, 70) is less than 50 mm.

4. The arrangement of any the preceding aspects, wherein the majority of the length of the respective extension line along which the thickness or width changes continuously is at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98%.

4a. The arrangement of any the preceding aspects, wherein the majority of the length of the respective flow channel (210, 220) or centerline along which the cross-sectional areas change continuously is at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98%.

5. The arrangement of any of the preceding aspects, wherein the first flow channel outlet opening (10) has a width which differs by at least 3% from the width of the first flow channel inlet opening (110), and/or wherein the second flow channel outlet opening (20) has a width which differs by at least 3% from the width of the second flow channel inlet opening (120).

5a. The arrangement of any of the preceding aspects, wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at least 3% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at least 3% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2).

6. The arrangement of any of the preceding aspects, wherein the first flow channel outlet opening (10) has a width which differs by at most 100% from the width of the first flow channel inlet opening (110), and/or wherein the second flow channel outlet opening (20) has width differs by at most 100% from the width of the second flow channel inlet opening (120).

6a. The arrangement of any of the preceding aspects, wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at most 100% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at most 100% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2).

7. The arrangement of any of the preceding aspects, wherein the first centerline (Cl) and/or first extension line and/or the second centerline (C2) and/or the second extension line comprises a curved section.

8. The arrangement of aspect 7, wherein the curved section extends over more than 50% of the total length of the respective centerline (Cl, C2) or extension line, preferably over more than 60%, preferably over more than 70%, preferably over more than 80%, preferably over more than 90%. 9. The arrangement of any of the preceding aspects, wherein the first flow channel inlet opening (110) and the second flow channel inlet opening (120) constitute parts of an inlet opening (22) of the air duct element (2).

10. The arrangement of any of the preceding aspects, wherein the first flow channel outlet opening (10) and the second flow channel outlet opening (20) constitute outlet openings of the air duct element (2).

11. The arrangement of any of the preceding aspects, wherein the function showing the width of the first flow channel (210) in dependence on the location of the first extension line does not show a point of discontinuity, and/or wherein the function showing the width of the second flow channel (220) in dependence on the location of the second extension line does not show a point of discontinuity.

11a. The arrangement of any of the preceding aspects, wherein the function showing the cross-sectional areas of the first flow channel (210) normal to the first centerline (Cl) in dependence on the location of the first centerline does not show a point of discontinuity, and/or wherein the function showing the cross-sectional areas of the second flow channel (220) normal to the second centerline (C2) in dependence on the location of the second centerline does not show a point of discontinuity.

12. The arrangement of any of the preceding aspects, comprising the features of aspect 2, the air duct element further comprising a a third flow channel inlet opening (130), a third flow channel outlet opening (30), a third flow channel (130) extending from the third flow channel inlet opening (130) to the third flow channel outlet opening (30), thereby defining a third longitudinal extension line, preferably wherein the thickness or the width of the third flow channel (230) changes continuously at least along the majority of the length of the third extension line. 12a. The arrangement of any of the preceding aspects, comprising the features of aspect 2a, the air duct element further comprising a a third flow channel inlet opening (130), a third flow channel outlet opening (30), a third flow channel (130) extending from the third flow channel inlet opening (130) to the third flow channel outlet opening (30), thereby defining a third longitudinal centerline (C3), preferably wherein the cross-sectional areas of the third flow channel (230) normal to the third centerline (C3) change continuously at least along the majority of the length of the third flow channel (230).

13. The arrangement of any of the preceding aspects, wherein the distance (6) is less than 40 mm, preferably less than 30 mm, preferably less than 20 mm, preferably less than 10 mm.

14. The arrangement of any of the preceding aspects, wherein the airduct element (2) is made from a dielectrical material and/or a non- conductive material; and/or wherein the air duct element (2) is manufactured by additive manufacturing.

15. The arrangement of any of the preceding aspects, comprising the features of aspect 2 or 2a, wherein the shape of at least one of the first flow channel outlet opening (10) and the second flow channel outlet opening (20) matches the shape of an outer or inner edge of the bottom end (69, 79) of the winding (60, 70) and/or the inner or outer surface area (72, 74, 65, 67) of the winding, and/or at least one cooling gap provided in the transformer arrangement.

16. The arrangement of aspect 15, wherein at least one of the first flow channel outlet opening (10) and the second flow channel outlet opening (20) extends within a spatial area defined by two angular legs of an angle a whose angular vertex coincides with the longitudinal axis (L), wherein a is between 5° and 350° or between 5° and 360°, preferably between 10° and 270°, preferably between 20° and 180°, preferably between 25° and 100°. 17. The arrangement of any of aspect 15 or 16, wherein at least one of the first flow channel outlet opening (10) and the second flow channel outlet opening (20) matches the shape of the inner or outer edge of the bottom end (69, 79) of the winding (60, 70) and/or the inner or outer surface area (72, 74, 65, 67) of the winding to such a degree that at least 80% of the airflow exiting the airflow portion opening (10, 20, 30), preferably at least 90% of the airflow, preferably at least 95% of the airflow, even more preferably at least 98% of the airflow reaches and flows along the inner or outer surface area (72, 74, 65, 67) of the winding and/or at least one cooling gap provided in the transformer arrangement.

18. The arrangement of any of the preceding aspects, further comprising a fan (4) having a fan air outlet (42), the fan (4) being configured and arranged to generate an airflow (6) and to deliver the airflow (6) through the fan air outlet (42) to an air inlet opening (22) of the air duct element (2), preferably wherein inner surfaces of the air duct element (2) for guiding the airflow (6) from the air inlet opening (22) to at least one of the first flow channel outlet opening (10) and the second flow channel outlet opening (20) are smooth and without steps or sharp edges.

18b. The arrangement of any of the preceding aspects, comprising two air duct elements (2), provided on opposite sides of the transformer, preferably also comprising two fans (4), one for each air duct element (2).

19. An air duct element (2), configured to direct an airflow portion (62, 64, 66) to an outer or inner edge of a bottom end (69, 79) of a winding (60, 70) of a coil assembly of a transformer and/or along an inner or outer surface area (72, 74, 65, 67) of a winding (60, 70) of a coil assembly of a transformer and/or to at least one cooling gap provided in the transformer arrangement.

20. The air duct element (2) of aspect 19, wherein the air duct element (2) comprises a first flow channel inlet opening (110), a first flow channel outlet opening (10), a first flow channel (210) extending from the first flow channel inlet opening (110) to the first flow channel outlet opening (10), thereby defining a first longitudinal extension line, 1 a second flow channel inlet opening (120), a second flow channel outlet opening (20), a second flow channel (220) extending from the second flow channel inlet opening (120) to the second flow channel outlet opening (20), thereby defining a second longitudinal extension line, wherein the thickness or width of the first flow channel (210) and/or the thickness or width of the second flow channel (220) changes continuously at least along the majority of the length of the respective extension line.

20a. The air duct element (2) of aspect 19, wherein the air duct element (2) comprises a first flow channel inlet opening (110), a first flow channel outlet opening (10), a first flow channel (210) extending from the first flow channel inlet opening (110) to the first flow channel outlet opening (10), thereby defining a first longitudinal centerline (Cl), a second flow channel inlet opening (120), a second flow channel outlet opening (20), a second flow channel (220) extending from the second flow channel inlet opening (120) to the second flow channel outlet opening (20), thereby defining a second longitudinal centerline (C2), wherein the cross-sectional areas of the first flow channel (210) normal to the first centerline (Cl) and/or the cross-sectional areas of the second flow channel (220) normal to the second centerline (C2) change continuously at least along the majority of the length of the respective flow channel (210, 220) or centerline (Cl, C2).

20b. The arrangement of any of the preceding aspects 20 (20 and 20a), wherein the extension line and/or center line is seen in a cross-section of the air duct element (2), particularly a radial cross-section laying in a plane including the longitudinal axis (L) of a transformer to which the air duct element (2) is mounted so as to be in an operative state.

21. The air duct element (2) of aspect 20, wherein at least one of the first flow channel outlet opening (10) and the second flow channel outlet opening (20) matches the shape of an outer or inner edge of the bottom end (69, 79) of the winding (60, 70) and/or the inner or outer surface area (72, 74, 65, 67) of the winding, and/or at least one cooling gap provided in the transformer arrangement; and/or wherein at least one of the first flow channel outlet opening (10) and the second flow channel outlet opening (20) has a circumferentially closed form extending around the longitudinal axis (L).

22. The air duct element (2) of aspect 20 or 21, wherein the majority of the length of the respective extension line along which the width changes continuously is at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98% of the length of the respective extension line.

22a. The air duct element (2) of aspect 20 or 21, wherein the majority of the length of the respective flow channel (210, 220) or centerline along which the cross-sectional areas change continuously is at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98% of the length of the respective flow channel (210, 220) or centerline.

23. The air duct element (2) of any of aspects 20 to 22, wherein the first flow channel outlet opening (10) has a width which differs by at least 3% from the width of the first flow channel inlet opening (110), and/or wherein the second flow channel outlet opening (20) has a width which differs by at least 3% from the width of the second flow channel inlet opening (120).

23a. The air duct element (2) of any of aspects 20 to 22, wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at least 3% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at least 3% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2). 24. The air duct element (2) of any of aspects 20 to 23, wherein the first flow channel outlet opening (10) has a width which differs by at most 100% from the width of the first flow channel inlet opening (110), and/or wherein the second flow channel outlet opening (20) has a width which differs by at most 100% from the width of the second flow channel inlet opening (120).

24a. The air duct element (2) of any of aspects 20 to 23, wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at most 100% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at most 100% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2).

25. The air duct element (2) of any of aspects 20 to 24, wherein the first centerline (Cl) and/or the first extension line, and/or the second centerline (C2) and/or the second extension line comprises a curved section.

26. The air duct element (2) of aspect 25, wherein the curved section extends over more than 50% of the total length of the respective centerline (Cl, C2) or extension line, preferably over more than 60%, preferably over more than 70%, preferably over more than 80%, preferably over more than 90%.

27. The air duct element (2) of any of aspects 20 to 26, wherein the first flow channel inlet opening (110) and the second flow channel inlet opening (120) constitute parts of an inlet opening (22) of the air duct element (2).

28. The air duct element (2) of any of aspects 20 to 27, wherein the first flow channel outlet opening (10) and the second flow channel outlet opening (20) constitute outlet openings of the air duct element (2).

29. The air duct element (2) of any of aspects 20 to 28, wherein the function showing the width of the first flow channel (210) in dependence on the location of the first extension line does not show a point of discontinuity, and/or wherein the function showing the width of the second flow channel (220) in dependence on the location of the second extension line does not show a point of discontinuity.

29a. The air duct element (2) of any of aspects 20 to 28, wherein the function showing the cross-sectional areas of the first flow channel (210) normal to the first centerline (Cl) in dependence on the location of the first centerline does not show a point of discontinuity, and/or wherein the function showing the cross-sectional areas of the second flow channel (220) normal to the second centerline (C2) in dependence on the location of the second centerline does not show a point of discontinuity.

30. The air duct element (2) of any of aspects 20 to 29, further comprising a a third flow channel inlet opening (130), a third flow channel outlet opening (30), a third flow channel (130) extending from the third flow channel inlet opening (130) to the third flow channel outlet opening (30), thereby defining a third longitudinal extension line, preferably wherein the thickness or width of the third flow channel (230) changes continuously at least along the majority of the length of the third extension line.

30a. The air duct element (2) of any of aspects 20 to 29, further comprising a a third flow channel inlet opening (130), a third flow channel outlet opening (30), a third flow channel (130) extending from the third flow channel inlet opening (130) to the third flow channel outlet opening (30), thereby defining a third longitudinal centerline (C2), preferably wherein the cross-sectional areas of the third flow channel (230) normal to the third centerline (C3) change continuously at least along the majority of the length of the third flow channel (230) or centerline. 31. An air duct element (2) configured to be attached to a fan air outlet (42) of a fan (4) for cooling a dry-type transformer, preferably the air duct element of aspect 19 to 30a, wherein the air duct element (2) is configured to divide an airflow (6) generated by the fan (4) and delivered through the fan air outlet (42) into at least a first airflow portion (62) and a second airflow portion (64), wherein the air duct element (2) is configured to direct the first airflow portion (62) and the second airflow portion (64) to different individual parts of the transformer.

32. The air duct element (2) of aspect 31, wherein the first channel outlet opening (10) has two opposing edge regions (12, 14) being at least partially curved in an identical direction.

33. The air duct element of aspect 31 or 32, wherein the individual parts of the transformer are selected from a winding (60, 70) of the transformer, an outer surface area (72) of a winding (70) of the transformer, an inner surface area (74) of a winding of the transformer, a gap area (80) between two windings (60, 70) or within a winding of the transformer, and an outer surface area (52) of a core (50) of the transformer.

34. The air duct element of any of aspects 31 to 33, wherein the air duct element (2) comprises an air inlet opening (22) for receiving the airflow (6) generated by the fan (4), wherein the edge of the first flow channel outlet opening (10) has a length that is greater than the distance between the air inlet opening (22) and the first flow channel outlet opening (10).

35. The air duct element of any of aspects 31 to 34, wherein at least a segment of the first flow channel outlet opening (10) extends along an arc of a first circle.

36. The air duct element of aspect 35, wherein the arc of the first circle is defined by an angle a of at least 30°, preferably at least 60°, preferably at least 90°.

37. The air duct element of any of aspects 31 to 36, wherein the first flow channel outlet opening (10) has a circumferential closed form. 38. The air duct element of any of aspects 31 to 37, comprising the features of aspect 35, wherein the first airflow portion opening (10) has an arcual length S measured along the first circle and a radial thickness Ar measured perpendicular to the first circle, wherein the relation S/Ar fulfills 1.2 < S/Ar < 200, preferably 1.5 < S/Ar < 150, preferably 2 < S/Ar < 100, preferably 2 < S/Ar < 50.

39. The air duct element of aspect 38, comprising the features of aspect 32, wherein the arcual length S of the first airflow portion opening (10) is larger than the distance between the air inlet opening (22) and the first flow channel outlet opening (10).

40. The air duct element of any of aspects 31 to 39, wherein inner walls of the air duct element (2) for guiding the first airflow portion (62) and the second airflow portion (64) are shaped stepless.

41. The air duct element of any of aspects 31 to 40, wherein the air duct element (2) further comprises a second flow channel outlet opening (20) for outlet of the second airflow portion (64).

42. The air duct element of aspect 41, wherein the first flow channel outlet opening (10) and the second flow channel outlet opening (20) extend in one plane.

43. The air duct element of aspect 41 or 42, wherein the second flow channel outlet opening (20) has two opposing edge regions (22, 24) being at least partially curved in an identical direction.

44. The air duct element of aspect 43, wherein the two opposing edge regions (12, 14) of the first flow channel outlet opening (10) and the two opposing edge regions (22, 24) of the second flow channel outlet opening (20) are curved in the identical direction.

45. The air duct element of any of aspects 41 to 44, wherein at least a segment of the second flow channel outlet opening (20) extends along an arc of a second circle. 46. The air duct element of aspect 45, wherein the first circle and the second circle are formed so that they share a same center point (M).

46a. The air duct element of any of aspects 31 to 46, comprising the features of aspect 41, wherein the first flow channel opening (10) extends along an arc of a first circle, and the second flow channel opening (20) extends along an arc of a second circle, the arc of the first circle being defined by an angle a, and the arc of the second circle being defined by an angle P which is greater than the angle a, wherein preferably the first circle has a larger radius than the second circle.

47. The air duct element of any of aspects 31 to 46, wherein the air duct element (2) is further configured to divide the airflow (6) into a third airflow portion (66), wherein the air duct element (2) further comprises a third flow channel outlet opening (30) for outlet of the third airflow portion (66).

48. The air duct element of aspect 47, wherein the first flow channel outlet opening (10) and the third flow channel outlet opening (30) extend in different planes.

49. The air duct element of aspect 47 or 48, wherein the third flow channel outlet opening (30) has two opposing edge regions (32, 34) being at least partially curved in an identical direction.

50. The air duct element of aspect 49, wherein the two opposing edge regions (12, 14) of the first flow channel outlet opening (10) and the two opposing edge regions (32, 34) of the third flow channel outlet opening (30) are curved in the identical direction.

51. The air duct element of any of aspect 47 to 50, wherein at least a segment of the third flow channel outlet opening (30) extends along a third circle.

51a. The air duct element of any of aspects 31 to 51, further comprising an additional component (500) configured to direct an airflow portion leaving one of the flow channel outlet openings (10, 20, 30) between the respective flow channel outlet opening and the respective winding (60, 70) and/or cooling gap of the transformer arrangement.

51b. The air duct element of aspect 51a, the additional component (500) comprising an inlet opening configured to receive the airflow portion leaving the respective one of the flow channel outlet openings (10, 20, 30), the inlet opening of the additional component (500) being connected to the respective flow channel outlet opening, and at least one outlet opening (501, 502) configured to direct the received airflow portion further to a respective transformer part.

51c. The air duct element of any of aspects 51a to 51b, wherein the inlet opening of the additional component (500) is fluid-tightly connected to the respective flow channel outlet opening (10, 20, 30).

51d. The air duct element of any of aspects 51a to 51c, wherein the additional component (500) comprises at least two outlet openings (501, 502).

51e. The air duct element of any of aspects 51a to 51d, comprising the features of aspect 41, wherein - with respect to the longitudinal axis (L) of the transformer - the at least one outlet opening (501, 502) of the additional component (500) extends over a first angular range (61), and wherein a further one of the flow channel outlet openings (10, 20, 30) of the air duct element (2), which is not connected to the additional component (500), extends over a second angular range (62), which differs from the first angular range.

51f. The air duct element of aspect 51e, wherein - with respect to the longitudinal axis (L) of the transformer - the air duct element (2) comprises a first one (10) of the flow channel outlet openings (10, 20, 30) and a second one (30) of the flow channel outlet openings (10, 20, 30), the second one (30) of the flow channel outlet openings being radially closer to the longitudinal axis (L) of the transformer arrangement, with the additional component (500) being connected to the second one (30) of the flow channel outlet openings, wherein the first one (10) of the flow channel outlet openings extends over a first angular range (61) and the at least one outlet opening (501, 502) of the additional component (500) extends over a second angular range (62) which is larger than the first angular range (61).

51g. The air duct element of any of aspect 51f to 51f, wherein the first angular range (61) is smaller than 160°, preferably smaller than 150°, preferably smaller than 140°, and/or wherein the difference between the second angular range (62) and the first angular range (61) is at least 10°, preferably at least 20°, preferably at least 30°, preferably at least 40°.

52. A cooling system for cooling a dry-type transformer, comprising a fan (4) having a fan air outlet (42), and being configured to generate an airflow (6) and to deliver the airflow (6) through the fan air outlet (42), and at least one air duct element (2) according to any of aspects 31 to 51, attached to the fan air outlet (42).

53. A dry-type transformer, comprising a core (50), a coil assembly wound around the core (50), the coil assembly comprising at least one winding, for example an outermost winding (70) and an innermost winding (60), and a cooling system according to aspect 52 or an air duct element (2) according to any of aspects 31 to 51 for cooling the coil assembly and/or the core (50).

54. The dry-type transformer of aspect 53, wherein the first flow channel outlet opening (10) of the air duct element (2) is configured and arranged to direct the first airflow portion (62) along an outer surface area (72) of the outermost winding (70).

55. The dry-type transformer of aspect 53 or 54, wherein the second flow channel outlet opening (20) of the air duct element (2) is configured and arranged to direct the second airflow portion (64) into a gap area (80) formed by the coil assembly between the outermost winding (70) and the innermost winding (60).

56. The dry-type transformer of any of aspects 53 to 55, wherein the third flow channel outlet opening (30) of the air duct element (2) is configured and arranged to direct the third airflow portion (66) partially along an outer surface area of the innermost winding (60) and/or partially along an inner surface of the innermost winding (60).

57. The dry-type transformer of any of aspects 53 to 56, wherein the distance 6 between the coil assembly and the air duct element (2) is less than 10 cm, preferably less than 5 cm.

SHORT DESCRIPTION OF THE DRAWINGS

The subject-matter of the disclosure will be explained in more detail with reference to preferred exemplary embodiments which are illustrated in the attached drawings.

Fig. 1 is a schematic view of lower region of a transformer and a fan for cooling the transformer according to prior art.

Fig. 2 is a view of a lower region of a transformer comprising three coil assemblies, each coil assembly provided with a cooling system according to the present disclosure.

Fig. 3 is a perspective view of a first one of the cooling systems.

Fig. 4 is an enlarged section of Fig. 3.

Fig. 5 is a schematic cross-sectional view of an air duct element according to the present disclosure and adjacent portions of a fan and a transformer. Fig. 6 is a perspective view of a separated air duct element according to the present disclosure.

Fig. 7 is a rear view of the lower region of the transformer shown in Fig. 2.

Fig. 8a is a schematic sectional view of a core, an inner winding, and outer winding and an air duct element.

Fig. 8b is a schematic sectional view of a core, an inner winding, and outer winding and an alternatively shaped air duct element.

Fig. 9 is a schematic cross-sectional view of a lower portion of a transformer arrangement according to the present invention.

Fig. 10 is a schematic cross-sectional view of a further embodiment of an air duct element according to the present disclosure and adjacent portions of a transformer.

Fig. 11 is a more detailed view of the air duct element of Fig. 10.

Fig. 12 shows examples of two further design options for an air duct element.

Fig. 13 shows an example of an air duct element provided with an additional component, here exemplarily attached to the third flow channel outlet opening.

Fig. 14 shows a variation of the air duct element of Fig. 13, comprising a further first airflow portion opening, also referred to as a further first flow channel outlet opening, which is directed towards a further outer surface area of a corresponding winding when in an operative state in a transformer arrangement.

Fig. 15 shows a cross-sectional view perpendicular to the longitudinal axis of a transformer of a portion of a transformer arrangement, comprising two different air duct elements, one as shown in Fig. 13 (on the left), and another one as shown in Fig. 14 (on the right).

Fig. 16 shows a schematic sectional view of a core, an inner winding, and outer winding and air duct elements each of which comprising an additional component.

DETAILED DESCRIPTION

Fig. 2 is a view of a lower region of a dry-type transformer comprising three coil assemblies 7, 7', 7", each coil assembly provided with a corresponding cooling system 5, 5', 5" according to the present disclosure.

The transformer comprises a core having three linear core segments, wherein each coil assembly 7, 7', 7" is wound around a respective linear core segment.

The cooling systems 5, 5', 5" may be of the same configuration. Therefore, only one cooling system 5 is described in more detail below. The corresponding linear core segment is also referred to as "core" in the following for the sake of brevity.

Fig. 3 is a perspective view of the cooling system 5. The cooling system 5 comprises a fan 4 and an air duct element 2 attached to the fan 4. Fig. 4 is an enlarged section of Fig. 3. Fig. 5 shows a corresponding cross-sectional view. The air duct element 2 is preferably made from a dielectric material and may be manufactured by additive manufacturing, e. g. by 3D printing.

The fan 4 is configured to generate an airflow 6 and to deliver the airflow 6 through a fan air outlet 42. The air duct element 2 has an air inlet opening 22 for receiving the airflow 6 generated by the fan 4. The air duct element 2 may comprise a housing, wherein the air inlet opening 22 is an opening of said housing. The air duct element 2 may be attached directly to the fan air outlet 42, as sketched in Fig. 5. This is particularly advantageous if the edge of the fan air outlet 42 and the edge of the inlet opening 22 of the air duct element 2 extend at least approximately in the same plane.

Alternatively, as shown in Fig. 4, the cooling system may further comprise an intermediate piece or adapter 3 which connects the air duct element 2 to the fan 4. This is for example advantageous, if the edge of the fan air outlet 42 and the edge of the inlet opening 22 extend in two different planes which include an angle greater than 0°, since the intermediate piece 3 may be configured in such a case to connect the fan air outlet 42 and the air inlet opening 22 of the airduct element 2 by bridging the corresponding space in between, particularly in an air-tight manner.

The air duct element 2 is configured to divide the airflow 6 generated by the fan 4 and delivered through the fan air outlet 42 into at least a first airflow portion 62 and a second airflow portion 64. The air duct element 2 is configured to direct the first airflow portion 62 and the second airflow portion 64 to different individual parts of the transformer.

In the example illustrated in Fig. 5, an innermost winding 60 and an outermost winding 70 are wound around a linear core segment or core 50 for short.

Generally, more than two windings can be provided around each linear core section. In the example of Fig. 5, the number of windings wound around the core 50, is two so that here the outermost winding is an outer winding 70 and the innermost winding is an inner winding 60. The outer winding 70 comprises a bottom end 79 and the inner winding 60 comprises a bottom end 69.

Barrier elements 90 may be provided in a gap area 80 formed between the inner winding 60 and the outer winding 70. Typically, such barrier elements show practically no or at best little relevance with respect to heat generation by the transformer. Accordingly, the air duct element 2 may be configured not - or at least not specifically - to guide air to the barrier elements 90.

The core 50 extends along a longitudinal axis L which is typically oriented vertically. Fig. 8a shows a schematic cross-sectional view normal to the longitudinal axis L (not to scale). The windings 60, 70 are wound around the core 50 so that, when viewed in the normal crosssection, the core 50, the inner winding 60, and the outer winding 70 may share a common center point M.

In the example illustrated in Fig. 5, the air duct element 2 is configured to direct the first airflow portion 62 to an outer surface area 72 of the outer winding 70 and the second airflow portion 64 to an inner surface area 74 of the outer winding 70.

Fig. 6 shows a perspective view of the separated air duct element 2. The air duct element 2 comprises a first airflow portion opening 10 for outlet of the first airflow portion 62. The first airflow portion opening 10 is also referred to here as a first flow channel outlet opening 10. The first airflow portion opening 10 has two opposing edge regions 12, 14 being at least partially curved in an identical direction. In this way, the shape of the first airflow portion opening 10 can be particularly well adapted to the outer surface area 72 of the outer winding 70 to be cooled.

In the example illustrated in Fig. 6, the first airflow portion opening 10 extends along an arc of a first circle - here having a first radius R1 - defined by an angle a. Preferably, the angle a is at least 30°. The first airflow portion opening 10 may have an arcual length S measured along the first circle and a radial thickness Ar measured perpendicular to the first circle, wherein the relation 2 < S/Ar < 50 is fulfilled.

Generally, as sketched exemplarily in Fig. 8a, the angle a may be 360° so that the first airflow portion opening 10 has a circumferential closed form. In this way a particularly effective cooling of the respective part of the transformer, for example the outer surface area 72 of the outer winding70 can be achieved.

Alternatively, as sketched more simplified in a cross-sectional view in Fig. 8b, only a (true) first segment ol the first airflow portion opening 10 may extend along an arc of a first circle. A second segment o2 may extend for example straight. Also in such a case, the first airflow portion opening 10 may have a circumferential closed form as sketched exemplarily in Fig. 8b.

This may be advantageous for example in a case where a corresponding winding shows a normal cross-section having a shape of a rectangle with "rounded edges", as sketched in Fig. 8b. In this case, the first circle may match advantageously a corresponding rounded edge region of the corresponding winding 70. In the example shown in Fig. 8b, the first segment ol of the first airflow portion opening 10 is shaped so that the first circle has a center point Ml. A third segment o3 of the first airflow portion opening 10 may be shaped so that a corresponding further circle has a further center point M2, and so on. Thus, in the example shown in Fig. 8b, the first airflow portion opening 10 has circumferential closed form, however it is not shaped circular.

However, alternatively and more generally, the first airflow portion opening 10 may be shaped exclusively straight, for example, it may merely extend along the segment indicated by reference sign o2.

In the example shown in Figures 5 and 6, the edge of the air inlet opening 22 and the edge of the first airflow portion opening 10 extend in parallel planes.

It is generally advantageous if the path of the airflow within the air duct element 2 is kept comparatively short. To this end, it is advantageous if the length of the edge of the first airflow portion opening 10 is larger than the distance D, see Fig. 5, between the air inlet opening plane and the first airflow portion opening plane. Preferably, the arcual length S of the first airflow portion opening 10 is larger than the distance D.

In the example shown in Fig. 6, the air duct element 2 further comprises a second airflow portion opening 20 for outlet of the second airflow portion 64. The second airflow portion opening 20 is also referred to here as a second flow channel outlet opening 20.

The configuration may be so that the second airflow portion 64 is directed by the air duct element 2 to an inner surface area 74 of the outer winding 70. Advantageously, the first airflow portion opening 10 and the second airflow portion opening 20 extend in one plane. The second airflow portion opening 30 may extend along an arc of a second circle, having a radius R2 which is smaller than the radius R1 of the first circle. The first and the second circle may share a same center point M.

The air duct element 2 may comprise wall portions 29 separating the first airflow portion 62 and the second airflow portion 64. These wall portions 29 may extend to the plane of the air inlet opening 22. In other words, the air inlet opening 22 may comprise a first part and a second part (or more parts), the first part being designed to receive a first portion of the airflow 6 which forms the first airflow portion 62 after entry into the air duct element 2, and the second part being designed to receive a second portion of the airflow 6 which forms the second airflow portion 64 after entry into the air duct element 2.

The air duct element 2 may be further configured to divide the airflow 6 into a third airflow portion 66, wherein the air duct element 2 further comprises a third airflow portion opening 30 for outlet of the third airflow portion 66. The third airflow portion opening 30 is also referred to here as a third flow channel outlet opening 30. In the example illustrated in Fig. 5, the third airflow portion opening 30 faces the bottom end 69 of the inner winding 60. In the normal cross-section, as exemplarily shown in Fig. 8a, the projection of the third airflow portion opening 30 may include the inner winding 60, specifically, the bottom end 69 of the inner winding.

The configuration may be so that the third airflow portion 66 is directed by the air duct element 2 partially to an outer surface area 65 of the inner winding 60 and partially to an inner surface area 67 of the inner winding 60. Further, the third airflow portion opening 30 may be configured to match the shape of the bottom end 69 of the inner winding 60. Moreover, the inner winding 60 may comprise at least one internal gap extending parallel to the longitudinal axis L throughout the vertical length of the inner winding 60, where the third airflow portion 66 may be directed further through a gap area of the at least one gap of the internal winding 60.

As shown for example in Figures 5 and 6, the first airflow portion opening 10 and the third airflow portion opening 30 may extend in different planes. This is for example particularly advantageous if the inner winding 60 extends further down than the outer winding 70, as exemplarily illustrated in Fig. 5. The air duct element 2 may further comprise wall portions 39 separating the second airflow portion 64 and the third airflow portion 66. These wall portions 39 may extend - as the wall portions 29 - to the plane of the air inlet opening 22.

Fig. 7 shows a variation of an air duct element 2' in which the first airflow portion opening 10' is formed having a shorter length than in the above example. Furthermore, this variation differs in that the air duct element 2' further comprises a "further" first airflow portion opening 10", which is directed towards a further outer surface area of the outer winding 70. These first airflow portion openings 10', 10" may extend along two distinct segments of a common circle. These segments may each be defined by a corresponding angle a as described above. Generally, a plurality of corresponding segments may be provided.

This design can be advantageous, for example, if the outer surface of the outer winding 70 has a radially outwardly projecting region, such as for example a dome region 92. Here, the two first airflow portion openings 10', 10" can advantageously be arranged on both sides of the radially outwardly projecting region or dome region 92.

Fig. 9 is a schematic cross-sectional view of a lower portion of a transformer arrangement, for example the transformer, the front of which is shown exemplarily in Fig. 2 and the rear of which is shown in Fig. 7. The air duct element 2 may be disposed in the front as illustrated in Figures 5 and 9, and a further air duct element 2' according to the abovedescribed variation together with a respective further fan 4' is disposed in the rear, where the outer winding 70 shows the dome region 92. It is noted that Fig. 9 shows the second airflow portion opening (or second flow channel outlet opening) of the air duct element on the left side directed to the lower end of the outer winding 70. However, preferably said opening is directed to an air gap or to the inner surface of the outer winding 70. The same applies, mutatis mutandis, to the air duct element on the right side. Fig. 10 is a schematic cross-sectional view of a further embodiment of an air duct element 2 according to the present disclosure and adjacent portions of a transformer. Fig. 11 is a more detailed view of the air duct element of Fig. 10. The transformer comprises a core 50 defining a longitudinal axis L. A coil assembly of the transformer is wound around the core 50. The coil assembly may comprise an inner or low-voltage winding 60 and an outer or high- voltage winding 70. The cross-sectional view of the air duct element 2 is taken in a radial plane, radial with regard to the transformer longitudinal axis L. The air duct element is mounted in an operative state to provide air flow to the transformer windings.

The air duct element 2 is configured and arranged to direct airflow portions from an overall airflow leaving a fan to the transformer, such as a first airflow portion 62, a second airflow portion 64 and a third airflow portion 66.

The air duct element 2 comprises a first flow channel inlet opening 110, a first flow channel outlet opening 10, and a first flow channel 210 extending from the first flow channel inlet opening 110 to the first flow channel outlet opening 10, thereby defining a first longitudinal extension line and particularly a first longitudinal centerline Cl. The first flow channel 210 is configured to guide the first airflow portion 62. The first centerline Cl may coincide with a first longitudinal extension line of the first flow channel 210.

The air duct element 2 further comprises a second flow channel inlet opening 120, a second flow channel outlet opening 20, and a second flow channel 220 extending from the second flow channel inlet opening 120 to the second flow channel outlet opening 20, thereby defining a second longitudinal centerline C2. The second flow channel 220 is configured to guide the second airflow portion 64. The second centerline C2 may coincide with a second longitudinal extension line of the second flow channel 220.

The air duct element 2 further comprises a third flow channel inlet opening 130, a third flow channel outlet opening 30, and a third flow channel 230 extending from the third flow channel inlet opening 130 to the third flow channel outlet opening 30, thereby defining a third longitudinal centerline C3. The third flow channel 230 is configured to guide the third airflow portion 66. The third centerline C3 may coincide with a third longitudinal extension line of the third flow channel 230.

Generally speaking, an air duct element according to the present disclosure may comprise one, two, three or more flow channels. The first, second and third flow channel inlet openings 110, 120, 130 of the air duct element 2 may be in one plane, referred to here as air inlet opening plane.

The cross-sectional area of the first flow channel inlet opening 110, i. e. the area of the opening in the air inlet opening plane, may differ from the cross-sectional area of the first flow channel outlet opening 10. For example, the cross-sectional area of the first flow channel outlet opening 10 may be smaller than the cross-sectional area of the first flow channel inlet opening 110. However, alternatively, the first flow channel outlet opening 10 may also be larger than the first flow channel inlet opening 10. The cross-sectional area of the first flow channel outlet opening 110 may differ for example by at least 3% from the cross-sectional area of the first flow channel inlet opening 110. The cross-sectional area of the first flow channel outlet opening 110 may differ for example by at most 100% from the cross-sectional area of the first flow channel inlet opening 110. The same applies with respect to each of the other flow channels 220, 230.

The statements made herein with regard to the cross-sectional area equally apply to the width of the channel and/or its inlet and/or outlet opening when seen in a radial cross section; and vice versa.

The cross-sectional areas of the first flow channel 210 normal to the first centerline Cl change continuously at least along a majority of the length of the first flow channel 210. This means that the cross-sectional area of the first flow channel 210 changes continuously when viewed in corresponding normal cross-sections taken in a progressive, quasi-continuous manner along the first centerline Cl. The change in the cross-sectional area may be for example between 0.01% and 5% per mm centerline Cl, preferably between 0.01% and 3%.

The areas of the inlet openings 110, 120, 130 may range between 5'000 mm² and 30'000 mm². The areas of the outlet openings 10, 20, 30 may range between 3'000 mm² and 20'000 mm². The distance between the air inlet opening plane and the first flow channel outlet opening plane may be between 20 mm and 200 mm.

At least one of the centerlines Cl, C2, C3 may comprise a curved section.

As further sketched in Fig. 10, a clamp 400 may be provided in the lower area of the transformer, which serves to keep the core 50 in a compressed state. The third flow channel 230 may be shaped so that it extends around the clamp 400, enabling a particularly spacesaving design. An additional component 500 of the air duct element 2, for example in the form of a flow deflector element may be provided between a flow channel outlet opening, for example the third flow channel outlet opening 30 as exemplarily sketched in Figures 11, 13 and 14, and the respective part of the transformer, for example the bottom end or surfaces 65, 67 of the low voltage winding 60.

The additional component comprises an inlet opening which is fluid-tightly attached to the third airflow channel outlet opening 30 to receive the corresponding airflow portion leaving the third flow channel outlet opening 30.

The additional component 500 comprises two outlet openings 501, 502, a first outlet opening 501 configured to direct cooling air to the outer surface 65 of the low voltage winding 60, and the second outlet opening 502 configured to direct cooling air to the inner surface 67 of the low voltage winding 60. The two outlet openings 501, 502 may each extend along an arc of a circle/circle segment, a first circle corresponding to the first outlet opening 501 having a larger radius than a second circle corresponding to the second outlet opening 502. Both circles may share a same center which preferably is located at least essentially on the longitudinal axis L of the transformer.

Fig. 13 shows that - when regarded with respect to the longitudinal axis L of the transformer - the first flow channel opening 10 extends over a first angular range 61, and the first outlet opening 501 of the additional component 500 extends over a second angular range 62 which is larger than the first angular range 61.

The first angular range 61 may be smaller than 150°, for example between 120° and 140°. The second angular range 62 may be for example between 160° and 178°. Preferably, the second angular range is a bit smaller than 180°. In this way, two corresponding air duct elements may be used to cool a winding of a transformer arrangement, for example by positioning the two air duct elements on opposing sides of a transformer.

The distance between the outlet openings 501, 502 of the additional component 500 and the bottom end of the respective winding, here the low voltage winding 60, is preferably less than 50 mm. With regard to this distance, the above specifications also apply here accordingly.

Fig. 14 shows a variation of the air duct element shown in Fig. 13. Here, the air duct element comprises two first flow channel outlet openings 10', 10" as described above with respect to Fig. 7. (Note that these openings are denominated above as two first airflow portion openings 10', 10".) The shapes of the two outlet openings 501, 502 may comprise a straight section adapted to dome region of a corresponding winding.

Fig. 15 shows a cross-sectional view perpendicular to the longitudinal axis L of the transformer. An air duct element as shown in Fig. 13 is positioned on the left side, and a further air duct element as shown in Fig. 14 is positioned on the opposite side. As can be seen, the outlet openings of the two respective additional components together approximately form a circle.

Fig. 12 shows examples of two further design options for an air duct element. In the example shown on the left, the air duct element has four channels, whereby - in comparison to the example shown in Fig. 11 - an additional channel is used to direct cooling air into a gap located inside the HV winding. In the example shown on the right, unlike the example shown in Fig. 11, the air duct element has two flow channels that direct cooling air to the LV coil, on the one hand to its inner surface and on the other hand to its outer surface.

Fig. 16 shows a schematic sectional view of a core, an inner winding, and outer winding and air duct elements on both sides of the core, each of which comprising an additional component.

As already described above, an air duct element according to the present disclosure is particularly advantageous, since it enables guiding cooled air in a very specific manner to parts of the transformer which need cooling during operation. More specifically, as shown in Fig. 5, the configuration may be such that a distance 6 between the coil assembly, for example a lower edge or bottom end 79 of the outer winding 70, and the air duct element 2, for example the edge of the first airflow portion opening 10, is less than 10 cm, preferably less than 5 cm, even more preferably less than 3 cm, for example less than 2 cm. In this way a particularly high cooling efficiency can be achieved.

Some of the advantages achievable with the invention are listed in the following:

• Cooling air can be guided very precisely and specifically to parts of the transformer which need to be cooled during operation, such as the windings and the core.

• Cooling air can also be supplied to locations that cannot or cannot suitably be supplied with cooling air according to the state of the art. It can be achieved that the cooling air is practically not lost before it reaches the parts to be cooled, for example the windings.

• The air can be guided through a confined space up to the very edge of the windings.

• The technology makes it possible, with comparable performance, to reduce the size, the weight, and the required material of the transformer.

• The disclosed technology is of particular benefit for applications where there are restrictions in the maximum airflow permitted to cool the transformer, such as for example in case of wind turbines.

• The transformer according to the present disclosure allows for a significant increase in the power of the transformer, for example by as much as about 10%.

• The air duct element according to the present disclosure can be easily adapted to requirements of different transformers.

• A cooling system according to the present disclosure is suited to be implemented in a large variety of transformers, regardless of whether they have an enclosure or not.

Claims

1. A transformer arrangement, comprising a transformer core (50), defining a longitudinal axis (L), a coil assembly wound around the core (50), the coil assembly comprising a winding (60, 70), and an air duct element (2) configured and arranged to direct an airflow portion (62, 64, 66) to a bottom end (69, 79) of the winding (60, 70) and/or along an inner or outer surface area (72, 74; 65, 67) of the winding (60, 70) for cooling the coil assembly and/or the core (50), wherein the air duct element (2) comprises a first flow channel inlet opening (110), a first flow channel outlet opening (10), a first flow channel (210) extending from the first flow channel inlet opening (110) to the first flow channel outlet opening (10), thereby defining a first longitudinal centerline (Cl), a second flow channel inlet opening (120), a second flow channel outlet opening (20), a second flow channel (220) extending from the second flow channel inlet opening (120) to the second flow channel outlet opening (20), thereby defining a second longitudinal centerline (C2), wherein the cross-sectional areas of the first flow channel (210) normal to the first centerline (Cl) and/or the cross-sectional areas of the second flow channel (220) normal to the second centerline (C2) change continuously at least along the majority of the length of the respective flow channel (210, 220).

2. The arrangement of claim 1, wherein a distance (6) between the air duct element (2) and the bottom end (69, 79) of the winding (60, 70) is less than 50 mm.

3. The arrangement of the preceding claims, wherein the majority of the length of the respective flow channel (210, 220) is at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98% of the length of the flow channel.

4. The arrangement of any of the preceding claims, wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at least 3% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at least 3% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2), and/or wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at most 100% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at most 100% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2).

5. The arrangement of any of the preceding claims, wherein the first centerline (Cl) and/or the second centerline (C2) comprises a curved section, preferably wherein the curved section extends over more than 50% of the total length of the respective centerline (Cl, C2), preferably over more than 60%, preferably over more than 70%, preferably over more than 80%, preferably over more than 90%.

6. The arrangement of any of the preceding claims, wherein the first flow channel inlet opening (110) and the second flow channel inlet opening (120) constitute parts of an inlet opening (22) of the air duct element (2).

7. The arrangement of any of the preceding claims, wherein the airduct element (2) is made from a dielectrical material and/or a non- conductive material; and/or wherein the air duct element (2) is manufactured by additive manufacturing.

8. The arrangement of any of the preceding claims, further comprising a fan (4) having a fan air outlet (42), the fan (4) being configured and arranged to generate an airflow (6) and to deliver the airflow (6) through the fan air outlet (42) to an air inlet opening (22) of the air duct element (2), preferably wherein inner surfaces of the air duct element (2) for guiding the airflow (6) from the air inlet opening (22) to at least one of the first flow channel outlet opening (10) and the second flow channel outlet opening (20) are smooth and without steps or sharp edges.

9. An air duct element (2), configured to direct an airflow portion (62, 64, 66) to an outer or inner edge of a bottom end (69, 79) of a winding (60, 70) of a coil assembly of a transformer and/or along an inner or outer surface area (72, 74, 65, 67) of a winding (60, 70) of a coil assembly of a transformer and/or to at least one cooling gap provided in the transformer arrangement, wherein the air duct element (2) comprises a first flow channel inlet opening (110), a first flow channel outlet opening (10), a first flow channel (210) extending from the first flow channel inlet opening (110) to the first flow channel outlet opening (10), thereby defining a first longitudinal centerline (Cl), a second flow channel inlet opening (120), a second flow channel outlet opening (20), a second flow channel (220) extending from the second flow channel inlet opening (120) to the second flow channel outlet opening (20), thereby defining a second longitudinal centerline (C2), wherein the cross-sectional areas of the first flow channel (210) normal to the first centerline (Cl) and/or the cross-sectional areas of the second flow channel (220) normal to the second centerline (C2) change continuously at least along the majority of the length of the respective flow channel (210, 220).

10. The air duct element (2) of claim 9, wherein the majority of the length of the respective flow channel (210, 220) is at least 55%, preferably at least 60%, preferably at least 70 %, preferably at least 80 %, preferably at least 90 %, preferably at least 95 %, preferably at least 98%.

11. The air duct element (2) of 9 or 10, wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at least 3% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at least 3% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2), and/or wherein the first flow channel outlet opening (10) has a cross-sectional area normal to the first centerline (Cl) which differs by at most 100% from a cross-sectional area of the first flow channel inlet opening (110) normal to the first centerline (Cl), and/or wherein the second flow channel outlet opening (20) has a cross-sectional area normal to the second centerline (C2) which differs by at most 100% from a cross-sectional area of the second flow channel inlet opening (120) normal to the second centerline (C2).

12. The air duct element (2) of any of claims 9 to 11, wherein the first centerline (Cl) and/or the second centerline (C2) comprises a curved section, preferably wherein the curved section extends over more than 50% of the total length of the respective centerline (Cl, C2), preferably over more than 60%, preferably over more than 70%, preferably over more than 80%, preferably over more than 90%.

13. The air duct element (2) of any of claims 9 to 12, wherein the first flow channel inlet opening (110) and the second flow channel inlet opening (120) constitute parts of an inlet opening (22) of the air duct element (2).