EP3545536B1

EP3545536B1 - Transformer and transformer assembly

Info

Publication number: EP3545536B1
Application number: EP16798533.2A
Authority: EP
Inventors: Adam Theander; Daniel KRSTIC
Original assignee: Preh GmbH
Current assignee: Preh GmbH
Priority date: 2016-11-22
Filing date: 2016-11-22
Publication date: 2020-10-07
Anticipated expiration: 2036-11-22
Also published as: CN209947601U; EP3545536A1; WO2018095512A1

Description

The present invention relates to a transformer comprising a hollow middle portion extending along a longitudinal axis and enclosing a duct. The coil former further comprises a first end portion and a second end portion each positioned adjacent to the middle portion and opposing each other. The first end portion comprises a cooling portion adapted for conduction cooling of the coil former. The cooling portion comprises cooling ribs extending parallel to the longitudinal axis. The transformer further comprises a magnetic core component extending through the duct and forming a closed loop.
Transformers are used e.g. to transfer electrical energy between two or more electronic circuits via electromagnetic induction. They may be designed to efficiently change AC voltages from one voltage level to another.
Such a transformer is for example disclosed in document RO 128339 A2 . The transformer comprises a coil former around which coil windings are wound and which is adapted to cool these windings. The coil former is formed out of two parts which both comprise cooling fins. The first part has its cooling fins on its top which are integrally formed with a cylindrical surface and a surface from which the heat is taken away. The heat is transmitted to the ambient environment, by convection and conduction.
US 2013/328654 A1 as well as US 2015/061808 A1 each disclose transformers according to the preamble of claim 1.
A general topic when using a transformer is the temperature increase within the magnetic core component and thus within the coil former. This temperature increase is caused by the alternating voltages generating alternating magnetic fields which orient the magnetic elements within the magnetic core component. As these magnetic elements are oriented over and over again the temperature of the magnetic core component increases which results in an energy loss. As the core component is positioned within the coil former around which the windings of the coils are wound also the coil former as well as the windings heat up.
The solutions known from the prior art only provide an insufficient heat transfer away from the magnetic core component and are not adapted to efficiently reduce the temperature of the windings.
It is therefore an object of the present invention to provide a transformer with an improved heat transfer from the magnetic core component in order to reduce the energy loss due to heat increase.
This object is achieved by a transformer comprising the features of claim 1 and by a transformer assembly according to claim 9. Preferred embodiments are set out in the dependent claims.
According to the present invention the magnetic core component has an end face positioned in proximity to the cooling ribs and being oriented perpendicular to the longitudinal axis. The cooling ribs project parallel to the longitudinal axis to such an extent that they are level with the end face of the magnetic core component. The coil former consists of a material having a thermal conductivity in plain of at least 3 W m^-1 K^-1 (Watts meter^-1 Kelvin-1). Due to its highly thermal conductive material the coil former itself is used to transfer the heat away from the magnetic core component and/or the windings into the cooling ribs of the coil former. As the cooling ribs are level to an end face of the magnetic core component they together form a cooling plane. This arrangement enables the magnetic core component as well as the cooling ribs to efficiently transfer the heat away via conduction cooling. In other words, the end face defines a cooling plane up to which the cooling ribs project along the longitudinal axis. Thus, the end face and the cooling ribs are adapted to abut a plane contact surface in order to transfer the heat away from the transformer.
In connection with the present invention the term "highly thermal conductive material" defines a material having a thermal conductivity in plane of at least 3 W m¹ K^-1 Conventional materials used for the production of coil formers are plastics e.g. phenolic having a thermal conductivity in plane of 0,7 W m^-1 K^-1. Experiments in the context of the present invention have shown that the use of highly thermal conductive materials for the production of the coil former results in a significant temperature decrease in the magnetic core component as well as in the windings compared to known solutions. In particular hot spots within the coil former are avoided as the use of highly conductive material leads to a substantially isotherm temperature profile within the component. Thus, the durability of the coil former was also improved.
The method which was used to determine the thermal conductivity in plane of the coil former material is defined in DIN EN821. In the context of the present invention the term "thermal conductivity in plane" defines the ability of a material to conduct heat within the material along a plane.
In a preferred embodiment the coil former consists of a material having a conductivity in plane in the range of 5 W m^-1 K^-1 to 20 W m^-1 K^-1 more preferably in the range of 10 W m^-1 K^-1 to 20 W m^-1 K^-1 most preferably of 15 W m^-1 K^-1. The higher the thermal conductivity in plane of the material the greater is the amount of heat which is transferred away from the magnetic core component and/or the windings by the coil former. On the other hand, the higher the thermal conductivity of the coil former the more expensive is the material. Thus, a compromise between the benefits arising from the use of highly thermal conductive material for the coil former and the production costs arising therefrom has to be found.
Preferably, the coil former consists of a polyphenylsulphone (PPS) having a thermal conductivity in plain of 15 W/(m K) as well as a thermal conductivity through plane of 3,5 W/(m K). However, it has to be understood, that also other materials having a thermal conductivity which lies within the claimed ranges may be used for example such as polyamide 12.
Further according to the present invention, the middle portion has an outer diameter which varies along the longitudinal axis, such that the middle portion comprises a barrel-shaped shell surface. Due to this shape of the shell surface the inner coil windings are positioned around the middle portion out of the fringing flux field generated by the alternating voltages. Thus, the temperature increase of the coil windings caused by the fringing flux field is decreased.
According to another embodiment of the present invention the first end portion has a collar extending in an outward direction perpendicular to the longitudinal axis, wherein the cooling ribs comprise two primary webs positioned on the collar and being located opposite to each other with a distance there-between. Preferably the webs comprise a wing-shape when seen from above, wherein each primary web is at least partially positioned adjacent to the duct of the coil former such that at least a portion of the primary web elongates the duct of the coil former along the longitudinal axis.
In a preferred embodiment the magnetic core component extends from the duct in an outward direction perpendicular to the longitudinal axis in between the opposing primary webs, wherein the end face of the magnetic core component is positioned parallel to the collar. Optionally the magnetic core component almost fills up the distance in between the primary webs. If the end face is positioned parallel to the collar, the cooling rips are thoroughly level with the end face to preferably enable a full-faced contact with a contact surface in order to improve conduction cooling.
Also preferred is an embodiment according to which the cooling ribs further comprise secondary webs connected to one of the primary webs, wherein the secondary webs and the corresponding primary web enclose a pointing angle. The secondary webs increase the surface of the cooling portion in order to increase the amount of heat being transferred from the cooling portion away by conduction cooling.
Optionally, the secondary webs together with the corresponding primary web each form a cooling unit, wherein the cooling units are point symmetric to each other with regard to the longitudinal axis. Preferably, the magnetic core component is positioned such that it almost fills up the distance between the opposing webs, wherein the end face of the magnetic core component is also point symmetric with regard to the longitudinal axis.
Also preferred as an embodiment according to which the coil former is integrally formed and consists of one single piece. This improves the thermal conductivity of the coil former as there are no gaps in between the coil former which would interrupt or reduce the thermal flow flowing through the coil former.
The present invention also relates to a transformer assembly, comprising a casing having a receiving section for receiving a transformer and a transformer according to the present invention positioned within said receiving section. Preferably the casing comprises a contact surface which is abutted by the end face of the transformer as well as by the cooling ribs. Thus, an increased heat transfer from the transformer into the casing is ensured.
Further preferred is an embodiment according to which the receiving section is formed as a tub having a bottom wall and surrounding side walls. In order to further increase the heat transfer between the transformer and the casing the transformer is at least partially surrounded by the tub.
Also preferred is an embodiment according to which the cooling ribs as well as the end face of a magnetic core component abut the bottom wall. Optionally, the longitudinal axis of the coil former is oriented perpendicular to the bottom wall when the cooling ribs as well as the end face comes to rest on the bottom wall of the tub within the casing.
In another embodiment the side walls of the receiving section have cooling ribs oriented parallel to the longitudinal axis of the transformer and extending in a fan-shaped manner away from the longitudinal axis. This increases the cooling surface of the tub through which heat is lead away from the transformer towards the surrounding of the casing.
According to an unclaimed embodiment of the invention, the tub is filled with conductive potting compound. As conductive potting compound has a higher thermal conductivity as air and as the potting compound fills up all gaps in-between the transformer and the tub of the casing this measure improves the heat transfer of the transformer towards the casing.
The invention will be described in the following in connection with various examples of preferred arrangements in the drawings, in which

Fig. 1: shows a perspective view of a transformer assembly,
Fig. 2: shows a perspective view of a transformer according to Fig. 1,
Fig. 3: shows a perspective view of a coil former and
Fig. 4: shows a front view of the coil former according to Fig.3.

Figure 1 shows a transformer assembly 1, comprising a transformer 2 positioned in a receiving section 3 of a casing 4. The receiving section 3 is formed as a tub 5 having a bottom wall (not shown) and surrounding side walls 6. The receiving section 3 is filled with conductive potting compound 7.
The side wall 6 of the receiving section 3 have cooling ribs 8 which are oriented parallel to a longitudinal axis 9 of the transformer 2. The cooling ribs 8 extend in a fan-shaped manner away from the longitudinal axis 9.
Moreover, the casing 4 comprises a cooling pipe 10 positioned underneath the receiving section 3. The cooling pipe may be coupled to a cooling system (not shown) using a cooling liquid streaming through the cooling pipe 10 in order to cool the casing 4.
According to Figure 2 the transformer 2 comprises a coil former 11 around which coil windings 12 of two different coils 13 are wound. The coils 13 are connected to contacts 14 in order to apply an alternating voltage to one of the coils 13 and to pick a second alternating voltage of a different level from the other coil 13.
The transformer 2 further comprises a magnetic core component 15 extending through the coil former 11 and forming a closed loop 16. The magnetic core component 15 is formed out of two pieces 17 each formed as a trident with two outer arms and one inner arm (not shown). Moreover, the magnetic core component 15 has an end face 18 oriented perpendicular to the longitudinal axis 9.
As can be seen in particular in the Figures 3 and 4, the coil former 11 has a hollow middle portion 19, extending along the longitudinal axis 9 and enclosing a duct 20. The duct 20 is adapted to receive the inner arms of the magnetic core component 15, wherein the two pieces 17 of the magnetic core component 15 (Figure 2) are inserted into the duct 20 from below and from above of the coil former 11, respectively, in such a way that the magnetic core component 15 extends through the duct 20.
The middle portion 19 has an outer diameter which varies along the longitudinal axis 9, such that the middle portion 19 comprises a barrel-shaped shell surface 21. Thus, the inner windings of the coil winding 12 which are wound around the middle portion 19 of the coil former 11 are positioned at varying distances relative to the longitudinal axis 9 along the longitudinal axis 9.
The coil former 11 further has a fist end portion 22 and a second end portion 23 each positioned adjacent to the middle portion 19 and opposing each other.
The first end portion 22 comprises a cooling portion 24 adapted for conduction cooling of the coil former 11. A cooling portion 24 comprises cooling ribs 25 extending parallel to the longitudinal axis 9. The cooling ribs 25 project parallel to the longitudinal axis 9 to such an extent that they are level with the end face 18 of the magnetic core component 15 (Figure 2). Thus, when the transformer 2 is put into the receiving section 3 of the casing 4, the cooling ribs 25 as well as the end face 18 of the magnetic core component 15 abut the bottom wall (not shown) of the receiving section 3 (Figure 1).
Referring to Figure 3 and 4, the cooling ribs 25 comprise two primary webs 26 positioned on a collar 27 of the first end portion extending in an outward direction perpendicular to the longitudinal axis 9. The primary webs 26 are located opposite to each other with a distance there between.
The cooling ribs 25 further comprise secondary webs 28, wherein the secondary webs 28 and the corresponding primary web 26 enclose a pointing angle. The Secondary webs 28 together with the corresponding primary web 26 each form a cooling unit 29. The cooling units 29 are point symmetric to each other with regard to the longitudinal axis 9.
The coil former 11 is integrally formed and consists of one single piece. The coil former 11 is made out of a material having a thermal conductivity in plane of at least 3 W/(m K). Preferably, the coil former 11 is made of a PPS. However, it has to be understood that the coil former 11 may be also made out of other materials having a thermal conductivity in plane of at least 3 W/(m K).
As can be seen in particular in figure 2 to 4 the magnetic core component 15 extends from the duct 20 of the coil former 11 in an outward direction perpendicular to the longitudinal axis 9 in-between the opposing primary webs 26. The end face 18 of the magnetic core component 15 is positioned parallel to the collar 27 and is point symmetric with regard to the longitudinal axis 9.
In the following the assembly of the transformer assembly 1 shall be described with regard to the figures 1 to 4.
The two different coils 13 are wound around the shell surface 21 of the middle portion 19 and are electrically connected to the contacts 14 of the coil former 11.
The two pieces 17 of the magnetic core component 15 are subsequently inserted into the duct 20 from below and above of the coil former 11, respectively, such that the magnetic core component 15 extends through the duct 20 and forms a closed loop 16. The magnetic core component 15 is positioned in-between the cooling units 29 such that the end face 18 of the magnetic core component 15 is level with the cooling ribs 25 of the coil former 11. After completion of these steps the transformer 2 is assembled.
Subsequently the transformer 2 is inserted into the tub 5 of the casing 4 such that the end face 18 as well as the cooling ribs 25 abut the bottom wall (not shown) of the tub 5. When having filled the tub 5 with potting compound 7 and having connected an electronic system to the contacts 14 of the coil former 11 the transformer assembly 1 is completed.

Claims

Transformer comprising:
a coil former (11) having

a hollow middle portion (19) extending along a longitudinal axis (9) and enclosing a duct (20),

a first end portion (22) and a second end portion (23) each positioned adjacent to the middle portion (19) and opposing each other,

wherein the first end portion (22) comprises a cooling portion (24) adapted for conduction cooling of the coil former (11),

wherein the cooling portion (24) comprises cooling ribs (25) extending parallel to the longitudinal axis (9) and,

wherein the transformer (2) further comprises a magnetic core component (15) extending through the duct (20) and forming a closed loop (16), wherein the magnetic core component (15) has an end face (18) positioned in proximity to the cooling ribs (25) and being oriented perpendicular to the longitudinal axis (9),

wherein the cooling ribs (25) project parallel to the longitudinal axis (9) to such an extent that they are level with the end face (18) of the magnetic core component (15) and,

characterized in that the coil former (11) consists of a material having a thermal conductivity in plane of at least 3 W m^-1 K^-1 and in that the middle portion (19) has an outer diameter which varies along the longitudinal axis (9), such that the middle portion (19) comprises a barrel-shaped shell surface (21).
Transformer according to claim 1, characterized in that the coil former (11) consists of a material having a thermal conductivity in plane in the range of 5 W m^-1 K^-1 to 20 W m^-1 K^-1 more preferably in the range of : 10 W m^-1 K^-1 to 20 W m^-1 K^-1, further most preferably of 15 W m^-1 K^-1.
Transformer according to one of the preceding claims, characterized in that the first end portion (22) has a collar (27) extending in an outward direction perpendicular to the longitudinal axis (9), wherein the cooling ribs (25) comprise two primary webs (26) positioned on the collar (27) and being located opposite to each other with a distance there between.
Transformer according to claim3, characterized in that the magnetic core component (15) extends from the duct (20) in an outward direction perpendicular to the longitudinal axis (9) in between the opposing primary webs (26), wherein the end face (18) of the magnetic core component (15) is positioned parallel to the collar (27).
Transformer according to claim 3, characterized in that the cooling ribs (25) further comprise secondary webs (28) connected to one of the primary webs (26), wherein the secondary webs (28) and the corresponding primary web (26) enclose an pointing angle.
Transformer according to claim 5, characterized in that the secondary webs (28) together with the corresponding primary web (26) form a cooling unit (29), wherein the cooling units (29) are point symmetric to each other with regard to the longitudinal axis (9).
Transformer according to one of the preceding claims, characterized in that the coil former (11) is integrally formed and consists of one single piece.
Transformer assembly comprising a casing (4) having a receiving section (3) being formed as a tub (5) and having a bottom wall and surrounding side walls (6) and the transformer (2) according to one of the preceding claims being positioned within said receiving section (3).
Transformer assembly according to claims 8, characterized in that the cooling ribs (25) as well as the end face (18) of the magnetic core component (15) abut the bottom wall.
Transformer assembly according to claim 8, characterized in that the side walls (6) of the receiving section (3) have other cooling ribs (8) oriented parallel to the longitudinal axis (9) of the transformer and extending in a fan-shaped manner away from the longitudinal axis (9).
Transformer assembly according to claim 8, characterized in that the tub (5) is filled with conductive potting compound (7).