MEDIUM FREQUENCY TRANSFORMER WITH PARALLEL WINDINGS

Abstract

A medium frequency transformer for a DC/DC converter includes: a core having an air gap and a coil surrounding a core section and having a plurality of windings; a medium voltage electric insulation, surrounding the coil each winding including a first and second termination, and a conductor wound around a portion of the core in at least one turn between the first and second termination; a plurality of terminals provided outside the insulation, each connected to a different first termination by one of a plurality of connectors, a channel extending from an outside of the insulation into and at least partially through said electric insulation, wherein the connectors extend through the channel and are insulated against one another by means of a low voltage insulation within the channel. The second terminations are connected to one another within or inside the insulation and connected to a second terminal outside of the insulation by a second connector.

Claims

1. A medium frequency transformer for a resonant DC/DC converter or a dual active bridge DC/DC converter, comprising: a core having an air gap; a first coil surrounding a first section of the core; a medium voltage electric insulation surrounding the first coil; wherein the first coil comprises a plurality of M first windings; each of the plurality of M first windings comprising: a first termination and a second termination, and a conductor wound around the first portion of the core in at least one turn between the first and second termination; a plurality of M first terminals provided outside of the insulation, each of said first terminals connected to a different one of the first terminations by one of a plurality of M first connectors, thus connecting each first terminal to a respective first termination; the transformer further comprising: a first channel extending from an outside of the electric insulation into and at least partially through said electric insulation, wherein the plurality of M first connectors extend through the first channel; wherein the plurality of M first connectors are insulated against one another by means of a low voltage insulation within the channel, and wherein no medium voltage and/or high voltage insulation is present between any two of the first connectors; the second terminations are connected to one another within or inside the electric insulation; and a second terminal is provided outside of the electric insulation, and connected to the second terminations by a second connector.

2. The transformer according to claim 1, further comprising: a plurality of M second terminals provided outside of the electric insulation, each of said second terminals connected to a different one of the second terminations by one of a plurality of M second connectors, thus connecting each second terminal to a respective second termination; the transformer further comprising: a second channel extending from an outside of the electric insulation into and at least partially through said electric insulation, wherein the plurality of M second connectors extend through the second channel; wherein the plurality of M second connectors are insulated against one another by means of a low voltage insulation within the channel, and wherein preferably no medium voltage and/or high voltage insulation is present between any of the second connectors.

3. The transformer according to claim 1, wherein a wall surrounding the first and/or second channel provides medium or high voltage insulation, in particular a medium or high voltage insulation of first and/or second connectors against the electrical insulation.

4. The transformer according to claim 1, wherein the electric insulation comprises an electrically insulating fluid, in particular oil, in a tank, vessel or other container in which fluid the first coil, preferably the entire transformer, is immersed, and wherein the first channel is provided in a bushing extending through a wall of the container and at least partially into the fluid.

5. The transformer according to claim 1, wherein the electric insulation is cast around the coil.

6. The transformer according to claim 1, wherein each of the first and/or second connectors is made from litz wire.

7. The transformer according to claim 1, wherein the conductors of each windingare formed by litz wire, and wherein each of the first and/or second connectorsis integrally formed with the conductor it connects to by the same litz wire.

8. The transformer according to claim 7 wherein the litz wire comprises an insulating sheath or cladding, preferably extending at least essentially along its entire length, said insulating sheath or cladding providing low voltage insulation, and preferably not providing medium voltage and/or high voltage insulation, and wherein a thickness of the insulating sheath or cladding is preferably below 5 mm, below 2.5 mm, below 1 mm, or below 0.5 mm.

9. The transformer according to claim 1, wherein the first channel extends at least approximately in a direction perpendicular to the first section of the core, and/or at least approximately in a direction perpendicular to a longitudinal direction as defined by the windingsand/or the first coil.

10. The transformer according to claim 1, further comprising: a second coil surrounding the first or a second section of the core; a medium voltage electric insulation, surrounding the second coil; wherein the second coil comprises a plurality of M' second windings; each of the plurality of M' second windings comprising: a third termination and a fourth termination, a conductor wound around the first or the second portion of the core in at least one turn between the third and the fourth termination, a plurality of M' third terminals provided on an outside of the insulation, each of said third terminals connected to a different one of the third terminations by one of a plurality of M' third connectors, thus connecting each third terminal to a respective third termination; the transformer further comprising: a third channel extending from an outside of the electric insulation into and at least partially through said electric insulation, wherein the plurality of M' third connectors extend through the third channel; wherein the plurality of M third connectors are insulated against one another by means of a low voltage insulation within the third channel, and wherein preferably no medium voltage and/or high voltage insulation is present between any two of the third connectors.

11. The transformer according to claim 10, wherein the first windings form a primary winding of the transformer, and the second windingsform a secondary winding of the transformer.

12. The transformer according to claim 11, wherein the first coil and the second coil both surround the first section of the core in an at least essentially a co-axial arrangement.

13. The transformer according to claim 10, wherein the first coil surrounds the second coil, or vice versa.

14. The transformer according to claim 10, wherein the plurality of M first windings comprises: a pair of windings, said pair of windings comprising: a first winding made of a first conductive foil strip and comprising a first plurality of turns surrounding one another; a second winding made of a second conductive foil strip and comprising a second plurality of turns surrounding one another, with each turn of the first plurality of turns adjacently surrounded by a turn of the second plurality of turns; wherein innermost endings of the first and second winding form the second terminations of the respective winding; and outermost endings of the first and second winding form the first terminations of the respective winding.

15. The transformer according to claim 6 wherein the litz wire comprises an insulating sheath or cladding, preferably extending at least essentially along its entire length, said insulating sheath or cladding providing low voltage insulation, and preferably not providing medium voltage and/or high voltage insulation, and wherein a thickness of the insulating sheath or cladding is preferably below 5 mm, below 2.5 mm, below 1 mm, or below 0.5 mm.

16. The transformer according to claim 10, wherein the first coil and the second coil both surround the first section of the core in an at least essentially a co-axial arrangement.

17. The transformer according to claim 1, wherein the plurality of M first windings comprises: a pair of windings, said pair of windings comprising: a first winding made of a first conductive foil strip and comprising a first plurality of turns surrounding one another; a second winding made of a second conductive foil strip and comprising a second plurality of turns surrounding one another, with each turn of the first plurality of turns adjacently surrounded by a turn of the second plurality of turns; wherein innermost endings of the first and second winding form the second terminations of the respective winding; and outermost endings of the first and second winding form the first terminations of the respective winding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The subject matter will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

[0068] FIG. 1 illustrates a basic, generic, prior art DC/DC converter.

[0069] FIG. 2a) illustrates a basic, prior art DC/DC dual active bridge (DAB) converter.

[0070] FIG. 2b) illustrates a basic, prior art resonant DC/DC converter.

[0071] FIG. 3 shows a more detailed schematic of one possible embodiment of the DC/DC converter from FIG. 1.

[0072] FIG. 4 schematically illustrates a transformer in accordance with the invention.

[0073] In principle, identical reference symbols in the figures denote identical features or elements.

DETAILED DESCRIPTION

[0074] For background information, FIG. 1a) illustrates a basic, generic, prior art DC/DC converter 1 as part of which the present invention may be used. A DC/AC converter 11 is configured to convert a DC voltage and/or current from a DC source, preferably comprising a DC link capacitor, connected to its input into an AC voltage and/or current of medium frequency, i.e. preferably in a frequency range between 500 Hz and 500 kHz. Said AC voltage and/or current is fed into an AC intermediate circuit 12 comprising a transformer 141, in particular a medium frequency transformer (MFT), said transformer comprising a primary and a secondary side, and providing galvanic insulation between said sides. The transformer may, inter alia, be characterized by coupled inductances L.sub.m and L.sub.m' and a stray inductance L.sub.s, with its primary side winding or windings connected to the DC/AC converter via an inductance element having an impedance Z.sub.1, which may also be a parasitic inductance, in particular of a wire or other connection. The transformer transforms voltage and/or current at its primary side in a known manner to a secondary side voltage and/or current. Said secondary side voltage and/or current is subsequently converted by AC/DC converter 16, in particular a rectifier, into a DC voltage and/or current at the output of said AC/DC converter 16. DC/AC converter 12 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration as shown in FIG. 1a, or arranged in a full-bridge configuration as shown in FIG. 1b). Likewise, AC/DC converter 16 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1a, or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c).

[0075] FIG. 2a) illustrates a basic, prior art DC/DC dual active bridge (DAB) converter 1' which may be considered as an embodiment of the DC/DC converter 1 shown in FIG. 1a), and as another potential starting point for the present invention. DC/AC converter 11 is configured to convert a DC voltage and/or current from a DC source, preferably comprising a DC link capacitor, connected to its input into an AC voltage and/or current of medium frequency, i.e. preferably in a frequency range between 500 Hz and 500 kHz. Said AC voltage and/or current is fed into an AC intermediate circuit 14' comprising a transformer 141', in particular a medium frequency transformer (MFT), said transformer comprising a primary and a secondary side, and providing galvanic insulation between said sides. The transformer may, inter alia, be characterized by coupled inductances L.sub.m and L.sub.m' and a stray inductance L.sub.s, with its primary side winding or windings connected to the DC/AC converter via an inductor as impedance element, with said inductor, sometimes referred to as an energy transfer inductor, having an inductance L.sub.DAB .sub.1. The transformer transforms voltage and/or current at its primary side in a known manner to a secondary side voltage and/or current. Said secondary side voltage and/or current is subsequently converted by AC/DC converter 16', in particular a rectifier, into a DC voltage and/or current at the output of said AC/DC converter 16. An optional inductor connected between the secondary side of the transformer and the AD/DC converter preferably has an inductance L.sub.DAB .sub.2 which preferably is at least essentially identical to L.sub.DAB .sub.1. DC/AC converter 12 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). Likewise, AC/DC converter 16 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). Dual active bridge converters are also exemplary described in Swiss patent application publication CH 707 533 A2 or U.S. Pat. application publication U.S. 2018/0159435 A1.

[0076] FIG. 2b) illustrates a basic, prior art resonant DC/DC converter 1" which may be considered as another embodiment of the DC/DC converter 1 shown in FIG. 1a), and as yet another potential starting point for the present invention. DC/AC converter 11 is configured to convert a DC voltage and/or current from a DC source, preferably comprising a DC link capacitor, connected to its input into an AC voltage and/or current of medium frequency, i.e. preferably in a frequency range between 500 Hz and 500 kHz. Said AC voltage and/or current is fed into an AC intermediate circuit 14" comprising a transformer 141", in particular a medium frequency transformer (MFT), said transformer comprising a primary and a secondary side, and providing galvanic insulation between said sides. The transformer may, inter alia, be characterized by coupled inductances L.sub.m and L.sub.m' and a stray inductance L.sub.s, with its primary side winding or windings connected to the DC/AC converter via capacitor as impedance element, with said capacitor having a capacitance C.sub.resl. The capacitor together with the stray inductance is part of a resonant tank comprised by the AC intermediate circuit, which may store electric energy, and which is characterized by a resonance frequency, which in turn depends on the values of L.sub.s and C.sub.resl. The capacitor is therefore commonly referred to as a resonant capacitor. The transformer transforms voltage and/or current at its primary side in a known manner to a secondary side voltage and/or current. Said secondary side voltage and/or current is subsequently converted by AC/DC converter 16, in particular a rectifier, into a DC voltage and/or current at the output of said AC/DC converter 16. DC/AC converter 12 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). Likewise, AC/DC converter 16 may, in particular, comprise a plurality of semiconductor switches arranged in a half-bridge configuration corresponding to the one shown in FIG. 1b), or arranged in a full-bridge configuration corresponding to the one shown in FIG. 1c). As an alternative to the variant comprising active bridges as described above and allowing for bi-directional electric power flow, AC/DC converter 16 may, in particular, be embodied without semiconductor switches and comprise diodes only arranged in a half-bridge or full-bridge configuration if only unidirectional electric power flow is required. Resonant DC/DC converters are exemplary described in PCT patent application publication WO 2018/141092 A1.

[0077] FIG. 3 shows a more detailed schematic of one possible embodiment of the DC/DC converter from FIG. 1a), where two parallel windings are provided on both the primary side 1001 and the secondary side 1002 of the transformer, and impedance elements Z.sub.1 and Z.sub.2 have been split and distributed between the parallel windings. Also shown, merely for background information, is a voltage source connected to the first DC link 10, a resistive load connected to the second DC link 18 and characterized by a resistance R.sub.load, and (in gray) a reluctance network 19 of a core and a stray flux of the transformer.

[0078] FIG. 4 schematically illustrates a transformer in accordance with various embodiments employed in an exemplary resonant DC/DC converter as an embodiment of the DC/DC converter from FIG. 3. A first coil 100 on a primary side of the transformer comprises a pair of M=2 first windings 101, 102, and a pair of first capacitors 121, 122, with each first capacitor being connected in series with a respective one of the first windings. The transformer is immersed in an electrically insulating oil 40 contained in a tank 4. First and second bushings 41 and 42 are arranged in a wall of the tank to allow for electric connection to the first coil being established in a simple, secure, and reliable manner. A pair of first terminals 411, 412 is provided on an end of the first bushing facing away from the tank, wherein each first terminal may, in particular, allow for cable shoes to be attached. Two first connectors 413, 414 connect first terminals 411, 412 to first terminations of coils 101, 102, respectively. The first connectors extend through a first channel 410 provided in first bushing 41. Second terminations of the first windings 101, 102 are connected together inside the insulating oil 40 an thus within tank 4 at node T.sub.2. A second terminal 421 is provided on an end of the second bushing 42 facing away from the tank, wherein the second terminal may, in particular, allow for cable shoes to be attached. A single second connector 423 connects second terminal 421 to node T.sub.2. A second coil 200 on a secondary side of the transformer also comprises a pair of M=2 second windings 201, 202, and a pair of second capacitors 221, 222, with each second capacitor being connected in series with a respective one of the second windings 201, 202. Third and fourth bushings 43 and 44 are provided, which are at least essentially identical to first and second bushings 41 and 42, respectively; and arranged in an at least essentially analogous manner to allow for electric connection to the second coil being established in a correspondingly simple, secure, and reliable manner.

[0079] Unless specified otherwise, a connection, in particular between any two entities, including in particular nodes, points, terminals, elements, devices, etc. or combinations thereof, may refer to an electrically conductive connection, as in particular established by a wire, cable, busbar, a conductive track, trace or line on e.g. a (printed) circuit board, solder, etc. The electrically conductive connection is preferably at least substantially direct, in particular without any discrete elements, as, in particular, resistors, capacitors, inductors, or other passive or active elements or devices connected between the connected entities. The electrically conductive connection thus has at least essentially negligible resistance, capacitance and inductance, preferably at least essentially zero resistance, capacitance and inductance. In particular, resistance, capacitance and inductance of the electrically conductive connection are exclusively parasitic by nature. Further, resistance, capacitance and inductance of the electrically conductive connection significantly smaller (preferably by a factor of ⅟100, ⅟1000 or ⅟10000) than resistances, capacitances and impedances of resistors, capacitors or inductors, respectively, connected by the electrical conductive connection, and/or comprised by an electric circuit or network which comprises the electrically conductive connection.

[0080] Unless specified otherwise, an electric connection or electrical connection is identical to connection as defined above.

[0081] Unless specified otherwise, if two entities, including in particular nodes, points, terminals, elements, devices, etc. or combinations thereof, are said to be connected, electrically connected or to be (electrically) connected together, a connection as defined above exists between the two entities.

[0082] Unless specified otherwise, if a first and a second entity, including in particular a first and second node, point, terminal, element, device, etc. or combinations thereof, are said to be connected via a third entity, including in particular a third node, point, terminal, element, device, or with such a third entity (in) between, a connection as described above exists between the first and third entities as well as between the third and second entities. However, no connection as described above, in particular no at least substantially direct connection exists between the first and second entities. If explicitly specified, the third element may in particular also be a connection, in particular a conductor, wire, cable, busbar etc. In such case, it may be assumed that no connection as described above other than the specified one is present.

[0083] Unless stated otherwise, it is assumed that throughout this patent application, a statement a ≈ b implies that la-bl/(lal+lbl) < 10, preferably la-bl/(lal+lbl) < 100, wherein a and b may represent arbitrary variables as described and/or defined anywhere in this patent application, or as otherwise known to a person skilled in the art. Further, a statement that a is at least approximately equal or at least approximately identical to b implies that a ≈ b, preferably a = b. Further, unless stated otherwise, it is assumed that throughout this patent application, a statement a >> b implies that a > 10b, preferably a > 100b; and statement a << b implies that 10a < b, preferably 100a < b. Further, unless stated otherwise, it is assumed that throughout this patent application, a statement that a >> b, or that a is significantly larger or much larger than b, implies that a > 10b, preferably a > 100b; and statement that a << b, or that a is significantly smaller or much smaller than b implies that 10a < b, preferably 100a < b. Further, a statement that two values a and b substantially deviate from one another, or differ significantly, implies that a ≈ b does not hold, in particular that a >> b or a << b.

[0084] This description and the accompanying drawings that illustrate aspects and embodiments of the present disclosure should not be taken as limiting the claims defining the protected subject matter. In other words, while the subject matter has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. Various mechanical, compositional, structural, electrical, and operational changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the various embodiments. Thus, it will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different and/or individual embodiments as described above and below. Embodiments in accordance with the invention may, in particular, include further and/or additional features, elements, aspects, etc. not shown in the drawings or described above.

[0085] Method steps listed in the description and, in particular, in the claims, are preferably carried out in the order as listed, but may alternatively be carried out in any other order in as far as technically and practically feasible.

[0086] The disclosure also covers all further features shown in the Figures, individually, although they may not have been described in the afore or following description. Also, individual alternatives of the embodiments described in the Figure and the description and individual alternatives of features thereof can be disclaimed from the subject matter of the invention or from disclosed subject matter. The disclosure comprises subject matter consisting of the features defined in the claims or the exemplary embodiments as well as subject matter comprising said features.

[0087] Furthermore, in the claims the word “comprising” does not exclude further or additional features, elements, steps etc., and the indefinite article “a” or “an” does not exclude a plurality. A single unit or step may fulfil the functions of several features recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The terms “essentially”, “about”, “approximately” and the like in connection with an attribute, property or a value particularly also comprise exactly the attribute, property or value, respectively, as stated. The term “approximately” or “about” in the context of a given numerate value or range refers to a value or range that is, e.g., within 20%, within 10%, within 5%, or within 2% of the given value or range, and, in particular, also comprises the exact value or range as stated. Components described as coupled or connected may be electrically or mechanically directly coupled, or they may be indirectly coupled via one or more intermediate components. Any reference signs in the claims shall not be construed as limiting the scope.

[0088] Further embodiments of the various embodiments are disclosed in the following aspects: [0089] 1) A transformer, in particular a medium frequency transformer for a resonant DC/DC converter (1") or a dual active bridge DC/DC converter (1'), comprising, [0090] a) a core, in particular a core having an air gap; [0091] b) a first coil (100) surrounding a first section of the core; [0092] c) an electric insulation, in particular a medium voltage electric insulation (40), surrounding the first coil; [0093] d) wherein the first coil comprises a plurality of M first windings (101, 102); [0094] e) each of the plurality of M first windings comprising [0095] i) a first termination and a second termination, [0096] ii) a conductor wound around the first portion of the core in at least one turn between the first and second termination, [0097] f) a plurality of M first terminals (411, 412) provided outside of the insulation, each of said first terminals connected to a different one of the first terminations by one of a plurality of M first connectors (413, 414), thus connecting each first terminal to a respective first termination; the transformer further comprising: [0098] g) a first channel (410) extending from an outside of the electric insulation into and at least partially through said electric insulation, wherein the plurality of M first connectors extend through the first channel; wherein [0099] h) the plurality of M first connectors are insulated against one another by means of a low voltage insulation (415) within the channel, and wherein preferably no medium voltage and/or high voltage insulation is present between any two of the first connectors. [0100] 2) The transformer according to aspect 1, wherein [0101] a) the second terminations are connected to one another within or inside the electric insulation; [0102] b) a second terminal (421) is provided outside of the electric insulation, and connected to the second terminations by a second connector (423). [0103] 3) The transformer according to aspect 1, further comprising [0104] a) a plurality of M second terminals provided outside of the electric insulation, each of said second terminals connected to a different one of the second terminations by one of a plurality of M second connectors, thus connecting each second terminal to a respective second termination; the transformer further comprising: [0105] b) a second channel extending from an outside of the electric insulation into and at least partially through said electric insulation, wherein the plurality of M second connectors extend through the second channel; wherein [0106] c) the plurality of M second connectors are insulated against one another by means of a low voltage insulation within the channel, and wherein preferably no medium voltage and/or high voltage insulation is present between any of the second connectors. [0107] 4) The transformer according to one of the preceding aspects, wherein a wall surrounding the first and/or second channel provides medium or high voltage insulation, in particular a medium or high voltage insulation of first and/or second connectors (413, 414, 423) against the electrical insulation. [0108] 5) The transformer according to one of the preceding aspects, wherein the electric insulation comprises an electrically insulating fluid, in particular oil, in a tank (4), vessel or other container in which fluid the first coil (100), preferably the entire transformer, is immersed, and wherein the first channel is provided in a bushing extending through a wall of the container and at least partially into the fluid. [0109] 6) The transformer according to one of aspects 1 to 4, wherein the electric insulation is cast around the coil (100). [0110] 7) The transformer according to one of the preceding aspects, wherein each of the first and/or second connectors (413, 414, 423) comprises litz wire, in particular is made from litz wire. [0111] 8) The transformer according to one of the preceding aspects, wherein the conductors of each winding (101, 102) are formed by litz wire, and wherein each of the first and/or second connectors (413, 414, 423) is integrally formed with the conductor it connects to by the same litz wire, in particular as a single strand of litz wire. [0112] 9) The transformer according to the aspect 7 or 8 wherein the litz wire comprises an insulating sheath or cladding, preferably extending at least essentially along its entire length, said insulating sheath or cladding providing low voltage insulation, and preferably not providing medium voltage and/or high voltage insulation, an wherein a thickness of the insulating sheath or cladding is preferably below 5 mm, below 2.5 mm, below 1 mm, or below 0.5 mm. [0113] 10) The transformer according to one of the preceding aspects, wherein the first channel (410) extends at least approximately in a direction perpendicular to the first section of the core, and/or at least approximately in a direction perpendicular to a longitudinal direction as defined by the windings (101, 102) and/or the first coil (100). [0114] 11) The transformer according to one of the preceding aspects, further comprising [0115] a) a second coil (200) surrounding the first or a second section of the core; [0116] b) an electric insulation, in particular a medium voltage electric insulation (40), surrounding the second coil; [0117] c) wherein the second coil comprises a plurality of M' second windings (201, 202); [0118] d) each of the plurality of M' second windings comprising [0119] i) a third termination and a fourth termination, [0120] ii) a conductor wound around the first or the second portion of the core in at least one turn between the third and the fourth termination, [0121] e) a plurality of M' third terminals provided on an outside of the insulation, each of said third terminals connected to a different one of the third terminations by one of a plurality of M' third connectors, thus connecting each third terminal to a respective third termination; the transformer further comprising: [0122] f) a third channel extending from an outside of the electric insulation into and at least partially through said electric insulation, wherein the plurality of M' third connectors extend through the third channel; wherein [0123] g) the plurality of M' third connectors are insulated against one another by means of a low voltage insulation within the third channel, and wherein preferably no medium voltage and/or high voltage insulation is present between any two of the third connectors. [0124] 12) The transformer according to one of the preceding aspects, wherein the first windings (101, 102) form a primary winding of the transformer, and the second windings (201, 202) form a secondary winding of the transformer. [0125] 13) The transformer according to one of aspects 11 or 12, wherein the first coil (100) and the second coil (200) both surround the first section of the core, in particular in an at least essentially a co-axial arrangement. [0126] 14) The transformer according to one of aspects 11 to 13, wherein the first coil surrounds the second coil, or vice versa. [0127] 15) The transformer according to one of the preceding aspects, wherein the first coil comprises [0128] a) a pair of windings (101, 102), said pair of windings comprising: [0129] i) a first winding (101) made of a first conductive foil strip (111, 111', 111") and comprising a first plurality of turns surrounding one another; [0130] ii) a second winding (102) made of a second conductive foil strip (112, 112', 112") and comprising a second plurality of turns surrounding one another, with each turn of the first plurality of turns adjacently surrounded by a turn of the second plurality of turns; wherein [0131] iii) innermost endings of the first and second winding form the second terminations of the respective winding; [0132] iv) outermost endings of the first and second winding form the first terminations of the respective winding.