GB2564453A

GB2564453A - A transformer and a method of manufacturing a transformer

Info

Publication number: GB2564453A
Application number: GB1711136.0A
Authority: GB
Inventors: Phillips Steve
Original assignee: INVERTEK DRIVES Ltd
Current assignee: INVERTEK DRIVES Ltd
Priority date: 2017-07-11
Filing date: 2017-07-11
Publication date: 2019-01-16
Also published as: GB201711136D0

Abstract

A transformer 18 includes a former (bobbin) 19 having first 21 and second 22 ends and a primary coil 25 formed around the former wherein first and second ends of the coil are positioned at a different distance from the respective ends of the former (see distances D2 and D3) such that electrical isolation is larger on one side of the coil. First and second margin tapes may fill the gaps 30 and 31 created by the respective distances D2 and D3 and the widths of each tape may be equal to the aforementioned spacing distances. In this way, sufficient isolation may be provided to meet the safety requirements (creepage clearance) for a low weight or low cost transformer configured to step down a high voltage to a low user safe voltage. The transformer also includes a secondary coil 33 which is formed around the primary coil. A further coil 34 may also be included which may also be isolated with margin tape 38 (distance D5) and 39 (distance D6). A screening or shielding layer 32 may also be included. The transformer may be used in a variable frequency drive unit.

Description

A transformer and a method of manufacturing a transformer

Technical field

The present invention relates to a transformer and a method of manufacturing a transformer. The present invention more particularly relates to an electrically isolated transformer and a method of manufacturing an electrically isolated transformer.

Background

An electrical transformer 1 typically comprises a high voltage side 2 and a low voltage side 3, as shown in figure 1 of the accompanying drawings.

The high voltage side 2 comprises a primary winding 4 which is coupled to primary winding connectors 5, 6. The primary winding connectors 5, 6 are configured to be connected to a high voltage power supply, such as a mains power supply or a power supply operating at 600V.

The low voltage side 3 of the transformer 1 comprises at least one secondary winding. In this example, the transformer 1 comprises a first secondary coil incorporating a plurality of safety isolated secondary windings 7 and second secondary coil incorporating a plurality of non-isolated secondary windings 8.

The safety isolated secondary windings 7 are coupled to safety isolated connectors 9-11. The non-isolated secondary windings are coupled to nonisolated connectors 12-14.

The non-isolated secondary windings 8 provide a low voltage output from the transformer 1 via the non-isolated connectors 12-14. This non-isolated output is conductively isolated from the primary winding 4 by the inductive coupling of the transformer 1. However, the non-isolated output is not considered to be a user-safe output since there is only a small clearance distance 15 between the primary winding 4 and the non-isolated secondary windings 8 and/or the nonisolated connectors 12-14. The small clearance distance 15 is not considered to be sufficient to meet the safety requirements for a transformer which is configured to step down a high voltage to a low voltage and provide a user-safe low voltage to a user.

The safety isolated secondary windings 7 and the safety isolated connectors 9-11 are positioned at a sufficient safety clearance distance 16 from the high voltage side 2 and a sufficient safety clearance distance 17 from the nonisolated low voltage portion of the transformer 1. The safety clearance distances 16, 17 are each a sufficiently large distance to meet a safety requirement for a transformer which steps down a high voltage to a low voltage and provides the low voltage to a user.

In the example shown in figure 1, the safety isolated secondary windings 7 and the non-isolated secondary windings 8 are provided on the same transformer 1. In order to achieve the safety clearance distances 16, 17, a conventional transformer typically has a large or oversized former or bobbin. The large former enables the safety isolated secondary windings 7 to be positioned at a safe clearance distance 16, 17 from the non-isolated secondary windings 8 and the high voltage side 2. While this provides sufficient isolation for the safety isolated secondary windings 7, the large former increases the overall size of the transformer, making the transformer heavier, bulkier and more expensive to manufacture than a smaller sized transformer. This is undesirable, particularly in applications where the transformer is for use within a device housing where space is limited or in a device which is required to have a low weight or low cost.

As an alternative to providing a large sized former to achieve a required safety clearance distance, it has been proposed to use a separate isolated power supply circuit to provide a user safe output from a transformer. However, this is also undesirable because the separate isolated power supply circuit increases in the complexity, cost and size of the transformer.

There is a need for an improved transformer and method of manufacturing a transformer that addresses at least the problems outlined above.

The present invention seeks to provide an improved transformer and method of manufacturing a transformer.

Summary of invention

According to one aspect of the present invention, there is provided a transformer comprising: a former incorporating a former body having a first end and a second end; a primary coil formed at least partly around the former body; and a secondary coil formed at least partly around part of the primary coil, wherein a first end of the primary coil is positioned at a first primary coil spacing distance from the first end of the former body and a second end of the primary coil is positioned at a second primary coil spacing distance from the second end of the former body, the second primary coil spacing distance being greater than the first primary coil spacing distance such that the electrical isolation from the primary coil is greater at the second end of the former body than at the first end of the former body.

Preferably, the second primary coil spacing distance is substantially three times greater than the first primary coil spacing distance.

Conveniently, the transformer further comprises: a first margin tape provided at least partly around the former body between the first end of the former body and the first end of the primary coil; and a second margin tape provided at least partly around the former body between the second end of the former body and the second end of the primary coil, wherein the width of the second margin tape is greater than the width of the first margin tape.

Advantageously, the width of first margin tape is substantially equal to the first primary coil spacing distance and the width of the second margin tape is substantially equal to the second primary coil spacing distance.

Preferably, the transformer further comprises: a further secondary coil formed at least partly around part of the primary coil, wherein the secondary coil is formed at least partly around part of the further secondary coil.

Conveniently, a first end of the further secondary coil is positioned at a first further secondary coil spacing distance from the first end of the former body and a second end of the further secondary coil is positioned at a second further secondary coil spacing distance from the second end of the former body, the second further secondary coil spacing distance being greater than the first further secondary coil spacing distance.

Advantageously, the second further secondary coil spacing distance is substantially three times greater than the first further secondary coil spacing distance.

Preferably, the transformer further comprises: a first set of electrical connectors which is positioned at a first connector distance from the first end of the former body, the primary coil being connected electrically by primary conductors to the first set of electrical connectors; and a second set of electrical connectors which is positioned at a second connector distance from the second end of the former body, the secondary coil being connected electrically by secondary conductors to the second set of electrical connectors.

Conveniently, the first set of electrical connectors is positioned at a first clearance distance from the first end of the primary coil and the second set of electrical connectors is positioned at a second clearance distance from the second end of the primary coil, the second clearance distance being greater than the first clearance distance.

Advantageously, the first connector distance is substantially equal to the second connector distance.

Preferably, the transformer further comprises: a third set of electrical connectors which is positioned adjacent to the first set of electrical connectors, the further secondary coil being connected electrically by further secondary conductors to the third set of electrical connectors.

Conveniently, the transformer further comprises: a plurality of further secondary conductor electrical insulator elements, each further secondary conductor electrical insulator element being provided at least partly around part of one of the further secondary conductors.

Advantageously, the transformer further comprises: a plurality of primary conductor electrical insulator elements, each primary conductor electrical insulator element being provided at least partly around part of one of the primary conductors.

Preferably, each electrical insulator element is of Polytetrafluoroethylene (PTFE).

Conveniently, the transformer further comprises: a first enlarged former end which is coupled to the first end of the former body; and a second enlarged former end which is coupled to the second end of the former body.

Advantageously, the first set of electrical connectors is coupled to the first enlarged former end and the second set of electrical connectors is coupled to the second enlarged former end.

Preferably, the transformer further comprises: a screening layer positioned between the primary coil and the or each secondary coil to at least partly electrically screen the or each secondary coil from the primary coil.

According to another aspect of the present invention, there is provided a variable frequency drive unit comprising a transformer as defined in any one of claims 1 to 17 hereinafter.

According to a further aspect of the present invention, there is provided a method of manufacturing a transformer, the method comprising: providing a former incorporating a former body having a first end and a second end; forming a primary coil at least partly around the former body; and forming a secondary coil at least partly around part of the primary coil, wherein a first end of the primary coil is positioned at a first primary coil spacing distance from the first end of the former body and a second end of the primary coil is positioned at a second primary coil spacing distance from the second end of the former body, the second primary coil spacing distance being greater than the first primary coil spacing distance such that the electrical isolation from the primary coil is greater at the second end of the former body than at the first end of the former body.

Conveniently, the method further comprises: winding a first margin tape at least partly around the former body between the first end of the former body and the first end of the primary coil; and winding a second margin tape at least partly around the former body between the second end of the former body and the second end of the primary coil, wherein the width of the second margin tape is greater than the width of the first margin tape.

Preferably, the method further comprises: forming a further secondary coil at least partly around part of the primary coil, wherein the method comprise forming the secondary coil at least partly around part of the further secondary coil.

Preferably, the method further comprises: positioning a first set of electrical connectors at a first connector distance from the first end of the former body; connecting the primary coil to the first set of electrical connectors using a plurality of primary conductors; positioning a second set of electrical connectors at a second connector distance from the second end of the former body; and connecting the secondary coil to the second set of electrical connectors using a plurality of secondary conductors.

Preferably, the method further comprises: positioning a third set of electrical connectors adjacent to the first set of electrical connectors; and connecting the further secondary coil to the third set of electrical connectors using a plurality of further secondary conductors.

Conveniently, the method further comprises: providing a plurality of further secondary conductor electrical insulator elements and positioning each further secondary conductor electrical insulator element at least partly around part of one of the further secondary conductors.

Advantageously, the method further comprises: providing a plurality of primary conductor electrical insulator elements and positioning each primary conductor electrical insulator element at least partly around part of one of the primary conductors.

Conveniently, the method further comprises: providing a first enlarged former end which is coupled to the first end of the former body; and providing a second enlarged former end which is coupled to the second end of the former body.

Advantageously, the method further comprises: coupling the first set of electrical connectors to the first enlarged former end; and coupling the second set of electrical connectors to the second enlarged former end.

Preferably, the method further comprises: providing a screening layer between the primary coil and the or each secondary coil to at least partly electrically screen the or each secondary coil from the primary coil.

Brief description of drawings

So that the present invention may be more readily understood, embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram showing an example of a transformer,

Figure 2 is a schematic diagram showing a cross-sectional view of part of a transformer of some embodiments,

Figure 3 is a schematic diagram showing a cross-sectional view of a transformer of some embodiments, and

Figure 4 is a schematic diagram showing the windings of the transformer of figure 3.

Detailed description

Referring now to figure 2 of the accompanying drawings, a transformer 18 of some embodiments comprises a former 19 which may alternatively be referred to as a bobbin. The former 19 comprises a former body 20 having a first end 21 and a second end 22. The former body 20 forms part of the core of the transformer 18.

In this embodiment, the former 19 comprises a first enlarged former end 23 which is coupled to the first end 21 of the former body 20 and a second enlarged former end 24 which is coupled to the second end 22 of the former body 20. In some embodiments, the first and second enlarged former ends 23, 24 are connected to or formed integrally with the former body 20. In further embodiments, at least one of the first or second enlarged former ends 23, 24 is omitted.

The transformer 18 comprises a primary coil 25 which is wound or formed at least partly around the former body 20. The primary coil 25 comprises a plurality of windings which are wound or formed around the former body 20 during the manufacture of the transformer 18. In this embodiment, the primary coil 25 is connected electrically by primary conductors (not shown) to a first set of electrical connectors 26 (only one of which is visible in figure 2).

The first set of electrical connectors 26 is positioned at a first connector distance D1 from the former body 20. The first connector distance D1 is a distance between a part of the former body which is closest to part of the first set of electrical connectors 26.

In some embodiments, the first set of electrical connectors 26 is coupled to the first enlarged former end 23. In other embodiments, the first set of electrical connectors is coupled to a separate component, such as a housing of the transformer 18.

The primary coil 25 is formed around the former body 20 with a first end 27 of the primary coil 25 being at a first primary coil spacing distance D2 from the first end 21 of the former body 20. The first primary coil spacing distance D2 is preferably the distance between the first end 27 of the primary coil 25 and a plane extending from the first end 21 of the former body 20, perpendicularly to the longitudinal length of the former body 20.

In some embodiments, all of the windings of the primary coil 25 are positioned at the first primary coil spacing distance D2 from the first end 21 of the former body 20. In other embodiments, only a portion of the windings of the primary coil 25 are positioned at the first primary coil spacing distance D2 from the first end 21 of the former body 20. In a preferred embodiment, at least the outermost primary winding 28 of the primary coil 25 is positioned at the first primary coil spacing distance D2 from the first end 21 of the former body 20. A second end 29 of the primary coil 25 is positioned at a second primary coil spacing distance D3 from the second end 22 of the former body 20. The second primary coil spacing distance D3 is preferably the distance between the second end 29 of the primary coil 25 and a plane extending from the second end 22 of the former body 20, perpendicularly to the longitudinal length of the former body 20.

In some embodiments, the first primary coil spacing distance D2 is greater than the second primary coil spacing distance D3. The different first and second spacing distances D2, D3 result in the transformer 18 having an asymmetric structure. The level of asymmetry depends on the safety clearance distances that are required for the transformer 18. The level of asymmetry increases as the required safety clearance distances between the primary coil 25 and the secondary coil 33 increases.

For example, in some embodiments, the second primary coil spacing distance D3 is substantially or exactly three times greater than the first primary coil spacing distance D2.

In some embodiments, all of the windings of the primary coil 25 are positioned at the second primary coil spacing distance D3. In other embodiments, only a portion of the windings or at least the outermost winding 28 of the primary coil 25 are positioned at the second primary coil spacing distance D3 from the second end 22 of the former body 20.

In some embodiments, a first margin tape (not shown) is provided at least partly around the former body 20 to at least partly fill a space 30 between the first and 27 of the primary coil 25 and the first end 21 of the former body 20. The first margin tape is an elongate tape which is wound around the former body 20. The first margin tape has a first margin tape width which is preferably equal to or substantially equal to the first primary coil spacing distance D2.

In some embodiments, the transformer 18 comprises a second margin tape (not shown) which is provided around the former body 20 to substantially fill a space 31 between the second end 29 of the primary coil 25 and the second end 22 of the former body 20. The second margin tape has a second margin tape width which is preferably greater than the width of the first margin tape. In some embodiments, the second margin tape width is equal to or substantially equal to the second primary coil spacing distance D3.

In some embodiments, the transformer 18 comprises a screening or shielding layer 32. The screening layer 32 comprises an electrically insulating material to provide an insulating layer at least partly around the primary coil 25. In some embodiments, the shielding layer 32 comprises a metallic layer to provide an inductive shield at least partly around the primary coil 25.

The transformer 18 further comprises a secondary coil 33 which is formed at least partly around the primary coil 25. In some embodiments, such as the embodiments shown in figure 2, the transformer 18 comprises a further secondary coil 34 which is formed at least partly around the primary coil 25. In these embodiments, the secondary coil 33 is formed at least partly around the further secondary coil 34. However, in other embodiments, the further secondary coil 34 may be omitted.

The shielding layer 32 is positioned between the primary coil 25 and each further secondary coil 33, 34 to provide a conductive and preferably also an inductive shielding to shield each secondary coil 33, 34 from the primary coil 25.

The transformer 18 comprises a second set of electrical connectors 35 (only one of which is visible in figure 2). The second set of electrical connectors 35 is positioned at a second connector distance D4 from the second end 22 of the former body 20. The second connector distance D4 is a distance between a part of the former body which is closest to part of the second set of electrical connectors 35.

In some embodiments, the second connector distance D4 is equal to or substantially equal to the first connector distance D1.

The secondary coil 33 is connected electrically by secondary conductors (not shown) to the second set of electrical connectors 35. In some embodiments, the transformer 18 further comprises a third set of electrical connectors (not shown) which are positioned adjacent to the first set of electrical connectors 26 and preferably at the first connector distance D1 from the first end 21 of the former body 20.

In some embodiments, such as the embodiments shown in figure 2, the first set of electrical connectors 26 is positioned at an opposite end of the former 19 from the second set of electrical connectors 35. The second set of electrical connectors is therefore positioned remotely from the first set of electrical connectors and preferably also remotely from the third set of electrical connectors.

In some embodiments, a first end 36 of the further secondary coil 34 is positioned at a first further secondary coil spacing distance D5 from the first end 21 of the former body 20. The first further secondary coil spacing distance D5 is preferably the distance between the first end 36 of the further secondary coil 34 and a plane extending from the first end 21 of the former body 20, perpendicularly to the longitudinal length of the former body 20. A second end 37 of the further secondary coil 34 is positioned at a second further secondary coil spacing distance D6 from the second end 22 of the former body 20. The second further secondary coil spacing distance D6 is preferably the distance between the second end 37 of the further secondary coil 34 and a plane extending from the second end 22 of the former body 20, perpendicularly to the longitudinal length of the former body 20.

The second further secondary coil spacing distance D6 is preferably greater than the first further secondary coil spacing distance D5. For example, in some embodiments, second further secondary coil spacing distance D6 is three times greater than the first further secondary coil spacing distance D5.

The different first and second further secondary coil spacing distances D5, D6 results in the transformer 18 having an additional asymmetric structure. The additional level of asymmetry depends on the safety clearance distances that are required for the transformer 18. The level of asymmetry increases as the required safety clearance distances between the further secondary coil 34 and the second set of electrical connectors 35 increases. A third margin tape (not shown) is preferably provided within the space 38 between the first end 36 of the further secondary coil 34 and the first end 21 of the former body 20. A fourth margin tape (not shown) is preferably provided in a space 39 between the second end 37 of the further secondary coil 34 and the second end 22 of the former body 20. The width of the fourth margin tape is preferably greater than the width of the third margin tape.

The asymmetrical or off-centre positioning of the primary coil 25 within the transformer 18 ensures that the second set of electrical connectors 34 is positioned at a first safe clearance distance CD1 from the primary coil 25. The first safe clearance distance CD1 is preferably equal to or greater than a set safety clearance for user-safe electrical connectors on a transformer. The second set of electrical connectors 35 is therefore electrically isolated from the primary coil 25 and configured to provide a user-safe low voltage electrical connectors on the transformer 18.

The asymmetric or off-centre positioning of the further secondary coil 34 relative to the former body 20 ensures that the second set of electrical connectors 35 is at a second safe clearance distance CD2 from the further secondary coil 34. The second set of electrical connectors 35 is therefore electrically isolated from the further secondary coil 34.

The asymmetric or off-centre positioning of the primary coil 25 and preferably also the further secondary coil 34 enables the second set of electrical connectors 35 to be provided at the safe clearance distances CD1, CD2 without having to increase the size of the former 19. The transformer 18 can therefore be small in size while still achieving the required safety clearance distances. The construction also avoids the need for a separate isolated power supply circuit.

Referring now to figures 3 and 4 of the accompanying drawings, a transformer 40 of some embodiments comprises many of the same components as the embodiments described above and like reference numerals will be used for equivalent components.

In some embodiments, the transformer comprises a plurality of primary conductor electrical insulator elements 41, 42. Each primary conductor electrical insulator element 41, 42 is provided at least partly around 1 of the primary conductors.

In some embodiments, the transformer further comprises a plurality of further secondary conductor electrical insulator elements 43-46. Each further secondary conductor electrical insulator element 43-46 is provided at least partly around one of the further secondary conductors.

Each electrical insulator element is preferably of Polytetrafluoroethylene (PTFE). In some embodiments, each electrical insulator element is of Teflon®. In other embodiments, each electrical insulator element is of a different electrically insulating material.

The transformer of some embodiments is configured to step down an input voltage of 100-400V to an output voltage of 5-42V.

In some embodiments, a variable frequency drive unit comprises a transformer of embodiments of the invention.

Some embodiments comprise a method of manufacturing a transformer of any of the embodiments described herein. A person skilled in the art is familiar with methods of manufacturing a transformer and would be familiar with how to manufacture a transformer of embodiments of the invention. A method of manufacturing a transformer of some embodiments comprises providing a former incorporating a former body having a first end and a second end and forming a primary coil at least partly around the former body. The method further comprises forming a secondary coil at least partly around part of the primary coil, wherein a first end of the primary coil is positioned at a first primary coil spacing distance from the first end of the former body and a second end of the primary coil is positioned at a second primary coil spacing distance from the second end of the former body. The second primary coil spacing distance is greater than the first primary coil spacing distance such that the electrical isolation from the primary coil is greater at the second end of the former body than at the first end of the former body.

When used in this specification and the claims, the term “comprises” and “comprising” and variations thereof mean that specified features, steps or integers and included. The terms are not to be interpreted to exclude the presence of other features, steps or compounds.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A transformer comprising: a former incorporating a former body having a first end and a second end; a primary coil formed at least partly around the former body; and a secondary coil formed at least partly around part of the primary coil, wherein a first end of the primary coil is positioned at a first primary coil spacing distance from the first end of the former body and a second end of the primary coil is positioned at a second primary coil spacing distance from the second end of the former body, the second primary coil spacing distance being greater than the first primary coil spacing distance such that the electrical isolation from the primary coil is greater at the second end of the former body than at the first end of the former body.

2. The transformer of claim 1, wherein the second primary coil spacing distance is substantially three times greater than the first primary coil spacing distance.

3. The transformer of claim 1 or claim 2, wherein the transformer further comprises: a first margin tape provided at least partly around the former body between the first end of the former body and the first end of the primary coil; and a second margin tape provided at least partly around the former body between the second end of the former body and the second end of the primary coil, wherein the width of the second margin tape is greater than the width of the first margin tape.

4. The transformer of claim 3, wherein the width of first margin tape is substantially equal to the first primary coil spacing distance and the width of the second margin tape is substantially equal to the second primary coil spacing distance.

5. The transformer of any one of the preceding claims, wherein the transformer further comprises: a further secondary coil formed at least partly around part of the primary coil, wherein the secondary coil is formed at least partly around part of the further secondary coil.

6. The transformer of claim 5, wherein a first end of the further secondary coil is positioned at a first further secondary coil spacing distance from the first end of the former body and a second end of the further secondary coil is positioned at a second further secondary coil spacing distance from the second end of the former body, the second further secondary coil spacing distance being greater than the first further secondary coil spacing distance.

7. The transformer of claim 6, wherein the second further secondary coil spacing distance is substantially three times greater than the first further secondary coil spacing distance.

8. The transformer of any one of the preceding claims, wherein the transformer further comprises: a first set of electrical connectors which is positioned at a first connector distance from the first end of the former body, the primary coil being connected electrically by primary conductors to the first set of electrical connectors; and a second set of electrical connectors which is positioned at a second connector distance from the second end of the former body, the secondary coil being connected electrically by secondary conductors to the second set of electrical connectors.

9. The transformer of claim 8, wherein the first set of electrical connectors is positioned at a first clearance distance from the first end of the primary coil and the second set of electrical connectors is positioned at a second clearance distance from the second end of the primary coil, the second clearance distance being greater than the first clearance distance.

10. The transformer of claim 8 or claim 9, wherein the first connector distance is substantially equal to the second connector distance.

11. The transformer of any one of claims 8 to 10 as dependent on claim 6 or claim 7, wherein the transformer further comprises: a third set of electrical connectors which is positioned adjacent to the first set of electrical connectors, the further secondary coil being connected electrically by further secondary conductors to the third set of electrical connectors.

12. The transformer of claim 11, wherein the transformer further comprises: a plurality of further secondary conductor electrical insulator elements, each further secondary conductor electrical insulator element being provided at least partly around part of one of the further secondary conductors.

13. The transformer of any one of the preceding claims, wherein the transformer further comprises: a plurality of primary conductor electrical insulator elements, each primary conductor electrical insulator element being provided at least partly around part of one of the primary conductors.

14. The transformer of claim 12 or claim 13, wherein each electrical insulator element is of Polytetrafluoroethylene (PTFE).

15. The transformer of any one of the preceding claims, wherein the transformer further comprises: a first enlarged former end which is coupled to the first end of the former body; and a second enlarged former end which is coupled to the second end of the former body.

16. The transformer of claim 15 as dependent on any one of claims 8 to 12, wherein the first set of electrical connectors is coupled to the first enlarged former end and the second set of electrical connectors is coupled to the second enlarged former end.

17. The transformer of any one of the preceding claims, wherein the transformer further comprises: a screening layer positioned between the primary coil and the or each secondary coil to at least partly electrically screen the or each secondary coil from the primary coil.

18. A variable frequency drive unit comprising a transformer according to any one of the preceding claims.

19. A method of manufacturing a transformer, the method comprising: providing a former incorporating a former body having a first end and a second end; forming a primary coil at least partly around the former body; and forming a secondary coil at least partly around part of the primary coil, wherein a first end of the primary coil is positioned at a first primary coil spacing distance from the first end of the former body and a second end of the primary coil is positioned at a second primary coil spacing distance from the second end of the former body, the second primary coil spacing distance being greater than the first primary coil spacing distance such that the electrical isolation from the primary coil is greater at the second end of the former body than at the first end of the former body.

20. The method of claim 19, wherein the second primary coil spacing distance is substantially three times greater than the first primary coil spacing distance.

21. The method of claim 19 or claim 20, wherein the method further comprises: winding a first margin tape at least partly around the former body between the first end of the former body and the first end of the primary coil; and winding a second margin tape at least partly around the former body between the second end of the former body and the second end of the primary coil, wherein the width of the second margin tape is greater than the width of the first margin tape.

22. The method of claim 21, wherein the width of first margin tape is substantially equal to the first primary coil spacing distance and the width of the second margin tape is substantially equal to the second primary coil spacing distance.

23. The method of any one of claims 19 to 22, wherein the method further comprises: forming a further secondary coil at least partly around part of the primary coil, wherein the method comprise forming the secondary coil at least partly around part of the further secondary coil.

24. The method of claim 23, wherein a first end of the further secondary coil is positioned at a first further secondary coil spacing distance from the first end of the former body and a second end of the further secondary coil is positioned at a second further secondary coil spacing distance from the second end of the former body, the second further secondary coil spacing distance being greater than the first further secondary coil spacing distance.

25. The method of claim 24, wherein the second further secondary coil spacing distance is substantially three times greater than the first further secondary coil spacing distance.

26. The method of any one of claims 19 to 25, wherein the method further comprises: positioning a first set of electrical connectors at a first connector distance from the first end of the former body; connecting the primary coil to the first set of electrical connectors using a plurality of primary conductors; positioning a second set of electrical connectors at a second connector distance from the second end of the former body; and connecting the secondary coil to the second set of electrical connectors using a plurality of secondary conductors.

27. The method of claim 26, wherein the first set of electrical connectors is positioned at a first clearance distance from the first end of the primary coil and the second set of electrical connectors is positioned at a second clearance distance from the second end of the primary coil, the second clearance distance being greater than the first clearance distance.

28. The method of claim 26 or claim 27, wherein the first connector distance is substantially equal to the second connector distance.

29. The method of any one of claims 26 to 28 as dependent on any one of claims 23 to 25, wherein the method further comprises: positioning a third set of electrical connectors adjacent to the first set of electrical connectors; and connecting the further secondary coil to the third set of electrical connectors using a plurality of further secondary conductors.

30. The method of claim 29, wherein the method further comprises: providing a plurality of further secondary conductor electrical insulator elements and positioning each further secondary conductor electrical insulator element at least partly around part of one of the further secondary conductors.

31. The method of any one of claims 19 to 30, wherein the method further comprises: providing a plurality of primary conductor electrical insulator elements and positioning each primary conductor electrical insulator element at least partly around part of one of the primary conductors.

32. The method of claim 30 or claim 31, wherein each electrical insulator element is of Polytetrafluoroethylene (PTFE).

33. The method of any one of claims 19 to 32, wherein the method further comprises: providing a first enlarged former end which is coupled to the first end of the former body; and providing a second enlarged former end which is coupled to the second end of the former body.

34. The method of claim 33 as dependent on any one of claims 26 to 30, wherein the method further comprises: coupling the first set of electrical connectors to the first enlarged former end;and coupling the second set of electrical connectors to the second enlarged former end.

35. The method of any one of claims 19 to 34, wherein the method further comprises: providing a screening layer between the primary coil and the or each secondary coil to at least partly electrically screen the or each secondary coil from the primary coil.