WO1999057737A1

WO1999057737A1 - Transformer

Info

Publication number: WO1999057737A1
Application number: PCT/EP1999/002781
Authority: WO
Inventors: Udo Fromm; Christian Sasse; Thorsten Schütte
Original assignee: Abb Ab
Priority date: 1998-05-01
Filing date: 1999-04-23
Publication date: 1999-11-11
Also published as: AU4135499A; GB9809430D0

Abstract

A transformer comprises a core (1) having a plurality of limbs, e.g. the sides of one or more squares, and winding packages (2a, 2b, 3a, 3b), each comprising turns of a primary winding intermixed with turns of a secondary winding, arranged on at least two adjacent limbs of the core.

Description

- 1 -

TRANSFORMER

BACKGROUND TO THE INVENTION

The present invention relates to a transformer.

The conventional method of w±nding a single-phase 5 transformer involves producing a primary winding in a first package and a secondary winding in a second package. If the magnetically permeable core is square shaped, the first package is usually wound around a 1 τm > of the core forming one side of the square and the second package is wound α -axnund the limb on the opposite side.

It has also been proposed to produce a transformer with low impedance by intermixing the primary and secondary windings. As described in our Bri ish Patent Application No. 9725331.4, each package may comprise concentric sets of

15.primary and secondary winding turns with the currents running in opposite directions to reduce short circuit forces. These forces are reduced even further if one of the windings is formed by a plurality of parallel-connected subturns and the primary and secondary windings are arranged

20 in a chessboard pattern, as viewed in cross-section.

To date, however, these intermixed windings have only been produced in packages which follow the conventional pattern, that is, two packages on opposite limbs of a square core for a single-phase transformer, or one package on each

25 of three transverse parallel limbs of a 3-phase transformer.

SUMMARY OF THE INVENTION

It is one object of the invention to provide a transformer in which the total length of cable in the windings is reduced.

30 Accordingly, the invention provides a transformer - 2 - having a core comprising a plurality of limbs, and winding packages, each comprising turns of a primary winding intermixed with turns of a secondary winding, arranged on at least two adjacent limbs of the core. The expression "adjacent limbs" means limbs which meet at an apex or junction.

Preferably, in the case of a square or rectangular core, the four limbs of the core are each wound with a package. In order to make the best use of the available space, the packages are preferably of different shapes. For example, if the core is square, two identical packages having an axial length equal to or slightly less than the internal limb length of the core and a relatively small height can be arranged on opposite limbs, whilst two identical packages having an axial length equal to the difference between the internal limb length of the core and the combined height of the other two packages, and a height equal to half the internal dimension of the core can be arranged on the other two limbs.

A 3-phase transformer according to the invention comprises a conventional core having two apertures and winding packages arranged on all seven limbs of the core.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which: -

Figure 1 is a schematic plan view of a single phase transformer according to an embodiment of the invention, and

Figure 2 is a schematic plan view of a 3-phase transformer according to an alternative embodiment. - 3 -

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in Figure 1, a tr nsformer comprises a core 1 of magnetically permeable material such as soft iron. The core is of constant, square cross-section and forms a generally square closed figure.

Winding packages 2a, 2b, 3a and 3b are formed on all four limbs of the core. Each winding package comprises intermixed turns of both a primary and a secondary winding. The packages 2a, 2b which lie on two opposite limbs have an axial length slightly less than the internal limb length of the core and a height (the shortest distance from the surface of the core to the outermost turns of the package) of about one quarter of the internal limb length. The space between the two packages 2a, 2b is occupied by the other packages 3a, 3b which have an axial length of approximately half the internal core limb length and a height also approximately half the internal core limb length.

By distributing the winding packages in this manner the total length of cable needed to wind the transformer can be reduced by about 25%.

Figure 2 shows an embodiment of the invention comprising a three-phase transformer having a core 11 of conventional configuration. Winding packages 12a, 12b, 12c, 12d are wound on the four longitudinal limbs and winding packages 13a, 13b, 13c are wound on the three parallel transverse limbs. Packages 12a, 12c and 13a form the windings of one phase, package 13b forms those of the second phase and packages 12b, 12d and 13c form the windings of the third phase. Again, a reduction in cable length is achieved compared to a conventional three-phase transformer wound only on the three transverse limbs.

To facilitate the intermixing of the windings, the cable used for the transformer is preferably of the type - 4 - described in our International Patent Application No. WO 97/45923 and comprises conductive strands surrounded in turn by semiconductive insulating and semiconductive layers. These layers are preferably polymeric, the semiconductive layers including carbon black or metallic particles. A transformer using such a cable does not require a complicated oil based insulation system and is therefore safer and more environmentally friendly.

A particularly advantageous embodiment of the invention is a booster transformer of the type described in our British Patent Application No. 9809432.9. The cable of this transformer comprises coaxial inner and outer conductors, one of which forms the pri ary and the other the secondary winding. The transformer has a very low impedance and a transformation ratio of almost exactly 1:1.

It will therefore be appreciated that the term "intermixed" as used herein includes such coaxial cables.

The winding packages can be connected together in an appropriate manner depending on the application, for example in series, in parallel (for a current transformer of lower impedance) , or in a series-parallel combination.

Claims

- 5 - CLAIMS

1. A transformer comprising a core having a plurality of limbs, and winding packages, each comprising turns of a primary winding intermixed with turns of a secondary winding, arranged on at least two adjacent limbs of the core.

2. A transformer according to c3aim 1, wherein one winding package is arranged on each limb of the core.

3. A transformer according to claim 1 or 2 wherein the core has four limbs forming a square or rectangle.

4. A transformer according to claim 3 , wherein first winding packages on two opposite limbs of the core each have a first axial length and a first height, and second winding packages on the other two limbs each have a second axial length less than the first axial length and a second height greater than the first height.

5. A transformer according to claim 4, wherein the first axial length is substantially equal to the internal length of the limbs on which the first packages are arranged.

6. A transformer according to claim 4 or 5, wherein the first height is substantially equal to one half of the difference between the internal length of the limb on which the second packages are arranged and the second axial length.

7. A transformer according to claim 4, 5 or 6, wherein the second height is substantially equal to one half of the internal length of the limb on which the first packages are arranged. - 6 -

8. A transformer according to claim 1 or 2 , wherein the core has seven limbs forming two squares or rectangles sharing one side in common.