AU773539B2 - Endless core for a multiphase transformer and a transformer incorporating same - Google Patents

Description

WO 00/30130 PCT/AU99/01006 -1- Title ENDLESS CORE FOR A MULTIPHASE TRANSFORMER AND A TRANSFORMER INCORPORATING SAME Field of the Invention The present invention relates to an endless core for multiphase transformer and a transformer incorporating such a core.

Background of the Invention Multiphase transformers are well known and are used in a variety of applications including for stepping up or stepping down line voltage in power transmission systems, to provide phase shifting, modulation, star-delta converters and general power supplies.

A typical multiphase transformer has a planar core provided with a number of square or rectangular windows each window being bound by upper and lower branches of the core, and on opposite sides by vertical legs forming part of the core. A primary winding is wound through each window, either on a branch or leg of the window.

similarly a secondary winding is would through each window. Irrespective of the number of phases, if the core has N windows then it will have N 1 vertical legs.

This provides an inherent magnetic and therefore electrical imbalance between the phases. This arises because the magnetic flux created by current flow in the primary windings cannot circulate equally about the respective windows because of the additional vertical leg. As a result, assuming each primary phase voltage is of the same magnitude and each secondary winding has the same number of turns, then the secondary outputs cannot be the same. The transformation process is not identical between the phases due to the difference in magnetic paths surrounding each window. In order to produce equalised outputs on the secondary windings, ie the same magnitude output on each winding, some of the primary or secondary windings must vary the number of turns to take account of the difference in flux distribution circulating about different windows of the transformer core. Such transformers also have an inherent inefficiencies due to flux leakage caused by the end windows having only a single flux return path.

08/04 2004 15:04 FAX 61 8 9221 4196. GIF~ AKPRH PASRLAI10 GRIFFITH BACK PERTH 4 IP AUSTRALIA Z005 -2- It is an object of the present invention to provide a transfoffmer core and an associated trasformer that attempts to alleviate at least the abovemnentioned problems in the prior art.

Acc-ording to a first aspect of the present invention there is provided a core for a multiphase transformer, said core comprising a body made of two or more rigs having a common central axis, each rin comprising of a strip of magnetically permeable material wound, about said central axis, said body provided with a plurality of windows passing radially through said body, each window bound by opposed axially extending legs and opposed circuniferentially extending branches, wherein said branches of each window are provided in respective axially adajcent rings, said branches and legs of each window defining a closed magnetic circuit of substantially uniform magnetic permeability through which magnetic flux can circulate about said windows.

Preferably the core includes a plurality of primary windings, one primar y winding being provided for each electrical phase, each primary winding having at least one turn wound directly about a branch or a leg of a corresponding window.

Preferably said primary windings are wholly would directly about one or more of the 420 branches or legs of said corresponding window.

Preferably said primary windings are evenly spaced about said central axis.

Preferably said windows are formed as an array of windows circumferentially about and axially along said body.

Preferably in one embodiment each primary winding has a plurality of tunw and said turns are wound about more than one branch or one leg of said corresponding window.

COMS ID No: SMBI-00702408 Received by IP Australia: Time 17:11 Date 2004-04-08 08/04 2004 15:04 FAX 61 8 9221 4196GRFIH AC PETIPUSALA IQ0 4 IP AUSTRALIA Q006 GRIFFITH HACK PERTH -2/1 According to the present invention there is also provided a multiphase transformer comprising: a core according to said one form of the present invention; a plurality of primary windings, one primary winding being provided for each electrical phase of said transformer, and, a plurality of scondary windings; each priimary winding having at least one turn is wound directly about a branch or a leg of a corresponding window to produce lines of magnetic flux which circulate about said corresponding window; and, I at least one of said secondary windings having at least one turn wound directly about a branch or a leg of a window about which said lines of magnetic flux circulate to induce the current in said at least one secondary winding.

According to the present invention there is also provided a core for a multi-phase transformer, 20 said core comprising a body made of magnetically permeable material in the shape and configuration of a loop about a central axis, said body provided with a plurality of windows passing axially through said body, each window defined by radially opposite branches and circumferentially opposite legs, where each leg is common to two circumferentinily adjacent windows, According to a fiurther aspect of the present invention there is provided a method of constnucting a core for a multiphase transformer according to the first aspect of this invention, the method comprising the steps of stamping and winding about said central axis a strip of magnetically permeable material to form said body, said stamping arranged to produce said plurality of 3o windows passing radially through said body.

COMS ID No: SMBI-00702408 Received by IP Australia: Time 17:11 Date 2004-04-08 08/04 2004 15:05 FAX 61 8 9221 4196 GRIFFITH HACK PERTH IP AUSTRALIA Z007 2/2 According to a further aspect of the present invention there is provided a method of constructing a core for a multiphase transformer according to the first aspect of this invention, the method comprising the steps of continuous winding about said central axis a strip of magnetically permeable material to form said body; and machining, cutting or otherwise forming said plurality of windows radially through said body.

0 ee h2mtkinflfwtJ4ZS3 *Mclce-Epd Tqc.2. 2/I, 2/2- Air/I ZOO' COMS ID No: SMBI-00702408 Received by IP Australia: Time 17:11 Date 2004-04-08 PCT/AU99/01006 Received 19 December 2000 -3 Brief Description of the Drawings Embodiments of the present invention will now be described by way of example only with reference to the accompany drawings in which: Figure 1 is a perspective view of a core in accordance with the present invention and a six phase transformer incorporating that core; Figure 2 is a perspective view of a second embodiment of the core and a 12 phase transformer incorporating that core; Figure 3 is a perspective view of a third embodiment of the core in accordance with the present invention; Figure 4 is a perspective view of a fourth embodiment of the core; and, Figure 5 is a cutaway perspective view of an electric motor incorporating a core in accordance with the present invention.

Detailed Description of the Preferred Embodiments Referring to Figure 1, there is illustrated an endless core 10 for a multiphase (in this example, six phase) transformer 12. The core 10 is formed as an endless circular or annular loop. A plurality of windows 14,-146 (referred to in general as windows 14,) are formed through and about the core 10. Adjacent windows 14, share a common portion or leg 16,j where i and j designate the adjacent windows. For example, leg 16,2 is the portion of core 10 between adjacent windows 14, and 142; and leg 1645 is the portion or leg of core 10 between adjacent windows 144 and 145. It will be appreciated that because the core 10 is endless, there are no dead ends in so far as magnetic flux is concerned and therefore the core 10 facilitates the existence of i WO 00/30130 PCT/AU99/01006 -4symmetrical magnetic flux through the core Each window 14, is bound on opposite sides by the adjacent, core portions or legs 16,j and, by upper and lower branches and Thus, for example window 14, is bound on the left side by common core portion 16,,2; on the right side by common core portion 166,,; upper branch BU; and, lower branch B,.

Multiphase transformer 12 is constructed by winding respective primary and secondary windings through the windows 14,. In the embodiment shown, primary windings 18, and 186 (referred to in general as primary windings 18,) link with respective windows 14,. More particularly, two primary windings 18, (of the same phase) are provided for each window 14,, with one primary winding about the upper branch B U and another primary winding about a lower branch B, of each window 14-,.

For example, looking at window 14, a pair of primary windings 18, is provided, one of each formed about the upper branch B, and lower branch B, of the window 14,.

When the primary windings 18, are coupled to respective phases of a six phase AC power supply lines of magnetic flux Oi are generated and circulate about at least the window through which the primary winding 18, is wound. Again taking for example window 14, when the primary windings 18, are connected to one phase of the six phase AC power supply, lines of magnetic flux 0, are generated that circulate about window 14,. However, it must be appreciated that the magnetic flux generated can also circulate or return about other windows 14,. Thus a part of the magnetic flux 0, can circulate about both windows 14, and 142 returning through legs 162,3 and 166, and circulate about windows 14,, 142 and 146 returning via legs 162.3 and 165.6.

The placement of secondary windings through the windows 14, is dependent upon the desired output. If it is desired that the phase of the output from the secondary windings is to be the same as the phase of the corresponding primary winding then secondary windings 20,, 20s6 can be wound for example about the lower branch B, of each window 14, 146 respectively. (Of course in a variation, the secondary windings 206 can be placed about the upper branches B, of each window or WO 00/30130 PCT/AU99/01006 even alternate between the upper and lower branches.) It will be appreciated that because of the symmetric distribution of magnetic flux Oi about each of the windows 14,, assuming that the primary voltage for each phase is of the same magnitude, the magnitude of the voltage output from the secondary windings 20,i will be the same if each of the secondary windings 20,, have the same number of turns. Thus, the core and transformer 12 provide the ability to have secondary output of equal magnitude where the secondary windings 20,, 20,6 have the same number of turns.

As discussed above in relation to the prior art, because of the inherent magnetic imbalance of known cores and transformers, in order to have secondary outputs of equal magnitude in a multiphase transformer one must deliberately design some of the coils to have different number of turns.

The core 10 and transformer 12 also allow for an infinite possibility of phase shifting or combining. If one wanted to obtain a secondary output of a phase halfway between the phase of say the primary voltages supplying primary windings 18, and 182 then a secondary winding 20,p (shown in phantom) can be wound through both windows 14, and 142 ie about the common core portion 16,,2. Now, the second winding 20,p links with the magnetic flux 4, and 02 and thus the secondary output is of a magnitude and phase corresponding to the vector or phasor addition of the voltage induced by fluxes and 2. This provides a 1:1 transformed combination of the phases feeding primary windings 18, and 182. However combinations of other ratios and thus different amounts of phase shifting can be achieved at will by simply winding the secondary winding 20,p about the upper or lower branches Bu,B, or common core portions 16ij of different windows. For example, in the embodiment shown in Figure 1, the primary phases are 600 apart. To obtain a secondary output having a phase 150 (ie /4 the phase difference) in advance of the phase of the primary voltage feeding primary winding 18, a secondary winding (not shown) is provided having a 1:4 turn ratio about branch B, of window 14, and branch B, of window 142, ie the secondary winding has four turns passing through window 142 for every turn passing through window 14,.

WO 00/30130 PCT/AU99/01006 -6- Figure 2 illustrates a core 10' suitable for constructing a twelve phase transformer 12'. Here, the core 10' is again in shape of a ring or annulus but this time provided with twelve windows 14, 14,,2 and twelve common core portions 16,j, one of each between respective adjacent windows 14,. A primary winding 18, is wound about lower branch B, of each window 14,. A secondary winding 20, is wound about the upper branch B u of each window 14,. The phase of the output of any secondary winding 20, is the same as the phase of voltage driving the corresponding primary winding 18,. However, as with the previous embodiment, the secondary winding can be wound partially about the upper and lower branches B, and B, or common core portions 16,,j of different windows in any desired combination to produce a desired phase output in accordance with standard transformer design technics.

Figure 3 illustrates an extending (vertically stacked) core 10" and a multiphase transformer 12" constructed using the core 10". The core 10" can be considered as being two six window cores vertically stacked upon each other. Thus the core has a lower set of windows 14, 146 and an upper set of windows 147 14,2 with windows 14, and 14,+6 in vertical alignment. Primary windings 18, 18, are wound about the lower branches B, of windows 14, 146 respectively; and, primary windings 187 18,,2 are wound about the upper branches B, of the upper set of windows 147 141 2 A set of secondary windings 20 are wound about the middle branch Bm between vertically adjacent windows 14,, 14,+6. Therefore, in this particular illustrated embodiment, there are only six secondary coils 20. The output of any particular secondary winding 20 would be the transformed phasor or vector addition of voltages induced by the magnetic flux generated by the primary windings linked with the windows common to that particular secondary winding 20. In order to avoid saturation it is preferred that the volume of core constituting the middle branch Bm is the sum of the volume of the core constituting the lower branch B, and upper branch B, of the windows 14,, 14,+6. This embodiment then allows the combination of two six phase supplies that are out of phase with each other. For example, if there are two six phase power supplies, one providing input to coils 18, 18, and another providing input to primary windings 187 181,2, the two power sources can be combined to provide a six phase output through the secondary WO 00/30130 PCT/AU99/01006 -7windings 20. This could be particularly useful in for example coupling two multiple phase power supplies to a common power transmission grid. The core configuration will also allow for the ability to have 6 primary and 12 secondary windings. Also a turns ratio of 1/0.5 primary to secondary, or secondary to primary, as well as incorporating other windows will produce any fraction of volts required.

In a different configuration (not illustrated) the primary windings 18, 181,2 of transformer 12" can be connected to a different phase of a twelve phase power supply and primary windings 20 round through various windows 14, to provide a transformed twelve phase output. Again, the phasing of the output from the secondary windings can be arranged as required in accordance with known transformer design techniques to provide the desired secondary phase output.

Figure 4 further illustrates a further embodiment of the core 10"' and a corresponding In the embodiments shown in Figures 1-3 the core 10 and windows 14i are arranged so that the core 10, 10' and 10"' is endless about a first axis that is perpendicular to the axis of any particular window 14,. With the core 10"' of Figure 4, the axis of the core 10 is parallel with the axis of any window 14,. As with all previous embodiments, core 10"' is configured as an endless loop having a plurality of windows 14i where adjacent windows share a common portion of core 16,j so that they number of windows 14, equals the number of common core portions 16,j. More specifically, three windows 14, 143 are formed in the core 10"' with a primary winding 18, 183 respectively wound about the lower (radially outer most) branches B, of each window 14,. Respective secondary windings 20, 203 are wound through the windows 14, 143 respectively about the corresponding upper (radially inner most) branches B

U

It is preferred that the core 10"' is configured so that the volume of core in the upper and lower branch portions Bu of each window 14, is the same. This assists in avoiding saturation of the core. This can be achieved by appropriate placement or configuration of the windows 14,.

Figure 5 illustrates an application of the core 10 shown in Figure 1. The core 10 is used in this application in a transverse flux motor 26. Full operation and WO 00/30130 PCT/AU99/01006 -8constructional details of the transverse flux motor are described in the Applicant's Australian Application No PP 7124 the contents of which is incorporated herein by way of reference. The structure of core 10 and the placement of primary windings 18, 186 is identical to that described in the first embodiment described in relation to Figure 1. However, instead of multi turn electrically separate secondary windings a single turn secondary winding between 20, is provided about each common core portion 16ij with each of the single turn secondary windings 20, being in mutual electrical connection. Thus, the single turn secondary windings 20, 206 form a wheel like structure 30 having an inner rim 32 and outer rim 34 joined by radially extending spokes 36. The outer rim 34 is depicted as residing in the air gap 38 of a cockcroft ring 40. Without going into the detail of operation of the motor 26, currents are induced through the single turn secondary windings 20, 206 that interact with magnetic flux passing through the air gap 38 of the cockcroft ring thereby generating transverse forces on the outer rim 34 of the wheel 30 causing it to move. The path of motion of the wheel 30 can be controlled at will by variation of the magnitude and frequency of the primary voltages supplied to the primary coil 18, 186 and the phase relationship therebetween.

Now that embodiments of the present invention have been described in detail it will be apparent to those skilled in the relevant arts and numerous modifications and variations may be made without departing from the basic inventive concepts. For example, in each of the embodiments shown, the core 10 is depicted essentially as being in a ring, annulus or circular type form. However it can assume other shapes provided that it is continuous or endless and is provided with equal numbers of windows and common core portions. Also, the exact number of windows provided is simply dependent upon the application and in particular the number of primary phases. Also, the position and placement of the secondary windings 20i is dictated solely by the desired magnitude and phase of the secondary outputs. The core 10", 10"' can be made by casting; continuous stamping and winding of an insulated strip of magnetically permeable material; winding of a strip of material then machining/cutting the windows. Further the core can be split through a plane passing through the windows 14: to facilitate mechanical/automatic winding of the WO 00/30130 PCT/AU99/01006 -9primary and/or secondary windings about the window branches or loading of prewound bobbins on the common core portions 16,j. All such variations and modifications together with others that would be obvious to a person of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the aforegoing description.

Claims (18)

1. A core for a multi-phase transformer, said core comprising a body made of two or more rings having a common central axis, each ring comprising of a strip of magnetically permeable material wound about said central axis, said body provided with a plurality of windows passing radially through said body, each window bound by opposed axially extending legs and opposed circunifereutially extending branches, wherein said branches of each window are provided in respective axially adaj cent rings, said branches and legs of each window defining a closed magnetic circuit of substantially uniform magnetic permeability through which magnetic flux can circulate about said windows.

2. The core according to claim 1 compri sing a plurality of pimary windings, one primary winding provided for each electrical phase, each primary winding having at 015 least one turn wound directly about a branch or a leg of a corresponding window.

3. The core according to claim 2 wherein at least one of said primary windings is wholly wound about one or both branches of said corresponding window.

4. The core according to claim 2 wherein at least one of said primary windings is wholly wound about one or both legs of said corresponding window. 0 0 @9005. The core according to claim 2 wherein at least one of said primary w-indings has a plurality of turns wherein at least one of said turns is wound about one branch of said corresponding window and at least one turn is wound about one leg of said corresponding window.

6. A multi-phase transformer comprising at least: a core according to claim 1; Unt~aftnpdr KIM. 0bkv I-U -AWOU COMS ID No: SMBI-00702408 Received by IP Australia: Timne (11:m) 17:11 Date 2004-04-08 08/04 2004 15:05 FAX 61 8 9221 4196 GRFIhBCPET IASALA []0 GRIFFITH HACK PERTH 4 IP AUSTRALIA Z009 -Il- a plurality of primary windings, one primary winding being provided for each electrical phase of said transformer, and, a plurality of secondary windings; each primary winding having at least one turn wound directly about a branch or a leg of a corresponding window to produce lines of magnetic flux which circulate about said corresponding window; and, at least one of said secondary windings having at least one turn wound directly about a branch or a leg of a window about which said lines of inagnetic flux :*~:circulate to induce the current in said at least one secondary winding. C7. The transformer according to claim 6 wherein at least one primary winding is 1S wound directly about at one or both branches of one window, and at least one secondary winding is wound directly about one or both branches of said one window.

8. The transformer according to claim 6 wherein at least one primary winding is wound directly about one or both branches of one window, and at leat one secondary winding is wound directly about one or both legs of said one window. a The transformer according to claim 6 where in at least one primary winding is wound directly about one or both branches of one window, and at least one secondary winding is wound directly about a branch or a leg of said one window. and directly about a branch or a leg of another window. h,-ge* u)w~jp42ofl m-M- dna 1-2X -lil 2254 COMS ID No: SMBI-00702408 Received by IP Australia: Time 17:11 Date 2004-04-08 08/04 2004 15:05 FAX 61 8 9221 4196 GRIFFITH HACK PERTH IP AUSTRALIA Z0O10

12- 11. The transformer according to claim 6 wherein at least one primary winding is wound directly about one or both legs of one window, and at least one secondary winding is wound directly about one or both branches of said one window. 12. The transfonner according to claim 6 wherein at least one primary winding is wound directly about one or both legs of one window, and at least one secondary winding is wound directly about one or both less of said one window.

13. The transformer according to claim 6 wherein at least one primary winding is wound directly about one or both legs of one window, and at least one secondary winding is wound directly about at least one branch and at least one leg of said one window. :14. The transfoniner according to claim 6 wherein at least one primary winding is 1 wound directly about oneas or e bregan wiow and aton leastf one secndaryindinglas oescnaywnigis wound directly about at es n branch or on leg of said one window. bota The transformer according to claim 6 wherein at least one primary winding is wound directly about at least one branch and at least one leg of one window, and at least one secondary winding is wound directly about at es n branch rd t legs one inow of sai on.idw

17. A core for a multi-phase transforner, said core comprising a body made of magnetically permeable material in the shape and configuration of a loop about a central axis, said body provided with a plurality of windows passing axially through said body, 24~~ i- Apiti S COMS ID No: SMBI-00702408 Received by IP Australia: Time (I-tm) 17:11 Date 2004-04-08 08/04 2004 15:05 FAX 61 8 9221 4196 GRIFFITIH BACK PERTH -+IP AUSTRALIA Z 011 -13- each window defined by radially opposite branches and circumferentially opposite legs, where each leg is common to two circumfentially adjacent windows.

18. A core for a multi-phase transformer according to claim 17, comprising a plurality of primary windings, one primary winding provided for each electrical phase, each primary winding having at least one turn wound directly about a branch or a leg of a corresponding window.

19. A core for a multi-phase transformer according to claim 18 wherein the radially opposite branches of each window are configured to have the sane volume of magnetically permeable material. 0 20. A core according to any one of claims 17-19 wherein said loop is in the ftrm of a 15 disc provided with a central axially extending through hole, wherein said windows are provided about said central through hole.

21. A method of constructing a core according to any one of claims 1-5, said method comprising the steps of stamping and winding about said central axis a strip of magnetically permeable material to form said body, said stinping arranged to produce said plurality of windows passing radially through said body.

22. The method according to claim 21 comprising the step of splitling said core "through a plane passing through said windows.

23. A method of constructing a core according to any one of claims 1-5, said method comprising the steps of continuous winding about said central axis a strip of magnetically permeable material to form said body, and machining, cutting or otherwise forming said plurality of windows radially through said body.

24. The method according to claim 23 comprising the step of splitling said core through a plane passing through said windows. COMS ID No: SMBI-00702408 Received by IP Australia: Time 17:11 Date 2004-04-08 08/04 2004 15:06 FAX 61 8 9221 4196 GRIFFITH HACK PERTH -IF AUSTRALIA 0~J012 14- 5 S S S *OSS -The method according to claims 22 or 24 comprising the step of loading a prewound bobbin on one or more legs of said core.

26. A core for a multi-phase transformer according to claims 1 or 17 substantially as herein described with reference to and as illustrated in the accompanying drawings.

27. A multi-phase transformer substantially as herein described with reference to and as illustrated in the accompanying drawings.

28. A method of constructing a core for a multi-phase transformer substantially as herein descrbed with reference to and as illustrated in the accompanying drawings. COMS ID No: SMBI-00702408 Received by IP Australia: Time 17:11 Date 2004-04-08