PRIORITY DOCUMENTS

I ^' QO l] The present application claims priority from Australian Provisional Patent Application

No. 2013903359 titled "A WOUND TRANSFORMER CORE AND A METHOD FOR MAKING THE

SAME" and filed on 3 September 2013, the content of which is ^' hereby incorporated by reference in its entirety.

TECHNICAL FIELD

1 0021 The present invention relates to wound magnetic cores for transformers, BACKGROUND

10003] Wound transformer cores of the type formed by concentrically arranging and nesting together a series of magnetic steel strip laminations are known in the art. An example of wound core technology is the present applicant ^' s UMCORE® transformer core technology which may be used for core-type, single leg and shell-type, single and 3-phase distribution and general purpose transformers.

[ 00041 A wound transformer core may have a generally rectangular geometry consisting of a pair of opposing core legs separated by opposing core ends or yokes. The thickness of the core legs and ends is referred to as the core build-up (BUP) and is a constant parameter which is. redetermined for a given core,

[00051 A wound core is energised by a magnetising current which flows ttaough a primary ^' winding (e.g. copper coil) around the core. Magnetic flux flows around the core and induces a voltage into a secondary winding around the core. The magnetic .flux: per unit area perpendicular to the direction of magnetic flow is referred to as the magnetic f!ux density.

1 00 J W en wound cores are manufactured, individual laminations must be bent and cut and the arranged together during core assembly. The locations where the laminations are bent (i .e. stressed) in the corner regions and where the laminations are cut (forming discontinuities) are locations where a core typically exhibits its greatest losses. Core loss is defined as the electrical power expended in the. form of heat within the core when the core is subjected to alternating magnetising force. The greater the core loss, the higher the magnetisation current that is required to energise the core,

[0007] It is desirable to produce an efficient wound transformer core that is capable of reducing the core loss and required magnetising current. SUMMARY

[0008] According to a first aspect of the invention, there is provided a wound transformer core, including:

a plurality of magnetic steel strip laminations nested together to form a series of concentric layers which together define:

a first core leg for receiving a conductive coil and having a first leg thickness;

a second core leg opposed to the first core leg and having a second leg thickness;

a first core end extending perpendicularly between the first and second core legs and having a first end thickness; and

a second core end extending perpendicularly between the first and second core legs, the second core end opposed to the first core end and having a second end thickness,

wherein, at least one of the second leg thickness, first end thickness and second end thickness is greater than the first leg thickness.

[0009] in one embodiment, one or both of the first and second end thicknesses are greater than the first leg thickness,

[001 Oj In one embodiment, at least one layer of the core has overlapping end segments at the first and/or second core end.

[ 00111 In one embodiment, the first and/or second end thickness is double the first leg thickness.

[ 0012] In one embodiment, at least one layer of the core has end segmen ts at the first and/or second core end that are in butted engagement.

[0013 [ i one embodiment, the second leg thickness is greater than the first leg thickness.

[0014 | In one em bodiment, at least one l ayer of the core has overlapping kg segments on. the secon d core leg.

[001.5] In one embodiment, at least one l ayer of the core has leg segments on the second core leg that are in butted, engagement.

[0016 hi one embodiment, the laminations are cut along the first and/or second core leg. [0017] In one embodiment, the magnetic steel strip laminations are made from amorphous steel. 10018] In one embodiment, a conductive coil or winding is able to be directly wound onto one or both of the core legs,

[0019] According to a second aspect of the invention, there is provided a wound transformer core, including:

first and second core segments joined together to define a pair of lengthwise extending core legs and first and second core ends disposed generally perpendicularly to the core legs, the core legs having a leg build-up defining a- leg thickness, the first core end having a first core end buikl-up defining a first end thickness and the second core end having a second core end build-up defining a second end thickness- each core segment formed by nesting together a plurality of packets of generally C-shaped magnetic steel strip laminations such that adjacent packets have spaced apart end portions, and

wherein, the core segments are joined together b overlapping the end portions of each packet of the first core segment with correspond ing end portions of each packet of the second core segment such that both the first and second core end build-ups are greater than the leg build-up.

[0020] In one embodiment, substantially linear slots are formed between the spaced apart end portions of adjacent packets of each core segment.

100211 In one embodiment, for each core segment the length of the end portions of each packet progressively decrease from an innermost packet to an outermost packet.

[0022 f In one embodiment, each packet has 'η' laminations, where 2 n< t0.

[0023] In one embodiment, the wound transformer core is for use in a single phase transformer.

(0024 J In one embodiment, the wound transformer core is for use in a three phase transformer.

[0025] According to a third aspect of the invention, there is provided a wound transformer core, including:

a plurality of core segments formed by nesting together a plurality of packets of generally C- shaped magnetic steel strip laminations, tire core segments joined together to define a plurality of lengthwise extending core legs, each core leg for receiving conductive coil and having first and second core ends disposed generally perpendicularly to the core legs, the core legs having a leg build-up defining a kg thickness, each first core end having a first core end build-up defining a first end thickness and each second core end having a second core end build-up defining a second end thickness,

wherein, for each core segment, at least one of the first end thickness and second end thickness is 10026 ] Accordin to a fourth aspect of the invention, there is provided a transformer, including:

a wound core including a plurality of magnetic steel, strip laminations nested together to form a series of concentric layers which together define:

a first core leg having a first leg thickness;

a second core leg opposed to the first core leg and having a second leg thickness; a first core end extending perpendicularly between the first and second core legs and having a first end thickness; and

a second core end extending perpendicularly between the first and second core legs, the second core end opposed to the first core end and having a second end thickness; and a conductive coil that is w-oimd about the first core leg;

wherein, at least one of the second leg thickness, first end thickness and second end thickne s is greater than the first leg thickness.

BRIEF DESCRIPTION OF DRAWINGS

[0027] Embodiments of the present invention will be discussed with reference to the accompanying drawings wherein;

100281 Figure 1 is a perspecti ve view of a wound transformer core according to an embodiment of the invention; j 00291 Figure 2 is a top view of the wound transformer core of Figure 1 ;

[ 0030] Figure 3 A is an enlarged top view of the upper right corner of the wound transformer core of Figure 2;

[0031] Figure 3B is an enlarged top view of the lower right corner of the wound transformer core of Figure 2;

[0032] Figure 4 is a top view of a first core segment of the wound transformer core of Figure 1 ;

[0033] Figures 5A-5C. depict a sequence of top views illustratin a method of assembling a wound transformer core according to an embodiment ; 0034] Figure 6 is a top view of core segments of a wound transformer core arranged in a back-to-back configuration;

[0035] Figure 7 is a top view of an assembled single-phase wound transformer; [0036] Figure 8 is a top view of a wound transformer core according to a farther embodiment of the invention;

[0037] Figure 9 A is a schematic representation of a wound transformer core according to a further embodiment of the invention having an increased end bui ld-up;

[0038] Figure 9B is a schematic representation of a wound transformer core according to a further embodiment of the invention having an increased end build-up;

[0039] Figure 9C is a schematic representation of a -wound transformer core according to a further embodiment of the inventio having an increased end build-up;

[0040] Figure 9D is a schematic representation of a wound transformer core according to a further embodiment of the invention having an increased end build-up;

[0041] Figure 10A is a schematic representation of a wound transformer core according to a further embodiment of the invention having an increased leg build-up;

[ 0042] Figure 10B is a schematic representation of a wound teansformer core according to a further embodiment of the invention having an increased leg build-up;

[ 0043] igure 10C is a schematic representation of a wound transformer core according to a further embodiment of the invention having an increased leg build-up; and

[ 0044 [ Figure I0D is a schematic representation of a wound transformer core according to a further embodiment of the invention having an increased leg build-up.

[00451 In the following description, like reference characters designate like or corresponding parts throughout the figures.

DESCRIPTION OF EMBODIMENTS

[0046] Referring now to Figure 1, there is shown a perspective view of a wound transformer core 1 according to an embodiment of the invention. A top view of the core 10 is shown in Figure 2, The core 10 includes a first core segment 100 and a second core segment 200 comprising packets of magnetic steel strip laminations which, are assembled together to form the core 10. The core 10 is of generally

rectangular configuration having core legs 12, 14 and core ends (or yokes) 16, 18. Each core leg 12, 14 has a leg build-up (of packets of the first r second core segment) defining a leg thickness 20. Each cote end 1 , I S has an end build-up (of packets of the first and second core segments) defining an end thickness 30. The depth or height of ^* the core 1.0 is a constant throughout,

[0047] The end build-up 30 of the core 10 is greater than the leg build-up 20. In one embodiment, the end-buildup 30 has twice the thickness as the leg build-up 20. The cross-seetional area of the ends 16, 18 (taken through section A- A.) is therefore greater than the cross -sectional area of the legs 12, 14 (taken through section B-B). This increase in cross-sectional area at the ends 16, 18 lowers the magnetic flux density at ends 16, 18 and creates a lower loss flux path. The greatest losses in core 10 occur in the corner regions where the laminations are bent (i.e. stressed) and where gaps or discontinuities arc introduced at the end joints. By lowering the magnetic flux density locall in these regions the overall core loss can be reduced. A further advantage of core 10 is that a conductive coil or winding (e.g. copper coil) is able to he directly wound onto core legs 12 or 14 prior to assembly of core segments 100 and 200.

| 0048 ^' ) Figures 3A-3B show enlarged top views of the upper right corner and lower right corner of the core 10 respectively. These magnified views illustrate several packets 110, 210 of the respective core segments 100, 200 and show that each packet 1 1 ø, 210 comprises a plurality of magnetic steel strip laminations 5. Each magnetic steel strip lamination 5 in a packet t 10, 210 is bent and cut to form a generally C-shaped lamination having a web section or leg 2 and flange or end sections 4, 6. The laminations 5 also comprise angled corner sections 7, 8·. The flange or end sections 4, 6 are disposed generally perpendicularly to the web section or leg 2 of each lamination 5. A plurality of laminations 5 are grouped together to form a packet 1 10, 10. Each packet has 'η' laminations, where 2 n<10. The laminations 5 and packets .1 .10, 210 gradually increase in dimension from an. innermost packet 1 10', 210* to an outermost packet 110", 210" such that adjacent packets within a core segment may be nestably engaged.

[0049] By way of non-limiting examples, the core 1.0 may be made from strips of electrical steel such as grain oriented silicon steel or non-oriented electrical steel. Alternati vely, amorphous steel strips may be used to manufacture the core 10. The thickness of the strip materi al used to produce the laminations 5 may be in the range of 0.2 to 0.35mm.

[0050) Referring now to Figure 4, core segment 100 shall be described in further detail. Core segment 1 0 includes a plurality of packets 110 of generally C-shaped magnetic steel strip laminations 5, each packet 110 formed by nesting together a plurality of said laminations 5 such that each packet. 1 10 defines a lengthwise extending leg portion 1 12 having a leg stack thickness 145 and upper and lower end portions 1 1.4, 1 16 respectively. The upper and lower end portions 1 14, 116 are disposed generally perpendicularly to the kg portion 1 12. The packets 1 10 also have angled corner portions 1 17, 1 18 disposed between the leg portion 112 and upper and lower end portions 1 14, 1 16. 10051] Each packet 110 is adapted to he nestably engaged with an adjacent packet such that the leg portion 1 12 of each packet engages the respecti ve leg portion 1.2 of an adjacent packet and the upper and lower end portions 1 14, 116 of each packet 1.10 are laterally spaced apart from the respective upper and lower end portions 1 1 , 1 6 of adjacent packets 1 1 , the lateral spacing 45 being at least as large as the leg stack thickness 145. In the embodiment shown in. Figure 4, the lateral spacing 45 is the same as the leg stack thickness 145.

(0052] The upper and. lower end portions 1 14, 3 16 of each packet 1 10 of laminations 5 are spaced apart to form substantially linear slots 40. ^" The purpose of the slots 40 is to provide receiving portions to enable the insertion of corresponding upper and lower end portions 214, 216 of the second core segment 200 during assembly of the core 10.

10053 [ Figures 5A-5C provide a; series of sequential views of the core assembly process illustrating how the upper end 16 of the core 10 is assembled. In these figures, the lower end of the core 18 has already been assembled. Figure 5A shows that with the lower end 18 assembled, the legs 12. 14 may pivot about the lower angled corner portions 1 18, 218 such that the upper ends of each core segmen t 100, 200 are pulled apart. Figure 5B shows the beginning of the overlapping engagement of the upper end portions of the first and second, core segments 100, 200. The first end portions to come into engagement arc of the innermost packets 1 1.0', 10' . The upper surface 214a' of the upper end portion 214" of the innermost packet 210' slidably engages with the bottom surface 1 14b' of the upper end portions 1 14 of the innermost packet 110'. The upper cud portion 214 of the second innermost packet of core segment 200 the begins to slide into the linear slot 40 formed between the upper end portion 1 34' of the innermost packet 110' and the upper aid portion of the second innermost packet of core segment 100.

[ 0054] Figure SC illustrates a further progression of the assembly process showing the progressive overlapping engagement of upper end portions 114, 214 of packets 110, 210 of the first and second core segments 100, 200 respectively. As shown, the upper end portions 11 , 214 of packets 1 i 0, 210 ma bend slightly about upper angled corner portions 117, 217 to enable the respective end portions to be inserted into gaps 40 between adjacent packets of each core segment. The progressive overlapping of packets 1 10, 210 continues until, the outermost packets 1.10", 2 0" are overlapped.

[0055 ] For ease of assembly, the length of the upper end portions 1 14, 214 of each packet 1 1 , 21 progressively decreases from an innermost packet 110', 210' to an outermost packet 110", 210".

Similarly, the length of the lower end portions of each packet progressively decreases from an innermost packe t to an outermost packet. As a result of this, the end face of each core segment 100, 200 is tapered as sees clearly for example in Figure 4. The end face tapers inward from the irmermost packet 110' to the outermost packet 110". Alternatively, the end face of each core segment 100, 200 may taper outward as shown for example in Figure S which illustrates another embodiment of a wound transformer core 10'. [0056] Referring now to Figure 6, there is shown a. top view of core segments 200 of a wound transformer core arranged in a back-to-back configuration. Core segments may be arranged in this manner for example when building a wound transformer 300 such as that shown in Figure 7 which i a single- phase transformer. The core of the transformer shown in Figure 7 has a central leg 12' (shown in Figure 6) whic has double th e build-up of the individual legs of each core segment 200. A coil or winding 350 (of conductive material such, as copper) may be wound directly onto the central leg 12' before the core is assembled together with mating core segments 100 using the method of progressively overlapping packets of each core segment as previously described.

10057] While the present invention has been described in some detail with respect to the wound core type shown in Figures 1-8, it is to be understood that the principles of the present invention may be applied to a wide range of wound transformer cores. In other embodiments, the core may have a plurality of core segments formed by nestin together a plurality of packets, of generally C-shaped magnetic steel strip laminations, the core segments joined together to define a plurality of lengthwise extending core legs, each core leg for receiving a conductive coil and having first and second core ends disposed generally perpendicularly to the core legs, the core legs having a leg build-up defining a leg thickness, each first core end having a first core end build-up defining a first end tliickness and each second core end having a second core end build-u defining a second end thickness. For each core segment, at least one of the first end thickness and second end thickness is greater than the leg thickness in order to lower magnetic flu density. In one embodiment, the core may have three core segments spaced radially apart at 120° for use in a three phase transformer.

[0058 ] Furthe illustrative embodiments of a wound transformer core according to the present invention are shown in Figures 9A-9D and IOA-1 D.

10059 ] Referring now to Figure 9 A there is shown a schematic representation of a wound transformer core iOA which is a type of distributed gap core having one cut per lamination. Laminations 50 A, 50B, 50C, SOD and 50E are nested together to form a series of concentric layers such that each subsequent lamination of the core is larger than a previ ous lamination.. Although only fi ve laminations are shown in Figure 9 A for illustrative purposes, it will be appreciated that a fully assembled core would have many more laminations. In an alternative method of construction, laminations could be grouped into packets of laminations and assembled in a similar manner to that shown in Figure 9A for individual laminations 50A-50D.

[0060] Each lamination has a pair of length wise extending legs, a first core end segmen and a pair of overlapping core end segments. With respect to innermost lamination 50A, the lamination has legs 52A, 54A. core end segment 53 A and overlapping end segments 55A, 56A. The assembled core 1 OA has a pair of opposing (and lengthwise extending} core legs 12, 14 and a pair of core ends 16, 18, The core ends 16, 18 extend generally perpendicularly between the core legs 12, 14. Core end 18 and legs 12, 14 have no cuts or discontinuities. The cuts are located at end 16 such that a series of small gaps or discontinuities 68 are formed.

10061 } in order to reduce losses in core K)A, the ^' build-up of end 16 (and thereby cross-sectional area) is increased relative to the build-up or crass-sectional area of legs .12, 14 and opposing end 18. When core Ι.0Α is energised, the increase in cross-sectional area lowers the magnetic flux density at end 16 where the discontinuities 68 ace introduced. Consequently, a lower loss flux path is created and the overall efficiency of the core is increased. The cross-sectional area of end 16 is increased by increasing the thickness or end build-up of end 16. For core I OA, the end build-up of end 16 is double the build-up or thickness of legs 12, 3.4 and end 18. This is achieved by overlapping end segments of each respective lamination 50A-50E at end 16. At end 16, each lamination has a pair of end segments which o verlap and then adjacent laminations overlap the previous, lamination in the stack. For example, the: innermost lamination 50A has overlapping end segments S5A, 56A. Adjacent lamination SOB Iras overlapping end segments 55B, S6B and end segment 55B overlaps end segment 56A of lamination 50A.

[0062] Referring now to Figure 9B, there is shown a schematic representation of an alternative embodiment of a distributed gap wound core 10B. Again only the first five laminations 50A-50.E are shown arranged to form a series of concentric layers for illustrative purposes and in an alternative method of construction, laminations could be grouped into packets of laminations and assembled in a. similar manner to that shown. in Figure 9 A for individual laminations 50A-50D.

[0063] Core 1GB differs from core 1.0A in that the build-up or thickness of end 16 is not double the build-up of legs 12, 14 and end 1 . The build-up of end 1 is less than double the build-up of legs 12, 14 and end 18. This is achieved by providing a. combination of butting and overlapping joints at end 16. in Figure B, laminations 50A.-50C have butting end portions 55A, 56A, 55B, 56.B, 55C, 56C respectively. As these end portions butt together, there is no increase in thickness or cross-sectional area across these laminations. Conversely, laminations 50D, 50E are arranged to overlap in the same way as described for the laminations of core iOA. For example, lamination SOD, has overlapping end segments 55D, 56.D while lamination SOE has overlapping end segments 55E, 56E. The arrangement of butring overlapping joints at end 1 may vary as appropriate in order to achieve a desired increase in end build-up or cross- sectional area in order to lower the flux density at end 16 to reduce core losses.

[0064 j Referring now to Figure 9C, there is shown schematic representation of a wound core 10C according to a further embodiment of the invention. Core IOC has a pair of opposing (and lengthwise extending) core legs 12, 14 and a pair of core ends 16, 18. The core ends 16, 18 extend generally perpendicularly between the core legs 12, 14. The core IOC shown in Figure 9C is a type of DUO UN-CORES' which is manufactured by the present applicant. Similar to a standard DUO UNICORE®, core 10C has laminations that are cut on the lengthwise extending legs 12, 14 to form discontinuities or gaps 68, Unlike a standard DUO UMCOREi) however, core I OC further includes cuts on ends 1.6, 18 which form discontinuities or gaps 78. Whereas each lamination of a DUO- UNICORE® is C-shaped, the laminations, of core IOC are generally L-shaped.

[0065] Core .1 OC is assembled in two hal ves, the first half comprising lamination 50A-50E and 50A'- 50E ^! and the second half comprising laminations 60A-60E and 60A'- 60E\When assembled, respective laminations of the two halves are nested together to form a series of concentric layers such that each subsequent lamination of the core is larger than a pre vious lamination. By way of example, the innermost layer of core IOC comprises laminations 50A, 5 A', 60A, 60A'. The thickness or build-up of the core ends 1 , 18 is double the thi ckness or build-up of core legs 12, 14, The increase in thickness results from overlapping end segments of the laminations. For example, the end segment of lamination 50A' is overlapped with the end segment of lamination 50A. The end segment, of lamination SOB is then overlapped with the end segment of lamination 5 OA'. Although only the first ten laminations of each half Of the core IOC are shown in Figure C it is to be appreciated that the fully assembled core will have many more laminations than shown.

[0066] Increasing the build-up or cross-sectional area of the ends 16, 18 requires cuts to be introduced at the respective ends which introduces gaps or discontinuities that a standard DUO IJNICORE® does not have. Although the cuts introduce further losses to the core, it has been found that the overall loss of the core is reduced due to the effect of the increase in cross-sectional area at the ends. The increase in cross- sectional area lowers the flu density which thereby creates lower loss flux path in areas where the greatest losses of the core occur.

1 0671 Referring now to Figure 9D there is shown a schematic representation of a wound core l ^' D according to a further embodiment of the invention. Core HID has a pair of opposing (and lengthwise extending) core legs 12, 14 and a pair of core ends 1.6, 18. The core ends 16, 18 extend generally perpendicularly between the core legs 12, 14. The core 0C shown in Figure 9C is a further type of DUO U CORBSs. Similar to a standard DUO UNICQRE#5, core I OC has laminations that are cut on the lengthwise extending legs 2, 14 to form discontinuities or gaps.68. Whereas the laminations of core I OC are all L-shaped, the laminations of core 1 D include a combination of C-shaped. and L-shaped laminations as shown in Figure D.

1 0681 Similar to core 1 OC, core 10D is assembled in two halves. In Figure 9D, the first half comprises lamination 50A, SOB, 50C, SOD, 50D\ SOE-and 50E', whi le the second half comprises laminations 60A,. 60B, 6GC, 60D, 60D\ 60E and 60E'. As shown, laminations 50A-50C and 60A-60C arc C-shaped laminations which are nested together at ends 16, 18 respecti vely. Laminations SOD, 50D', 50E, 50E' and 60D, 60D', 60E and 60E' are L-shaped. 10069 ] The thickness or build-up of the core ends 1 , 1 is greater than the thickness or build-up of core legs 12, 14. The increase i n. thickness results from overlapping end segments of the L-shaped laminations at each respective end. For example, the end segment of lamination 50D' is overlapped with the end segment of lamination SOD. The end segment of lamination 50E is then overlapped with the end segment of lamination SOD'. The nested C-shaped laminations do not contribute to the increased build-up.

Although only the First seven laminations of each half of the core !OD are shown in. Figure 9D it is to be appreciated that the fully assembled core will have many more laminations than shown. The number of C- shaped/L-shaped laminations that the core has is variable to suit the desired increase in build-up at the cor ends.

10070] The embodiments described thus far have all. related to cores having an increased build-up and thickness at a core end (or yoke) relative to the core leg about which a conductive winding (coil) is to be wound In order to reduce core losses and improve the efficiency of the core, it is to be appreciated however, that in other embodiments, core losses may be reduced by increasing the build-up and thickness of one of the core legs (the core leg that does not receive the conducting coil or winding).

[0071] Examples of core arrangements having an increased build-up or th ickness on one of the core legs arc shown with reference to Figures 1 OA- iOD. In particular, Figures 10A-10B show schematic representations of part of a distributed gap wound core whereas Figures 1 C-IQD sho schematic representations of part of a DUO U iCORE®. For each core, laminations are nested together to form a series of concentric layers. Only five layers of each core build-up are shown. It is of course to be appreciated that a complete core would have many more layers.

[0072] Referring now to Figure 10A, there is shown a wound core lOE including laminations 50A, SOB, 50C, SOD and 50E that are nested together to define a first core leg 12, a; second core leg 14 and core ends 16, .18 that extend perpendicularly between the core legs 12, 14. First core leg 12 is receivable of a conductive winding or coil and has minimal thickness. In the embodiment shown, core ends 1.6, 18 have the same build-up or thickness as core leg 12. The second core leg 14 however has an increased build-up or thickness relative to the first core leg 12. In the embodiment shown, the second core leg 14 has a second leg thickness which is double a first leg thickness of the first core leg 12.The increased build-u on core leg 14 is achieved by overlapping leg segments of each respective lamination 50A-50E. For example, with respect to the innermost layer of the core 1 OE, lamination 5 OA has overlapping leg segments 54A, 54A.' on core leg H.Each subsequent layer also has. overlapping end segments.

[0073] The increased leg build-up or thickness of core leg 14 may be varied between.0-1.00% of the build-up or thickness of cote kg 12 (that receives the conductive winding or coil). This is illustrated in Figure 10B whereby wound core 10F is sho wn with a combination of overlapping and butting leg segments to achieve an increased build-up between 0-100% that of core leg 12. For example, with respect to the innermost layer of the core I OF,, lamination 50A has leg segments 54A _S . 54A' on core leg 14 that arc in hutted engagement and which do n ot contribute to an increase in thickness of core leg 14. However, wi th respect to the second layer- of the core! OF, lamination 50B has overlapping leg segments 54B, 54 B' on core leg 14. The number of overlapping and butting leg segments, of the core can be. adjusted in order to vary the leg thickness of core leg 14 as appropriate .

[007 | Referring now to Figure IOC, there is shown a wound core 10G which is a type of DUO core that is assembled in two halves. A first half comprises laminations 50A, 508, 50C, 50D and 50E while a second mating half comprises laminations 6 A, 60B, 60C, 60.D and 6 ^' OE. The laminations are generally C-shaped. When the two halves are assembled, core 10G is formed having a first core leg 12, a second core leg 14 and core ends 16, 18 that extend perpendicularly between the core legs 12, 14. Core leg 12 has cuts or discontinuities formed at the intersection of respective leg segments 52A and 62A, 52B and 62B, 52C and 62C, 52.D and 62D and 52E and 62Έ. First core leg 12 is receivable of a conducting winding or coil and has minima! thickness. In. the embodiment shown, core ends 1 . 18 have the same build-up or thickness as core leg 12. The second core leg 14 however has an increased build-up or thickness relative to the first core leg 12. In the embodiment shown, the second core leg 1.4 has a second leg thickness which is double a first leg thickness of the first core leg 12.The increased build-up on core leg 14 is achieved by overlapping leg segments of respective laminations 50A-50E and 60A-60E. For example, with respect to the innermost layer of the core comprising laminations 5 and 60 A, le segments 54 A and 64A are overlapped. For subsequent layers, leg segments 54B, 64B are overlapped, leg segments 54C, 64C are overlapped, leg segments 54D, 64D are overlapped and finally leg segments 54E, 64E are overlapped in the outermost layer shown in Figure I C.

[0075 ] The increased leg build-up or thickness of core leg 14 in the DUO wound core arrangement ma also be varied between 0-1 0% of the build-u or thickness of core leg 12 (that receives the conductive winding or coil). This is illustrated in Figure 10D whereby wound core 10H is shown with a combination of overlapping and butting leg segments on core leg 14 to achieve an increased build-up between 0-100% that of core leg 12. For example, with respect to the innermost layer of the core lOFL lamination 50A has leg segment 54A that is in butted engagement with leg segment 64A of lamination 60 . Similarly, lamination 50B has leg segment 54B that is in butted engagement with leg segment 64B of lamination 60B and the outermost layer of the core has leg segment 54E of lamination 50E in butted engagement with leg segmen t 64E of lamination 60E. The third and fourth layers of the core 10H each have overlapping leg segments which increases the build-up or thickness of core leg 14 relati ve to core leg 12. As shown in. Figure 1 OD, leg segment 54C of lamination 50C is overlapped with leg segment 64C of lamination 60C and leg segment 54D of lamination SOD is overlapped with leg segment 64D of

lamination 60D. The number of overlapping and bu tting leg segments of the core can be adj usted in order to vary the build-up or thickness of core leg 14 as appropriate. 10076 ] The embodiments described herein illustrate that the principles of the present invention may be applied to many different types of wound transformer cores. In practice, the wound core will have at least one leg about which a conductive coil is to be wound. It is desirable for the leg that receives the coil to have minimal thickness in order to minimise the amount of coil materia! required (e.g. copper). The buildup or thickness of the remaining core leg (and/or core ends or yokes) can then be increased relative to the thickness of the core leg about which the coil is to be wound in order to lower the magnetic fl u densit and overall loss of the core. The amount of extra thickness added to lower losses and increase core efficiency must however be balanced against the increased amount of steel (and therefore cost) required to mam facture the core. In most of the described embodiments, additional cuts or discontinuities are introduced to the core in order to increase the build-up or thickness of an end or leg of the core. Although, these discontinuities, in and of themselves, create high loss magnetic flux paths, it has been found that overall losses of the core can still he reduced as a result of the increased build-up(s) that increase thickness arid cross-sectional area (and thereby lower flux density).

[0077] Throughout the specifieation and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as: "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer of group of integers.

[ 0078 [ The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

[ 0079] It: will be appreciated b those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and'or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, bu t is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.