Title of Invention	A TRANSFORMER HAVING A STACKED CORE WITH A SPLIT LEG AND A METHOD OF MAKING THE SAME
Abstract	The present invention is directed to a transformer having a stacked core (210) , which includes top and bottom yokes (212,214) and first and second outer legs (218, 220) . The core also includes an inner leg(216) that is formed from a pair of stacked plates, which abut each along a seam that extends in the longitudinal direction of the inner leg (216) . Each of the upper and lower yokes (212, 214) may be formed from a single stack of plates, or a plurality of stacks of plates. Each of the inner and outer legs (218 , 220) may also be formed from a single stack of plates, or a plurality of stacks of plates. The cross-section of the core may be rectangular or cruciform.

Title of Invention

A TRANSFORMER HAVING A STACKED CORE WITH A SPLIT LEG AND A METHOD OF MAKING THE SAME

Abstract

The present invention is directed to a transformer having a stacked core (210) , which includes top and bottom yokes (212,214) and first and second outer legs (218, 220) . The core also includes an inner leg(216) that is formed from a pair of stacked plates, which abut each along a seam that extends in the longitudinal direction of the inner leg (216) . Each of the upper and lower yokes (212, 214) may be formed from a single stack of plates, or a plurality of stacks of plates. Each of the inner and outer legs (218 , 220) may also be formed from a single stack of plates, or a plurality of stacks of plates. The cross-section of the core may be rectangular or cruciform.

Full Text	WO 2006/105026 PCT/US2006/011122 ATRANSFORMER HAVING A STACKED CORE WITH A SPLIT LEG AND A METHOD OF MAKING THE SAME FIELD OF THE INVENTION [0001] The invention relates to transformers and more particularly, to transformers having a stacked core and methods of making the same with reduced waste. BACKGROUND OF THE INVENTION [0002] A stacked transformer core is comprised of thin metallic laminate plates, such as grain oriented silicon steel. This type of material is used because the grain of 'the steel may be groomed-in certain directions to reduce the maqnetic field loss. The plates are stacked on too of each other to form a plurality of layers. A stacked core Is typically rectangular in shape and can have a rectangular or cruciform cross-section. A front view of a conventional three leg stacked core 10 for a three phase transformer is shown in Fig. 1. The core 10 comprises an upper yoke 12, a lower yoke 14, an inner leg 16, and first and second outer legs 18, 20. A pair of windows 22 are disposed between the inner leg 16 and the first and second outer legs 18, 20, respectively. Wire coils (not shown) are mounted to the inner leg 16 and the first and second outer legs 18, 20, respectively. [0003] The upper yoke 12 comprises a stack of plates 24, the lower yoke 14 comprises a stack of steel plates 26, the first outer leg 18 comprises a stack of plates 28 ' and the second outer leg 20 comprises a stack of plates 30. The plates 24,26 of the upper and lower yokes 12, 14 have opposing ends that form joints with opposing ends of the plates 28, 30 of the first and second outer legs 18, 20, respectively. A V-shaped upper notch 32 is formed in each of the plates 24 of the upper yoke 12 and a V-shaped lower notch 36 is formed in each of the plates 26 of the lower yoke 14. The upper notches 32 form an upper groove 38 in the upper yoke 12, while the lower notches 36 form a lower groove 40 in the lower yoke 14. The size of the individual plates 24-30 vary depending on the stacking technique used to assemble the core 10. 1 WO 2006/105026 PCT/US2006/011122 [0004] . The inner leg 16 comprises a stack of plates 42. Each of the plates 42 has an upper tined end 42a formed by a pair of miter cuts and a lower tined end 42b formed by a pair of miter cuts. The upper and lower tined ends 42a, b of the plates 42 provide the inner leg 16 with upper and lower tined ends 16a, b, which are adapted for receipt in the upper and lower grooves 38, 40 of the upper and lower yokes 12, 14, respectively. [0005] The manufacture of the conventional core 10 described above results in a significant amount of steel being cut away and discarded. For example, during the manufacture of the inner leg 16, four pieces of steel must be cut away from each plate 42 to provide the plate 42 with tined ends. Therefore, it would be desirable to provide a stacked transformer core and a method of making the same that reduces the amount of steel that is discarded and, thus, wasted. The present invention is directed to such a transformer core and method, SUMMARY OF THE INVENTION [0006] In accordance with the present invention, a transformer is provided having a stacked core. The core is provided with a first yoke formed from a stack of plates and having an outer side and an inner side with a groove formed therein. The groove extends in a stacking direction of the plates and is located inwardly from the outer side. The core is also provided with a second yoke formed from a stack of plates and having an outer side and an inner side with a groove formed therein. The groove extends in the stacking direction of the plates and is located inwardly from the outer side. A first end of an inner leg ■ is disposed in the groove of the first yoke and a second end of the inner leg is disposed in the groove of the second yoke. The inner leg includes a first stack of first plates abutting a second stack of second plates. A coil winding is mounted to the inner leg of the core. [0007] Also provided in accordance with the present invention is a method of forming a transformer with a stacked core. In accordance with the method, a plurality of first and second outer leg plates is provided. A plurality of inner leg plates and a plurality of first yoke plates are also provided. Each of the first yoke plates has an outer side and an inner side with a notch formed therein. The notch is located inwardly from the outer side. The inner leg plates, the first yoke plates and the first and second outer 2 WO 2006/105026 PCT/US2006/011122 leg plates are stacked to form first and second outer legs, a first yoke with a first . . groove, and an inner leg having a first end disposed in the first groove. The first outer leg is formed from the first outer leg plates, the second outer leg is formed from the second outer leg plates and the first yoke is formed from the first yoke plates. The inner leg is formed from a first stack of the inner leg plates abutting a second stack of the inner leg plates. The first groove extends in a stacking direction of the first yoke and is formed by the notches of the first yoke plates. The coil winding is mounted to the inner leg. BRIEF DESCRIPTION OF THE DRAWINGS [0008] The features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: [0009] Fig. 1 shows a front elevational view of a prior art transformer core; [0010] Fig. 2 shows a front elevational view of a transformer core constructed in accordance with a first embodiment of the present invention; [0011] Fig. 3 shows a close-up view of a connection between a first outer leg and an upper yoke of the transformer core; [0012] Fig. 4 shows an enlarged view of a portion of an inner leg spaced above a lower yoke of the transformer core; [0013] Fig. 5 shows a top plan schematic view of plates of inner leg plates being formed from a roll of steel; [0014] Fig. 6 shows a front elevational view of a transformer with the transformer core; [0015] Fig. 7 shows a front elevational view of a second transformer core embodied in accordance with a second embodiment of the present invention; [0016] Fig. 8 shows a cross-sectional view of an inner leg of the second transformer core; [0017] Fig. 9 shows a front elevational view of a third transformer core embodied in accordance with a third embodiment of the present invention; and 3 WO 2006/105026 PCT/US2006/011122 [0018]. Fig. 10 shows an enlarged view of a portion of an inner leg spaced above a lower yoke in the third transformer core. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS [0019] It should be noted that in the detailed description that follows, identical components have the same reference numerals, regardless of whether they are shown in different embodiments of the present invention. It should also be noted that in order to clearly and concisely disclose the present invention, the drawings may not necessarily be to scale and certain features of the invention may be shown in somewhat schematic form. [0020] The present invention is directed to a transformer 100 (shown in Fig. 6), such as a distribution transformer, having a stacked core 102. The transformer 100 may be an oil-filled transformer, i.e., cooled by oil, or a dry-type transformer, i.e., cooled by air. The construction of the core 102, however, is especially suitable for use in a dry transformer. Referring now to Fig. 2, the core 102 has a rectangular shape and generally comprises an ■ upper yoke 104, a lower yoke 106, first and second outer legs 108, 110 and an inner leg 112. Upper ends of the first and second outer legs 108, 110 are connected to first and second ends of the upper yoke 104, respectively, while lower ends of the first and second outer legs 108, 110 are connected to first and second ends of the lower yoke 105. The inner leg 112 is disposed about midway between the first and second outer legs 108,110 and has an upper end connected to the upper yoke 104 and a lower end connected to the lower yoke 106. With this construction, two windows 113 are formed between the inner leg 112 and the first and second outer legs 108,110. [0021] The upper yoke 104 has an inner side 104a and an outer side 104b, and the lower yoke 106 has an inner side 106a and an outer side 106b. The upper yoke 104 comprises a stack of plates 114, while the lower yoke 106 comprises a stack of plates 116. Both the plates 114 and the plates 116 are arranged in groups. In one exemplary embodiment of the present invention, the groups are groups of seven. Of course, groups of different numbers may be used, such as groups of four, which are used herein for ease of description and illustration. Each of the plates 114, 116 is composed of grain-oriented 4 WO 2006/105026 PCT/US2006/011122 silicon steel and has a thickness in a range of from about 7 mils to about 14 mils, with the particular thickness being selected based on the application of the transformer 100. The plates 114,116 each have a unitary construction and are trapezoidal in shape. In each of the plates 114,116, opposing ends of the plate 114,116 are mitered at oppositely-directed angles of about 45°, thereby providing the plate 114,116 with major and minor side edges. The plates 114 have the same width to provide the upper yoke 104 with a rectangular cross-section and the plates 116 have the same width to provide the lower yoke 106 with a rectangular cross-section. However, the lengths of the plates 114 are not a!! the same and the lengths of the plates 116 are not all the same. More specifically, the lengths within each group of plates 114 are different and the lengths within each group of plates 116 are different; The pattern of different lengths is the same for each group of plates 114 and the pattern of different lengths is the same for each group of plates 116. The difference in lengths within each group permits the formation of multi-stop lap joints with plates 120. 122 of the first and second outer legs 108, 110 as will be described more fully below. [0022] A V-shaped upper notch 124 is formed in each of the plates 114 of the upper yoke 104 by an upper interior edge 126 and a V-shaped lower notch 128 is formed in each of the plates 116 of the lower yoke 106 by a lower interior edge 130, The upper interio! edges 126 in adjacent plates 114 of the upper yoke 104 have different depths for forming ' vertical lap joints with upper ends of inner leg plates 152 of the inner leg 112, as wil! be described more fully below. Similarly, the lower interior edges 130 in adjacent plates 116 of the lower yoke 106 have different depths for forming vertical lap joints with lower ends of the inner leg plates 152 of the inner leg 112, as will be described more fully beiow. The upper notches 124 form an upper groove 136 in the upper yoke 104, while the lower notches 128 form a lower groove 138 (shown best in Fig. 4) in the lower yoke 104. The upper groove 136 is located inwardly from the outer side 104b, and the lower groove 138 is located inwardly from the outer side 106b. The upper and lower grooves 136,138 extend in the stacking directions of the upper and lower yokes 104, 106, respectively. [0023] The first outer leg 108 comprises a stack of the plates 120, while the second outer leg 110 comprises a stack of the plates 122. Both the plates 120 and the plates 122 are arranged in groups of the same number as the plates 114, 116. Each of the plates 5 WO 2006/105026 PCT/US2006/011122 120,122 is composed of grain-oriented silicon steel and has a thickness in a range of from about 7 mils to about 14 mils, with the particular thickness being selected based on the application of the transformer 100. The plates 120,122 each have a unitary construction and are trapezoidal in shape. In each of the plates 120, 122, opposing ends of the plate are mitered at oppositely-directed angles of about 45°, thereby providing the plate 120,122 with major and minor side edges. The plates 120 have the same width to provide the first outer leg 108 with a rectangular cross-section and the plates 122 have the same width to provide the second outer leg 110 with a rectangular cross-section. However, the lengths of the plates 120 are not all the same and the lengths of the plates 122 are not all the same. More specifically, the lengths within each group of plates 120 are different and the lengths within each group of plates 122 are different. The pattern of different lengths is the same for each group of plaies 120 and the pattern of different lengths is the same for each group of plates 12?. The difference in lengths within each group permits the formation of the multi-step joints with the plates 114,116 of the upper and lower yokes 104,106, as will be described more fully below. [0024] Referring now to Fig. 3 there is shown an enlarged view of a portion of the connection (represented by reference number 142) between the upper end of the first outer leg 108 and the first end of the upper yoke 104. More specifically, the ends of first, second, third and fourth plates 120a, b, c, d of the first outer leg 108 abut (form joints with) the ends of first, second, third and fourth plates 114a, 114b, 114c, 114d of the upper yoke 104, respectively. The first through fourth plates 120a-d of the first outer leg 108 and the first through fourth plates 14a-d of the upper yoke 104 are successively disposed farther inwardly. The first through fourth plates 120a-d have successively longer lengths, whereas .: the first through fourth plates 14a-d have successively shorter lengths. With this construction, the first plate 114a overlaps the joint between the second plates 114b, 120b, the second plate 114b overlaps the joint between the third plates 114c, 120c and the third plate 114coverlaps the joint between the fourth plates 114d, 120d. As shown, outer points of plates 120b-d of the first outer leg 108 protrude beyond the upper yoke 104. These outer points may be removed to improve the appearance of the core 102. Although not shown, additional groups of four plates 114,120 are provided and repeat the pattern of the 6 WO 2006/105026 PCT/US2006/011122 first through fourth plates 114a-d and the first through fourth plates 120a-d. In this manner, multi-step lap joints are formed between the plates 114 of the upper yoke 104 and the plates 120 of the first outer leg 108, with plates 114 of the upper yoke 104 overlapping plates 120 of the first outer leg 108. [0025] The other connections (represented by reference numerals 144, 146, 148) between the first and second outer legs 108,110 and the upper and lower yokes 104, 106 are constructed in the same manner as the connection 142 so as to have multi-step lap joints. It should be appreciated, however, that the connections 142-148 may have a different type of construction. For example, instead of the connections 142-148 having a four step lap joint pattern, the connections 142-148 may have a seven, or other number step lap joint pattern. In addition, instead of having plates 114, 116 of the upper and lower yokes 104, 106 overlapping plates 120, 122 of the first and second outer legs 108, 110. plates 120, 122 of the first-and second outer legs 103, 110 may overlap pialos 114, 116 of the upper and lower yokes 104, 106. With this construction, outer points of the plates 114, 116 would protrude beyond the first and second outer legs 108, 110, respectively. [0026] The inner leg 112 comprises a first stack 150 of inner leg plates 152 and a second stack 154 of inner leg-plates 152, In each of the first and second stacks 150, 154, the inner ieg. plates 152 are-arranged in groups of the same number as the plates 114, 116. The first and second stacks 150, 154 abut each other along a seam 158 that extends in the longitudinal direction of the inner leg 112. Upper ends of the first and second stacks 150, 154 are disposed in the upper groove 136 of the upper yoke 104 and lower ends of the first and second stacks 150, 154 are disposed in the lower groove 138 of the lower yoke 106. The inner leg plates 152 form vertical multi-step lap joints with the plates 114, 116 of the upper and lower yokes 104,106, as will be described further below. The inner leg plates 152 may all have the same length if the joints are offset by vertically shifting the inner leg plates 152. Alternately, the inner ieg plates 152 may have a plurality of different lengths if the joints are offset by the different lengths of adjacent inner leg plates 152. Each of the inner leg plates 152 has a unitary construction and is trapezoidal in shape. In each of the inner leg plates, opposing ends of the inner leg plate 152 are mitered at oppositely-directed angles of about 45°, thereby providing the inner leg plate with major 7 WO 2006/105026 PCT/US2006/011122 and minor side edges. The lengths of the inner leg plates 152 are determined by the major side edges. Each of the inner leg plates 152 is composed of grain-oriented silicon steel and has a thickness in a range of from about 7 mils to about 14 mils, with the particular thickness being selected based on the application of the transformer 100. [0027] Referring now to Fig. 4 there is shown an enlarged view of a portion of the lower end ofthe inner leg 112 spaced from the loweryoke 106. When the lower end of the inner leg 112 is disposed in the lower groove 138, the ends of first, second, third and fourth inner leg plates 152a, b, c, d of the first and second stacks 150,154 abut (form joints with) the lower interior edges 130a, b, c, d of first, second, third and fourth plates 116a, b, c, d of the loweryoke 106, respectively. In each of the first and second stacks 150,154, the first through fourth inner leg plates 152a-d are vertically offset such that lower ends thereof are located successively farther downward. In order to accommodate these differences in length, the Iower interior edges 130a-d of the- plates 116a d are cut successively deeper. With this construction, the first plate 116a overlaps the joints between the second inner leg plates 152b and the second plate 116b, the second plate 116b overlaps the joints between the third inner leg plates 152c and the third plate 116c, and the third plate 116c overlaps the joints between the fourth inner leg plates 152d and the fourth plate 116d. Although not shown, additional groups ofthe plates 116 and inner leg plates 152 are provided and repeat the pattern of the first through fourth plates 152a-d and the first through fourth plates 116a-116d. In this manner, multi-step lap joints are formed between the plates 116 ofthe loweryoke 106 and the inner leg plates 152 ofthe first and second stacks 150,154, with plates 116 of the lower yoke 106 overlapping plates 152 of the first and second stacks 150, 154. [0028] Since the lower ends ofthe first through fourth inner leg plates 152a-d ofthe first and second stacks 150,154 are located successively farther downward-, upper ends of the first through fourth inner leg plates 152a-d of the first and second stacks 150,154 are located successively farther downward. As a result, the upper interior edges 126 (and, thus, the upper notches 124) of the plates 114 within each group are successively shallower, which is the inverse of the loweryoke 106. With this construction, vertical multi- step lap joints are formed between the plates 114 ofthe upper yoke 104 and the first inner 8 WO 2006/105026 PCT/US2006/011122 leg .plates 152 of the first and second stacks 150, 154, with inner leg plates 152 overlapping plates 114 of the upper yoke. [0029] It should be appreciated that the inner leg plates 152 of the first and second slacks 150, 154 may be offset differently so as to have plates 114 of the upper yoke 104 overlapping inner leg plates 152, and inner leg plates 152 overlapping plates 116 of the lower yoke 106. In addition, the inner leg plates 152 of the first and second stacks 150,154 may be offset to form a seven or other number step lap joint pattern, instead of the four step lap joint pattern. [0030] In the embodiment where the inner leg plates 152 have different lengths, such as four different lengths, vertical multi-step lap joints are formed between the plates 114, 116 of the upper and lower yokes 104, 106 in a manner similar to that described above, however, the upper interior edges 126 (and thus the upper notches 124) of the plates 114 of the upper yoke 104 may have the same arrangement as the lower Interior edges 130 (and thus the lower notches 128) of the plates 116 of the lower yoke 106 with regard to depth, because there is no vertical shifting of the inner leg plates 152. [0031] Referring now to Fin. 5, the inner leg plates 152 are formed from one or more pieces of steel 160, which are typically received from a supplier in one or more rolls 162. The steel piece(s) 160 in the roll(s) 162 is/are unrolled and cut by a cutting machine (not shown), which is operable to make two or more cuts simultaneously. !n the description below, the cutting machine is operable to make two cuts simultaneously. The cuts are made at oppositely directed angles of about 45 °and are separated so as to form an inner leg plate 152 with a length of L1, i.e., a major side length of L1. Fig. 5 shows a portion of a steel piece 160 that has been unwound from its roll 162 and is being cut by the cutting machine. The cutting machine makes a first cut 168 and a second cut 170 in the steel piece 160 simultaneously. The first and second cuts 168, 170 form a first inner leg plate 152a and a scrap piece 172, which is discarded. The steel piece 160 is then further unwound and advanced (relative to the cutting machine) by the distance L1. The cutting machine makes a third cut 174 and a fourth cut 176 in the steel piece 160 simultaneously. The third and fourth cuts 174,176 form a second inner leg plate 152b and. a third inner leg plate 152c. This procedure of unwinding, advancing and cutting is continued until the 9 WO 2006/105026 PCT/US2006/011122 required number of inner leg plates 152 is formed. [0032] In the description of the cutting of the inner leg plates set forth above, the inner.leg plates 152 ai! have the same length L1. If the inner leg plates 152 are provided with different lengths, such as L1-L4, the requisite number of inner leg plates 152 with the length L1 may be cut first. The cutting machine may then be reconfigured to change the spacing of the cuts and the advancement distance of the steel piece 160 so as to produce plates having a length L2. The requisite number of inner leg plates with L2 may then be cut. In a similar manner, the cutting machine is reconfigured and run to produce the requisite number of inner leg plates 152 with lengths L.3 and L4. [0033] The method of assembling the core 102 is dependent on the size of the core 102. If the core 102 is large, such as would be the case if the transformer 100 was greater than 3000 kva, the core 102 is assembled with the lower yoke 106, the inner leg 112 and the first and second outer legs 108, 110 initially being disposed horizontally, i.e., the lower yoke 106, the inner leg 112 and the first and second outer legs 108, 110 are stacked in a vertical direction. In such a case the core 102 is assembled on a mounting fixture in a plurality of layers. In a first layer, a group of plates 116 is laid on the mounting fixture, with the major side edges disposed outwardly. Next, a group of plates 120 and a group of plates 122 are laid on the mounting fixture, with their major side edges disposed outwardly and their ends abutting the ends of the group of plates 116,respectively, to form multi-step lap joints. First and second groups of offset inner leg plates 152 are-then laid on the mounting fixture, with the major side edges of the inner leg plates 152 of the first group abutting the major side edges of the inner leg plates 152 of the second group, and the ends of the inner leg plates 152 of the first and second groups abutting opposing portions of the lower interior edges 130 of the plates 11*6, respectively, to form two series of multi-step vertical lap joints, respectively. This laying process is repeated for each layer until a desired stacking configuration is achieved. Once the lower yoke 106, the inner leg 112 and the first and second outer legs 108, 110 have been formed, the lower yoke 106 is clamped between a pair of end frames or supports 177 and bands 178 are disposed around the inner leg 112 and the first and second outer legs 108,110, respectively, as shown in Fig. 6. The partially formed core 102 is then moved to an upright position so that the inner leg 10 WO 2006/105026 PCT/US2006/011122 112 and the first and second outer legs 108,110 extend vertically. Coil windings 180 are then disposed over the inner leg 112 and the first and second outer legs 108, 110, respectively. The upper yoke 104 is then stacked in groups of plates 114 onto the ends of the inner leg 112 and the first and second outer legs 108, 110. [0034] If the core 102 is smaller, such as would be the case if the transformer 100 was less than 3000 kva, the core 102 is assembled in a similar manner as described above, except the core 102 is formed while being disposed vertically, i.e., the components of the core 102 are stacked in a horizontal direction. [0035] After the core 102 with the coil windings 180 is fully constructed, the core 102 is enclosed within a housing (not shown). If the transformer 100 is an oil-filled type of transformer, the core 102 is immersed in oil within a compartment in the housing. If the transformer 100 is a dry-type of transformer, the core 102 is not immersed in oil and tho housing is provided with louvers to permit air to enter the housing snd pass-ovor Uio core 102 and the coil windings 180. [0036] Although the assembly of the core 102 set forth above describes, three coil windings 180 being mounted to the core 102, such as occurs when the transformer 100 is a three-phase transformer, it should be appreciated that in another embodiment, a single coil winding 180 may be mounted to the inner ieg 112 of the core 102, such as occurs when the transformer 100 is a single phase transformer. In another embodiment, three inner legs 190 may be provided, wherein the coil windings 180 are mounted to the inner legs 190, respectively. In such a case, three upper grooves 136 would be formed in the upper yoke 104 and three lower grooves 138 would be formed in the lower yoke 106. In addition, four windows 113 would be formed. [0037] Referring now to Fig. 7, there is shown a core 184 embodied in accordance with a second embodiment of the present invention. The core 184 has substantially the same construction as the core 102, except for the differences set forth below. The core 184 comprises upper and lower yokes 186, 188 an inner leg 190 and first and second outer Iegs192,194. The inner leg 190 comprises a first stack 196 of inner leg plates 198anda second stack 200 of inner leg plates 198. The first and second stacks 196, 200 abut each other along a seam 202 that extends in the longitudinal direction of the inner leg 190. Each 11 WO 2006/105026 PCT/US2006/011122 of the upper and lower yokes 186, 188 the inner leg 190 and the first and second outer legs 192, 194 has a cruciform cross-section, instead of a rectangular cross-section, as in the core 102. The cruciform cross-sections of these components increase the strength of the core 184 and provide the inner leg 190 and the first and second outer legs 192, 194 with larger surface areas for supporting coils. The cruciform cross-sections of the components of the core 184 are formed by providing the constituent plates of the components with different widths. For example, and with reference now to Fig. 8, sections 204a,b,c,d,e,f,g of the inner leg plates 198 first successively increase in width and, then after the midpoint, successively decrease in width. The sections 204a,b,c,d,e,f,g each comprise one or more groups of inner leg plates 198. Thus, the outermost inner leg plates 198 in sections 204a and 204g each have a width W1, which is the smallest of the widths of the inner leg plates 198, and the. inner log plates 198 in the middle section 204d each have a width Wn, which is the larqest of the widths of the inner leg plates 198 in each of first and second stacks 196, 200, the major side edges of the inner leg plates 198 are aligned at the seam 202. The different widths, however, cause the minor.sides to be offset, which helps form the cruciform cross-section of the inner leg .190. The thickness of the sections 204a-g in the stacking direction may vary. For example, as shown, the center section 204d may be substantially thicker than the other sections 204a,b,c,e,f,g. [0038] The components of the core 184 are cut and assembled in substantially the same manner as the components of the core 102, except for each component, a plurality of steel pieces with different widths (configured in a plurality of rolls) are cut to form the constituent plates of varying width. [0039] Referring now to Fig. 9, there is shown a core 210 embodied in accordance with a third embodiment of the present invention. The core 210 has substantially the same construction and is constructed in substantially the same manner as the core 102, except for the differences set forth below. The core 210 comprises upper and lower yokes 212, 214, an inner leg 216 and first and second outer legs 218, 220. Like the inner leg 112 of the core 102, the inner leg 216 is comprised of a pair of stacks of plates. Unlike the upper and lower yokes 104,106 in the core 102, however, the upper and lower yokes 212,214 of the core 210 are comprised of a plurality of stacks of plates. The upper and lower yokes 12 WO 2006/105026 PCT/US2006/011122 212, 214 are constructed in a similar manner and, thus, for purposes of brevity only the -lower yoke 212 will be described. [0040] . The lower yoke 214 of the core 210 comprises an outer stack 224 of first plates 226, a first inner stack 228 of second plates 230 and a second inner stack 232 of second plates 230. As with the lower yoke 106 of the core 102, the outer stack 224 and the first and second inner stacks 228, 232 are arranged in groups of plates to form multi-step lap joints. More specifically, within each group of the second plates 230 of the first and second inner stacks 228, 232, the inner ends of the second plates 230 are offset, either by shifting the second plates 230, or by providing the. second plates 230 with different lengths. The groups in the first and second inner stacks 228, 232 are arranged in the same manner and are aligned so as to form pairs of corresponding second plates 230 (from the first and second inner stacks 228, 232 respectively). Each of the first plates 226 is unitary in structure and has an elongated trapezoidal shape, with major and minor side edges. The first plates 226 have opposing ends that form multi-step lap joints with plates of the first and second outer legs 218, 220, respectively. A portion of the first plates 226 have V- shaped notches 234 formed therein. The second plates 230. each have major and minor side edges and outer mitered ends. The first and second inner stacks 228, 232 are disposed on the outer stack 224 such that the major side edges of the second plates 230 are disposed against the minor side edges of the first plates 226. The first and second inner stacks 228, 232 abut the outer stack 224 along a pair of seams 236, respectively, that extend in the longitudinal direction of the outer stack 224. The first and second plates 226, 230 all have the same width and, thus, may be formed from the same piece of steel. [0041] Referring now to Fig. 10, in each layer of the lower yoke 214, a V-shaped notch 238 is at least partially formed by inner ends of a pair of corresponding second plates 230 (from the first and second inner stacks 228, 232 respectively). In a first pair of corresponding second plates 230a, the second plates 230a have mitered inner ends that abut at a lower point, thereby forming a notch 238a. In a second pair of corresponding second plates 230b, inner ends of second plates 230b are separated by a spacing that cooperates with a notch 234b in a corresponding first plate 226b to form a notch 238b. In the remaining pairs of corresponding second plates 230, the inner ends of the second 13' WO 2006/105026 PCT/US2006/011122 plates 230 are also spaced apart and cooperate with notches 234 in the first plates 226 to form notches 238. In this manner, a vertical series of multi-step V-shaped inner edges 240 (and, thus, the notches 238) is formed. In subsequent pairs of groups, the pattern repeats with the first pair of corresponding second plates 230 having abutting inner ends and the subsequent pairs of corresponding second plates 230 having spaced-apart inner ends. The inner edges 240 form multi-step vertical lap joints with lower ends of the inner leg plates of the inner leg. [0042] The first and second outer legs 218, 220 may each be comprised of a single stack of plates, as in the core 102, or the first and second outer legs 218, 220 of the core 210 may each be comprised of a plurality of stacks of plates, as is shown in Fig. 9. The first and second out legs 218, 220 are constructed in a similar manner and, thus, for purposes of brevity, only the first outer leg. 218 will be described. [0043] The first outer leg 218 comprise a first stack 244 of leg plates 246 and a second stack 248 of leg plates 246. The first and second stacks 244, 248 abut each other along a seam 250 that extends in the longitudinal direction of the first outer leg 218. In both the first and second stacks 244, 248, the lea plates 246 are arranged in groups. The leg plates 246 each have a unitary construction and are trapezoidal in shape. The leg plates 246 in the first stack 244 have the same width as the leg plates 246 in the second stack 248. in each of the ieg piates 246, opposing ends of the leg plate 246 are mitered at oppositely-directed angles of about 45°, thereby providing the leg plate 246 with major and minor side edges. The first and second stacks 244, 248 abut each other such that the major side edges of the leg plates 246 of the second stack 248 are disposed against the minor side edges of the leg plates 246 of the first stack 24.4. In both the first and second stacks 244, 248, the lengths within each group of ieg plates 246 are different to permit the formation of multi-step lap joints with the plates of the upper and lower yokes 212, 214. The leg plates 246 in the first stack 244 may be formed from the same piece of steel as the leg plates 246 in the second stack 248. [0044] A transformer core embodied in accordance with the present invention provides a number of benefits over conventional transformer cores. The construction of an inner leg of a core in a pair of stacks reduces the amount of steel that is cut away and 14 WO 2006/105026 PCT/US2006/011122 discarded. For example, assuming that a layer of an inner leg is formed from one piece of rectangular steel, only two pieces of steel have to be discarded if the inner leg has two stacks, while six pieces of steel have to be discarded if the inner leg has only one stack. Of course, this savings increases when more than one layer is formed from a piece of steel, which is typically the case. [0045] In addition to saving steel, the present invention also permits a core to be manufactured in sizes larger than the cutting machine and/or the steel pieces would otherwise permit. For example, assuming that the cutting machine can only cut a 16 inch wide piece of steel, or only a 16 inch wide piece of steel is available, the present invention permits a 32 inch wide inner leg (or other core component) to be constructed. [0046] While the invention has been shown and described with respect to particular embodiments thereof, those embodiments are for the purpose of illustration rather than limitation,and other variations end modifications of the specific- embodiments herein described will be apparent to those skilled in the art, all within the intended spirit and scope of the invention. Accordingly, the invention is not to be limited in scope and effect to the specific embodiments herein described, nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention. 15 WO 2006/105026 PCT/US2006/011122 WHAT IS CLAIMED IS: 1. A transformer comprising: (a.) a core comprising: a first yoke comprising a stack of plates and having an outer side and an inner side with a groove formed therein, said groove extending in a stacking direction of the plates and being located inwardly from the outer side; a second yoke comprising a stack of plates and having an outer side and an inner side with a groove formed therein, said groove extending in the stacking direction of the plates and being located inwardly from the outer side; an inner leg having a first end disposed in the groove of the first yoke and a second end disposed in the groove of the second yoke, said leg comprising a first slack of first plates abutting a second slack of second plates; and (b.) a coll winding, mounted-to the inner leg. 2. The transformer of claim 1, wherein the core further comprises first and second outer legs extending between the-first and second yokes, said first and second outer legs each comprising a-stack of plates; and wherein the inner leg is disposed between the first and second outer legs. 3. The transformer of claim 2, wherein the first stack of the inner leg abuts the second stack of the inner leg along a seam extending in the longitudinal direction of the first and second stacks. 4. The transformer of claim 3, wherein the first plates of the first stack are equal in number to, and are aligned with, the second plates of the second stack so as to provide the inner leg with a plurality of layers, each of which comprises one of the first plates and one of the second plates; and wherein in each of the layers of the inner leg, the first plate has the same width as the second plate. 16 WO 2006/105026 PCT/US2006/011122 5. The transformer of claim 4, wherein the inner leg has a cruciform cross- section. 6. The transformer of claim 4, wherein the inner leg has a rectangular cross-section. 7. The transformer of claim 2, wherein the plates of the first and second outer legs each have opposing mitered ends, and each of the plates of the first and second yokes have opposing mitered ends; wherein the mitered ends of the plates of the first outer leg forms first joints and second joints with the mitered ends of the plates of the first and second yokes, respectively; and wherein the mitered ends of the plates of the second outer leg forms third joints and . fourth joints with the mitered ends of the plates of the first and second yokes, respectively. 8. The transformer of claim 7, wherein the first, second, third and fourth joints are muiti-step lap joints. 9. The transformer of claim 7, wherein each of the plates of the first yoke is unitary. 10. The transformer of claim 7, wherein the stack of plates of the first yoke is a first stack of plates, and wherein the first yoke further comprises second and third stacks of plates, said second and third stacks abutting the first stack in a longitudinal direction of the first yoke, said second and third stacks each having an inner end and an outer end; and wherein the inner ends of the second and third stacks at least partially define the lower groove of the lower yoke. 11. The transformer of claim 1, wherein each of the plates of the first yoke has a V-shaped notch defined by an inner edge, said notches forming the groove of the first yoke; wherein first ends of the first and second plates form the first end of the inner ieg; and 17 WO 2006/105026 PCT/US2006/011122 wherein the first ends of the first and second plates form joints with the inner edges of the first yoke. 12. The transformer of claim 11, wherein adjacent ones of the inner edges are vertically offset; and wherein adjacent ones of the first ends of the first plates are offset and adjacent ones of the first ends of the second plates are offset; and wherein the joints between the first ends of the first and second plates and the inner edges of the first yoke are vertical multi-step lap joints. 13. The transformer of claim 1, wherein the transformer is a dry-type transformer. 14. A method of forming a transformer comprising: (a.) providing a plurality of first and second, outer leg plates; (b.) providing a plurality of inner leg plates: (c.) providing a plurality of first yoke plates, each of said first yoke plates having an outer side and an inner side with a notch formed therein, wherein the notch is located inwardly from the outer side; (d.) stacking the inner leg plates, the first yoke plates and the first and second outer leg plates to form first and second outer legs, a first yoke with a first groove, and an inner leg having a first end disposed in the first groove, wherein said first outer leg comprises the first outer leg plates, said second outer leg comprises the second outer leg plates, said first yoke comprises the first yoke plates, and said inner leg comprises a first stack of the inner leg plates abutting a second stack of the inner leg plates, said first groove extending in a stacking direction of the first yoke and being formed by the notches of the first yoke plates; and (d.) mounting a coil winding to the inner leg. 15. The method of claim 14, wherein the step of providing a plurality of inner leg 18 WO 2006/105026 PCT/US2006/011122 plates comprises: (al) providing a piece of metal; (a2.) cutting the piece of metal to form an inner leg plate, wherein the inner leg plate has a trapezoidal shape with a major side edge and a minor side edge; and (a3.) repeating steps (a1.) and (a2.). 16. The method of claim 15, wherein the piece of metal comprises a roil of metal and the step of providing a plurality of the inner leg plates further comprises unrolling at least a portion of the roll of metal, and wherein the cutting of the piece of metal comprises making a pair of oppositely-directed diagonal cuts. 17. The method of claim 15, wherein the stacking of the inner leg plates, the first yoke plates and hte first and second outer log plates comprises: (d1.) forming a core section'by: forming joints between ends of a group of the first yoke plates and ends of a group of the first outer leg plates; forming joints between other ends of the group of the first yoke plates and ends of a group of the second outer leg piates; and positioning a pair of groups of the inner leg plates such that the major side edges of one of the groups of the inner leg plates abut the major side edges of , the other of the groups of the inner leg plates and such that ends of the inner leg plates are disposed in the notches of the group of the first yoke piates; and (d2.) repeating step (d1) to form a plurality of the core sections and thereby form the first yoke, the inner leg and the first and second outer legs; and wherein the forming of the core sections is performed such that the joints between the first yoke and the first and second outer legs are multi-step lap joints. 18. The method of claim 17, further comprising: providing a plurality of second yoke plates, each of said second yoke plates having an outer side and an inner side with a notch formed therein, wherein the notch 19 WO 2006/105026 PCT/US2006/011122 is located inwardly from the outer side; and after the winding is mounted to the inner leg, stacking the second yoke plates on the inner leg and the first and second outer legs to form a second yoke with a second groove, said second groove be.ing formed by the notches of the second yoke piates and receiving a second end of the inner leg. 19. The transformer of claim 17, wherein each of the first yoke plates is unitary. 20. A transformer formed by the method of claim 14. 20 The present invention is directed to a transformer having a stacked core (210), which includes top and bottom yokes (212,214) and first and second outer legs (218, 220). The core also includes an inner leg(216) that is formed from a pair of stacked plates, which abut each along a seam that extends in the longitudinal direction of the inner leg (216) . Each of the upper and lower yokes (212, 214) may be formed from a single stack of plates, or a plurality of stacks of plates. Each of the inner and outer legs (218 , 220) may also be formed from a single stack of plates, or a plurality of stacks of plates. The cross-section of the core may be rectangular or cruciform.

Full Text

WO 2006/105026 PCT/US2006/011122
ATRANSFORMER HAVING A STACKED CORE
WITH A SPLIT LEG AND A METHOD OF MAKING THE SAME
FIELD OF THE INVENTION
[0001] The invention relates to transformers and more particularly, to transformers
having a stacked core and methods of making the same with reduced waste.
BACKGROUND OF THE INVENTION
[0002] A stacked transformer core is comprised of thin metallic laminate plates,
such as grain oriented silicon steel. This type of material is used because the grain of
'the steel may be groomed-in certain directions to reduce the maqnetic field loss. The
plates are stacked on too of each other to form a plurality of layers. A stacked core Is
typically rectangular in shape and can have a rectangular or cruciform cross-section. A
front view of a conventional three leg stacked core 10 for a three phase transformer is
shown in Fig. 1. The core 10 comprises an upper yoke 12, a lower yoke 14, an inner
leg 16, and first and second outer legs 18, 20. A pair of windows 22 are disposed
between the inner leg 16 and the first and second outer legs 18, 20, respectively. Wire
coils (not shown) are mounted to the inner leg 16 and the first and second outer legs
18, 20, respectively.
[0003] The upper yoke 12 comprises a stack of plates 24, the lower yoke 14
comprises a stack of steel plates 26, the first outer leg 18 comprises a stack of plates 28 '
and the second outer leg 20 comprises a stack of plates 30. The plates 24,26 of the upper
and lower yokes 12, 14 have opposing ends that form joints with opposing ends of the
plates 28, 30 of the first and second outer legs 18, 20, respectively. A V-shaped upper
notch 32 is formed in each of the plates 24 of the upper yoke 12 and a V-shaped lower
notch 36 is formed in each of the plates 26 of the lower yoke 14. The upper notches 32
form an upper groove 38 in the upper yoke 12, while the lower notches 36 form a lower
groove 40 in the lower yoke 14. The size of the individual plates 24-30 vary depending on
the stacking technique used to assemble the core 10.
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[0004] . The inner leg 16 comprises a stack of plates 42. Each of the plates 42 has an
upper tined end 42a formed by a pair of miter cuts and a lower tined end 42b formed by a
pair of miter cuts. The upper and lower tined ends 42a, b of the plates 42 provide the inner
leg 16 with upper and lower tined ends 16a, b, which are adapted for receipt in the upper
and lower grooves 38, 40 of the upper and lower yokes 12, 14, respectively.
[0005] The manufacture of the conventional core 10 described above results in a
significant amount of steel being cut away and discarded. For example, during the
manufacture of the inner leg 16, four pieces of steel must be cut away from each plate 42
to provide the plate 42 with tined ends. Therefore, it would be desirable to provide a
stacked transformer core and a method of making the same that reduces the amount of
steel that is discarded and, thus, wasted. The present invention is directed to such a
transformer core and method,
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, a transformer is provided having a
stacked core. The core is provided with a first yoke formed from a stack of plates and
having an outer side and an inner side with a groove formed therein. The groove extends in
a stacking direction of the plates and is located inwardly from the outer side. The core is
also provided with a second yoke formed from a stack of plates and having an outer side
and an inner side with a groove formed therein. The groove extends in the stacking
direction of the plates and is located inwardly from the outer side. A first end of an inner leg ■
is disposed in the groove of the first yoke and a second end of the inner leg is disposed in
the groove of the second yoke. The inner leg includes a first stack of first plates abutting a
second stack of second plates. A coil winding is mounted to the inner leg of the core.
[0007] Also provided in accordance with the present invention is a method of
forming a transformer with a stacked core. In accordance with the method, a plurality of
first and second outer leg plates is provided. A plurality of inner leg plates and a
plurality of first yoke plates are also provided. Each of the first yoke plates has an outer
side and an inner side with a notch formed therein. The notch is located inwardly from
the outer side. The inner leg plates, the first yoke plates and the first and second outer
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leg plates are stacked to form first and second outer legs, a first yoke with a first . .
groove, and an inner leg having a first end disposed in the first groove. The first outer
leg is formed from the first outer leg plates, the second outer leg is formed from the
second outer leg plates and the first yoke is formed from the first yoke plates. The inner
leg is formed from a first stack of the inner leg plates abutting a second stack of the
inner leg plates. The first groove extends in a stacking direction of the first yoke and is
formed by the notches of the first yoke plates. The coil winding is mounted to the inner
leg.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The features, aspects, and advantages of the present invention will
become better understood with regard to the following description, appended claims,
and accompanying drawings where:
[0009] Fig. 1 shows a front elevational view of a prior art transformer core;
[0010] Fig. 2 shows a front elevational view of a transformer core constructed in
accordance with a first embodiment of the present invention;
[0011] Fig. 3 shows a close-up view of a connection between a first outer leg and
an upper yoke of the transformer core;
[0012] Fig. 4 shows an enlarged view of a portion of an inner leg spaced above a
lower yoke of the transformer core;
[0013] Fig. 5 shows a top plan schematic view of plates of inner leg plates being
formed from a roll of steel;
[0014] Fig. 6 shows a front elevational view of a transformer with the transformer
core;
[0015] Fig. 7 shows a front elevational view of a second transformer core
embodied in accordance with a second embodiment of the present invention;
[0016] Fig. 8 shows a cross-sectional view of an inner leg of the second
transformer core;
[0017] Fig. 9 shows a front elevational view of a third transformer core embodied
in accordance with a third embodiment of the present invention; and
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[0018]. Fig. 10 shows an enlarged view of a portion of an inner leg spaced above
a lower yoke in the third transformer core.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0019] It should be noted that in the detailed description that follows, identical
components have the same reference numerals, regardless of whether they are shown
in different embodiments of the present invention. It should also be noted that in order
to clearly and concisely disclose the present invention, the drawings may not
necessarily be to scale and certain features of the invention may be shown in
somewhat schematic form.
[0020] The present invention is directed to a transformer 100 (shown in Fig. 6), such
as a distribution transformer, having a stacked core 102. The transformer 100 may be an
oil-filled transformer, i.e., cooled by oil, or a dry-type transformer, i.e., cooled by air. The
construction of the core 102, however, is especially suitable for use in a dry transformer.
Referring now to Fig. 2, the core 102 has a rectangular shape and generally comprises an ■
upper yoke 104, a lower yoke 106, first and second outer legs 108, 110 and an inner leg
112. Upper ends of the first and second outer legs 108, 110 are connected to first and
second ends of the upper yoke 104, respectively, while lower ends of the first and second
outer legs 108, 110 are connected to first and second ends of the lower yoke 105. The
inner leg 112 is disposed about midway between the first and second outer legs 108,110
and has an upper end connected to the upper yoke 104 and a lower end connected to the
lower yoke 106. With this construction, two windows 113 are formed between the inner leg
112 and the first and second outer legs 108,110.
[0021] The upper yoke 104 has an inner side 104a and an outer side 104b, and the
lower yoke 106 has an inner side 106a and an outer side 106b. The upper yoke 104
comprises a stack of plates 114, while the lower yoke 106 comprises a stack of plates 116.
Both the plates 114 and the plates 116 are arranged in groups. In one exemplary
embodiment of the present invention, the groups are groups of seven. Of course, groups of
different numbers may be used, such as groups of four, which are used herein for ease of
description and illustration. Each of the plates 114, 116 is composed of grain-oriented
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silicon steel and has a thickness in a range of from about 7 mils to about 14 mils, with the
particular thickness being selected based on the application of the transformer 100. The
plates 114,116 each have a unitary construction and are trapezoidal in shape. In each of
the plates 114,116, opposing ends of the plate 114,116 are mitered at oppositely-directed
angles of about 45°, thereby providing the plate 114,116 with major and minor side edges.
The plates 114 have the same width to provide the upper yoke 104 with a rectangular
cross-section and the plates 116 have the same width to provide the lower yoke 106 with a
rectangular cross-section. However, the lengths of the plates 114 are not a!! the same and
the lengths of the plates 116 are not all the same. More specifically, the lengths within each
group of plates 114 are different and the lengths within each group of plates 116 are
different; The pattern of different lengths is the same for each group of plates 114 and the
pattern of different lengths is the same for each group of plates 116. The difference in
lengths within each group permits the formation of multi-stop lap joints with plates 120. 122
of the first and second outer legs 108, 110 as will be described more fully below.
[0022] A V-shaped upper notch 124 is formed in each of the plates 114 of the upper
yoke 104 by an upper interior edge 126 and a V-shaped lower notch 128 is formed in each
of the plates 116 of the lower yoke 106 by a lower interior edge 130, The upper interio!
edges 126 in adjacent plates 114 of the upper yoke 104 have different depths for forming '
vertical lap joints with upper ends of inner leg plates 152 of the inner leg 112, as wil! be
described more fully below. Similarly, the lower interior edges 130 in adjacent plates 116 of
the lower yoke 106 have different depths for forming vertical lap joints with lower ends of
the inner leg plates 152 of the inner leg 112, as will be described more fully beiow. The
upper notches 124 form an upper groove 136 in the upper yoke 104, while the lower
notches 128 form a lower groove 138 (shown best in Fig. 4) in the lower yoke 104. The
upper groove 136 is located inwardly from the outer side 104b, and the lower groove 138 is
located inwardly from the outer side 106b. The upper and lower grooves 136,138 extend in
the stacking directions of the upper and lower yokes 104, 106, respectively.
[0023] The first outer leg 108 comprises a stack of the plates 120, while the second
outer leg 110 comprises a stack of the plates 122. Both the plates 120 and the plates 122
are arranged in groups of the same number as the plates 114, 116. Each of the plates
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120,122 is composed of grain-oriented silicon steel and has a thickness in a range of from
about 7 mils to about 14 mils, with the particular thickness being selected based on the
application of the transformer 100. The plates 120,122 each have a unitary construction
and are trapezoidal in shape. In each of the plates 120, 122, opposing ends of the plate
are mitered at oppositely-directed angles of about 45°, thereby providing the plate 120,122
with major and minor side edges. The plates 120 have the same width to provide the first
outer leg 108 with a rectangular cross-section and the plates 122 have the same width to
provide the second outer leg 110 with a rectangular cross-section. However, the lengths of
the plates 120 are not all the same and the lengths of the plates 122 are not all the same.
More specifically, the lengths within each group of plates 120 are different and the lengths
within each group of plates 122 are different. The pattern of different lengths is the same
for each group of plaies 120 and the pattern of different lengths is the same for each group
of plates 12?. The difference in lengths within each group permits the formation of the
multi-step joints with the plates 114,116 of the upper and lower yokes 104,106, as will be
described more fully below.
[0024] Referring now to Fig. 3 there is shown an enlarged view of a portion of the
connection (represented by reference number 142) between the upper end of the first outer
leg 108 and the first end of the upper yoke 104. More specifically, the ends of first,
second, third and fourth plates 120a, b, c, d of the first outer leg 108 abut (form joints with)
the ends of first, second, third and fourth plates 114a, 114b, 114c, 114d of the upper yoke
104, respectively. The first through fourth plates 120a-d of the first outer leg 108 and the
first through fourth plates 14a-d of the upper yoke 104 are successively disposed farther
inwardly. The first through fourth plates 120a-d have successively longer lengths, whereas
.: the first through fourth plates 14a-d have successively shorter lengths. With this
construction, the first plate 114a overlaps the joint between the second plates 114b, 120b,
the second plate 114b overlaps the joint between the third plates 114c, 120c and the third
plate 114coverlaps the joint between the fourth plates 114d, 120d. As shown, outer points
of plates 120b-d of the first outer leg 108 protrude beyond the upper yoke 104. These
outer points may be removed to improve the appearance of the core 102. Although not
shown, additional groups of four plates 114,120 are provided and repeat the pattern of the
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first through fourth plates 114a-d and the first through fourth plates 120a-d. In this manner,
multi-step lap joints are formed between the plates 114 of the upper yoke 104 and the
plates 120 of the first outer leg 108, with plates 114 of the upper yoke 104 overlapping
plates 120 of the first outer leg 108.
[0025] The other connections (represented by reference numerals 144, 146, 148)
between the first and second outer legs 108,110 and the upper and lower yokes 104, 106
are constructed in the same manner as the connection 142 so as to have multi-step lap
joints. It should be appreciated, however, that the connections 142-148 may have a
different type of construction. For example, instead of the connections 142-148 having a
four step lap joint pattern, the connections 142-148 may have a seven, or other number
step lap joint pattern. In addition, instead of having plates 114, 116 of the upper and lower
yokes 104, 106 overlapping plates 120, 122 of the first and second outer legs 108, 110.
plates 120, 122 of the first-and second outer legs 103, 110 may overlap pialos 114, 116 of
the upper and lower yokes 104, 106. With this construction, outer points of the plates 114,
116 would protrude beyond the first and second outer legs 108, 110, respectively.
[0026] The inner leg 112 comprises a first stack 150 of inner leg plates 152 and a
second stack 154 of inner leg-plates 152, In each of the first and second stacks 150, 154,
the inner ieg. plates 152 are-arranged in groups of the same number as the plates 114,
116. The first and second stacks 150, 154 abut each other along a seam 158 that extends
in the longitudinal direction of the inner leg 112. Upper ends of the first and second stacks
150, 154 are disposed in the upper groove 136 of the upper yoke 104 and lower ends of
the first and second stacks 150, 154 are disposed in the lower groove 138 of the lower
yoke 106. The inner leg plates 152 form vertical multi-step lap joints with the plates 114,
116 of the upper and lower yokes 104,106, as will be described further below. The inner
leg plates 152 may all have the same length if the joints are offset by vertically shifting the
inner leg plates 152. Alternately, the inner ieg plates 152 may have a plurality of different
lengths if the joints are offset by the different lengths of adjacent inner leg plates 152.
Each of the inner leg plates 152 has a unitary construction and is trapezoidal in shape. In
each of the inner leg plates, opposing ends of the inner leg plate 152 are mitered at
oppositely-directed angles of about 45°, thereby providing the inner leg plate with major
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WO 2006/105026 PCT/US2006/011122
and minor side edges. The lengths of the inner leg plates 152 are determined by the major
side edges. Each of the inner leg plates 152 is composed of grain-oriented silicon steel
and has a thickness in a range of from about 7 mils to about 14 mils, with the particular
thickness being selected based on the application of the transformer 100.
[0027] Referring now to Fig. 4 there is shown an enlarged view of a portion of the
lower end ofthe inner leg 112 spaced from the loweryoke 106. When the lower end of the
inner leg 112 is disposed in the lower groove 138, the ends of first, second, third and fourth
inner leg plates 152a, b, c, d of the first and second stacks 150,154 abut (form joints with)
the lower interior edges 130a, b, c, d of first, second, third and fourth plates 116a, b, c, d of
the loweryoke 106, respectively. In each of the first and second stacks 150,154, the first
through fourth inner leg plates 152a-d are vertically offset such that lower ends thereof are
located successively farther downward. In order to accommodate these differences in
length, the Iower interior edges 130a-d of the- plates 116a d are cut successively deeper.
With this construction, the first plate 116a overlaps the joints between the second inner leg
plates 152b and the second plate 116b, the second plate 116b overlaps the joints between
the third inner leg plates 152c and the third plate 116c, and the third plate 116c overlaps
the joints between the fourth inner leg plates 152d and the fourth plate 116d. Although not
shown, additional groups ofthe plates 116 and inner leg plates 152 are provided and
repeat the pattern of the first through fourth plates 152a-d and the first through fourth
plates 116a-116d. In this manner, multi-step lap joints are formed between the plates 116
ofthe loweryoke 106 and the inner leg plates 152 ofthe first and second stacks 150,154,
with plates 116 of the lower yoke 106 overlapping plates 152 of the first and second stacks
150, 154.
[0028] Since the lower ends ofthe first through fourth inner leg plates 152a-d ofthe
first and second stacks 150,154 are located successively farther downward-, upper ends of
the first through fourth inner leg plates 152a-d of the first and second stacks 150,154 are
located successively farther downward. As a result, the upper interior edges 126 (and,
thus, the upper notches 124) of the plates 114 within each group are successively
shallower, which is the inverse of the loweryoke 106. With this construction, vertical multi-
step lap joints are formed between the plates 114 ofthe upper yoke 104 and the first inner
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leg .plates 152 of the first and second stacks 150, 154, with inner leg plates 152
overlapping plates 114 of the upper yoke.
[0029] It should be appreciated that the inner leg plates 152 of the first and second
slacks 150, 154 may be offset differently so as to have plates 114 of the upper yoke 104
overlapping inner leg plates 152, and inner leg plates 152 overlapping plates 116 of the
lower yoke 106. In addition, the inner leg plates 152 of the first and second stacks 150,154
may be offset to form a seven or other number step lap joint pattern, instead of the four
step lap joint pattern.
[0030] In the embodiment where the inner leg plates 152 have different lengths,
such as four different lengths, vertical multi-step lap joints are formed between the plates
114, 116 of the upper and lower yokes 104, 106 in a manner similar to that described
above, however, the upper interior edges 126 (and thus the upper notches 124) of the
plates 114 of the upper yoke 104 may have the same arrangement as the lower Interior
edges 130 (and thus the lower notches 128) of the plates 116 of the lower yoke 106 with
regard to depth, because there is no vertical shifting of the inner leg plates 152.
[0031] Referring now to Fin. 5, the inner leg plates 152 are formed from one or more
pieces of steel 160, which are typically received from a supplier in one or more rolls 162.
The steel piece(s) 160 in the roll(s) 162 is/are unrolled and cut by a cutting machine (not
shown), which is operable to make two or more cuts simultaneously. !n the description
below, the cutting machine is operable to make two cuts simultaneously. The cuts are
made at oppositely directed angles of about 45 °and are separated so as to form an inner
leg plate 152 with a length of L1, i.e., a major side length of L1. Fig. 5 shows a portion of a
steel piece 160 that has been unwound from its roll 162 and is being cut by the cutting
machine. The cutting machine makes a first cut 168 and a second cut 170 in the steel
piece 160 simultaneously. The first and second cuts 168, 170 form a first inner leg plate
152a and a scrap piece 172, which is discarded. The steel piece 160 is then further
unwound and advanced (relative to the cutting machine) by the distance L1. The cutting
machine makes a third cut 174 and a fourth cut 176 in the steel piece 160 simultaneously.
The third and fourth cuts 174,176 form a second inner leg plate 152b and. a third inner leg
plate 152c. This procedure of unwinding, advancing and cutting is continued until the
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WO 2006/105026 PCT/US2006/011122
required number of inner leg plates 152 is formed.
[0032] In the description of the cutting of the inner leg plates set forth above, the
inner.leg plates 152 ai! have the same length L1. If the inner leg plates 152 are provided
with different lengths, such as L1-L4, the requisite number of inner leg plates 152 with the
length L1 may be cut first. The cutting machine may then be reconfigured to change the
spacing of the cuts and the advancement distance of the steel piece 160 so as to produce
plates having a length L2. The requisite number of inner leg plates with L2 may then be
cut. In a similar manner, the cutting machine is reconfigured and run to produce the
requisite number of inner leg plates 152 with lengths L.3 and L4.
[0033] The method of assembling the core 102 is dependent on the size of the core
102. If the core 102 is large, such as would be the case if the transformer 100 was greater
than 3000 kva, the core 102 is assembled with the lower yoke 106, the inner leg 112 and
the first and second outer legs 108, 110 initially being disposed horizontally, i.e., the lower
yoke 106, the inner leg 112 and the first and second outer legs 108, 110 are stacked in a
vertical direction. In such a case the core 102 is assembled on a mounting fixture in a
plurality of layers. In a first layer, a group of plates 116 is laid on the mounting fixture, with
the major side edges disposed outwardly. Next, a group of plates 120 and a group of plates
122 are laid on the mounting fixture, with their major side edges disposed outwardly and
their ends abutting the ends of the group of plates 116,respectively, to form multi-step lap
joints. First and second groups of offset inner leg plates 152 are-then laid on the mounting
fixture, with the major side edges of the inner leg plates 152 of the first group abutting the
major side edges of the inner leg plates 152 of the second group, and the ends of the inner
leg plates 152 of the first and second groups abutting opposing portions of the lower
interior edges 130 of the plates 11*6, respectively, to form two series of multi-step vertical
lap joints, respectively. This laying process is repeated for each layer until a desired
stacking configuration is achieved. Once the lower yoke 106, the inner leg 112 and the first
and second outer legs 108, 110 have been formed, the lower yoke 106 is clamped
between a pair of end frames or supports 177 and bands 178 are disposed around the
inner leg 112 and the first and second outer legs 108,110, respectively, as shown in Fig. 6.
The partially formed core 102 is then moved to an upright position so that the inner leg
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WO 2006/105026 PCT/US2006/011122
112 and the first and second outer legs 108,110 extend vertically. Coil windings 180 are
then disposed over the inner leg 112 and the first and second outer legs 108, 110,
respectively. The upper yoke 104 is then stacked in groups of plates 114 onto the ends of
the inner leg 112 and the first and second outer legs 108, 110.
[0034] If the core 102 is smaller, such as would be the case if the transformer 100
was less than 3000 kva, the core 102 is assembled in a similar manner as described
above, except the core 102 is formed while being disposed vertically, i.e., the components
of the core 102 are stacked in a horizontal direction.
[0035] After the core 102 with the coil windings 180 is fully constructed, the core 102
is enclosed within a housing (not shown). If the transformer 100 is an oil-filled type of
transformer, the core 102 is immersed in oil within a compartment in the housing. If the
transformer 100 is a dry-type of transformer, the core 102 is not immersed in oil and tho
housing is provided with louvers to permit air to enter the housing snd pass-ovor Uio core
102 and the coil windings 180.
[0036] Although the assembly of the core 102 set forth above describes, three coil
windings 180 being mounted to the core 102, such as occurs when the transformer 100 is
a three-phase transformer, it should be appreciated that in another embodiment, a single
coil winding 180 may be mounted to the inner ieg 112 of the core 102, such as occurs
when the transformer 100 is a single phase transformer. In another embodiment, three
inner legs 190 may be provided, wherein the coil windings 180 are mounted to the inner
legs 190, respectively. In such a case, three upper grooves 136 would be formed in the
upper yoke 104 and three lower grooves 138 would be formed in the lower yoke 106. In
addition, four windows 113 would be formed.
[0037] Referring now to Fig. 7, there is shown a core 184 embodied in accordance
with a second embodiment of the present invention. The core 184 has substantially the
same construction as the core 102, except for the differences set forth below. The core 184
comprises upper and lower yokes 186, 188 an inner leg 190 and first and second outer
Iegs192,194. The inner leg 190 comprises a first stack 196 of inner leg plates 198anda
second stack 200 of inner leg plates 198. The first and second stacks 196, 200 abut each
other along a seam 202 that extends in the longitudinal direction of the inner leg 190. Each
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WO 2006/105026 PCT/US2006/011122
of the upper and lower yokes 186, 188 the inner leg 190 and the first and second outer
legs 192, 194 has a cruciform cross-section, instead of a rectangular cross-section, as in
the core 102. The cruciform cross-sections of these components increase the strength of
the core 184 and provide the inner leg 190 and the first and second outer legs 192, 194
with larger surface areas for supporting coils. The cruciform cross-sections of the
components of the core 184 are formed by providing the constituent plates of the
components with different widths. For example, and with reference now to Fig. 8, sections
204a,b,c,d,e,f,g of the inner leg plates 198 first successively increase in width and, then
after the midpoint, successively decrease in width. The sections 204a,b,c,d,e,f,g each
comprise one or more groups of inner leg plates 198. Thus, the outermost inner leg plates
198 in sections 204a and 204g each have a width W1, which is the smallest of the widths
of the inner leg plates 198, and the. inner log plates 198 in the middle section 204d each
have a width Wn, which is the larqest of the widths of the inner leg plates 198 in each of
first and second stacks 196, 200, the major side edges of the inner leg plates 198 are
aligned at the seam 202. The different widths, however, cause the minor.sides to be offset,
which helps form the cruciform cross-section of the inner leg .190. The thickness of the
sections 204a-g in the stacking direction may vary. For example, as shown, the center
section 204d may be substantially thicker than the other sections 204a,b,c,e,f,g.
[0038] The components of the core 184 are cut and assembled in substantially the
same manner as the components of the core 102, except for each component, a plurality
of steel pieces with different widths (configured in a plurality of rolls) are cut to form the
constituent plates of varying width.
[0039] Referring now to Fig. 9, there is shown a core 210 embodied in accordance
with a third embodiment of the present invention. The core 210 has substantially the same
construction and is constructed in substantially the same manner as the core 102, except
for the differences set forth below. The core 210 comprises upper and lower yokes 212,
214, an inner leg 216 and first and second outer legs 218, 220. Like the inner leg 112 of
the core 102, the inner leg 216 is comprised of a pair of stacks of plates. Unlike the upper
and lower yokes 104,106 in the core 102, however, the upper and lower yokes 212,214 of
the core 210 are comprised of a plurality of stacks of plates. The upper and lower yokes
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WO 2006/105026 PCT/US2006/011122
212, 214 are constructed in a similar manner and, thus, for purposes of brevity only the
-lower yoke 212 will be described.
[0040] . The lower yoke 214 of the core 210 comprises an outer stack 224 of first
plates 226, a first inner stack 228 of second plates 230 and a second inner stack 232 of
second plates 230. As with the lower yoke 106 of the core 102, the outer stack 224 and the
first and second inner stacks 228, 232 are arranged in groups of plates to form multi-step
lap joints. More specifically, within each group of the second plates 230 of the first and
second inner stacks 228, 232, the inner ends of the second plates 230 are offset, either by
shifting the second plates 230, or by providing the. second plates 230 with different lengths.
The groups in the first and second inner stacks 228, 232 are arranged in the same manner
and are aligned so as to form pairs of corresponding second plates 230 (from the first and
second inner stacks 228, 232 respectively). Each of the first plates 226 is unitary in
structure and has an elongated trapezoidal shape, with major and minor side edges. The
first plates 226 have opposing ends that form multi-step lap joints with plates of the first
and second outer legs 218, 220, respectively. A portion of the first plates 226 have V-
shaped notches 234 formed therein. The second plates 230. each have major and minor
side edges and outer mitered ends. The first and second inner stacks 228, 232 are
disposed on the outer stack 224 such that the major side edges of the second plates 230
are disposed against the minor side edges of the first plates 226. The first and second
inner stacks 228, 232 abut the outer stack 224 along a pair of seams 236, respectively,
that extend in the longitudinal direction of the outer stack 224. The first and second plates
226, 230 all have the same width and, thus, may be formed from the same piece of steel.
[0041] Referring now to Fig. 10, in each layer of the lower yoke 214, a V-shaped
notch 238 is at least partially formed by inner ends of a pair of corresponding second
plates 230 (from the first and second inner stacks 228, 232 respectively). In a first pair of
corresponding second plates 230a, the second plates 230a have mitered inner ends that
abut at a lower point, thereby forming a notch 238a. In a second pair of corresponding
second plates 230b, inner ends of second plates 230b are separated by a spacing that
cooperates with a notch 234b in a corresponding first plate 226b to form a notch 238b. In
the remaining pairs of corresponding second plates 230, the inner ends of the second
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WO 2006/105026 PCT/US2006/011122
plates 230 are also spaced apart and cooperate with notches 234 in the first plates 226 to
form notches 238. In this manner, a vertical series of multi-step V-shaped inner edges 240
(and, thus, the notches 238) is formed. In subsequent pairs of groups, the pattern repeats
with the first pair of corresponding second plates 230 having abutting inner ends and the
subsequent pairs of corresponding second plates 230 having spaced-apart inner ends. The
inner edges 240 form multi-step vertical lap joints with lower ends of the inner leg plates of
the inner leg.
[0042] The first and second outer legs 218, 220 may each be comprised of a single
stack of plates, as in the core 102, or the first and second outer legs 218, 220 of the core
210 may each be comprised of a plurality of stacks of plates, as is shown in Fig. 9. The first
and second out legs 218, 220 are constructed in a similar manner and, thus, for purposes
of brevity, only the first outer leg. 218 will be described.
[0043] The first outer leg 218 comprise a first stack 244 of leg plates 246 and a
second stack 248 of leg plates 246. The first and second stacks 244, 248 abut each other
along a seam 250 that extends in the longitudinal direction of the first outer leg 218. In
both the first and second stacks 244, 248, the lea plates 246 are arranged in groups. The
leg plates 246 each have a unitary construction and are trapezoidal in shape. The leg
plates 246 in the first stack 244 have the same width as the leg plates 246 in the second
stack 248. in each of the ieg piates 246, opposing ends of the leg plate 246 are mitered at
oppositely-directed angles of about 45°, thereby providing the leg plate 246 with major and
minor side edges. The first and second stacks 244, 248 abut each other such that the
major side edges of the leg plates 246 of the second stack 248 are disposed against the
minor side edges of the leg plates 246 of the first stack 24.4. In both the first and second
stacks 244, 248, the lengths within each group of ieg plates 246 are different to permit the
formation of multi-step lap joints with the plates of the upper and lower yokes 212, 214.
The leg plates 246 in the first stack 244 may be formed from the same piece of steel as the
leg plates 246 in the second stack 248.
[0044] A transformer core embodied in accordance with the present invention
provides a number of benefits over conventional transformer cores. The construction of an
inner leg of a core in a pair of stacks reduces the amount of steel that is cut away and
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WO 2006/105026 PCT/US2006/011122
discarded. For example, assuming that a layer of an inner leg is formed from one piece of
rectangular steel, only two pieces of steel have to be discarded if the inner leg has two
stacks, while six pieces of steel have to be discarded if the inner leg has only one stack.
Of course, this savings increases when more than one layer is formed from a piece of
steel, which is typically the case.
[0045] In addition to saving steel, the present invention also permits a core to be
manufactured in sizes larger than the cutting machine and/or the steel pieces would
otherwise permit. For example, assuming that the cutting machine can only cut a 16 inch
wide piece of steel, or only a 16 inch wide piece of steel is available, the present invention
permits a 32 inch wide inner leg (or other core component) to be constructed.
[0046] While the invention has been shown and described with respect to
particular embodiments thereof, those embodiments are for the purpose of illustration
rather than limitation,and other variations end modifications of the specific-
embodiments herein described will be apparent to those skilled in the art, all within the
intended spirit and scope of the invention. Accordingly, the invention is not to be limited
in scope and effect to the specific embodiments herein described, nor in any other way
that is inconsistent with the extent to which the progress in the art has been advanced
by the invention.
15

WO 2006/105026 PCT/US2006/011122
WHAT IS CLAIMED IS:
1. A transformer comprising:
(a.) a core comprising:
a first yoke comprising a stack of plates and having an outer side and an
inner side with a groove formed therein, said groove extending in a stacking
direction of the plates and being located inwardly from the outer side;
a second yoke comprising a stack of plates and having an outer side and an
inner side with a groove formed therein, said groove extending in the stacking
direction of the plates and being located inwardly from the outer side;
an inner leg having a first end disposed in the groove of the first yoke and a
second end disposed in the groove of the second yoke, said leg comprising a first
slack of first plates abutting a second slack of second plates; and
(b.) a coll winding, mounted-to the inner leg.
2. The transformer of claim 1, wherein the core further comprises first and second
outer legs extending between the-first and second yokes, said first and second outer legs
each comprising a-stack of plates; and
wherein the inner leg is disposed between the first and second outer legs.
3. The transformer of claim 2, wherein the first stack of the inner leg abuts the
second stack of the inner leg along a seam extending in the longitudinal direction of the
first and second stacks.
4. The transformer of claim 3, wherein the first plates of the first stack are equal in
number to, and are aligned with, the second plates of the second stack so as to provide the
inner leg with a plurality of layers, each of which comprises one of the first plates and one
of the second plates; and
wherein in each of the layers of the inner leg, the first plate has the same width as
the second plate.
16

WO 2006/105026 PCT/US2006/011122
5. The transformer of claim 4, wherein the inner leg has a cruciform cross- section.
6. The transformer of claim 4, wherein the inner leg has a rectangular cross-section.
7. The transformer of claim 2, wherein the plates of the first and second outer legs
each have opposing mitered ends, and each of the plates of the first and second yokes
have opposing mitered ends;
wherein the mitered ends of the plates of the first outer leg forms first joints and
second joints with the mitered ends of the plates of the first and second yokes,
respectively; and
wherein the mitered ends of the plates of the second outer leg forms third joints and .
fourth joints with the mitered ends of the plates of the first and second yokes, respectively.
8. The transformer of claim 7, wherein the first, second, third and fourth joints are
muiti-step lap joints.
9. The transformer of claim 7, wherein each of the plates of the first yoke is unitary.
10. The transformer of claim 7, wherein the stack of plates of the first yoke is a first
stack of plates, and wherein the first yoke further comprises second and third stacks of
plates, said second and third stacks abutting the first stack in a longitudinal direction of the
first yoke, said second and third stacks each having an inner end and an outer end; and
wherein the inner ends of the second and third stacks at least partially define the
lower groove of the lower yoke.
11. The transformer of claim 1, wherein each of the plates of the first yoke has a
V-shaped notch defined by an inner edge, said notches forming the groove of the first
yoke;
wherein first ends of the first and second plates form the first end of the inner
ieg; and
17

WO 2006/105026 PCT/US2006/011122
wherein the first ends of the first and second plates form joints with the inner
edges of the first yoke.
12. The transformer of claim 11, wherein adjacent ones of the inner edges are
vertically offset; and
wherein adjacent ones of the first ends of the first plates are offset and adjacent
ones of the first ends of the second plates are offset; and
wherein the joints between the first ends of the first and second plates and the
inner edges of the first yoke are vertical multi-step lap joints.
13. The transformer of claim 1, wherein the transformer is a dry-type
transformer.
14. A method of forming a transformer comprising:
(a.) providing a plurality of first and second, outer leg plates;
(b.) providing a plurality of inner leg plates:
(c.) providing a plurality of first yoke plates, each of said first yoke plates having
an outer side and an inner side with a notch formed therein, wherein the notch is
located inwardly from the outer side;
(d.) stacking the inner leg plates, the first yoke plates and the first and second
outer leg plates to form first and second outer legs, a first yoke with a first groove, and
an inner leg having a first end disposed in the first groove, wherein said first outer leg
comprises the first outer leg plates, said second outer leg comprises the second outer
leg plates, said first yoke comprises the first yoke plates, and said inner leg comprises a
first stack of the inner leg plates abutting a second stack of the inner leg plates, said
first groove extending in a stacking direction of the first yoke and being formed by the
notches of the first yoke plates; and
(d.) mounting a coil winding to the inner leg.
15. The method of claim 14, wherein the step of providing a plurality of inner leg
18

WO 2006/105026 PCT/US2006/011122
plates comprises:
(al) providing a piece of metal;
(a2.) cutting the piece of metal to form an inner leg plate, wherein the inner leg
plate has a trapezoidal shape with a major side edge and a minor side edge; and
(a3.) repeating steps (a1.) and (a2.).
16. The method of claim 15, wherein the piece of metal comprises a roil of metal
and the step of providing a plurality of the inner leg plates further comprises unrolling at
least a portion of the roll of metal, and wherein the cutting of the piece of metal
comprises making a pair of oppositely-directed diagonal cuts.
17. The method of claim 15, wherein the stacking of the inner leg plates, the first
yoke plates and hte first and second outer log plates comprises:
(d1.) forming a core section'by:
forming joints between ends of a group of the first yoke plates and ends of
a group of the first outer leg plates;
forming joints between other ends of the group of the first yoke plates and
ends of a group of the second outer leg piates; and
positioning a pair of groups of the inner leg plates such that the major side
edges of one of the groups of the inner leg plates abut the major side edges of
, the other of the groups of the inner leg plates and such that ends of the inner leg
plates are disposed in the notches of the group of the first yoke piates; and
(d2.) repeating step (d1) to form a plurality of the core sections and thereby form
the first yoke, the inner leg and the first and second outer legs; and
wherein the forming of the core sections is performed such that the joints
between the first yoke and the first and second outer legs are multi-step lap joints.
18. The method of claim 17, further comprising:
providing a plurality of second yoke plates, each of said second yoke plates
having an outer side and an inner side with a notch formed therein, wherein the notch
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WO 2006/105026 PCT/US2006/011122
is located inwardly from the outer side; and
after the winding is mounted to the inner leg, stacking the second yoke plates on
the inner leg and the first and second outer legs to form a second yoke with a second
groove, said second groove be.ing formed by the notches of the second yoke piates and
receiving a second end of the inner leg.
19. The transformer of claim 17, wherein each of the first yoke plates is unitary.
20. A transformer formed by the method of claim 14.
20

The present
invention is directed to a transformer
having a stacked core (210), which
includes top and bottom yokes
(212,214) and first and second outer
legs (218, 220). The core also
includes an inner leg(216) that is
formed from a pair of stacked plates,
which abut each along a seam that
extends in the longitudinal direction
of the inner leg (216) . Each of the
upper and lower yokes (212, 214)
may be formed from a single stack
of plates, or a plurality of stacks of
plates. Each of the inner and outer
legs (218 , 220) may also be formed
from a single stack of plates, or a
plurality of stacks of plates. The
cross-section of the core may be
rectangular or cruciform.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=97/eBDu2Vav1oS8QwQ7ZWg==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

279830

Indian Patent Application Number

3635/KOLNP/2007

PG Journal Number

05/2017

Publication Date

03-Feb-2017

Grant Date

31-Jan-2017

Date of Filing

26-Sep-2007

Name of Patentee

ABB TECHNOLOGY AG

Applicant Address

AFFOLTERNSTRASSE 44, CH-8050 ZURICH

Inventors:

#	Inventor's Name	Inventor's Address
1	SARVER CHARLIE	14506 NORTH SCENIC HIGHWAY, ROCKY GAP, VA 24366
2	PAULEY WILL E	319 WHITE PINE DR., BLAND, VA 24315
3	HORTON RUSH B	870 ROLLING HILLS DR., WYTHERVILLE, VA 24382

PCT International Classification Number

H01F 27/245

PCT International Application Number

PCT/US2006/011122

PCT International Filing date

2006-03-27

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/093551	2005-03-30	U.S.A.