The invention relates to transformers and more particularly, to methods of making transformers having a stacked core with a cruciform leg.
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 magnetic field loss. The plates are stacked on top 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 cruciform cross-section increases the strength of a stacked core. In addition, a core leg having a cruciform cross-section provides more surface area for supporting a coil. An example of a conventional stacked transformer core having a cruciform cross-section is shown in U.S. Pat. No. 4,283,842 to DeLaurentis et al. The core of the DeLaurentis et al. patent has upper and lower yokes with cruciform cross-sections, as well as legs with cruciform cross-sections.
Although a stacked core having a cruciform cross-section, such as the core of the DeLaurentis et al. patent, provides additional support and strength, such a core is typically more difficult to manufacture and results in more wasted steel. Therefore, it would be desirable to provide a stacked transformer core that has the benefits of a cruciform cross-section, but is simpler to manufacture and reduces the amount of steel that is wasted. The present invention is directed to such a transformer core and a method of making the same.
In accordance with the present invention, a method of forming a transformer is provided. In accordance with the method, a plurality of outer leg plates, a plurality of inner leg plates and plurality of yokes plates are provided. Not all of the inner leg plates have the same width. Each of the yoke plates has an outer side and an inner side with a notch formed therein. The notch is located inwardly from the outer side. All of the yoke plates have the same width. The outer leg plates, the inner leg plates and the yoke plates are stacked to form a pair of outer legs, a yoke with a groove, and an inner leg having a first end disposed in the groove. The outer legs include the outer leg plates, the inner leg includes the inner leg plates and the yoke included the yoke plates. The groove extends in a stacking direction of the yoke and is formed by the notches of the yoke plates. The inner leg plates are stacked so as to provide the inner leg with a cruciform cross-section and the yoke plates are stacked so as to provide the yoke with a rectangular cross-section. A coil winding is mounted to the inner leg.
Also provided in accordance with the present invention is a method of forming a transformer, wherein a plurality of first leg plates, a plurality of second leg plates, a plurality of first yoke plates and a plurality of second yoke plates are provided. Not all of the second leg plates have the same width, whereas all of the first yoke plates have the same width and all of the second yoke plates have the same width. The first leg plates, the second leg plates and the first yoke plates are stacked to form a core section having first and second legs extending from a first yoke. The first leg includes the first leg plates, the second leg includes the second leg plates and the first yoke includes the first yoke plates. The second leg plates are stacked so as to provide the second leg with a cruciform cross-section and the first yoke plates are stacked so as to provide the first yoke with a rectangular cross-section. A coil winding is mounted to the second leg. The second yoke plates are stacked over the core section to form a second yoke having a rectangular cross-section.
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:
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.
The present invention is directed to a transformer 10 (shown in
The upper yoke 14 has an inner side 14a and an outer side 14b, and the lower yoke 16 has an inner side 16a and an outer side 16b. The upper yoke 14 comprises a stack of plates 26, while the lower yoke 16 comprises a stack of plates 28. Both the plates 26 and the plates 28 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 26, 28 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 10. The plates 26, 28 each have a unitary construction and are trapezoidal in shape. In each of the plates 26, 28, opposing ends of the plate 26, 28 are mitered at oppositely-directed angles of about 45°, thereby providing the plate 26, 28 with major and minor sides. The plates 26 have the same width to provide the upper yoke 14 with a rectangular cross-section and the plates 28 have the same width to provide the lower yoke 16 with a rectangular cross-section. However, the lengths of the plates 26 are not all the same and the lengths of the plates 28 are not all the same. More specifically, the lengths within each group of plates 26 are different and the lengths within each group of plates 28 are different. The pattern of different lengths is the same for each group of plates 26 and the pattern of different lengths is the same for each group of plates 28. The difference in lengths within each group permits the formation of multi-step lap joints with plates 30, 32 of the first and second outer legs 18, 20 as will be described more fully below.
A V-shaped upper notch 34 is formed in each of the plates 26 of the upper yoke 14 by an upper interior edge 36 and a V-shaped lower notch 38 is formed in each of the plates 28 of the lower yoke 16 by a lower interior edge 40. The upper interior edges 36 in adjacent plates 26 of the upper yoke 14 have different depths for forming vertical lap joints with upper ends of inner leg plates 70 of the inner leg 22, as will be described more fully below. Similarly, the lower interior edges 40 in adjacent plates 28 of the lower yoke 16 have different depths for forming vertical lap joints with lower ends of the inner leg plates 70 of the inner leg 22, as will be described more fully below. The upper notches 34 form an upper groove 46 in the upper yoke 14, while the lower notches 38 form a lower groove 48 in the lower yoke 14. The upper groove 46 is located inwardly from the outer side 14b, and the lower groove 48 is located inwardly from the outer side 16b. The upper and lower grooves 46, 48 extend in the stacking directions of the upper and lower yokes 14, 16, respectively.
The first outer leg 18 comprises a stack of the plates 30, while the second outer leg 20 comprises a stack of the plates 32. The plates 30, 32 have varying widths so as to provide the first and second outer legs 18, 20 with cruciform cross-sections. More specifically, the plates 30 are arranged in sections 50 of different widths and the plates 32 are arranged in sections 52 of different widths. In each section 50, the plates 30 have the same width and in each section 52, the plates 32 have the same width. For example, and with reference now to
Within each section 50, 52, the plates 30, 32 are arranged in groups of the same number as the plates 26, 28. Each of the plates 30, 32 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. The plates 30, 32 each have a unitary construction and are trapezoidal in shape. In each of the plates 30, 32, opposing ends of the plate 30, 32 are mitered at oppositely-directed angles of about 450, thereby providing the plate 30, 32 with major and minor side edges. The lengths of the plates 30 are not all the same and the lengths of the plates 32 are not all the same. More specifically, the lengths within each group of plates 30 are different and the lengths within each group of plates 32 are different. The pattern of different lengths is the same for each group of plates 30 and the pattern of different lengths is the same for each group of plates 32. The difference in lengths within each group permits the formation of the multi-step joints with the plates 28 of the first and second outer legs 18, 20, as will be described more fully below.
Referring now to
The other connections (represented by reference numerals 58, 60, 62) between the first and second outer legs 18, 20 and the upper and lower yokes 14,16 are constructed in the same manner as the connection 54 so as to have multi-step lap joints. It should be appreciated, however, that the connections 54, 58, 60, 62 may have a different type of construction. For example, instead of the connections 54, 58, 60, 62 having a four step lap joint pattern, the connections 54, 58, 60, 62 may have a seven, or other number step lap joint pattern. In addition, instead of having plates 26, 28 of the upper and lower yokes 14,16 overlapping plates 30, 32 of the first and second outer legs 18, 20, plates 30, 32 of the first and second outer legs 18, 20 may overlap plates 26, 28 of the upper and lower yokes 14,16.
The inner leg 22 comprises a stack of inner leg plates 70. The inner leg plates 70 have varying widths so as to provide the inner leg 22 with a cruciform cross-section. More specifically, the inner leg plates 70 are arranged in sections 72 of different widths, wherein in each section 72, the inner leg plates 70 have the same width. This is best illustrated in
Within each section 72, the inner leg plates 70 are arranged in groups of the same number as the plates 26, 28 (e.g. four). Each of the inner leg plates 70 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 10. The inner leg plates 70 each have a unitary construction and include upper and lower pointed or tined ends, wherein each of the upper and lower tined ends is formed by a pair of miter cuts of about 45° each. The inner leg plates 70 may all have the same length if the joints are offset by vertically shifting the inner leg plates 70. Alternately, the inner leg plates 70 may have a plurality of different lengths if the joints are offset by the different lengths of adjacent inner leg plates 70.
Referring now to
Since the lower ends of the first through fourth inner leg plates 70a-d of the inner leg 22 are located successively farther downward, upper ends of the first through fourth inner leg plates 70a,b,c,d of the inner leg 22 are located successively farther downward. As a result, the upper interior edges 36 (and, thus, the upper notches 34) of the plates 26 within each group are successively shallower, which is the inverse of the lower yoke 16. With this construction, vertical multi-step lap joints are formed between the plates 26 of the upper yoke 14 and the inner leg plates 70 of the inner leg 22, with inner leg plates 70 overlapping plates 26 of the upper yoke 14.
It should be appreciated that the inner leg plates 70 of the inner leg 22 may be offset differently so as to have plates 26 of the upper yoke 14 overlapping inner leg plates 70 and inner leg plates 70 overlapping plates 28 of the lower yoke 16. In addition, the inner leg plates 70 may be offset to form a seven or other number step lap joint pattern, instead of the four step lap joint pattern.
In the embodiment where the inner leg plates 70 have different lengths, vertical multi-step lap joints are formed between the plates 26, 28 of the upper and lower yokes 14, 16 in a manner similar to that described above, however, the upper interior edges 36 (and thus the upper notches 34) of the plates 26 of the upper yoke 14 may have the same arrangement as the lower interior edges 40 (and thus the lower notches 38) of the plates 28 of the lower yoke 16 with regard to depth, because there is no vertical shifting of the inner leg plates 70.
The method of assembling the core 12 is dependent on the size of the core 12. If the core 12 is large, such as would be the case if the transformer 10 was greater than 3000 kva, the core 12 is assembled with the lower yoke 16, the inner leg 22 and the first and second outer legs 18, 20 initially being disposed horizontally, i.e., the lower yoke 16, the inner leg 22 and the first and second outer legs 18, 20 are stacked in a vertical direction. In such a case the core 12 is assembled on a mounting fixture in a plurality of layers. In a first layer, a group of plates 28 is laid on the mounting fixture, with the major side disposed outwardly. Next, a group of plates 30 and a group of plates 32 are laid on the mounting fixture, with their major sides disposed outwardly and their ends abutting the ends of the group of plates 28, respectively, to form multi-step lap joints. A group of offset inner leg plates 70 are then laid on the mounting fixture, with the tined lower ends of the inner leg plates 70 abutting the lower interior edges 40 of the plates 28, respectively, to form multi-step vertical lap joints. This laying process is repeated for each layer until a desired stacking configuration is achieved. Once the lower yoke 16, the inner leg 22 and the first and second outer legs 18, 20 have been formed, the lower yoke 16 is clamped between a pair of end frames or supports 76 and bands 78 are disposed around the inner leg 22 and the first and second outer legs 18,20, respectively, as shown in
If the core 12 is smaller, such as would be the case if the transformer 10 was less than 3000 kva, the core 12 is assembled in a similar manner as described above, except the core 12 is formed while being disposed vertically, i.e., the components of the core 12 are stacked in a horizontal direction.
After the core 12 with the coil windings 80 is fully constructed, the core 12 is enclosed within a housing (not shown). If the transformer 10 is an oil-filled type of transformer, the core 12 is immersed in oil within a compartment in the housing. If the transformer 10 is a dry-type of transformer, the core 12 is not immersed in oil and the housing is provided with louvers to permit air to enter the housing and pass over the core 12.
Although the assembly of the core 12 set forth above describes three coil windings 80 being mounted to the core 12, such as occurs when the transformer 10 is a three-phase transformer, it should be appreciated that in another embodiment, a single coil winding 80 may be mounted to the inner leg 22 of the core 12, such as occurs when the transformer 10 is a single phase transformer.
Referring now to
The inner leg plates 90 have varying widths so as to provide the inner leg 86 with a cruciform cross-section. More specifically, the inner leg plates 90 are arranged in sections 96 of different widths, wherein each section 96 comprises a portion of the first stack 88 and an adjacent portion of the second stack 92. The inner leg plates 90 in each section 96 have the same width. In each of the first and second stacks 88, 92, the major side edges of the inner leg plates 90 are aligned at the seam 94. The different widths, however, cause the minor sides to be offset, which helps form the cruciform cross-section of the inner leg 86.
The inner leg plates 90 in each section 96 may be cut from the same roll of metal in the manner described in U.S. Pat. No. 7,199,696, entitled “A TRANSFORMER HAVING A STACKED CORE WITH A SPLIT LEG AND A METHOD OF MAKING THE SAME”, which is assigned to the assignee of the present invention and is hereby incorporated by reference.
Referring now to
The upper yoke 106 comprises a center stack 110 of plates 112 and first and second outer stacks 114, 116 of plates 118. Similarly, the lower yoke 108 comprises a center stack 120 of plates 122 and first and second outer stacks 124,126 of plates 130. Each of the plates 112,122 is elongated and has opposing tined ends. Each of the plates 118, 130 is trapezoidal in shape and has opposing ends mitered at oppositely-directed angles of about 45°. In the upper yoke 106, an inner end of the first outer stack 114 cooperates with a first end of the center stack 110 to define the upper groove 46a, while an inner end of the second outer stack 116 cooperates with a second end of the center stack 110 to define the upper groove 46c. Similarly, in the lower yoke 108, an inner end of the first outer stack 124 cooperates with a first end of the center stack 120 to define the lower groove 48a, while an inner end of the second outer stack 126 cooperates with a second end of the center stack 120 to define the lower groove 48c. The upper groove 46b is formed in the center stack 110, and the lower groove 48b is formed in the center stack 120.
In the upper yoke 106, the first and second outer stacks 114,116 may simply abut the center stack 110, i.e., form seams with the center stack 110, or the plates 118 of the first and second outer stacks 114,116 may form multi-step lap joints with the plates 112 of the center stack 110. Similarly, in the lower yoke 108, the first and second outer stacks 124, 126 may simply abut the center stack 120, i.e., form seams with the center stack 120, or the plates 130 of the first and second outer stacks 124,126 may form multi-step lap joints with the plates 122 of the center stack 120.
A transformer core embodied in accordance with the present invention provide a number of benefits over conventional transformer cores. For example, providing the transformer core with legs having cruciform cross-sections increases the strength of the core and provides the legs with larger surface areas for supporting coil windings, while providing the transformer core with yokes having rectangular cross-sections simplifies the construction of the yokes (and, thus, the core) and reduces the amount of metal wasted in constructing the yokes (and, thus, the core).
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 and 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.
This application is a divisional application of, and claims priority from, U.S. patent application Ser. No. 11/093,408 filed on Mar. 30, 2005, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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Parent | 11093408 | Mar 2005 | US |
Child | 11779729 | Jul 2007 | US |