The invention relates to transformers and more particularly, to transformers having a stacked core and methods of making the same with reduced waste.
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. Examples of conventional stacked transformer cores include U.S. Pat. No. 3,157,850 to Winter; U.S. Pat. No. 4,136,322 to Maezima and U.S. Pat. No. 4,200,854 to DeLaurentis et al.
The manufacture of a conventional stacked core typically results in a significant amount of steel being cut away and discarded. 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.
In accordance with the present invention, a transformer with a stacked core and a method of making the same are provided. The transformer includes a ferromagnetic core having first and second yokes and a pair of outer legs. Each of the first and second yokes includes a stack of consecutive yoke plates. Each of the yoke plates in the stack has a unitary construction. Each of the first and second outer legs includes a stack of outer leg plates. Each of the outer leg plates has a unitary construction and a trapezoidal shape with an inner longitudinal edge, an outer longitudinal edge and mitered edges extending between the inner and outer longitudinal edges. The mitered edges meet the inner longitudinal edges at inner points, respectively. The core is arranged in a plurality of layers. Each of the layers includes a pair of the yoke plates and a pair of the outer leg plates. In an innermost layer, the width of each yoke plate is less than the width of each outer leg plate. In each of the layers, the inner points of the outer leg plates are substantially in contact with the yoke plates. At least one coil winding is mounted to one of the outer legs.
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.
Referring now to
The transformer 10 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 18, however, is especially suitable for use in a dry transformer. The transformer 10 may be a distribution transformer having a kVA rating in a range of from about 26.5 kVA to about 15,000 kVA. The voltage of the high voltage windings may be in a range of from about 600 V to about 35 kV and the voltage of the low voltage windings may be in a range of from about 120 V to about 15 kV.
Each outer leg 22 comprises a stack of outer leg plates 50. In each outer leg 22, the outer leg plates 50 are arranged in groups. In one exemplary embodiment of the present invention, the groups each comprise seven outer leg plates 50. 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 outer leg plates 50 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 outer leg plates 50 each have a unitary construction (i.e., are monolithic or undivided) and are trapezoidal in shape. In each of the outer leg plates 50, opposing ends of the plate 50 are mitered at oppositely-directed angles of about 45°, thereby providing the plate 50 with inner (minor) and outer (major) longitudinal edges 51, 52. The outer leg plates 50 have the same width (W1) between the inner and outer longitudinal edges 51, 52, thereby providing each outer leg 22 with a rectangular cross-section. However, the lengths of the outer leg plates 50 are not all the same. More specifically, the lengths within each group of outer leg plates 50 are different. The pattern of different lengths is the same for each group of outer leg plates 50. The difference in lengths within each group permits the formation of the multi-step joints with plates of the yokes, as will be described more fully below.
Each of the yokes 24 has an inner side and an outer side. Each yoke 24 comprises a stack of yoke plates 54 that are arranged in groups of the same number as the outer leg plates 50 of the outer legs 22. Each plate 54 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 yoke plates 54 each have a unitary construction (i.e., are monolithic or undivided) and are trapezoidal in shape. In each of the yoke plates 54, opposing ends of the plate 54 are mitered at oppositely-directed angles of about 45°, thereby providing the plate 54 with inner (minor) and outer (major) longitudinal edges. The yoke plates 54 have the same width (W2) between the inner and outer longitudinal edges thereof, thereby providing each yoke 24 with a rectangular cross-section. However, the lengths of the yoke plates 54 are not all the same. More specifically, the lengths within each group of yoke plates 54 are different. The pattern of different lengths is the same for each group of yoke plates 54. The difference in lengths within each group permits the formation of multi-step lap joints with the outer leg plates 50 of the outer legs 22, as will be described more fully below.
A V-shaped notch 60 (shown in
The inner leg 26 comprises a stack of inner leg plates 70 arranged in groups of the same number as the yoke plates 54 of the yokes 24. Upper ends of the inner leg plates 70 are disposed in the groove 66 of the upper yoke 24 and lower ends of the inner leg plates 70 are disposed in the groove 66 of the lower yoke 24. The inner leg plates 70 form vertical multi-step lap joints with the yoke plates 54 of the upper and lower yokes 24, as will be described further below. The inner leg plates 70 have the same width (W1) between the longitudinal edges thereof, thereby providing the inner leg 26 with a rectangular cross-section. 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. Each of the inner leg plates 70 has a unitary construction (i.e., are monolithic or undivided) and is trapezoidal in shape. Each end of each inner leg plate 70 is pointed, i.e., V-shaped, so as to fit into a notch 60 of a corresponding yoke plate 54. 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.
In the core 18 described above, the outer leg plates 50 have the same width (W1) as the inner leg plates 70. Thus, the outer legs 22 have the same width (W1) as the inner leg 26. The yoke plates 54 have a width (W2) that is less than the width (W1) of the outer and inner leg plates 50, 54. Thus, the yokes 24 have a width (W2) that is less than the outer and inner legs 22, 26. W2 may be from about 1% to about 50% less than W1, more particularly from about 1% to about 35% less than W1, still more particularly from about 1% to about 15% less than W1. In one embodiment of the invention, W2 is seven inches and W1 is eight inches.
Referring now to
The other connections between the first and second outer legs 22 and the upper and lower yokes 24 are constructed in the same manner as the connection 74 so as to have multi-step lap joints. It should be appreciated, however, that all of the connections may have a different type of construction. For example, instead of the connections having a four step lap joint pattern (as shown), the connections may have a seven, eight or other number step lap joint pattern.
Referring now to
If the inner leg plates 70 are the same length, upper ends of the first through fourth inner leg plates 70a-d of the inner leg 26 are located successively farther upward since the lower ends of the first through fourth inner leg plates 70a-d of the inner leg 26 are located successively farther upward. As a result, the upper interior edges (and, thus, the upper notches 60) of the yoke plates 54 within each group are successively deeper, which is the inverse of the lower yoke 24. With this construction, vertical multi-step lap joints are formed between the yoke plates 54 of the upper yoke 24 and the first inner leg plates 70 of the inner leg 26, with yoke plates 54 of the upper yoke 24 overlapping inner leg plates 70. If the inner leg plates 70 are not of the same length, the arrangement of the joints between the inner leg plates 70 and the upper yoke 24 may be the same as that between the inner leg plates 70 and the lower yoke 24.
Referring now to
Referring now to
In each of the first and second stacks 106, 108, the inner leg plates 110 are arranged in groups of the same number as the yoke plates 114. The first and second stacks 106, 108 abut each other along a seam 120 that extends in the longitudinal direction of the inner leg 104. Upper ends of the first and second stacks 106, 108 are disposed in an upper groove of the upper yoke 112 and lower ends of the first and second stacks 106, 108 are disposed in a lower groove of the lower yoke 112. The inner leg plates 110 form vertical multi-step lap joints with the yoke plates 114 of the upper and lower yokes 112. The inner leg plates 110 may all have the same length if the joints are offset by vertically shifting the inner leg plates 110. Alternately, the inner leg plates 110 may have a plurality of different lengths if the joints are offset by the different lengths of adjacent inner leg plates 110. Each of the inner leg plates 110 has a unitary construction and is trapezoidal in shape. In each of the inner leg plates, opposing ends of the inner leg plate 110 are mitered at oppositely-directed angles of about 45°, thereby providing the inner leg plate with major and minor side edges. The lengths of the inner leg plates 110 are determined by the major side edges. Each of the inner leg plates 110 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. Each of the inner leg plates 110 has a width (W3), which is one-half of the width (W1) of the outer leg plates 50 of the outer legs 22. In this manner, the inner leg has 104 has substantially the same width as the outer legs 22.
In one embodiment of the present invention, the yoke plates 114 of the yokes 112 may have the same width (W3) as the inner leg plates 110. In this manner, the yoke plates 114 and the inner leg plates 110 may be formed from the same roll(s) of metal.
In the embodiments described above, the legs and yokes have rectangular cross-sections. It should be appreciated, however, that embodiments of the present invention may be provided, wherein at least the legs are provided with cruciform cross-sections. Such an embodiment is shown in
With reference now to
Each yoke 126 may have sections 148, 150, 152, 154, 156, 158, 160 with varying widths. The sections 148-160 may have widths that provide each yoke 126 with a semi-cruciform cross-section, as shown in
The sections 134-146 of the outer legs 130 correspond to the sections 148-160 of the yokes, respectively, e.g., the plates of the sections 134 form step lap joints with the plates of the sections 148 etc. Within the corresponding sections of the yokes 126 and the outer legs 130, the plates of the yokes 126 have a narrower width than the plates in the outer legs 130, except for two or more of the outer sections. For example, as shown in
Although only three-phase transformers have been shown and described, the present invention is not limited to a three-phase transformer. Single-phase transformers constructed in accordance with the present invention may also be provided. Single-phase transformers may be provided having substantially the same construction as the transformer 10 and the transformer 120, respectively, except for the differences described below. The core of each single-phase transformer does not have the inner leg (26 or 128, as the case may be). In addition, in the core of each single-phase transformer, the yoke plates do not have the V-shaped notches and are shorter in length so that the outer legs (22 or 130, as the case may be) are positioned closer together. In each single-phase transformer, only one winding assembly 12 is provided and is mounted to one of the outer legs (22 or 130, as the case may be).
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.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2011/032476 | 4/14/2011 | WO | 00 | 2/5/2013 |
Number | Date | Country | |
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61326850 | Apr 2010 | US |