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 is a distribution transformer and has a kVA rating in a range of from about 112.5 kVA to about 15,000 kVA. The voltage of the high voltage coil 32 is in a range of from about 600 V to about 35 kV and the voltage of the low voltage coil is in a range of from about 120 V to about 15 kV.
Referring now to
The winding mandrel 40, with the insulation spool 44 and the low voltage coil mounted thereon, is located adjacent to a dispensing machine 64 that is operable to simultaneously dispense a conductor strip 66 and an insulation strip 68 in an overlapping manner, with the conductor strip 66 being disposed over the insulation strip 68. The dispensing machine 64 includes a rotatable roll of the conductor strip 66 and a rotatable roll of the insulation strip 68. The conductor strip 66 is output from the dispensing machine 64 through the nip of a pair of rollers and the insulation strip 68 is output from the dispensing machine 64 through the nip of another pair of rollers. The conductor strip 66 is comprised of a conductive metal, such as copper or aluminum, and has a width to thickness ratio of greater than 20:1, more particularly from about 250:1 to about 25:1, more particularly from about 200:1 to about 50:1. In one particular embodiment, the conductor strip is between about 0.008 to about 0.02 inches thick and between about 1 and 2 inches wide, more particularly about 0.01 inches thick and about 1.5 inches wide. The insulation strip 68 may be comprised of a polyimide film, such as is sold under the trademark Nomex®; a polyamide film, such as is sold under the trademark Kapton®, or a polyester film, such as is sold under the trademark Mylar®. The insulation strip 68 is about 0.375 inches wider than the conductor strip 66. The insulation strip 68 has a width that is about the same as the width of each of the notches 60.
Initially, the winding mandrel 40 is moved in an axial direction to align a dispensing outlet of the dispensing machine 64 with a first series of notches 60 aligned around the circumference of the high/low insulation barrier 46. A first end of the conductor strip 66 may be welded to a first coil lead at this time, or may be welded to the first coil lead after the winding operation is completed. The insulation strip 68 and the conductor strip 66 are secured to the insulation spool 44 and at least partially disposed in the first series of aligned notches 60. The winding mandrel 40 is then rotated so that the insulation spool 44 rotates about its longitudinal axis in a direction away from the dispensing machine 64, i.e., in a counter-clockwise direction as viewed from a first end 12a of the coil assembly 12. As the insulation spool 44 rotates, the insulation strip 68 and the conductor strip 66 are pulled from the dispensing machine 64 and wrapped around the insulation spool 44 to form a first disc winding 36a comprising a plurality of concentric turns or layers of the conductor strip 66 interleaved with a plurality of concentric turns or layers of the insulation strip 68. The first disc winding 36a is radially supported on the guide strips 48 and the support strips 50 and is held in the first series of notches 60. In this manner, the first disc winding 36a is secured from radial and axial movement. Since the insulation strip 68 is wider than the conductor strip 66, edge portions of the insulation strip 68 form insulation areas between the turns of the conductor strip 66 and the pairs of teeth 58 forming the circumferentially-aligned notches 60.
After the first disc winding 36a is formed, the rotation of the winding mandrel 40 is halted and the conductor strip 66 is prepared for the formation of a second disc winding 36b. The preparation of the conductor strip 66 is dependent on how the disc windings 36 will be connected to each other. If the disc windings 36 are to be connected together by welding after the winding process is completed, the conductor strip 66 is cut after the first disc winding 36a is formed. If, however, the disc windings 36 are connected together by being formed from the same length of conductor strip 66, an offset 74 is formed in the conductor strip 66 after the first disc winding 36a is formed. Referring now to
With the second portion 66b of the conductor strip 66 at least partially disposed in the second series of notches 60, the winding mandrel 40 is rotated again so that the insulation spool 44 rotates about its longitudinal axis in a direction away from the dispensing machine 64. As the insulation spool 44 rotates, the insulation strip 68 and the conductor strip 66 are pulled from the dispensing machine 64 and wrapped around the insulation spool 44 to form the second disc winding 36b, which also comprises a plurality of concentric turns or layers of the conductor strip 66 interleaved with a plurality of concentric turns or layers of the insulation strip 68.
After the second disc winding 36b is formed, the rotation of the winding mandrel 40 is again halted and the conductor strip 66 is again either folded or cut to prepare the conductor strip 66 for the formation of a third disc winding 36c. The winding mandrel 40 is again axially moved and the third disc winding 36c is formed in the same manner as the first and second disc windings 36a, 36b.
The above described steps are repeated until the requisite number of disc windings 36 are formed. The rotation of the winding mandrel 40 is stopped and the conductor strip 66 is cut. The coil assembly 12 may then be removed from the winding mandrel 40. If the disc windings 36 have not been formed from the same length of conductor strip 66, the disc windings 36 are then welded together. A second end of the conductor strip 66 is welded to a second coil lead and, if not already performed, the first end of the conductor strip 66 is welded to the first coil lead. Typically, the first and second coil leads extend to one end of the coil assembly 12.
Although the conductor strip 66 and the insulation strip 68 are shown and/or described as being stored separately and dispensed from the dispensing machine 64 separately, it should be appreciated that in another embodiment of the present invention, the conductor strip 66 and the insulation strip 68 may be secured together before they are dispensed from the dispensing machine 64. More specifically, the conductor strip 66 may be joined by adhesive to the insulation strip 68 to form a combined conductor/insulation strip that is stored in and dispensed from a single roll. The combined conductor/insulation strip may further be coated with a resin before the combined conductor/insulation strip is wound into the disc windings 36.
After the disc windings 36 have been formed, interconnected and welded to the first and second coil leads, the coil assembly 12 is coated with a resin, such as in a vacuum-pressure impregnation (VPI) process. The resin may be a polyester resin, an epoxy resin, a silicone resin, an acrylic resin, a polyurethane resin, an imide resin, or a mixture of any of the foregoing. In a VPI process, the coil assembly 12 is first pre-heated in an oven to remove moisture from the coil assembly 12. The coil assembly 12 is then placed in a vacuum chamber, which is evacuated to remove any remaining moisture and gases in the coil assembly 12 and to eliminate any voids between adjacent turns in the disc windings 36. The resin, in liquid form, is then applied to the coil assembly 12, while the vacuum chamber is still under a vacuum. The resin may be applied to the coil assembly 12 by submerging the coil assembly 12 in a vat filled with the resin. The vacuum is held for a short time interval, which allows the resin to impregnate the coil assembly 12, and then the vacuum is released and the pressure is increased in the vacuum chamber. This will force the resin to impregnate the remaining voids in the coil assembly 12. The coil assembly 12 is then removed from the chamber and is allowed to drip dry. The coil assembly 12 is then placed in an oven to cure the resin. Additional coatings of different resins may be applied to provide a better appearance and/or better protection from the environment.
Once the coil assemblies 12 for the transformer 10 are constructed and coated with the resin, as described above, the coil assemblies 12 are mounted to the core 18, which is placed in an upright condition, with the upper yoke 24 removed. The coil assemblies 12 are disposed over the legs 22 of the core 18, respectively, with opposing pairs of end fins 56 of each coil assembly 12 resting on a pair of support blocks 30. The upper yoke 24 is then secured in place over the legs 22.
Although the transformer 10 is shown and described as being a three phase transformer, it should be appreciated that the present invention is not limited to three phase transformers. The present invention may utilized in single phase transformers, as well.
It is to be understood that the description of the foregoing exemplary embodiment(s) is (are) intended to be only illustrative, rather than exhaustive, of the present invention. Those of ordinary skill will be able to make certain additions, deletions, and/or modifications to the embodiment(s) of the disclosed subject matter without departing from the spirit of the invention or its scope, as defined by the appended claims.