This invention relates to transformers and more particularly to open wound transformers having disc windings.
As is well known, a transformer converts electricity at one voltage to electricity as another voltage, either of higher or lower value. A transformer achieves this voltage conversion using a primary coil and a secondary coil, each of which is wound on a ferromagnetic core and comprise a number of turns of an electrical conductor. The primary coil is connected to a source of voltage and the secondary coil is connected to a load. The ratio of turns in the primary coil to the turns in the secondary coil (“turns ratio”) is the same as the ratio of the voltage of the source to the voltage of the load. Two main winding techniques are used to form coils, namely layer winding and disc winding. The type of winding technique that is utilized to form a coil is primarily determined by the number of turns in the coil and the current in the coil. For high voltage windings with a large number of required turns, the disc winding technique is typically used, whereas for low voltage windings with a smaller number of required turns, the layer winding technique is typically used.
In the disc winding technique, the conductor turns required for a coil are wound in a plurality of discs serially disposed along the axial length of the coil. In each disc, the turns are wound in a radial direction, one on top of the other, i.e., one turn per layer. The discs are connected in a series circuit relation and are typically wound alternately from inside to outside and from outside to inside so that the discs can be formed from the same conductor. An example of such alternate winding is shown in U.S. Pat. No. 5,167,063.
A transformer with disc windings may be cooled by a liquid dielectric or may be dry, i.e., cooled by air as opposed to a liquid dielectric. One type of dry transformer is a so-called open wound transformer, wherein the windings are coated, impregnated or encapsulated with a varnish such as by dipping or using a vacuum and pressure application process.
The present invention is directed to improvements in an open wound transformer having disc windings.
The present invention is directed to a method of manufacturing a dry power distribution transformer. In accordance with the method, a winding is formed over a mandrel and is then mounted to a ferromagnetic core. The winding includes a plurality of serially connected discs arranged in an axial direction of the winding. The forming of the winding includes forming each disc by winding a conductor and an insulating strip around the mandrel to form a radially-inner section of the disc that has a plurality of concentric and alternating layers of the insulating strip and the conductor. Each pair of adjacent layers in the radially-inner section are in contact with each other. A plurality of spacers are disposed around the circumference of the radially-inner section. The conductor and the insulating strip are wound around the spacers to form a radially-outer section of the disc that has a plurality of concentric and alternating layers of the insulating strip and the conductor. Each pair of adjacent layers in the radially-outer section are in contact with each other. The radially-outer section is separated from the radially-inner section by a plurality of spaces arranged in a circumferential configuration.
Also provided in accordance with the present invention is a power distribution transformer having a ferromagnetic core and a winding mounted to the ferromagnetic core. The winding has a plurality of serially connected discs arranged in an axial direction of the winding. Each disc includes a radially-inner section that has a plurality of concentric and alternating layers of an insulating strip and a conductor. Each pair of adjacent layers in the radially-inner section are in contact with each other. A plurality of spacers are disposed around the circumference of the radially-inner section. A radially-outer section is disposed around the spacers and is connected to the radially-inner section. The radially-outer section includes a plurality of concentric and alternating layers of the insulating strip and the conductor. Each pair of adjacent layers in the radially-outer section are in contact with each other. The radially-outer section is separated from the radially-inner section by a plurality of spaces arranged in a circumferential configuration.
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 a distribution transformer having a kVA rating in a range of from about 112.5 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 28 may be in a range of from about 120 V to about 15 kV.
Although the transformer 10 is shown and described as being a three phase distribution transformer, it should be appreciated that the present invention is not limited to three phase transformers or distribution transformers. The present invention may utilized in single phase transformers and transformers other than distribution transformers.
Each disc 32 comprises a plurality of concentric layers of a conductor 40. The conductor 40 is composed of a metal such as copper or aluminum and may be in the form of a wire with an elliptical or rectangular cross-section. Alternately, the conductor 40 may be in the form of a foil, wherein the conductor 40 is thin and rectangular, with a width as wide as the disc 32 it forms. In the embodiments shown and described, it has been found particularly useful to use foil conductors, more specifically foil conductors having 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, still more particularly about 150:1. In one particular embodiment, the foil conductor 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. In each disc 32, the turns of the conductor 40 are wound in a radial direction, one on top of the other, i.e., one turn per layer. A layer of insulating material 42 (shown in
In each section of a disc 32, the layers of the conductor 40 and the insulating material 42 are tightly wound so that there are no gaps between any two adjacent layers, i.e., in each pair of adjacent layers, the layers are in contact with each other. In addition, the radially-inner sections of the discs 32 have the same number of layers so that the radially-inner sections have substantially the same radius. The radially-outer sections of the discs 32 may also have the same number of layers so that the radially-outer sections have substantially the same radius. The circumferential gaps 34 in the discs 32 have substantially the same width and are aligned from disc to disc. With the discs 32 being constructed as described above, the aligned circumferential gaps 34 form cooling passages 44 that extend axially through all of the discs 32.
In each pair of adjacent sections of a disc 32, the sections are connected together by a portion of the conductor 40 that extends through a gap 34 between the two sections, as shown in
In forming the series of discs 32, the conductor 40 can be continuously wound from disc 32 to disc 32 or may be provided with “drop-downs” 41 between discs 32 (as shown in
The discs 32 may be connected together in the manner shown in
The radially-inner sections of the discs 32 may be formed on a cylindrical high/low insulation barrier 60 having comb structures 62, as shown in
After the last turn or layer of the conductor 40 is wound over the insulation barrier 60 to form the radially-inner section, a layer of spacers 70 are formed around the circumference of the radially-inner section. The layer of spacers 70 may be formed using a spacer tape 68 that comprises a plurality of the spacers 70, arranged in a spaced-apart manner and secured to a piece of insulating tape 72, which may be comprised of an insulating material, such as polyimide, polyamide, or polyester. The spacers 70 may be attached to the tape 72 before the tape is secured over the radially-inner section (as shown) or afterwards. Each spacer 70 is hollow, has a rectangular cross-section and may be composed of a fiber reinforced plastic in which fibers, such as fiberglass fibers, are impregnated with a thermoset resin, such as a polyester resin, a vinyl ester resin, or an epoxy resin. The spacers 70 are secured to the tape 72 by an adhesive and extend longitudinally along the width of the tape 72. In the embodiment where the conductor 40 forming the discs 32 is comprised of foil, the lengths of the spacers 70 and the width of the tape 72 are about the same as the width of the conductor 40. The spacer tape 68 is wrapped onto the radially-inner section of the disc winding 36 to form a single turn such that the tape 72 adjoins the radially-inner section and the spacers 70 extend radially outward like spokes. Ends of each piece of spacer tape 68 may be fastened together (such as by adhesive tape) to form a loop that is disposed radially outward from the radially-inner section of the disc 32. The loop may be secured to the radially-inner section of the disc 32.
As indicated above, a loop of the tape 72 may first be secured over the radially-inner section of the disc 32 and thereafter the spacers 72 may be attached to the tape 72 by adhesive, tape or other securing means.
The number of spacers 70 that are used may be the same as the number of comb structures 62. If so, the spacers 70 may be aligned with the comb structures 62 so as to be disposed between pairs of teeth 66, respectively, or the spacers 70 may be disposed between the comb structures 62 so as to not be disposed between pairs of teeth 66 (as shown in
After the layer of spacers 70 has been formed, the radially-outer section of the disc 32 is formed over the layer of spacers 70 so as to be supported on the spacers 70 and spaced from the radially-inner section of the disc 32. An initial layer of the insulating material 42 directly contacts the spacers 70. Thereafter, alternating layers of the conductor 40 and the insulating material 70 are wound over the initial layer to form the radially-outer section of the disc 32. When the radially-outer section of the disc 32 is complete, the next disc 32 may be wound from the same piece of conductor 40 and the same piece of insulating material 42 in the same manner as described above. This process is continued until all of the discs 32 in the high voltage winding 30 are formed. In this manner, all of the discs 32 in the high voltage winding 30 may be formed from one continuous piece of the conductor 40 and one continuous piece of the insulating material 42.
Once the winding of the discs 32 is complete, each disc 32 comprises a radially-inner section (e.g. section 32a1) electrically connected to a radially-outer section (e.g. section 32a2), wherein the radially-inner section and the radially-outer section are concentrically arranged, axially aligned and radially separated by circumferential gaps 34 (e.g. gaps 34a). The gaps 34 are circumferentially separated by the spacers 70.
The circumferential gaps 34 may be formed using methods and devices other than the spacers 70. For example, spacer inserts 76 may be used to form the circumferential gaps 34. Referring now to
A disc 32 is formed by first winding the conductor 40 and the insulating material 42 through a circumferentially-arranged series of gaps formed by teeth 66 of the comb structures 62 so as to form a radially-inner section of the disc 32. After the radially-inner section of a disc 32 is formed, a spacer insert 76 is installed in each comb structure 62 so as to extend across the gap in the teeth 66 of the comb structure 62 through which the radially-inner section extends. Each spacer insert 76 is installed such that portions of the teeth 66 forming the gap extend through the notches in the spacer insert 76, respectively, and the spacer insert 76 rests against the radially-inner section. In this manner, the spacer inserts 76 extend across the width of the radially-inner section of the disc 32 and are secured from axial and lateral movement. With the spacer inserts 76 so installed, the radially-outer section of the disc 32 is then formed over the spacer inserts 76 so as to be supported on the spacer inserts 76 and spaced from the radially-inner section of the disc 32. Subsequent discs 32 are then formed in the same manner. As with the use of the spacers 70, all of the discs 32 may be formed from a single piece of the conductor 40.
The circumferential gaps 34 may also be formed using spacer supports 80. When the spacer supports 80 are used, the comb structures 62 are not utilized. Referring now to
A disc 32 is formed by first winding the conductor 40 and the insulating material 42 over the insulation barrier 60 so as to form a radially-inner section of the disc 32. Once the radially-inner section is complete, a plurality of spacer supports 80 are disposed around the circumference of the radially-inner section so that the radially-inner section extends through the bottom channels 90 of the spacer supports 80. With the spacer inserts 76 so installed, the radially-outer section of the disc 32 is then formed by winding the conductor 40 and the insulating material 42 through the top channels 88 and over the center bar 84 of the spacer inserts 76. In this manner, the radially-outer section of the disc 32 is supported on the center bars 84 of the spacer inserts 76 and is spaced from the radially-inner section of the disc 32. Subsequent discs 32 are then formed in the same manner. As with the use of the spacers 70 and the spacer inserts 76, all of the discs 32 may be formed from a single piece of the conductor 40.
Once a high voltage winding 30 has been fully wound, the high voltage winding 30 is removed from the winding mandrel 64 and then coated, impregnated or encapsulated with an insulating varnish, such as by dipping or using a vacuum and pressure application process. The insulating varnish comprises a resin, such as an epoxy resin or a polyester resin.
In one embodiment, the high voltage winding 30 is heated in an oven to remove moisture from the insulating layers and the conductor layers and then placed in a vacuum chamber. The vacuum chamber is evacuated to remove any remaining moisture and gases in the high voltage winding 30 and to eliminate any voids between adjacent turns in the discs 32. The insulating varnish is then applied to the high voltage winding 30, while the vacuum is maintained. The vacuum is held for a predetermined time interval to allow the insulating varnish to impregnate the discs 32. The vacuum is then released. Pressure may then be applied to the high voltage winding 30 to force the insulating varnish to impregnate any remaining voids. Heat may subsequently be applied to high voltage coil 30, such as in an oven, to dry/cure the varnish.
The high voltage winding 30 coated/impregnated/encapsulated with the insulating varnish is then mounted to the core 18, over the low voltage winding 28.
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.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US11/31122 | 4/4/2011 | WO | 00 | 10/4/2012 |
Number | Date | Country | |
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61321860 | Apr 2010 | US |