The present invention relates to transformers and more particularly to dry type transformers with improved cooling features.
As is well known, a transformer converts electricity at one voltage to electricity at 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 are 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.
A transformer may be cooled by air or a liquid dielectric. An air-cooled transformer is typically referred to as a dry-type transformer. In many applications, such as in or around commercial buildings, it is preferable to use a dry-type transformer instead of a liquid-cooled transformer. Often, the coils of a dry-type transformer are coated with, or cast in, a dielectric resin using vacuum chambers, gelling ovens etc. Encapsulating a coil in a dielectric resin protects the coil, but creates heat dissipation issues. To dissipate the heat from around the coil, cooling ducts are often formed at predetermined positions within the coil. Such cooling ducts improve the operating efficiency of the coil and extend the operational life of the coil. An example of a resin-encapsulated coil with cooling ducts is disclosed in U.S. Pat. No. 7,023,312 to Lanoue et al., which is assigned to the assignee of the present invention and is hereby incorporated by reference.
Although the use of cooling ducts produces good results, the creation of cooling ducts in a coil increases the labor and material costs of the coil. Accordingly, it would be desirable to provide a transformer with resin-encapsulated coils that reduces or eliminates the use of cooling ducts. The present invention is directed to such a transformer.
In accordance with the present invention, a distribution transformer is provided and includes a coil assembly mounted to a ferromagnetic core. The coil assembly includes a resin-encapsulated low voltage coil, a resin-encapsulated first high voltage coil disposed around the low voltage coil, and a resin encapsulated second high voltage coil disposed around the first high voltage coil. The first high voltage coil is separated from the low voltage coil by an annular first space, and the second high voltage coil is separated from the first high voltage coil by an annular second space. The low voltage coil and the first and second high voltage coils are arranged concentrically.
Also provided in accordance with the present invention is a method of making a distribution transformer. The method includes providing a ferromagnetic core, a resin-encapsulated low voltage coil, a resin-encapsulated first high voltage coil, and a resin-encapsulated second high voltage coil. The low voltage coil is mounted to the core and the first high voltage coil is disposed around the low voltage coil so as to form an annular first space therebetween. The second high voltage coil is disposed around the first high voltage coil so as to form an annular second space therebetween.
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 includes at least one coil assembly 12 mounted to a core 18 and enclosed within an outer housing (not shown). If the transformer 10 is a single-phase transformer, only one coil assembly 12 is provided, whereas if the transformer 10 is a three-phase transformer, three coil assemblies 12 are provided (one for each phase). The core 18 is comprised of ferromagnetic metal (such as silicon grain-oriented steel) and may be generally rectangular in shape. The core 18 includes at least one leg 22 extending between a pair of yokes 24 (only one of which is shown). Three evenly-spaced apart legs 22 may extend between the yokes 24. If the transformer 10 is a single phase transformer, the single coil assembly 12 may be mounted to and disposed around a center one of the legs 22, whereas, if the transformer 10 is a three-phase transformer, the three coil assemblies 12 are mounted to, and disposed around, the legs 22, respectively. As best shown in
Each coil assembly 12 comprises a low voltage coil member 26 including a resin insulation or encapsulation, also referred to herein as resin-encapsulated low voltage coil 26 and a high voltage coil assembly 28 that includes a first high voltage coil member 30 and second high voltage coil member 32, both of which have resin insulation or encapsulation, and which members 30, 32 are also referred to herein as resin-encapsulated first and second high voltage coils 30, 32. As will be described in more detail below, each of the low voltage coil 26, the first high voltage coil 30 and the second high voltage coil 32 are produced separately and then mounted to the core 18. The low voltage coil 26 and the first and second high voltage coils 30, 32 may each be cylindrical in shape. If the transformer 10 is a step-down transformer, the high voltage coil assembly 28 forms a primary coil structure and the low voltage coil 26 forms a secondary coil structure. Alternately, if the transformer 10 is a step-up transformer, the high voltage coil assembly 28 forms a secondary coil structure and the low voltage coil 26 forms a primary coil structure. In each coil assembly 12, the first and second high voltage coils 30, 32 and the low voltage coil 26 are mounted concentrically, with the low voltage coil 26 being disposed within and radially inward from the first and second high voltage coil 30, 32. As best shown in
The first high voltage coil 30, the second high voltage coil 32 and the low voltage coil 26 all have different axial lengths. More specifically, the low voltage coil 26 has a greater axial length than the first high voltage coil 30, which has a greater axial length than the second high voltage coil 32. These differences in axial length are best shown in
One or more taps extend from the first high voltage coil 30 and one or more taps extend from the second high voltage coil 32. The number and arrangement of these taps depends on the winding structure of the first and second high voltage coils 30, 32, as will be described in more detail below. As shown in
Referring now also to
The low voltage coil 26, the first high voltage coil 30 and the second high voltage coil 32 are each formed separately. Each of these coils may be formed using a layer winding technique, wherein a conductor is wound in one or more concentric conductor layers connected in series. The conductor may be foil strip(s), sheet(s), or wire with a rectangular or circular cross-section. The conductor may be composed of copper or aluminum. A layer of insulation material is disposed between each pair of conductor layers.
Instead of being formed by a layer winding technique, each of the first and second high voltage coils 30, 32 may be formed using a disc winding technique, such as is shown in
As shown in
It should be appreciated that other high voltage coils may be provided having a winding structure different from that shown in
In the embodiment shown in
In the embodiment of the present invention shown in
For each of the coil members 26, 30, 32, once the conductor has been wound, the wound conductor is encapsulated in an insulating resin 82 using a casting process. The wound conductor is placed in a metal mold and pre-heated in an oven to remove moisture from the insulation and the windings. This pre-heating step can also serve to cure any adhesive/resin impregnated in the insulating layers interposed between the turns of the conductor. The wound conductor/mold assembly is then placed in a vacuum casting chamber, which is then evacuated to remove any remaining moisture and gases. The resin 82 (in liquid state) is then introduced into the mold, which is still maintained under a vacuum, until the wound conductor is completely submerged. The conductor is held submerged in the resin 82 for a period of time sufficient to permit the resin 82 to impregnate the insulation layers and fill all spaces between adjacent conductor windings. The vacuum is then released and the wound conductor/mold assembly is removed from the chamber. The wound conductor/mold assembly is subsequently placed in an oven to cure the resin 82 to a solid state. After the resin 82 is fully cured, the wound conductor/mold assembly is removed from the oven and the mold is removed from the coil member.
The insulating resin 82 may be an epoxy resin or a polyester resin. An epoxy resin has been found particularly suitable for use as the insulating resin 82. The epoxy resin may be filled or unfilled. An example of an epoxy resin that may be used for the insulating resin 82 is disclosed in U.S. Pat. No. 6,852,415, which is assigned to ABB Research Ltd. and is hereby incorporated by reference. Another example of an epoxy resin that may be used for the insulating resin 82 is Rutapox VE-4883, which is commercially available from Bakelite AG of Iserlohn of Germany.
After the coils 26, 30, 32 have been individually formed, the coils 26, 30, 32 are mounted to a leg 22 of the core 18. The support blocks 50 are placed in their desired positions on top of the lower yoke 24 around the leg 22. The support blocks 50 may be secured to the yoke 24 by adhesive or physical fasteners. The low voltage coil 26 is first disposed over the leg 22 and positioned to rest on the support surfaces 52a of the support blocks 50, with the spacer 54a disposed radially outward from an outer surface of the low voltage coil 26. The first high voltage coil 30 is then disposed over the low voltage coil 26 and positioned to rest on the support surfaces 52b of the support blocks, with the spacer 54a disposed radially inward from an inner surface of the first high voltage coil 30 and the spacer 54b disposed radially outward from an outer surface of the first high voltage coil 30. The second high voltage coil 32 is then disposed over the first high voltage coil 30 and positioned to rest on the support surfaces 52c of the support blocks 50, with the spacer 54b disposed radially inward from an inner surface of the second high voltage coil 32. The first and second high voltage coils 30, 32 may be electrically connected together before or after the first and second high voltage coils 30, 32 are mounted to the leg 22.
Although only two high voltage coils 30, 32 have been shown and described, it should be appreciated that additional high voltage coils may be utilized. For example, a transformer may be provided having three or four concentrically arranged high voltage coils that are separated by annular cooling spaces. In addition, instead of providing a singular low voltage coil 26, a plurality of concentrically arranged low voltage coils separated by annular cooling spaces may be provided.
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.
This application claims the benefit of U.S. provisional patent application No. 61/221,836 filed on Jun. 30, 2009, which is hereby incorporated by reference in its entirety.
Number | Name | Date | Kind |
---|---|---|---|
3996544 | Mori et al. | Dec 1976 | A |
4471337 | Mausz et al. | Sep 1984 | A |
4488134 | Pfeiffer | Dec 1984 | A |
4523171 | Altmann et al. | Jun 1985 | A |
5194841 | Galloway et al. | Mar 1993 | A |
5267393 | Purohit et al. | Dec 1993 | A |
5461772 | Puri | Oct 1995 | A |
5596305 | Puri | Jan 1997 | A |
5621372 | Purohit | Apr 1997 | A |
5684446 | Adkins et al. | Nov 1997 | A |
5986532 | Kikuta et al. | Nov 1999 | A |
6160464 | Clarke et al. | Dec 2000 | A |
6201334 | Sargeant et al. | Mar 2001 | B1 |
6223421 | Lanoue et al. | May 2001 | B1 |
6806803 | Hopkinson et al. | Oct 2004 | B2 |
7023312 | Lanoue et al. | Apr 2006 | B1 |
20020171524 | Tsai | Nov 2002 | A1 |
20090096562 | Nakadai et al. | Apr 2009 | A1 |
Number | Date | Country |
---|---|---|
57118618 | Jul 1982 | JP |
60065505 | Apr 1985 | JP |
0039819 | Jul 2000 | WO |
2011002650 | Jan 2011 | WO |
Entry |
---|
First Office Action for counterpart patent application No. 201080029566.7, State Intellectual Property Office of the People's Republic of China, issued Dec. 20, 2013 (translation). |
Number | Date | Country | |
---|---|---|---|
20100328005 A1 | Dec 2010 | US |
Number | Date | Country | |
---|---|---|---|
61221836 | Jun 2009 | US |