The description below relates to polymer sheet insulation for use with a transformer core and coil assembly.
Transformers often include a core and coil assembly formed from a pair of coils interconnected by a conductive core. A three phase transformer includes three coils with multiple cores. The core and coil assembly may be positioned in a tank that is filled with a dielectric fluid. The dielectric fluid serves to cool the assembly and electrically isolate the core and coil assembly from the tank.
Insulation used in the transformer core and coil assembly typically is constructed using kraft or cotton-based pressboard, which is known to degrade over time as a function of temperature. This insulation normally is made from multiple individual pieces that may require cutting to the correct size. Also, the insulation needs to be thoroughly dried prior to filling the tank with dielectric fluid because moisture contributes to and increases the degradation rate, especially when combined with heat. Typical kraft-based pressboard materials absorb moisture in a range from approximately 3% to 10%, or more, based on the length of exposure to humidity. This moisture should be removed to a level of approximately 1% prior to filling the transformer with dielectric fluid. Current kraft or cotton-based pressboard material absorbs moisture and degrades rapidly at temperatures from 130° C. to 170° C. Further moisture developed during the degradation process of kraft or cotton-based pressboard, accelerates aging and degradation of the pressboard.
Techniques are used to provide a polymer sheet core and coil insulation for transformers such as, for example, single-phase and multi-phase transformers. The polymer sheet core and coil insulation may be used, for example, as a barrier insulation including use as a phase-to-phase barrier insulation and as a phase-to-ground barrier insulation, and further may be used as a transformer coil support.
In one general aspect, a transformer includes a core defining a core window, a first coil surrounding a portion of the core and including a portion located within the core window, a second coil surrounding a portion of the core and including a portion located within the core window, and a polymer barrier insulation member that is located at least partially within the core window and positioned between the first coil and the second coil.
Implementations may include one or more of the following features. For example, the transformer may be a three phase transformer, a single phase transformer, or a step voltage regulator. The polymer barrier insulation member may include at least one ribbed polymer sheet, at least one flat polymer sheet, and/or two or more stacked polymer sheets.
The polymer barrier insulation member may be made of a high temperature polymer configured to withstand an operating temperature of approximately 130 degrees Celsius, may be configured to withstand overload conditions through approximately 200 degrees Celsius, and may be configured so as to absorb no more than approximately 1% moisture. The high temperature polymer may be, for example, syndiotactic polystyrene, a polyester thermoset molding compound, or a vinylester thermoset molding compound. The high temperature polymer may be made using a variety of techniques and, for example, may be extruded, injection molded, compression molded or thermo-formed.
In another general aspect, a transformer includes a core defining a core window, a first coil surrounding a portion of the core and including a portion located within the core window, and a polymer barrier insulation member that is located at least partially within the core window and positioned between the first coil and the core.
In another general aspect, a transformer includes a core defining a core window, a first coil surrounding a portion of the core and including a portion located within the core window, and a polymer coil support member that is located at least partially within the core window and positioned between the first coil and the core so as to support the first coil.
Implementations may include one or more of the following features. For example, the transformer also may include a second coil surrounding a portion of the core and including a portion located within the core window, where the coil support is positioned between the second coil and the core so as to support the second coil. In another implementation, the coil support member includes one or more standoffs. The standoffs may have several shapes such as, for example, a circular shape, a truncated circular shape, or an egg crate shape.
The coil support member may include one or more coolant flow channels, and may be made, for example, of a thermoset material or a high temperature thermoplastic material. In one implementation, the coil support member is made of a high temperature polymer material configured to withstand an operating temperature of approximately 130 degrees Celsius.
In yet another general aspect, a transformer includes a core defining a core window, a first coil surrounding a portion of the core and including a portion located within the core window, a second coil surrounding a portion of the core and including a portion located within the core window, a first polymer barrier insulation member that is located at least partially within the core window and positioned between the first coil and the second coil, a second polymer barrier insulation member that is located at least partially within the core window and positioned between the first coil and the core, and a polymer coil support member that is located at least partially within the core window and positioned between the first coil and the core so as to support the first coil.
Other features will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
Referring to
Barrier insulation 305 is located adjacent coil 105 and between the coil 105 and the core 120 in the core window 205. Barrier insulation 305 serves as a coil-to-ground (core) barrier and is made of a polymer material. Barrier insulation 305 also provides dielectric and mechanical strength between the coil and the core. Typically, barrier insulation 305 is a flat or corrugated sheet. Cooling duct configurations may be included in the barrier insulation 305. Multiple pieces of barrier insulation may be used to fill the space to an appropriate thickness given the dielectric strength required. In certain implementations, the barrier insulation is made from interlocking pieces, such as, for example, corrugated pieces. In other implementations, the barrier insulation is made from flat pieces.
Coil support 310 is located between the coil 105 and the core 120 beneath the coil 105. Coil support 310 serves to support the weight of coil 105, and also serves as a dielectric barrier between the coil and the core. A barrier 315 may be located above coil 105 between coil 105 and core 120 in the core window 205.
Core window 210 of core 125 contains at least portions of coil 105, coil 110, barrier insulation 320, a coil support 325, and barrier insulation 330. Barrier insulation 320 is located between coil 105 and coil 110, and acts as a coil-to-coil insulation barrier. Barrier insulation 320 also provides dielectric and mechanical strength between the coils. In a similar manner to that described with respect to coil support 310, coil support 325 is located beneath at least a portion of coil 105 and at least a portion of coil 110, and serves to separate the coils 105 and 110 from the core 125. Barrier insulation 330 may be located on top of at least portions of coils 105 and 110, and serves to separate the coils 105 and 110 from the core 125 in a manner similar to that described with respect to barrier insulation 315.
Core window 215 of core 130 contains at least portions of coil 110, coil 115, barrier insulation 335, a coil support 340, and barrier insulation 345. Barrier insulation 335 may be placed between coil 110 and coil 115 in a manner similar to that described with respect to barrier insulation 320. Coil support 340 may be placed underneath a portion of coil 110 and a portion of coil 115 in a manner similar to that described with respect to coil support 325. Barrier insulation 345 may be placed on top of coil 110 and coil 115 in a manner similar to that described with respect to barrier insulation 330.
Core window 220 of core 135 contains at least portions of coil 115, barrier insulation 350, a coil support 355, and barrier insulation 360. Barrier insulation 350 is placed between coil 115 and core 135 in a manner similar to that described above with respect to barrier insulation 305. Coil support 355 is placed underneath coil 115 in a manner similar to that described above with respect to coil support 310. Barrier insulation 360 is placed on top of coil 115 in a manner similar to that described above with respect to barrier insulation 315.
Each of barrier insulation 305, 315, 320, 330, 335, 345, 350, and 360 is made of a polymer material. The polymer material may be, for example, a high temperature polymer with low water absorption properties. The polymer material used for insulation should have less than 1% moisture and should not absorb moisture when exposed to humid air. For example, it is possible to use a polymer material with less than 0.5% moisture. Temperatures of approximately 130° C. to approximately 200° C. may exist in the areas of the barrier material, and it is beneficial to use a barrier polymer material that does not absorb moisture beyond the 0.5% level, and that operates at elevated temperatures from 130° C. through 200° C. with minimal degradation. Polymer materials that operate in a transformer for extended periods of time, during overload conditions, at temperatures from 130° C. through 170° C. and excursions through 200° C. are very desirable. The material should also be cost effective.
The polymer material reduces the need to dry the insulation prior to filling the transformer with dielectric fluid and thereby reduces the transformer manufacturing cycle time. The barrier insulation may be molded or extruded as a single part, and molding or extrusion can be used to add functionality, such as, for example, coolant flow channels, locating features, interlocking features, and stacking features.
In particular implementations, the polymer material is of a heat resistant type, such as, for example, Questra (syndiotactic polystyrene), high temperature nylon, PPS (polyphenylene sulfide), RADAL-R (polyphenylsulfone), or another appropriate heat resistant or thermoset material. The polymer material typically has a superior dielectric strength to allow for a reduction in thickness of the electrical insulation, and consequently to allow a size and weight reduction in the transformer. The barrier insulation may be used in multi-phase transformers, shell-type single phase transformers, and step voltage regulators, among other applications. The barrier insulation may be used for coil-to-coil insulation barriers and coil-to-ground (core) barriers. The barriers typically serve as barriers for dielectric and mechanical strength. Within the transformer coils 105, 110, and 115, polymer sheet wire spacers may be used to space sections of the windings apart from one another.
Polymer coil supports 310, 325, 340, and 355 each insulate a coil end from a core ground plane. The coil supports may be formed to have a minimally obstructed oil flow horizontally above and below the coil in the core window, which provides for consistent cooling with lower thermal gradients. The coil supports provide mechanical support for the coils in the core windows. Sufficient support area is provided to prevent the crushing of the coil margins. The coil supports are sufficiently rigid to withstand telescoping forces during short circuit. When multiple layers are stacked together, the coil supports are designed to minimize the probability of allowing individual layers to move axially in relation to each other during shipping or short circuit. The use of the polymer coil supports reduces stacking time through, among other things, part count reduction. Use of the polymer coil supports also provides more consistent core coolant (oil) flow, improved thermal performance and consistency, and improved mechanical performance because among other properties, it does not compress.
With respect to the polymer coil supports 310, 325, 340, and 355, various production methods may be used for providing dielectric coolant flow to the side ducts of the coils 105, 110, and 115. For example, the polymer coil support 310, which insulates the ends of coil 105 from the core 120 ground plane, provides minimal obstruction of coolant flow horizontally above and below the coil 105 in the core window 205 and provides for consistent coolant flow. The coil support 310 also provides mechanical support for the coil 105 in the core window 205. This support serves to prevent crushing of the coil margins. In addition, the coil support 310 is sufficiently rigid to withstand telescoping forces during a short circuit. A single sheet or multiple stacked sheets may be used. Where stacked sheets are used, the coil support 310 is designed to minimize the probability of individual layers moving axially in relation to each other during shipping or short circuit. The coil support 310 has sufficient dielectric strength in the core window 205. The coil support 310 may be made from a high temperature thermoplastic or a thermoset material.
The staggered stack 610 includes sheets 500E, 500F, and 500G aligned in a staggered configuration. For example, corrugated barrier insulation sheet 500E is aligned to be offset with respect to the adjacent corrugated barrier insulation sheet 500F. A lower face 510F of sheet 500F is staggered with respect to a upper face 505E of sheet 500E, and an upper face 505F of sheet 500F is staggered with respect to a lower face 510G of sheet 500G The staggered pattern may continue as more layers are added. The number of layers in the stacked configuration will depend on, among other things, the dielectric strength required and the physical dimensions of the core and the coil.
The corrugated barrier insulation 800 has an overall length 825 that may be divided into a set of one or more distances 820 between consecutive ribs 810, a distance 830 from a rib 810 to an end 835, and a distance 840 from a rib 810 to the other end 835.
The barrier insulation has a thickness 960 and a total height from the lower surface 803 to the rib top 910.
The indentation 815 has corners 930 to form an indentation of depth 955, and corners 935 to form a total depth 950. A recess 945 is optional. Although rounded corners are shown, various other shapes may be used for the indentation. Also, other shapes may be used for the rib 810 and the indentation 815.
As discussed, rib 810 and indentation 815 are configured to engage and enable stacking of multiple sheets 800 in such a manner that the sheets do not slide transversely with respect to one another when subjected to compressive loading forces. The combination of rib 810 and indentation 815, or other corrugated shapes, enables, among other benefits, easier stacking of multiple sheets, and prevents sliding of the various sheets in a stack with respect to each other.
Although
The shape of the coil support 1700 is symmetric in the x and the y directions, and has the same shape on the top and the bottom. This allows for installation without regard to orientation. The coil support 1700 is of uniform wall thickness, improving material flow characteristics during the molding process. The repetitive design assists with tooling construction. This shape provides a high degree of flow area for the dielectric coolant and tends to minimize the potential for continuous blockage of any single coolant flow channel in the coil support 1700.
Other implementations are within the scope of the following claims.
This application claims priority from U.S. Provisional Application No. 60/444,968, filed Feb. 5, 2003, and titled “Polymer Sheet Core and Coil Insulation For Liquid Filled Transformers,” which is incorporated by reference.
Number | Name | Date | Kind |
---|---|---|---|
4673907 | Lee | Jun 1987 | A |
4833436 | Martin et al. | May 1989 | A |
4837543 | Humen et al. | Jun 1989 | A |
4890086 | Hill | Dec 1989 | A |
5194841 | Galloway et al. | Mar 1993 | A |
5319341 | Bisbee et al. | Jun 1994 | A |
5684446 | Adkins et al. | Nov 1997 | A |
6424246 | Kysely et al. | Jul 2002 | B1 |
Number | Date | Country | |
---|---|---|---|
20040150498 A1 | Aug 2004 | US |
Number | Date | Country | |
---|---|---|---|
60444968 | Feb 2003 | US |