Title of Invention

"A DRY-TYPE POWER DISTRIBUTION TRANSFORMER AND A METHOD FOR MAKING THE SAME"

Abstract

A dry-type power distribution transformer comprising: a resin encapsulated rectangular coil having a straight section; and an amorphous metal core having a rectangular core window defined therein; said coil and said core being sized and shaped such that the shape of said straight section of said coil conforms to the shape of said core window, said straight section of said coil being located within said core window when said coil and said core are assembled to form said power distribution transformer.

Full Text

This application claims the benefit of TJ.S. Prnvisinnnl Applinfltren The present invention relates to and a method for making the same to a dry-type power distribution transformer having a wound amorphous metal core and a generally rectargular resin encapsulated coil, . 2. Description Of The Prior Art V Conventional dry-type power distribution transformers have a round or toroidal open wound coil and a silicon steel or amorphous metal core of the wound or stacked variety. The :ransformer core typically has a rectangular shape defining a rectangular window within which the coil is located. Frequently, the toroidal shape of the coil creates a mismatch between the core and coil insofar as the core window is concerned, i.e. the shape of the rectangular window does not match the shape of the section of the coil that is located therein. This mismatch between the core and coil causes the size and cost of the transformer to be significantly larger than would be required if the transformer had more closely matched core and coil shapes. Wound cores used in power distribution transformers, whether silicon steel or amorphous metal, are rectangular in cros.s-section and do not conform 10 the round shape of the coil. Stacked silicon steel transformer cores, on the other hand, may have a cruciform cross-section that can approximately match the coil's toroidal shape. Due to the high expense: of casting or cutting an amorphous metal strip to a variety of widths, it is impractical to form a stacked amorphous metal core with a cruciform cross-section. For these reasons, in manufacture of dry-type power distribution transformers having amorphous metal cores, whether wound or stacked, the cross-sectional shape of the core (i.e. rectangular) and the shape of the coil (i.e. round) do not match. Usage of coil material is uneconomical, and transformer sizes are too large. Power distribution transformers may be installed in a variety of locations and subject to extreme environmental conditions such as, for example, paniculate matter (dust, dirt, etc,), moisture, caustic substances, and the like, which adversely effect the life span and performance of the transformer. Open wound coils provide ro protection against the effects of such the hiirsh environments. SUMMARY OF THE INVENTION The present invention provides a dry-type power distribution transformer having a wound amorphous metal cor Generally stated, the dry-type dry- power distribution transformer includes a resin encapsulated generally rectangular coil having a substantially straight section and an amorphous metal core having a generally rectangular core window definec therein. Th«: coil and the core are sized and shaped such that the shape of the substantially straight section of the coil substantially conforms to the shape of the core window Wh;n the coil and core arc assembled 10 form a power distribution transformer, the substantially straight section of said coil is located within the core window. The rcsiu encapsulation protects the coil against harsh environmental conditions, protects the insulation system of the coil, improves the coil strength und;r short-circuit conditions, and improves the; coil's cooling characteristics by providing a smooth, uniform surface about the coil's exterior over which air (either forced or convective) may smoothly and easily pass. Advantageously, the dry-type powtr distribution transformer of the invention is durable and robust. Coil and core materials are utilized in a highly economical manner that significantly decrease manufacturing cost and transformer size. These features are especially desirable in power distribution transformers where size, cost, and performance govern market acceptance. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood and further advantages will become apparent when reference is had to the following detailed description and the accompanying drawings, wherein like reference numerals denote similar elements throughout the several views and in which: Fig ; A is a frontal view of a shell-type singh phase transformer constructed in accordance with the present invention with the coil partially cut-away; Fig. IB is a cross-sectional view taken along line B-B of Fig. IA; Fig. 2A is a frontal view of a core-type single phase transformer constructed in accordance with the present invention; Fig. 2B is a cross-sectional view tal.en along line B-B of Fig. 2A; Fig. 3A is a frontal view of a three phase transformer constructed in accordance with the present invention; Fig. 3B is a cross-seclional view taken along line B-B of Fig. 3A; Fig. 4 is a perspective view of a generally rectangular, low voltage coil wound about a rectangular mandrel ir) accordance with the present invention; Fig. 5 is a perspective view of a generally rectangular, high voltage coil wound about a rectangular mandrel in accordance with the present invention; Fig. 6 is a perspective view of an epoxy cDntainment vessel configured for encapsulating a generally rectangular coil in accordance with the present invention; Fig. 7 is a top view of the epoxy containment vessel of Fig. 6 with a generally rectangular coil contained therein; and Fig. 8 is a block diagram of an encapsulation system for encapsulating a coil constructed in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION Referring to Figs. 1A and 2A of the drawings, there is shown two variations of a first embodiment of the present invention: a shell-type single phase power distribution transformer (Fig. 1A): and a core-type single phase power distribution transformer (Fig. 2A). Shell-type single phase transformer comprises a generally rectangular, resin encapsulated coil 40 and two amorphous metal cores 20. Core-type single phase transformer 10 comprises two generally rectangular, resin encapsulated coils 40 and a single amorphous metal core 20. A second embodiment of the invention is depicted in Fig. 3A. In that embodiment shell-type three-phase power distribution transformer 10 comprises three generally rectangular, :-esin encapsulated coils 40 and four amorphous metal cores 20. While the following detailed description is directed to the shell-type single phase embodiment, it will be understood by those skilled in the an that such description is also applicable to the core-type single phase and to the shell-type three phase transformer embodiments depicted in Figs. 2A, 2B, 3A and 3B. Furthermore, it will be obvious to persons skilled in the art that the present invention and the detailed description thereof provided below applies to various other dry-type power distribution transformer configurations and designs. Thus, the description provided below for a shell-type single phase transformer is shoiJd be interpreted as illustrative and not in a limiting sense. As used herein, the terms "amorphous metal" and "amorphous metallic alloys" means a metallic alloy that substantially lacks any long range order and is characterized by X-:*ay diffraction intensity maxima which are qualitatively similar to those observed for liquids or inorganic oxide glasses. Amorphous metal alloys are well suited for use in forming cores 20, because they have the following combination of properties: (a) low hysteresis loss; (b) low eddy current loss; (c) low coercive force; (d) high magnetic permeability; (e) high saturation value; and (f) minimum change in permeability with temperature. Such alloys are at least about 50% amorphous, as determined by :i-ray diffraction. Preferred amorphous metal alloys include those having the formula Meo-ooTo-is XIQ. is, wherein M is at least one of the elements iron, cobalt and nickel, T is at least one of the transition metal elements, and X is at least one of the metalloid elements of phosphorus, boron z.nd carbon, tip to 80 percent of the carbon, phosphorus and/or boron in X may be replaced by aluminum, antimony, beryllium, germanium, indium, silicon and tin. Used as cores of magnetic devices, such amorphous metal alloys evidence generally superior properties as compared to the conventional polycrystalline metal alloys commonly utilized. Preferably, s:rips of such amorphous alloys are at least 80% amorphous, more preferably yst, at least 95% amorphous. The amorphous alloys of cores 20 i.re preferably formed by cooling a melt at a rate of about 106 "C/sec. A variety of well-known techniques are available for fabricating rapidly-quenched continuous amorphous metal strip. When used in magnetic cores for amorphous metal transformers, the strip material of cores 20 typically has the form of a ribbon. This strip material is conveniently prepared by casting molten material directly onto a chill surface or irto a quenching medium of some sort. Such processing techniques considerably reduce the cost of fabrication, since no intermediate wire-drawing or ribbon-forming procedures are required. The amorphous metal alloys of which core 20 is preferably composed evidence high tensile strength, typically about 200,000 to 600,000 psi. depending on the particular composition. This is to be compared with polycrystaJJine alloys, which are used in the annealed condition and which usually range from about 40,000 [o 80,000 psi. A high tensile sirength is an important consideration in applications where high centrifugal forces are present, since higher strength alloys prolong the service life of the transformer. In addition, the amorphous metal alloys used to form core 20 evidence a high electrical resistivity, ranging from z.bout 160 to 180 microhm-cm at 25 °C, depending on the particular composition. Typical prior art materials have resistivities of about 45 to 160 microhm-cm. The high resistivity possessed by the amorphous metal alloys defined above is useful in AC applications for minimizing eddy current losses which, in turn, are a factor in reducing core loss. A further advantage of using amorphous metal alloys to form core 20 is that lower coercive forces are obtained than with prior art compositions of substantially the same metallic content, thereby permitting more iron, which is relatively inexpensive, to be utilized in the core 20, as compared with a greater proportion of nickel, which is more expensive. Each of the cores 20 is formed by winding successive turns onto a mandrel (not shown), keeping the strip material under tension to effect a tight formation. The number of turns is chosen depending upon the desired size of each core 20. The thickness of the strip material of cores 20 is preferably in the range of 1 to 2 mils. Due to the relatively high tensile strength of the amorphous metal alloy used herein, strip material having, a thickness of 1-2 mils can be ussd without fcar of breakage. It will be appreciated that keeping the strip material relatively thin increases the effective resistivity since the-e are many boundaries per unit of radial lengn which eddy currents must pass through. With continued reference to Figs. 1A and IB, i: shell-type single phase, dry-type power distribution transformer 10 includes a core/coil assembly 12 comprised of two amorphous metal cores 20 and an encapsulated, generally rectangular coil 40. Transformer 10 also includes a bottom frame 30 and top frame 34, having bottom and top coil supports 32, 36, respectively, and within which the core/coil assembly J2 ,s supportedly mounted. Each core 20 is preferably wound from a rlura 'ty of amorphous metal strips or layers 28 having a generally r.ctan ;ular cross-sectional shape (see Fig. IB). Each core 20 has two 1: ,g si JCS 24 and two shor; sides 26 that collectively define a generally rectangular core window 22 within which a substantially straipr' mir- "jrtion 52 of the generally rectangular coil 40 of the present / we ;a The desired shape of the coil 4C of the present invention is generally rectangular. However, othei geometric shapes are also considered within the scope of the present invention, provided, however, that such other geometric shapes include a substantially straight mid-section 52 that is sized and shaped to fit v/ithin the generally rectangular window 22 of the core 20. For example, the coil 40 may have rounded end sections 54 that are not located within the core window 22, and f generally straight mid-section 52 thai passes through and is located within the core window, e.g. an oval with aenerally straight mi(,-S'.-:tions. As shown more clearly in Fig. 1B, the generally -ecung'j/ ^r coil 40 of the present invention comprises a plurality of coil vinc;'igf 42 wound along with an insulating material 44 and with selectively pi i-;ed cooling duct spacers 46 (see Figs. 4 and 5). The generally \rct .ngujjr sha^e of the coil 40 is obtained by winding the coil compon/"tr (.e.g. windings 42 and insulation material 44) about a reciangur.r w -.d; Since the coil winding material is typically supplied on a spool, the material may retain a bend radius afier the coil 40 is wound, causing the coil 40 to bow or assume a gene'ally oval shape due to the memory of the winding material. This disadvantageous^ increases the build dimension of the coil, especially in the mid-section 52 which is preferably substantially straight, and may result in coils being too large to fit on the cores 20. It is thus necessary to ensure that coil windings 42 (and the coil 40) reta.ns its generally rcctanguiar sh.pc after , ,s removed from the winding mandrel 60. One sol .men provided by che present •nvcnuon involves using epoxy-dotted kraft paper as U : insulating matenal 44 between the coil windings 42. The epoxy he- ts :o the coil windings 42 End, upon curing, imparts rigidity to the w,r, ,ngs 42 that counteracts th* bowing tendency of the winding materia . . alternatively, a winding form 62 (see Figs. 4 and 5) may include „,*,,! c. .-ners 64 that form corners m the coil windings 42 and the coi! .-0 - .,ound on the mandrel 60. A third solution involves shiping * S > ;ra •. rectangular form of the coil 40 as the winding material i-. ^u^j.jr_,h?: mandrel 60 such as, for example, using a wooden blocTivd ->ton hrmmer. Still another solution involves leaving the cml^T^ne ending mandrel 60 and pressing the long legs of the winder- ,0 beiv ,e. clamps after the coil 40 has been completely wou-.1 a.^pHor to encapsulation. Ir addition to providing the generr.il- ,ecii*--,tar for.n to the coil 40, '.his latter solution serves to -rh^windngs •!' and nsulating matenal 44 in the sec :.ons where build-up should r unim zed, i.e. the substantially siraight mid-sections 52. To further minimize the size of ire finis /ed r. i 40, the cooling duct spacers 46 are not placed (and the coc-\:•+ du .3 (.8are not located) in the substantially straight mid-sections 5"- of t,; i;c.. This provides a distinct advantage over round or .oroi/.ai r.dls that require circumferentiiilly continuous cooling uots T'lU1,. j. circumfercmially discontinuous cooling duct, which is Mefn:d by V : selective placement of the spacers 46, is provided onl in the en" sections 54 of the substantially rectangular coil 40. The insulating materia' 4 ,; interspersed between adjacent layers of coil windings 42 to provicv ','- .trie isolatio*' thereaetween and forms the inner- and outer-most layers of the coil 40 (not coniidf.r.ng ti-.a t .ocy encapsulation described below). In a preferred ebo-ir.nent the insulating maierial 44 comprises a sheet o • sheets of paper i, ch as Dupont's Nomex® brand. It will be obvious to rw 'ailed ir (he art that various other insulating materials may be r- v, 'eo -/ithout /'.eparting from the spirit or intent of the present inv The inner-most and outer-most sliestf 'j. insulat .13 mat/rial 44 are preferably sized so as to extend nj-.pr 'umately 12 mm beyond the longitudinal «-nds of the coil 40 I- -';--..' tion, the insulating maierial 44 located on each side of rl,e joo'V duct spacers 46 also extends approximately 12 mrn ptv. .he end- of the coil 40. These sheets of extended insulation ; serial 44 are -ealed with a thick epoxy such as, for example, th.t r: -de by Magnoli;. Co.. pare number 3126, A/B. The epoxied extend'.d sheets of insulition material 44 then serve to contain any uncured rpoxy during the enc ipiulatio process (described in more detail below; of the coil 40. Cooling for dry-type power . ;'riou:ion transformers my be either convective cr forced-air. Cooling .i..,cti 38 are thus necessary between the coil windings to permit the p age o" air t'rethroMh. The cooling duct spacers 46 may be inserte ) b.;tweeii coil vindin;42 as the coil 40 is wound ard are removed s'.it the coil 4C his b-;n encapsulated (as described in further detail b-iov/). Since i( is dv ,ii-able to control the wound dimensions of the coi' 4'J to ensu i Mt i. will fit within the core window 22 of the core 20, Itv. cooling dcjji. jil 40 that will not be located within the core windowTre at thf iongi'udinally distal ends of the coil 40, as clearly sho\vs-r--Fil. I^V'in the assembled transformer 10. Thus the dimension of 'roil 40 is rontrollec1 in the section that will be located within the v idow 22 tsreby providing smaller (i.e. narrower) coils 40 that, in turn, produce smaller power distribution transformers. The generally rectangular shape of the coil of the present invention permits the use of cooling ducts 58 that are non-continuous about the circumference of the rectangular coil. The desirability of selectively locating the cooling ducts 58 and of providing circumferentially non-continuous cooling ducts 58 is clear considering the fact that the cooling ducts 58 increase the size of the coil -- which is undesirable especially in the substantially straight mid-section 52 of the coil 40. The generally rectangular shape of the coil 40 of the present invention provides four clearly delineated sides (which round or toroida' coils do not) which permit selective location of the cooling ducts 58 -a the end sections 54 of the coil 40. For low voltage coils, such as those typically used as T ic secondary winding of ;i power distribution transformer, the ecu windirg 42 comprises a sheet or sheets of aluminum or copper (see i-ig. 4). For high voltage coils, such as those typically used as i'it p-:mary winding of a power distribution transformer, the coil wind ng *,?. comprises a cross- sectionally rectangular or circular copper wire (se-. Fig. 5). For both low and high voltage coils, the coil 40 is wound on a 'octangular mandrel 60, preferably in conjunction with a winding form 67 having metal corners 64 having a predefined angular configuration. The , ubstantially rectangular coil 40 of the present invention may comprise i / ly a low voltage or a high voltage coil or, alternatively, it may comp'ise both low and high voltage coils. The wound coil 40 is completely contained in and encapsulated by an epoxy resin layer 50, as c escribed in more detail below. Referring to Figs. 4 and 5, there is shovn a generally rectangular coil 40 configured in accordance with the uresent invention for low voltage and high voltage applications, respectively. The low voltage coil 40 shown in Fig. 4 is formed by winding a coij winding 4! such as, for example, a sheet of copper or aluminum, about a general • rectangular winding mandrel 60. To electrically isolai-j a-ijacrnt l;iye i of windings 42, an insulating material 44 is interspersed therebetween 7 he insulating material 44 comprises the inner- and oute'-most layers .:' tne wound coil 40. Cooling ducts 58 are provided in th,*- 'vound cml The coil 40 of the present invention is encapsulated in an epoxy resin layer 50 using a containment vessel 70 as depicted in Fig. 6. The vessel 70 comprises a vessel shed 72 havmg first and second halves 72a, 72b, a vessel core 74, and a vessel bottom 76. The vessel core 74 may also comprise first and second halves '4a, 74b, or, alternatively, the vessel core 74 may comprise the rectangular winding mandrel 60 upon which the generally rectangular coil 40 o1' the present invention is wound and formed. Brackets 78 provided on th; first and second vessel halves 72a, 72b may be used to hold the two halves together during the encapsulation process. The encapsulation process will now be discussed in detail and with reference to Figs. 6. 7 and 8. The wound coil 40 is placed in the containment vessel 70 which preferably extends beyond the top of the coil 40 by approximately 100 mm to allow for any shrnkage in the epoxy after curing. The vessel 70 and coil 40 are then loaded into a vacuum chamber 80 that is connected to a vacuum source 82 and an epoxy source 84. The chamber 80 is then evacuated by the vacuum source 82 to approximate)} 150 torr. A low viscosity epoxy such as a bisphenol A epoxy resin of the type sold by Magnoliu Co. as part number II1-047, A/B, is introduced into and completely fills the contzinmenl vessel 70. When the vessel 70 is filled 10 the top w:th epoxy, thf; vacuum chamber 80 is further evacuated 10 approximately 20 torr. Additional epoxy is fed into the containment vessel 70 if the epoxy level therein drops during the above-described pressure changes within the chamber 80. Once the containment vessel 70 is completely filled with epoxy and the epoxy level is stabilized within the vessel 70, the epoxy is cured to produce an epoxy resin layer 50 the completely surrounds and encapsulates the coil 40. After the epoxy has cured, the coi) 40 is removed from the containment vessel 70 and the cooling duct spacers 46 ure removed from the coil 40. The generally rectangular, resin encapsulated coil 40 may now be used together with a wound amorphous rr.etal core 20 having a generally rectangular cross-section and a generally rectangular core window 22. The substantillly straight section 52 of the coil 40 is located within the core window 22 and substantially matches the size and shape of the window 22. Thus, the present invention provides a dry-type power distribution transformer having a wound amorphous metal core having a generally rectangular cross-sectional shape and a generally rectangular resin encapsulated coil. The encapsulation protects the roil against harsh environmental conditions, protects the insulation system of the coil, improves the coil strength under short-circuit conditions, and improves the coil's cooling characteristics by providing a smooth, uniform surface about the coil's exterior over which air (either forced or convective) may smoothly and easily pass. In addition, by matching the shape of the coil to that of the core's cross-section, the present i -vention provides a dry-type amorphous metal power distribu'.ion t •insfor-ner that is less expensive to manufacture, is Jess resistive and thus less lossy (less coil material is needed to wind the coil), and that i . more compact than prior art transformers having generally round or ciicular coils. The present invention thus provides a durable and robust dry-type power distribution transformer that uses the transformer materials in a more economical manner thereby reducing manufacturing costs and overall transformer size. Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to, but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the invention, as defined by the subjoined cl?iims. We Claim: 1. A dry-type power distribution transformer comprising: a resin encapsulated rectangular coil having a straight section; and an amorphous metal core having a rectangular core window defined therein; said coil and said core being sized and shaped such that the shape of said straight section of said coil conforms to the shape of said core window, said straight section of said coil being located within said core window when said coil and said core are assembled to form said power distribution transformer. 2. A dry-type power distribution transformer as claimed in claim 1, wherein said coil comprises: a plurality of rectangular concentric layers comprising a conductive coil winding and an insulating material providing electric isolation between adjacent concentric layers of said coil; and a resin layer that encapsulates said coil. 3. A dry-type power distribution transformer as claimed in claim 2, wherein said coil comprises a plurality of cooling ducts defined between adjacent ones of said plurality of concentric layers, said cooling ducts being circumferentially non-continuous about said rectangular coil and being located in a part of said coil that does not comprise said straight section. 4. A dry-type power distribution transformer as claimed in claim 2, wherein said coil winding is constructed of a material selected from the group of materials consisting of aluminum and copper. 5. A dry-type power distribution transformer as claimed in claim 1 comprising: a resin encapsulated rectangular coil having a straight section and being formed by alternatingly winding a conductive material and an insulating material on a rectangular winding form to form a plurality of rectangular concentric layers of insulating and conductive material and by thereafter forming an encapsulating resin layer that encapsulates said coil; and a rectangular amorphous metal core having a rectangular core window defined therein; said coil and said core being sized and shaped such that the shape of said straight section of said coil conforms to the shape of said core window, said straight section of said coil being located within said core window when said coil and said core are assembled to form said power distribution transformer. 6. A dry-type power distribution transformer as claimed in claim 5, wherein said conductive material is selected from a group of materials consisting of aluminum and copper. 7. A dry-type power distribution transformer as claimed in claim 5, wherein said coil comprises a plurality of cooling ducts defined between adjacent ones of said plurality of concentric layers, said cooling ducts being circumferentially non-continuous about said rectangular coil and being located in a part of said coil that does not comprise said straight section disposed within said core window. 8. A dry-type power distribution transformer as claimed in claim 1 and 5, wherein said core is a wound core. 9. A dry-type power distribution transformer as claimed in any of claims 1 and 5, wherein said core is made from an amorphous metal alloy having the formula M60-90 T0-15 X10-25, wherein M is at least one of the elements iron, cobalt and nickel, T is at least one of the transition metal elements, and X is at least one of the metalloid elements phosphorus, boron and carbon, and wherein up to 80 percent of the carbon, phosphorus and boron content may be replaced by aluminum, antimony, beryllium, germanium, indium, silicon and tin. 10. A dry-type power distribution transformer as claimed in claim 1 and 5, wherein said core window defines an aspect ratio of greater than 3.5 to 1. 11. A dry-type power distribution transformer as claimed in claim 1 and 5, wherein said core window defines an aspect ratio of between 3.5 to 1 and 4.5 to 1. 12. A rectangular resin encapsulated coil having a straight section as claimed in claim 1 said coil comprising: a plurality of rectangular concentric layers comprising a conductive coil winding and an insulating material providing electric isolation between adjacent concentric layers of said coil; and a resin layer that encapsulates said coil. 13. A rectangular resin encapsulated coil as claimed in claim 12, wherein said coil comprises a plurality of cooling ducts defined between adjacent ones of said plurality of concentric layers, said cooling ducts being circumferentially non-continuous about said rectangular coil and being located in a part of said coil that does not comprise said straight section. 14. A rectangular resin encapsulated coil as claimed in claim 12, wherein said coil winding is selected from a group of materials consisting of aluminum and copper. 15. A rectangular resin encapsulated coil as claimed in claims 2, 5 and 12, wherein said resin layer comprises a low viscosity epoxy resin. 16. A rectangular resin encapsulated coil as claimed in claims 5 and 15, wherein said low viscosity resin is a bisphenol A epoxy resin. 17. A rectangular resin encapsulated coil as claimed in claim 1, 5 and 12, wherein said coil is a low voltage coil. 18. A rectangular resin encapsulated coil as claimed in claims 1, 5 and 12, wherein said coil is a high voltage coil. 19. A rectangular resin encapsulated coil as claimed in claims 1, 5 and 12, wherein said coil comprises a low voltage coil and a high voltage coil. 20. A method of making a dry-type power distribution transformer as claimed in claim 1 comprising the steps of: (a) forming a rectangular coil having a straight section; (b) encapsulating said coil in an epoxy resin; (c) forming a core from amorphous metal, said core having a rectangular window defined therein; and (d) assembling a dry-type power distribution transformer from said encapsulated coil and said amorphous metal core such that said straight section of said coil is located within said core window and wherein the shape of said straight section of said coil conforms to the shape of said core window. 21. A method of making a dry-type power distribution transformer as claimed in claim 20, wherein said step (a) comprises: (e) alternatingly winding a conductive material and an insulating material on a rectangular winding form to form a plurality of concentric layers of insulating and conductive material, said insulating material providing electric isolation between adjacent concentric layers of said conductive material. 22. A method of making a dry-type power distribution transformer as claimed in claim 20, wherein said step (b) comprises: (f) placing said coil in a containment vessel; (g) pacing said containment vessel in a vacuum chamber; (h) vacating said vacuum chamber to a predetermined pressure; (i) filling said containment vessel with an epoxy resin; and (j) curing said epoxy resin so as to form an epoxy resin layer that encapsulates said coil. 23. A method of making a dry- type power distribution transformer as claimed in claim 22, wherein said predetermined pressure of said step (h) is approximately 150 torr. 24. A dry- type power distribution transformer as claimed in claim 9, wherein said core is made from an amorphous metal alloy having the formula Fe80B11Si 9.

Documents:

00220-del-2000-abstract.pdf

00220-del-2000-assignment.pdf

00220-del-2000-claims.pdf

00220-del-2000-correspondence-others.pdf

00220-del-2000-correspondence-po.pdf

00220-del-2000-description (complete).pdf

00220-del-2000-drawings.pdf

00220-del-2000-form-1.pdf

00220-del-2000-form-19.pdf

00220-del-2000-form-2.pdf

00220-del-2000-form-3.pdf

00220-del-2000-form-5.pdf

00220-del-2000-form-6.pdf

00220-del-2000-gpa.pdf

00220-del-2000-pct-210.pdf

00220-del-2000-pct-308.pdf

00220-del-2000-pct-331.pdf

00220-del-2000-pct-409.pdf

00220-del-2000-petition-137.pdf

00220-del-2000-petition-138.pdf