Patent Publication Number: US-11049647-B2

Title: Molded tap changer assemblies and methods for dry-type transformers

Description:
FIELD 
     This application relates to transformers used for electric power distribution, and more particularly to tap changer assemblies and methods for dry-type transformers. 
     BACKGROUND 
     Transformers are employed to increase or decrease voltage levels during electrical power distribution. To transmit electrical power over a long distance, a transformer may be used to raise the voltage and reduce the current of the power being transmitted. A reduced current level reduces resistive power losses from the electrical cables used to transmit the power. When the power is to be consumed, a transformer may be employed to reduce the voltage and increase the current to a level specified by the end user. 
     One type of transformer that may be employed is a submersible dry-type transformer described, for example, in U.S. Pat. No. 8,614,614. Such transformers may be employed underground, in underground sewer systems, and in submerged environments and thus may be designed to withstand harsh environments such as water exposure, humidity, pollution, and the like. Improved assemblies and methods for submersible and other dry-type transformers are desired. 
     SUMMARY 
     In some embodiments, a tap changer assembly of a dry-type transformer is provided. The tap changer assembly includes a first molding including multiple taps; a semi-conductive coating applied to an outer surface of the first molding; a conductive shield provided in contact with the semi-conductive coating; a grounding member comprising a ring of bosses interconnected by a grounding conductor; a second molding applied over at least a portion of the conductive shield and the grounding conductor, the second molding including a molded sealing surface; a conductive cover coupled to the ring of bosses; and a sealing member sealing between the molded sealing surface and the conductive cover. 
     In some embodiments, a dry-type transformer is provided. The dry-type transformer includes a coil assembly having an inner coil, an outer coil, and a tap changer assembly having multiple taps configured to allow voltage adjustments across the outer coil, the tap changer assembly, comprising: a first molding including the multiple taps; a semi-conductive coating applied to an outer surface of the first molding; a conductive shield provided in contact with the semi-conductive coating; a grounding member comprising a ring of bosses interconnected by a grounding conductor; a second molding applied over at least a portion of the conductive shield and the grounding conductor, the second molding including a molded sealing surface; a conductive cover coupled to the ring of bosses; and a sealing member sealing between the molded sealing surface and the conductive cover. 
     In some embodiments, a method of forming a tap changer assembly of a dry-type transformer is provided. The method includes forming a first molding including the multiple taps; applying a semi-conductive coating to the first molding; providing a conductive shield overtop some of the semi-conductive coating; providing a grounding member comprising a ring of bosses interconnected by a grounding conductor; and applying a second molding over at least a portion of the conductive shield and the grounding conductor, the second molding including a molded sealing surface. 
     Still other aspects, features, and advantages of this disclosure may be readily apparent from the following detailed description, which illustrates by a number of example embodiments. This disclosure may also be capable of other and different embodiments, and its several details may be modified in various respects. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings, described below, are for illustrative purposes only and are not necessarily drawn to scale. The drawings are not intended to limit the scope of the invention in any way. Wherever possible, the same or like reference numbers are used throughout the drawings to refer to the same or like parts. 
         FIG. 1A  illustrates a front plan view of a submersible dry-type transformer in accordance with embodiments provided herein. 
         FIG. 1B  illustrates a perspective view of a coil assembly including a tap changer assembly in accordance with embodiments provided herein. 
         FIG. 2A  illustrates a front plan view of a tap changer assembly with a conductive cover installed in accordance with embodiments provided herein. 
         FIG. 2B  illustrates a front plan view of a tap changer assembly with the conductive cover removed in accordance with embodiments provided herein. 
         FIG. 2C  illustrates a side cross-sectioned view of a tap changer assembly taken along section lines  2 C- 2 C in  FIG. 2A  in accordance with embodiments provided herein. 
         FIG. 2D  illustrates a top view of a grounding member having a ring of bosses interconnected by a grounding conductor (wire ring and grounding strap) in accordance with embodiments provided herein. 
         FIG. 2E  illustrates a partially cross-sectioned side view of a threaded boss attached to the grounding conductor in accordance with embodiments provided herein. 
         FIG. 3A  illustrates a cross-sectioned side view of a separately-molded component of an alternative tap changer assembly in accordance with embodiments provided herein. 
         FIG. 3B  illustrates a cross-sectioned side view of the alternative tap changer assembly in accordance with embodiments provided herein. 
         FIG. 4  illustrates a schematic diagram of taps and electrical connections to the outer coil of the transformer made in the tap chamber assembly in accordance with embodiments provided herein. 
         FIG. 5  illustrates a flowchart of a method of manufacturing a tap changer assembly in accordance with embodiments provided herein. 
     
    
    
     DETAILED DESCRIPTION 
     As mentioned above, submersible dry-type transformers may be employed underground, submerged, and/or in other environments that may expose the transformer components to water, humidity, pollutants, etc. Such dry-type transformers are often connected to deliver single or multiple phases of electrical power, such as 2-phase, 3-phase, for example. Common implementations are 3-phase configurations. 
     Such dry-type transformers can include for each high voltage coil thereof a tap changer such as is described in U.S. Pat. No. 9,355,772 entitled “Transformer Provided With A Taps Panel, An Electric Insulation Method For Taps Panel Of A Dry Distribution Transformer, And A Taps Panel For A Dry Distribution Transformer.” 
     Conventional tap changer configurations for submersible dry-type transformers are made on a front side of the transformers. For example, each high voltage coil of a transformer may have multiple taps that allow for adjustments to the voltage across the respective high voltage coils. However, existing implementations utilize expensive components and are prone to corrosion. Improved tap changer assemblies that offer improved corrosion resistance, sealing capability, and lower cost are desired. 
     In accordance with one or more embodiments described herein, improved tap changer assemblies such as for submersible dry-type transformers are provided. In some embodiments, the tap changer assembly includes a first molding including the taps molded therein, a semi-conductive coating applied to surfaces of the first molding, and a conductive shield provided overtop of portions of the semi-conductive coating, a grounding member having a grounding conductor and coupled threaded bosses (threaded inserts), and a second molding encapsulating the grounding member and forming a molded sealing surface. A sealing member is seated between the molded sealing surface and a conductive cover to seal the tap changer cavity. In some embodiments, a sealing surface enabling sealing between the conductive cover and the second molding comprises a molded O-ring groove. Other embodiments provide the second molding as a separately-molded member that is mechanically fastened to the first molding. 
     The above-described configurations provide an inexpensive, yet robust tap changer assembly construction capable of being readily manufactured and sealed. Thus, the dry-type transformer can be less expensive to manufacture, and can be less susceptible to corrosion and may offer improved sealing of the taps cavity. 
       FIG. 1A  is a front plan view of a dry-type transformer  100  in accordance with embodiments provided herein. The dry-type transformer  100  shown is a three-phase transformer, but in other embodiments, transformers with different number of phases may be employed (e.g., one or two phases). Dry-type transformer as used herein means a transformer that includes high and low voltage coils that are not submerged in an oil bath contained within an enclosure. Such dry-type transformers  100  have significant advantages, in that they do not utilize oil and are thus exposed directly to the environment such that the can run cooler via cooling by air or water (when submerged). 
     By way of example, the dry-type transformer  100  can include a core assembly  102  mounted between an upper frame portion  104 U and lower frame portion  104 L. Insulating sheets may be provided to insulate the sides of the core assembly  102  from the respective upper and lower frames  104 U,  104 L. Core assembly  102  may be made up of multiple laminations of a magnetic material. Example magnetic materials include iron, steel, amorphous steel or other amorphous magnetically permeable metals, silicon-steel alloy, carbonyl iron, ferrite ceramics, and more particularly laminated layers of one or more of the above materials, or the like. In some embodiments, laminated ferromagnetic metal materials having high cobalt content can be used. Other suitable magnetic materials can be used. 
     As shown, core assembly  102  can include multiple interconnected pieces, and can include vertical core columns  102 L,  102 C, and  102 R. Vertical core columns  102 L,  102 C, and  102 R can be assembled with top and bottom core members  102 T,  102 B. Construction may include step-laps between respective components of the core assembly  102 . Construction of the core assembly  102  can be as is shown in U.S. Pat. No. 4,200,854 or 8,212,645, for example. Other configurations of the core assembly  102  can be used. In some embodiments, within transformer  100 , each core column  102 L,  102 C, and  102 R can be surrounded by a coil assembly, namely coil assemblies  106 ,  108 ,  110 . 
       FIG. 1B  illustrates a perspective view of coil assembly  106 . Coil assembly  106  is shown and described herein by way of example, and coil assemblies  108 ,  110  can be identical or substantially identical thereto. The coil assembly  106  includes a low-voltage inner coil  112  and a high-voltage outer coil  114 , which may be concentric with the low-voltage inner coil  112 . Low-voltage inner coil  112  may be electrically isolated from the core assembly  102  and also from the high-voltage outer coil  114 . For example, low-voltage inner coil  112  may be surrounded by an insulating material such as a molded resin. Likewise, high-voltage outer coils  114  may include a multi-stage insulating material (e.g., resin) provided in multiple sequential molding processes, as will be described fully herein. Example insulating materials can include any suitable solid insulation, such as an epoxy, polyurethane, polyester, silicone, and the like. 
     Referring again to  FIG. 1A , the coil assemblies  106 ,  108 ,  110  and core assembly  102  can be separated by insulating sheets  116 A- 116 F and others) as described in U.S. Pat. No. 8,614,614 entitled “Submersible Dry Transformer.” Insulating sheets  116 A- 116 F and others (not shown) may be any suitable insulation material and collectively operate to seal the plane of a core window of the core assembly  102  to prevent a loop of water from being formed when submerged. Insulating sheets are also are included between the low-voltage inner coil  112  and a high-voltage outer coil  114 , and between the core columns  102 L,  102 C,  102 R and respective low-voltage inner coil  112  within the core window. 
     Referring again to  FIG. 1A , each of the coil assemblies  106 ,  108 ,  110  of the transformer  100  can be provided with high voltage terminals  118  that can be positioned at a top front of the respective coil assemblies  106 ,  108 ,  110 . Low voltage terminals  119  of the low voltage inner coil  112  ( FIG. 1B ) can be provided on a back side of the coil assemblies  106 ,  108 ,  110 . For example, as best shown in  FIG. 2C , the high voltage terminals  118  can be located on a top front of a columnar front extension  126 E of the coil housing  126  and the low voltage terminals  119  can be located on a rear part of the low-voltage inner coil  112 . However, the high voltage terminals  118  and low voltage terminals  119  could be located elsewhere. The high voltage terminals  118  provide electrical power connections to the high-voltage outer coils  114  of the respective coil assemblies  106 ,  108 ,  110 . Connectors (not shown), such as sealed plug-in connectors, may be provided to facilitate sealed connection of high voltage terminals  118  to electrical cables (not shown). Wye connections (not shown) or the like may be made with low voltage terminals  119 . Other suitable sealed connections are possible. 
     As best shown in  FIGS. 1A and 1C , the transformer  100  can also include delta connections  120 A,  120 B, and  120 C between the respective high-voltage outer coils  114  of the coil assemblies  106 ,  108 ,  110 . Delta connections  120 A,  120 B,  120 C may comprise shielded cables, for example. Each of the delta connections  120 A,  120 B,  120 C can be made to an upper delta terminal  122  and a lower delta terminal  124  of the high-voltage outer coil  114  of each of the coil assemblies  106 ,  108 ,  110 , as shown. The electrical connections can be sealed connections. The upper delta terminal  122  and lower delta terminal  124  can extend horizontally (as shown) from the columnar front extension  126 E of the coil housing  126 . For example, the upper delta terminal  122  and lower delta terminal  124  can extend outwardly from a front face  126 F of the columnar front extension  126 E in some embodiments. 
     The high-voltage outer coil  114  of each of the coil assemblies  106 ,  108 ,  110  can include a grounding terminal  128 . Grounding conductors  129 , such as braided cables can connect between the respective grounding terminals  128  of the high-voltage outer coils  114  and the lower frame  104 L, for example. A common grounding strap  130  can attach to the lower frame  104 L and can provide an earth ground. Each of the coil assemblies  106 ,  108 ,  110  includes an inventive tap changer assembly  132  to be described fully herein. 
     Additional details regarding conventional construction of submersible dry-type transformers  100  that may be employed in accordance with one or more embodiments provide herein and conventional tap changers are described in previously-mentioned U.S. Pat. Nos. 8,614,614 and 9,355,772, which are hereby incorporated by reference herein in their entirety for all purposes. 
     In an aspect with broad applicability to transformers, an improved tap changer assembly  132  is provided. A first example embodiment of a tap changer assembly  132  and components thereof is shown and described with reference to  FIGS. 2A-2E  herein. The tap changer assembly  132  may be included on each of the high-voltage outer coils  114 . For example, the tap changer assembly  132  can be provided as an extension from a front of the high-voltage outer coil  114 . More particularly, the tap changer assembly  134  can be, as shown in  FIG. 1B , an extension from the columnar front extension  126 E, and can be conical in shape. 
     The tap changer assembly  132  has multiple taps  234  (4 in the present embodiment) configured to allow voltage adjustments (e.g., +/− from a nominal (N) voltage) across the high-voltage outer coil  114 . For example, with four taps  234  shown in  FIG. 2B , adjustments of +5%, +2.5%, Normal (N), −2.5%, −5% can be made. Other % variations are possible by tapping at different points on the high-voltage outer coil  114 . Other numbers of taps  234  are possible, such as 4, 5, 6, or more, thus allowing finer gradations of voltage adjustments. The voltage adjustments can be made via various interconnections between respective pairs of the taps  234  with a bridge  235 . The bridge  235  can be a conductive strap, such as a highly-conductive metal (e.g., copper or aluminum, and the like, for example). Other conductive metals can be used. Ends of the bridge  235  may be connected between two selected taps  234  by conductive fasteners  237  (e.g., stainless steel fasteners) to facilitate connection to a location along the coils in the high-voltage outer coil  114 . 
       FIG. 4  illustrates an example schematic diagram of the taps  234  ( 4  shown) and their connections to the high-voltage outer coil  114 . The high-voltage outer coil  114  is shown as a number of coil windings or turns symmetric about a centerline (CL) axis. For illustration purposes, the coil  114  has been split into first portion  114 A, second portion  114 B, and third portion  114 C. Interconnecting across various taps  234  can allow current flow through all or some smaller portion of the high-voltage outer coil  114 . For example, coupling tap  1  with tap  3  via bridge  235  (solid line) can provide a nominal (N) voltage across the coil  114  by enabling current flow through first portion  114 A and second portion  114 B of the high-voltage outer coil  114 . Taps  234  used in order to adjust the quantity of windings of the high voltage outer coil  114  to a voltage of the network. 
     Alternatively, connection of bridge  235  (dotted line) between tap  1  and tap  4  can provide more turns for a lower voltage (e.g., −5% voltage from the nominal (N) voltage) across the high-voltage outer coil  114  by enabling current flow only through first portion  114 A of the high-voltage outer coil  114 . In another option, connection of the bridge  235  (dotted line) between tap  1  and tap  2  can provide the turns for a higher voltage (e.g., +5% voltage from the nominal (N) voltage) across the high-voltage outer coil  114  by enabling current flow through first portion  114 A, the second portion  114 B, and the third portion  114 C of the high-voltage outer coil  114 . Other incremental changes in voltage may be accomplished by choosing larger or small portions for the second portion  114 B and third portion  114 C. Furthermore, other numbers of taps  234  can be used. For example, a 5 voltage level adjustment (e.g., −5%, −2.5%, normal (N), +2.5%, and +5%) can be achieved using 6 taps. 
     Again referring to  FIG. 2C , the tap changer assembly  132  includes a first molding  236  including the multiple taps  234  (e.g., 4 taps in the disclosed embodiment). The multiple taps  234  can be contained in a tap cavity  238  of the first molding  236 . The first molding  236  can be molded about the high-voltage outer coil  114  by any suitable molding process, such as vacuum molding, injection molding, and the like using a suitable mold having the desired final outer dimensions ensuring suitable insulation about the high-voltage outer coil  114 . Taps  234  may be positioned and held in place using threaded inserts during molding or casting in a mold, for example. 
     One especially suited process is vacuum resin casting. During resin casting, a vacuum may applied to a mold inlet, such as an upper inlet, while resin is provided to another mold inlet, such as the lower inlet. Application of vacuum withdraws air from any area that will receive insulation and prevents the formation of air bubbles as the resin fills the intended area. Formation of air bubbles may result in electrical discharge when the high-voltage outer coil  114  is energized. Insulation insertion and/or removal processes are described, for example, in U.S. Patent Application Publication No. US 2014/0118101 A1, which is hereby incorporated by reference herein in its entirety for all purposes. In some embodiments, the first molding  236  may be formed from an epoxy resin, polyurethane, polyester, silicone, or the like. Other suitable insulating materials may be employed. Example resins can include, for example, ARADUR® HY 926 CH and/or Araldite® CY 5948 available from Huntsman Quimica Brasil Ltda. of Sao Paulo, Brazil. 
     The tap changer assembly  132  further includes a semi-conductive coating  240  applied to an outer surface  242  of the first molding  236 . In particular, the entire outer surface of the first molding  236  can be painted with the semi-conductive coating  240 . The semi-conductive coating  240  can be a semi-conductive paint. Semi-conductive coating  240  has an electrical resistivity at room temperature of greater than or equal to 500 Ohm/□ and lower than or equal to 20,000 Ohm/□ in some embodiments. Electrical resistivity at room temperature is measured per DIN EN 62631-3-2. 
     Example semi-conductive coatings  240  can be made from an epoxy material including a conductive pigment, or a polyester or polyurethane resin with mineral loading, such as coal, for example. Other suitable semi-conductive coating materials can be used. 
     The semi-conductive coating  240  may include a coating thickness of between about 30 microns and 500 microns, or even between 30 microns and 200 microns, for example. Other suitable thicknesses can be used. Semi-conductive coating  240  may be applied by any suitable process, such as bush, rolling, spraying, and dipping. Semi-conductive coating  240  may be applied over the entire surface of the first molding  236 , but should not be applied to the terminals. 
     The tap changer assembly  132  further includes a conductive shield  244  provided adjacent to and preferably in electrical contact with the semi-conductive coating  240 . The conductive shield  244  can be an electrically-conductive metal sheet, film, foil, mesh, and the like. The conductive shield  244  can be a conductive metal, such as stainless steel, aluminum, copper, and the like. The conductive shield  244  should be highly electrically conductive. For example, the conductive shield  244  should have an electrical conductivity of greater than or equal to 1.0×10 3  S/m, and greater than or equal to 1.0×10 5  S/m in some embodiments. Conducting shield  244  is applied to the cylindrical outside portions of the coil  114 , to the respective upper and lower ends of the coil  114 , to the cylindrical inner portion of the coil  114 , to the columnar extension  126   e , and at least to the sides of portion of the first molding  236  of the tap changer assembly  132 . Thickness of the conductive shielding  244  can be between about 0.01 mm and 2 mm, or between about 0.05 mm and 0.2 mm in some embodiments, for example. Other suitable thicknesses can be used. In some embodiments the conductive shielding  244  can include perforations or other suitable void patterns thereon to allow casting material to leave no void between the first molding  236  and the second molding  252  during molding/casting. Further, the perforations or void patterns can improve mechanical fixation between conductive shielding  244  and the surrounding casting material, and may also improve expansion capability due to warming and cooling of the high-voltage outer coil  114  in operation. In terms of function, the conductive shield  244  should have an electrical resistance of less than or equal to 5 Ohm measured per IEEE C57.12.91 between any location on the conductive shielding  244  and the ground terminal  128 . 
     The tap changer assembly  132  further includes a grounding member  245 . Grounding member  245  can be comprised of a ring of bosses  246  interconnected by a grounding conductor  248  as best shown in  FIGS. 2D-2E . Six equally-spaced bosses  246  are shown, but more or less can be used. The grounding conductor  248  can be an electrically-conductive metal wire, such as a copper, brass, or aluminum wire having a diameter of between about 0.1 mm and 10 mm, and between about 1 mm and 5 mm in some embodiments, for example. Other dimensions are possible. The metal wire can be provided in the form of a broken ring, which makes it easier to assemble the grounding member  245  in the mold. 
     The grounding conductor  248  can be connected to a bottom of each of the bosses  246  by fill  251  (e.g., metal fill) formed by braising, soldering, welding, and the like. Fill material  251  can seal the bottom of the threaded passage  253 . Bosses  246 , as shown in  FIG. 2E , can have a head portion  247  that can be cylindrical in shape, i.e., comprising a head portion having a circular shape in transverse cross section, and a body  249  that can be hexagonal in shape, i.e., a bottom portion having a hexagonal shape in transverse cross section, for example. Other shapes are possible. 
     The head portion  247  can be made smaller than the body  249  so that the second molding  252  can envelop the bosses  246  and retain them in place within the second molding  252 . Grounding member  245  can include a grounding interconnector  250 . Grounding interconnector  250  can connect between the grounding conductor  248  and the conductive shield  244 , and thus ground between the bosses  246  and the conductive shield  244 . A connector  254 , such as a rivet, crimp, or other mechanical fastener can be used to electrically interconnect the grounding interconnector  250  and the end portion of the conductive shield  244 . 
     Again referring to  FIG. 2C , the tap changer assembly  132  further includes a second molding  252  applied over the conductive shield  244  and the grounding member  245 . The second molding  252  includes a molded sealing surface  255 . The second molding  252  can have a thickness of between about 0.5 mm and 20 mm above the conductive shield  244 . Each of the first molding  236  and the second molding  252  can include tapered draft surfaces formed at an angle of about 5 degrees to 20 degrees to aid in removal from the mold. Other draft angles may be employed. 
     The conductive cover  258  is electrically coupled to the ring of bosses  246 , such as by a corresponding ring of fasteners  262 . Fasteners can be made from any electrically-conductive and corrosion resistant material such as stainless steel. Conductive cover  258  can be made of a corrosion resistant and electrically-conductive metal, such as brass, stainless steel, or the like. In some embodiments, the same material can be used for the second molding  252  as was for the first molding  236 . However, optionally, a different casting material can be considered for the second molding  252 . For example, the casting material can be a two-part, heat-activated epoxy, wherein no pressure is applied during the casting process for the second molding  252 . 
     Tap changer assembly  132  further includes a sealing member  256  configured to seal between a molded sealing surface  255  and an undersurface of the conductive cover  258 . Sealing member  256  can be of any suitable form and material to provide a water-tight seal. For example, sealing member  256  may be an O-ring seal, made of a silicone material, for example. Optionally, the sealing member can be a flexible gasket, such as a silicone gasket. Other suitable resilient or polymer materials can be used, such as rubber, fluorocarbon elastomer, and the like. The molded sealing surface  255  of the second molding  252  can be an O-ring groove, for example. However, in some embodiment, the molded sealing surface  255  can be a smooth molded surface and an O-ring groove may be cut into the bottom of the conductive cover  258 . The conductive cover  258  can further include one or more fill ports  267  that can be used to fill the taps cavity  238  with any suitable non-conductive sealant material, such as a potting compound or encapsulant material. For example, a two-part non-urethane encapsulant can be used. 
     Submersible dry-type transformers  100  including tap changer assemblies  132  provided in accordance with embodiments described herein may have lower material costs than other transformer designs. For example, the material cost of the sealing surface can be lower than the cost of using metal sealing components. The simplicity of the casting or molding of the molded sealing surface and labor time required for producing the tap changer assembly may also reduce costs. 
     With reference to  FIGS. 3A and 3B , an alternative embodiment of a tap changer assembly  332  is shown and described. Components of this tap changer assembly  332  can be molded as a separately-molded member  370  and then combined with the first molding  336 . In particular, the grounding member  245  comprising a ring of bosses  246  interconnected by a grounding conductor  248  as shown in  FIG. 2D , and the second molding  352  applied over at least a portion of the conductive shield  344  and the grounding conductor  248  comprises the separately-molded member  370 . A semi-conductive coating  340  can be applied to the inner surface of the conductive shield prior to molding. The separately-molded member  370  can be molded or cast in a separate process and mold including the contours of the separately-molded member  370  shown, for example. A portion  378  of the conductive shield  344  may not be provided in the mold and may be left unmolded/uncast. The remaining items of  FIG. 3A-3B  can be the same as discussed above for  FIG. 2C . 
     In the depicted embodiment of  FIG. 3B , the tap changer assembly  332  can comprise a third molding  372  applied over at least a portion of the second molding  352  and at least a portion of the first molding  336 . As installed, the tap changer assembly  332  can include an opening  374  in the separately-molded member  370  being received over a pilot  376  formed on the first molding  336 . Thus, it should be understood that the separately-molded member  370  is molded or cast as a separate piece and is mechanically joined with the first molding  336  in the depicted embodiment. The portion  378  of the conductive shield  344  that is unmolded/uncast, i.e., bare, can be folded over and placed in electrical contact with the portion of the conductive shield on the first molding  336  as the separately-molded member  370  is joined with the first molding  336 . The separately-molded member  370  can be held in place against the portion of the conductive shield  344  on the first molding  336  as the third molding  372  is applied. Electrically-conductive grease or an electrically-conductive resin may be applied at the interface of the portion  378  and the conductive shield  344  on the first molding  336 . 
     Now referring to  FIG. 5 , in some embodiments, a method of forming a tap changer assembly (e.g., tap changer assembly  132 ,  332 ) of a dry-type transformer (e.g., dry-type transformer  100 ) is provided. The method  500  includes, in  502 , forming a first molding (e.g., first molding  236 ,  336 ) including the multiple taps (e.g., taps  234  whose interconnection can control a voltage across the high-voltage outer coil  114 ). The forming of the first molding  236  can be by vacuum casting, injection molding, and the like and provides the coil housing  126  of an insulating coating all around the high-voltage outer coil  114  and around the sides and bottom of taps  234 . The first molding  236  can form the columnar front extension  126 E and the extending parts of the high voltage terminals  118 , the upper and lower delta terminals  122 ,  124 , and grounding terminal  128 . 
     The method  500  further includes, in  504 , applying a semi-conductive coating (e.g., semi-conductive coating  240 ) to the first molding (e.g., first molding  236 ,  336 ). The semi-conductive coating should be applied all over the surface  242  of the first molding  236 ,  336 , except on the terminal connections. 
     Further, the method  500  includes, in  506 , providing a conductive shield (e.g., conductive shield  244 ) overtop at least some, and preferably a substantial portion of the semi-conductive coating (e.g., semi-conductive coating  240 ). 
     Moreover, the method  500  includes, in  508 , providing a grounding member (e.g., grounding member  245 ) comprising a ring of bosses (e.g., bosses  246 ) interconnected by a grounding conductor (e.g., grounding conductor  248 ). 
     The method  500  further includes, in  510 , applying a second molding (e.g., second molding  252 ,  352 ) over at least a portion of the conductive shield (e.g., conductive shield  244 ,  344 ) and the grounding conductor (e.g., grounding conductor  248 ), wherein the second molding includes the molded sealing surface (e.g., molded sealing surface  255 ). The portion of the conductive shield  244 ,  344  covered by the second molding  252  can be at least the portion extending outwardly from the conductive shield portion underneath the columnar front extension  126 E. 
     Additionally, the method  500  can further include, in  512 , providing a sealing member (e.g., sealing member  256 ) seated against the molded sealing surface (e.g., molded sealing surface  255 ), and coupling (e.g., via conductive fasteners  262 ) a conductive cover (e.g., conductive cover  258 ) to the ring of bosses (e.g., bosses  246 ) wherein the sealing member seals between the conductive cover and the molded sealing surface. The sealing member  256  seals the tap cavity  238 ,  338 . 
     While the present disclosure is described primarily with regard to submersible dry-type transformers, it will be understood that the disclosed tap changer assemblies may also be employed with other types of transformers or coil assemblies including shielding. 
     The foregoing description discloses only example embodiments. Modifications of the above-disclosed assemblies and methods which fall within the scope of this disclosure will be readily apparent to those of ordinary skill in the art. For example, although the examples discussed above are illustrated for dry-type transformers, other embodiments in accordance with this disclosure can be implemented for other devices. This disclosure is not intended to limit the invention to the particular assemblies and/or methods disclosed, but, to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the scope of the claims.