Patent Publication Number: US-6663039-B2

Title: Process for manufacturing an electrical-power transformer having phase windings formed from insulated conductive cabling

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of German application DE 101 32 718.8, filed Jul. 5, 2001 in Germany. 
     1. Field of the Invention 
     The present invention relates to magnetic-induction devices such as electrical-power transformers. More specifically, the invention relates to the manufacture of an electrical-power transformer having phase windings formed from insulated conductive cabling. 
     2. Background of the Invention 
     Electrical-power transformers are used extensively in electrical and electronic applications. Transformers transfer electric energy from one circuit to another circuit through magnetic induction. Transformers are utilized to step electrical voltages up or down, to couple signal energy from one stage to another, and to match the impedances of interconnected electrical or electronic components. Transformers are also used to sense current, and to power electronic trip units for circuit interrupters. Transformers may also be employed in solenoid-equipped magnetic circuits, and in electric motors. The term “distribution transformer” is used to describe electrical-power transformers having power ratings of approximately 50 kVA to approximately 2,000 kVA; distribution transformers typically have high-voltage windings rated at approximately 10 kV to approximately 20 kV. 
     A typical electrical-power transformer includes two or more multi-turned coils of wire commonly referred to as “phase windings.” The phase windings are placed in close proximity so that the magnetic fields generated by the windings are coupled when the transformer is energized. Most electrical-power transformers have a primary winding and a secondary winding. The output voltage of a transformer can be increased or decreased by varying the number of turns in the primary winding in relation to the number of turns in the secondary winding. 
     The magnetic field generated by the current passing through the primary winding is typically concentrated by winding the primary and secondary windings on a core of magnetic material. More particularly, the primary and secondary windings are placed on one or more winding legs of the core. This arrangement increases the level of induction in the primary and secondary windings so that the windings can be formed from a smaller number of turns while still maintaining a given level of magnetic-flux. In addition, the use of a magnetic core having a continuous magnetic path ensures that virtually all of the magnetic field established by the current in the primary winding is induced in the secondary winding. 
     An alternating current flows through the primary winding when an alternating voltage is applied to the winding. The value of this current is limited by the level of induction in the winding. The current produces an alternating magnetomotive force that, in turn, creates an alternating magnetic flux. The magnetic flux is constrained within the core of the transformer and induces a voltage across the secondary winding. This voltage produces an alternating current when the secondary winding is connected to an electrical load. The load current in the secondary winding produces its own magnetomotive force that, in turn, creates a further alternating flux that is magnetically coupled to the primary winding. A load current then flows in the primary winding. This current is of sufficient magnitude to balance the magnetomotive force produced by the secondary load current. Thus, the primary winding carries both magnetizing and load currents, the secondary winding carries a load current, and the core carries only the flux produced by the magnetizing current. 
     FIG. 1 depicts a three-phase distribution transformer  100  of conventional design. The transformer  100  comprises a magnetic core  101 . The magnetic core  101  comprises a first winding leg  102 , a second winding leg  104 , and a third winding leg  106 . The transformer  100  also comprises an upper yoke  108  and a lower yoke  110 . The winding legs  102 ,  104 ,  106  and the upper and lower yokes  108 ,  110  each comprise a plurality of laminae  120  formed from a suitable magnetic material such as textured silicon steel or an amorphous alloy. The winding legs  102 ,  104 ,  106  and the upper and lower yokes  108 ,  110  are each formed by stacking (superposing) a respective set of laminae  120  to a predetermined depth and binding the laminae  120  using a suitable means such as adhesive. 
     Opposing ends of the winding legs  102 ,  104 ,  106  are fixedly coupled to the upper and lower yokes  108 ,  110  using a suitable means such as adhesive. A cylindrical phase winding  112  is positioned on each of the winding legs  102 ,  104 ,  106 . Each phase winding  112  comprises a low-voltage primary winding  112   a  and a concentric, high-voltage secondary winding  112   b  located radially outward of the primary winding  112   a . The primary and secondary windings  112   a ,  112   b  are each formed by multiple layers, or coils, of conductive cabling connected in series. Each layer is formed by a plurality of turns of the conductive cabling connected in series. 
     The conductive cabling used to form the phase windings  112  is typically non-insulated cabling. The use of non-insulated cabling necessitates the placement of an electrically-insulative material within the phase windings  112 . More particularly, a solid, electrically-insulative material such as epoxy resin is typically placed between adjacent turns, and between adjacent layers within the phase winding  112 . (The phase windings of oil-filled transformers are further insulated by the mineral oil that surrounds the phase windings within such transformers.) 
     The placement of insulation between the adjacent turns and layers of the phase winding  112  is necessary to prevent short-circuiting that would otherwise occur due to the differing electric potential between the adjacent layers and turns. Insulation is also necessary to prevent short circuiting between adjacent phase windings  112 , and between the phase windings  112  and adjacent conductive components. The solid insulative material is placed individually over each cable layer, and between adjacent turns in the particular layer, immediately after the layer has been wound. Hence, installation of the solid insulative material must be integrated into the winding process for each phase winding  112 . 
     The phase winding  112  can alternatively be formed from insulated conductive cabling (as shown in FIG.  1 ). For example, PCT application serial no. PCT/SE/9700875 (international publication no. WO 97/45847) discloses a transformer winding formed from an insulated conductive cable having an inner conductor surrounded by a concentric layer of semi-conductor material. The layer of semi-conductor material is surrounded by a concentric layer of solid insulative material. The layer of solid insulative material is surrounded by a concentric second layer of semi-conductor material that forms the outermost portion of the cable. Forming a phase winding from insulated conductive cabling eliminates the need to install additional solid insulative material within the phase winding as the phase winding is wound. Another example of insulated conductive cabling suitable for use in forming the phase winding  112  is disclosed in pending U.S. patent application Ser. No. 09/541,523, filed Apr. 3, 2000, which is incorporated herein by reference in its entirety. 
     The transformer  100  may be manufactured in accordance with the following conventional process. The phase windings  112  are formed using a suitable mandrel. More particularly, the mandrel is assembled, a primary winding  112   a  is wound thereon, and the corresponding secondary winding  112   b  is wound over the primary winding  112   a . The mandrel is subsequently disassembled to permit removal of the completed phase winding  112  therefrom. This process is repeated until the phase windings  112  for each of the winding legs  102 ,  104 ,  106  have been completed. 
     The winding legs  102 ,  104 ,  106  are fixedly coupled to the lower yoke  110  (the resulting assembly is commonly referred to as an “E-core”). Each completed phase winding  112  is subsequently placed over a respective winding leg  102 ,  104 ,  106 , and may be secured to the winding leg  102 ,  104 ,  106  by a suitable means such as brackets  107 . The upper yoke  108  is then fixedly coupled to the winding legs  102 ,  104 ,  106 . 
     An alternative conventional manufacturing process for the transformer  100  comprises placing the winding legs  102 ,  104 ,  106  in a suitable winding machine individually, winding the primary windings  112   a  directly on the winding legs  102 ,  104 ,  106 , and then winding the secondary winding  112   b  on each primary winding  112   a . The upper and lower yokes  108 ,  110  are subsequently coupled to the winding legs  102 ,  104 ,  106 . The presence of the phase windings  112  on the winding legs  102 ,  104 ,  106  usually necessitates the use of a suitable fixture to support the winding legs  102 ,  104 ,  106  as the upper and lower yokes  108 ,  110  are joined thereto. 
     Each of the above-described activities adds to the time and expense associated with manufacturing the transformer  100 . For example, the use of a mandrel to form the phase windings  112  requires the assembly and disassembly of the mandrel each time a phase winding  112  is formed. Winding the phase windings  112  directly on the winding legs  102 ,  104 ,  106  in the alternative process requires that each winding leg  102 ,  104 ,  106  be installed in and removed from a winding machine, and then placed in a support fixture so that the upper and lower yokes  108 ,  110  can be joined thereto. In addition, the stresses imposed on the winding legs  102 ,  104 ,  106  require that the laminae  120  that form the winding legs  102 ,  104 ,  106  be bound together more strongly than would otherwise be required. 
     Both of the above-described processes for assembling the transformer  100  require that the phase windings  112  be installed on the winding legs  102 ,  104 ,  106  prior to final assembly of the magnetic core  101 . This requirement represents a disadvantage because manufacture of the magnetic core  101  and final assembly of the transformer  100  often take place at different locations. Shipping the magnetic core  101  from its place of manufacture to the final assembly location usually necessitates installing the upper yoke  108  on the assembled E-core on a temporary basis. The upper yoke  108  is subsequently removed from the E-core to facilitate installation of the phase windings  112 . The upper yoke  108  is coupled to the winding legs  102 ,  104 ,  106  on a final basis after the phase windings  112  have been installed. 
     Neither of the above-described manufacturing processes are particularly advantageous when used in connection with a transformer having windings formed from insulated conductive cabling. In particular, insulated conductive cabling can be wound into a phase winding such as the phase winding  112  without a need to integrate a separate insulative material into the winding, as noted previously. Neither of the above-described processes offer manufacturing advantages that stem from this feature. 
     A need therefore exists for a process for manufacturing an electrical-power transformer that requires fewer activities and less equipment than a conventional assembly process. A manufacturing process that permits final assembly of the core without the corresponding phase windings installed thereon is desirable. A manufacturing process that provides advantages associated with the unique manufacturing characteristics of phase windings formed from insulated conductive cabling is also desirable. 
     SUMMARY OF THE INVENTION 
     A presently-preferred process for manufacturing an electrical-power transformer comprises stacking a plurality of laminae to form a first, a second, and a third winding leg and an upper and a lower yoke, and fixedly coupling the first, second, and third winding legs to the lower yoke. The presently-preferred process also comprises winding a first length of insulated conductive cabling on the first winding leg to form a first phase winding, winding a second length of the insulated conductive cabling on the second winding leg to form a second phase winding, and winding a third length of the insulated conductive cabling on the third winding leg to form a third phase winding after coupling the first, second, and third winding legs to the lower yoke. The presently-preferred process further comprises fixedly coupling the first, second, and third winding legs to the upper yoke after forming the first, second, and third phase windings. 
     Another presently-preferred a process for manufacturing an electrical-power transformer comprises stacking a plurality of laminae to form a first, a second, and a third winding leg and an upper and a lower yoke. The presently-preferred process also comprises fixedly coupling the first, second, and third winding legs to the lower yoke, and fixedly coupling the first, second, and third winding legs to the upper yoke. The presently-preferred process further comprises winding a first length of insulated conductive cabling on the first winding leg to form a first phase winding, winding a second length of the insulated conductive cabling on the second winding leg to form a second phase winding, and winding a third length of the insulated conductive cabling on the third winding leg to form a third phase winding after coupling the first, second, and third winding legs to the upper and lower yokes. 
     A presently-preferred process for manufacturing a magnetic-induction device comprises forming a plurality of laminae from a sheet of magnetic material, stacking the plurality of laminae to form a winding leg, a first yoke, and a second yoke, and fixedly coupling a first end of the winding leg to the first yoke. The presently-preferred process also comprises winding a length of insulated conductive cabling on the winding leg to form a phase winding after fixedly coupling the winding leg to the first yoke, and fixedly coupling a second end of the winding leg to the second yoke after forming the phase winding. 
     Another presently-preferred process for manufacturing a magnetic-induction device comprises forming a plurality of laminae from a sheet of magnetic material, stacking the plurality of laminae to form a winding leg, a first yoke, and a second yoke, and fixedly coupling a first end of the winding leg to the first yoke. The presently-preferred process also comprises fixedly coupling a second end of the winding leg to the second yoke, and winding a length of insulated conductive cabling on the winding leg to form a phase winding after fixedly coupling the winding leg to the first and second yokes. 
     Another presently-preferred process for manufacturing an electrical-power transformer comprises assembling an E-core. The presently-preferred process also comprises winding a first length of insulated conductive cabling on a first winding leg of the E-core to form a first phase winding, winding a second length of the insulated conductive cabling on a second winding leg of the E-core to form a second phase winding, and winding a third length of the insulated conductive cabling on a third winding leg of the E-core to form a third phase winding after assembling the E-core. The presently-preferred process further comprises fixedly coupling an upper yoke to the E-core after forming the first, second, and third phase windings. 
     Another presently-preferred process for manufacturing an electrical-power transformer comprises assembling a magnetic core. The presently-preferred process also comprises winding a first length of insulated conductive cabling on a first winding leg of the magnetic core to form a first phase winding, winding a second length of the insulated conductive cabling on a second winding leg of the magnetic core to form a second phase winding, and winding a third length of the insulated conductive cabling on a third winding leg of the magnetic core to form a third phase winding after assembling the magnetic core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of presently-preferred processes, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, the drawings depict a distribution transformer that is capable of being manufactured in accordance with the presently-preferred process. The invention is not limited, however, to use with the specific transformer disclosed in the drawings. In the drawings: 
     FIG. 1 is a diagrammatic illustration of a distribution transformer that can be manufactured in accordance with the presently-preferred process; 
     FIG. 2 is a side view of a fully assembled core of the distribution transformer shown in FIG. 1; 
     FIG. 3 is a partially exploded perspective view of the core shown in FIG. 2; 
     FIG. 4 is a perspective view of a portion of an insulated conductive cable used to form phase windings of the distribution transformer shown in FIG. 1; 
     FIG. 5 is a perspective view of the core shown in FIGS. 2 and 1 in a partially-assembled condition, with phase windings being wound thereon by a first type of winding guide; and 
     FIG. 6 is a perspective view of the core shown in FIGS. 2 and 3, with phase windings being wound thereon by a second type of winding guide. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention relates to the manufacture of a magnetic induction device such as an electrical-power transformer. A presently-preferred process is described in connection with a dry, three-phase, three-legged, core-type distribution transformer. This particular type of electrical-power transformer is described for exemplary purposes only; the presently-preferred process is applicable to virtually any transformer, including single-phase transformers, oil-filled transformers, and transformers having more or less than three legs. Furthermore, the presently-preferred process is applicable to magnetic-induction devices other than distribution transformers. 
     The previously-described transformer  100  can be manufactured in accordance with the presently-preferred process. The presently-preferred process is thus described herein in connection with the transformer  100 , for convenience. Significant details relating to the transformer  100  are repeated below, for clarity. 
     The transformer  100 , and individual components thereof, are depicted in FIGS. 1-6. Details of the transformer  100  in addition those shown in the figures, e.g., an outer casing, are not necessary for an understanding of the presently-preferred process, and therefore are not included in the figures. 
     The transformer  100 , as noted previously, comprises a magnetic core  101 . The magnetic core  101  comprises a first winding leg  102 , a second winding leg  104 , and a third winding leg  106 . The transformer  100  also comprises an upper yoke  108  and a lower yoke  110 . The winding legs  102 ,  104 ,  106  and the upper and lower yokes  108 ,  110  each comprise a plurality of laminae  120 , as described in detail below. (It should be noted that some of the laminae  120  are not depicted in FIGS. 3,  5 , and  6 , for clarity.) 
     Opposing ends of the winding legs  102 ,  104 ,  106  are fixedly coupled to the upper and lower yokes  108 ,  110  using a suitable means such as adhesive. A cylindrical phase winding  112  is positioned on each of the winding legs  102 ,  104 ,  106 . Each phase winding  112  comprises a low-voltage primary winding  112   a  and a concentric, high-voltage secondary winding  112   b  located radially outward of the primary winding  112   a . The primary and secondary windings  112   a ,  112   b  are each formed by multiple layers, or coils, of insulated conductive cabling  122  connected in series. Each layer is formed by a plurality of turns of the cabling  122  connected in series. 
     The insulated conductive cabling  122  is of the type disclosed in PCT application serial no. PCT/SE/9700875. The insulated conductive cabling  122  comprises an inner conductor  122   a  surrounded by a concentric first layer of semi-conductor material  122   b,  as shown in FIG.  4 . The first layer of semi-conductor material  122   b  preferably has a resistivity of approximately 1 Ω-cm to approximately 100 kΩ-cm, and a resistance per unit length of approximately 50 Ω/m to approximately 50 MΩ/m. 
     The first layer of semi-conductor material  122   b  is surrounded by a concentric layer of solid insulative material  122   c . The layer of solid insulative material  122   c  is surrounded by a concentric second layer of semi-conductor material  122   c  that forms the outermost portion of the conductive cabling  122 . The second layer of semi-conductor material  122   d  preferably has a resistivity of approximately 10 −6  Ω-cm to approximately 100 kΩ-cm, and a resistance per unit length of approximately 50 μΩ/m to approximately 5 MΩ/m. (It should be noted that specific details concerning the insulated conductive cabling  122  are presented for exemplary purposes only; the presently-preferred process can be used in connection with insulated conductive cabling having electrical properties and a physical configuration substantially different from those of the insulated conductive cabling  122 .) 
     A first presently-preferred process for manufacturing the transformer  100  is as follows. The winding legs  102 ,  104 ,  106  and the upper and lower yokes  108 ,  110  are each formed from a plurality of laminae  120 , as noted previously. The laminae  120  are cut, punched, or sheared from a sheet of suitable magnetic material such as textured silicon steel or an amorphous alloy. Each lamina  120  is formed with a size and shape corresponding to the constituent element of the magnetic core  101  in which that particular lamina  120  will be used, e.g., the upper yoke  108 . The laminae  120  are subsequently stacked to a predetermined depth and bound using a suitable means such as adhesive, thereby forming the winding legs  102 ,  104 ,  106  and the upper and lower yokes  108 ,  110 . 
     The winding legs  102 ,  104 ,  106  are fixedly coupled to the lower yoke  110  to form an E-core  126  (see FIGS.  3  and  5 ). More particularly, a lower end of the winding leg  102  is fixedly coupled to a first end of the lower yoke  110  using a suitable means such as adhesive. A lower end of the winding leg  106  is fixedly coupled to a second end of the lower yoke  110 , and a lower end of the winding leg  104  is fixedly coupled to the approximate mid-point of the lower yoke  110  in a likewise manner. 
     (It should be noted that directional terms such as “upper” and “lower” are used with reference to the component orientations depicted in FIG. 1; these terms are utilized for illustrative purposes only and, unless expressly stated otherwise, are not intended to limit the scope of the appended claims.) 
     The phase windings  112  are subsequently wound on the E-core  126  while the E-core  126  is in a vertical position, i.e., while the E-core  126  is in the position depicted in FIGS. 3 and 5. More particularly, the insulated conductive cabling  122  is wound on the winding legs  102 ,  104 ,  106  using one or more suitable winding guides  124  (the winding guides  124  are depicted in diagrammatical form in FIG.  5 ). Each winding guide  124  is adapted to draw the insulated conductive cabling  122  from a respective spool located in a reservoir (not shown) above the winding guide  124 . Each winding guide  124  is also adapted to rotate around a respective winding leg  102 ,  104 ,  106  as the winding guide  124  translates linearly in the upward or downward directions. (The direction of rotation, and the direction of linear travel of the winding guides  124  are denoted respectively by the arrows  136 ,  137  in FIG.  5 ). The noted motion of the winding guides  124  winds the insulated conductive cabling  122  around the winding leg  102 ,  104 ,  106  in a series of adjacent turns. 
     The winding guide  124  is adapted to reverse direction upon reaching the upper or lower limits of its linear travel. More particularly, the winding guide  124  begins translating upwardly (while continuing its rotational motion) upon reaching the lower limit of its travel. Similarly, the winding guide  124  begins translating downwardly upon reaching the upper limit of its travel. This motion forms adjacent layers of the insulated conductive cabling  122  on the winding leg  102 ,  104 ,  106 , and is repeated until a predetermined number of layers have been formed, i.e., until a primary winding  112   a  has been wound around the winding legs  102 ,  104 ,  106 . The insulated conductive cabling  122  is then cut to form a terminal on the primary winding  112   a . A secondary winding  112   b  is subsequently wound over the primary winding  112   a  using the above-described winding process. 
     The above-described winding process requires the use of three winding guides  124  to form all of the phase windings  112  on a simultaneous basis (the phase windings  112  may alternatively be formed on a individual basis). For example, FIG. 5 depicts the winding leg  102  at the start of the winding process. FIG. 5 also depicts the winding leg  104  with approximately one-third of the first layer of the primary winding  112   a  wound thereon; the winding leg  106  is depicted with approximately one-half of the first layer of the primary winding  112   a  wound thereon. 
     Forming the phase windings  112  on a simultaneous basis requires synchronization of the winding guides  124  to avoid interference between the winding guides  124  as the winding guides  124  translate upwardly and downwardly. (It should be noted that specific details relating to the winding guides  124  are presented for illustrative purposes only; the above-described winding process can be performed using any suitable winding guide.) 
     The top yoke  108  is fixedly coupled to the E-core  126 , i.e., to the winding legs  102 ,  104 ,  106 , after the phase windings  112  have been wound. More particularly, an upper end of the winding leg  102  is fixedly coupled to a first end of the upper yoke  108  using a suitable means such as adhesive. An upper end of the winding leg  106  is fixedly coupled to a second end of the upper yoke  108 , and an upper end of the winding leg  104  is fixedly coupled to the approximate mid-point of the upper yoke  108  in a likewise manner. 
     An alternative presently-preferred process for manufacturing the transformer  100  is as follows. The laminae  120  are formed and stacked in the above-described manner to form the constituent elements of the magnetic core  101 . The upper and lower yokes  108 ,  110  are fixedly coupled to the winding legs  102 ,  104 ,  106  to form the completed magnetic core  101 . More particularly, a lower end of the winding leg  102  is fixedly coupled to a first end of the lower yoke  110  using a suitable means such as adhesive. A lower end of the winding leg  106  is fixedly coupled to a second end of the lower yoke  110 , and a lower end of the winding leg  104  is fixedly coupled to the approximate mid-point of the lower yoke  110  in a likewise manner. 
     An upper end of the winding leg  102  is then fixedly coupled to a first end of the upper yoke  108  using a suitable means such as adhesive. An upper end of the winding leg  106  is fixedly coupled to a second end of the upper yoke  108 , and an upper end of the winding leg  104  is fixedly coupled to the approximate mid-point of the upper yoke  108  in a likewise manner. 
     The phase windings  112  are subsequently wound on the assembled magnetic core  101  while the magnetic core  101  is in a vertical position, i.e., while the magnetic core  101  is in the position depicted in FIG.  6 . More particularly, the insulated conductive cabling  122  is wound on the winding legs  102 ,  104 ,  106  using one or more suitable winding guides  132  (see FIG.  6 ). (It should be noted that the winding guides  132  are depicted in diagrammatical form in FIG. 6; specific details of a winding guide suitable for use with the presently-preferred method are disclosed in U.S. Pat. No. 3,174,699, which is incorporated herein by reference in its entirety.) 
     Operational details relating to the winding guides  132  are as follows. A length of the insulated conductive cabling  122  sufficient to form one of the primary windings  112   a  is placed in each of the winding guides  132 . The winding guides  132  each rotate around a respective winding leg  102 ,  104 ,  106  while translating linearly, in the upward or downward directions (the direction of rotation, and the direction of linear travel of the winding guides  132  are denoted respectively by the arrows  138 ,  139  in FIG.  6 ). This motion draws the insulated conductive cabling  122  from the winding guide  132 , and winds the insulated to conductive cabling  122  around the corresponding winding leg  102 ,  104 ,  106  in a series of adjacent turns. 
     The winding guide  132  is adapted to reverse its direction upon reaching the upper or lower limits of its linear travel. More particularly, the winding guide  132  begins translating upwardly (while continuing its rotational motion) upon reaching the lower limit of its travel. Similarly, the winding guide  132  begins translating downwardly upon reaching the upper limit of its travel. This motion forms adjacent layers of the insulated conductive cabling  122  on the winding legs  102 ,  104 ,  106 , and is repeated until a predetermined number of layers have been formed, i.e., until a primary winding  112   a  has been wound around the winding leg  102 ,  104 ,  106 . A secondary winding  112   b  is subsequently wound over the primary winding  112   a  in a likewise manner. 
     The winding process described above uses three of the winding guides  132  to form all of the phase windings  112  on a simultaneous basis. For example, FIG. 6 depicts the winding leg  102  at the start of the winding process. FIG. 6 also depicts the winding leg  104  with approximately one-third of the first layer of the primary winding  112   a  wound thereon; the winding leg  106  is depicted with approximately one-half of the first layer of the primary winding  112   a  wound thereon. Forming the phase windings  112  in this manner is only possible where the winding legs  102 ,  104 ,  106  are spaced apart sufficiently to prevent interference between adjacent winding guides  132 . (It should be noted that specific details relating to the winding guides  132  are presented for illustrative purposes only; the above-described winding process can be performed using any suitable winding guide.) 
     The presently-preferred processes for manufacturing an electrical-power transformer provides substantial advantages in relation to conventional processes. For example, winding the phase windings  112  directly on the winding legs  102 ,  104 ,  106  eliminates the need for mandrels during the manufacturing process. Hence, the expenses associated with purchasing mandrels, and the activities associated with assembling and disassembling the mandrels before and after each phase winding  12  is formed, can be eliminated through the use of the presently-preferred processes. 
     Special fixtures are not needed to support the winding legs  102 ,  104 ,  106  and the corresponding phase windings  112  during the presently-preferred processes because the phase windings  112  are placed on the winding legs  102 ,  104 ,  106  after the E-core  126  or the entire magnetic core  101  have been assembled. This feature also negates the need for a winding machine to form the phase windings  112 , thereby eliminating the time and expense associated with the use thereof. Eliminating the use of a winding machine also negates the need to bind the laminae  120  within the winding legs  102 ,  104 ,  106  more strongly than would otherwise be required to withstand the stresses imposed by the winding machine. 
     The presently-preferred manufacturing processes permit the phase windings  112  to be wound on a fully-assembled core, and thereby provide additional advantages. For example, the magnetic core  101  can be assembled on a final basis at its place of manufacture, and then shipped to another location for final assembly of the transformer  100 . In other words, the upper yoke  108  can be placed on the E-core  126  at a first location, and the phase windings  112  can subsequently be placed on the magnetic core  101  at another location without removing the upper yoke  108 . This feature is advantageous because, as previously noted, cores such as the magnetic core  101  are often manufactured at a location that differs from the location at which the transformer  100  is assembled. 
     Both of the presently-preferred processes are particularly well-suited for use with insulated conductive cabling such as the insulated conductive cabling  122 . More particularly, the insulated conductive cabling  122  can be formed into the phase windings  112  without a need to place additional insulative material between the turns and layers of the phase windings  112 , as noted previously. Hence, the phase windings  112  can be formed using a minimal amount of relatively simple, compact equipment such as the winding guides  124 ,  132 ; equipment that would otherwise be required to place additional insulative material in the phase windings  112  is not needed. In other words, the insulated conductive cabling  122  is particularly well suited for being wound directly onto the partially or fully assembled magnetic core  101  because the insulated conductive cabling  122  can be wound into the phase windings  112  using only the winding guides  124 ,  132 . 
     In addition, the primary and secondary windings  112   a ,  112   b  can be wound on a substantially continuous basis because additional insulative material does not have to be placed between adjacent turns and adjacent layers of the insulated conductive cabling  122 . In other words, the winding process does not have to be interrupted to facilitate the placement of additional insulative material within the phase windings  112 . The winding guides  124 ,  132  are particularly well suited for winding operations conducted on a continuous basis. Hence, the winding guides  124 ,  132  can form the phase windings  112  in a minimal amount of time when used in conjunction with the insulated conductive cabling  122 . 
     It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with specific details of a presently-preferred processes, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of the parts described herein, within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.