Patent Publication Number: US-11657961-B2

Title: Method and conductor structure for manufacturing an electric winding of an electromagnetic induction apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/EP2020/087937 filed on Dec. 28, 2020, which in turns claims priority to European Patent Application No. 20154715.5, filed on Jan. 30, 2020, the disclosures and content of which are incorporated by reference herein in their entirety. 
     BACKGROUND 
     The present disclosure relates to the field of electromagnetic induction apparatuses for electric power transmission and distribution grids, for example power transformers. 
     More particularly, the present disclosure relates to a method and a conductor structure for manufacturing an electric winding of an electromagnetic induction apparatus. 
     Electric windings of electromagnetic induction apparatuses may be manufactured at industrial level according to various methods. 
     A widely used method consists in winding a conductor around a winding direction, so that the electric winding has a plurality of adjacent turns arranged around said winding direction. 
     As it is known, generally, electric windings for electromagnetic induction apparatuses have axial and radial channels to ensure the passage of an electrically insulating medium (e.g. insulating fluid or solid cast resin) among the turns. 
     Traditionally, the axial channels of an electric winding are obtained by arranging insulating blocks oriented in parallel to the winding direction while electrically insulating spacers interposed between adjacent turns of the electric winding and oriented radially with respect to the winding direction are arranged to define the radial channels. 
     According to most traditional solutions of the state of the art, the above-mentioned insulating spacers are inserted manually between each pair of adjacent turns, during the winding process. 
     According to more recent manufacturing methods, insulating spacers are fixed along a suitable lateral surface of a conductor intended to form the turns of the electric winding. The conductor structure so obtained is then wound around a winding direction. In this way, insulating spacers take position between each pair of adjacent turns of said electric winding. 
     State-of-the-art electric windings for electromagnetic induction apparatuses generally perform their functions in a rather satisfying way. However, there are still some aspects to deal with. 
     In operation, electric windings often show deformed turns, particularly at the regions where radial channels are present. 
     Basically, this phenomenon is due to the fact that, in operation, an electric winding is subject to huge compressive forces along directions substantially parallel to its winding direction. 
     The above-illustrated technical issue may lead to a dangerous unbalancing condition of the overall winding structure, which may cause its collapse in certain operating conditions, e.g. when short-circuit currents flow along the electric winding and this latter is subject to huge mechanical stresses. DE 26 53 315 A relates to an isolating- and distancing body for axial isolation and distancing of coil conductors, wherein the isolating- and distancing body fills partly the space in between the conductors, and is formed by an upright isolation stripe which is adjustable to the curvature of the conductors. WO 2019/238558 A1 relates to a band that is applied to a side surface of the multiple parallel conductor in the longitudinal direction of the multiple parallel conductor. The band consists of spacer plates that are arranged in a manner distributed in the longitudinal direction on a strip. The multiple parallel conductor together with the strip and the spacer plates is wrapped with a wrapping. CN 209 496 640 U discloses an oil duct belt for a transposed conductor. The oil duct belt comprises an insulating layer and an insulating oil duct strip arranged on the insulating layer. The insulating oil duct strip comprises a plurality of isolation blocks, which are sequentially arranged at intervals, and a first oil way channel is formed between every two adjacent isolation blocks. 
     SUMMARY 
     The present disclosure provides a method and a conductor structure for manufacturing an electric winding of an electromagnetic induction apparatus, which allows the above-mentioned aspects to be overcome or mitigated. 
     Within this aim, another object of the present disclosure is providing a method and a conductor structure for manufacturing an electric winding, which allow obtaining an electric winding with a high structural balancing and a high resistance to mechanical stresses. Another object of the present disclosure is providing a method and a conductor structure for manufacturing an electric winding, which are relatively easy and inexpensive to implement at industrial level. 
     This aim and these objects, together with other objects that will be more apparent from the subsequent description and from the accompanying drawings, are achieved, according to the disclosure, by a method for manufacturing an electric winding of an electromagnetic induction apparatus, according to claim  1  and to the related dependent claims. 
     In a general definition, the method, according to some embodiments, comprises the following steps:
         providing a conductor structure comprising a conductor element extending longitudinally along a main extension direction and one or more spacer bands arranged on a corresponding lateral surface of said conductor element. Each spacer band includes a supporting structure made of electrically insulating material and spacer elements made of electrically insulating material arranged on said supporting structure. Said spacer elements are spaced one from another, along said supporting structure;   forming an electric winding by means of said conductor structure. Said electric winding extends axially along a winding direction and it has a plurality of turns arranged around said winding direction.       

     According to some embodiments, each turn of said electric winding is formed by a corresponding longitudinal portion of said conductor element. 
     According to some embodiments, said spacer elements are interposed between adjacent turns of said electric winding at opposite sides of said turns, when said electric winding is formed. 
     According to some embodiments, said spacer elements are arranged in such a way to bond with the surface of an adjacent turn, when said electric winding is formed. 
     According to some embodiments, said spacer elements are formed by shaped pads of electrically insulating material. 
     In some embodiments, said shaped pads of electrically insulating material are glued on said supporting structure. 
     In some embodiments, said shaped pads of electrically insulating material have a surface, on which a layer of gluing material is deposited. 
     According to some embodiments, said spacer elements are formed by shaped regions of electrically insulating material. 
     In some embodiments, said shaped regions of electrically insulating material are deposited on said supporting structure. 
     According to some embodiments, each spacer band includes spacer elements arranged on a same supporting surface of said supporting structure. 
     According to other embodiments, each spacer band includes spacer elements arranged on opposite supporting surfaces of said supporting structure. 
     According to other embodiments, each spacer band includes spacer elements arranged in such a way to pass through said supporting structure and protrude from opposite surfaces of said supporting structure. 
     According to some embodiments, each spacer band includes spacer elements made in one piece with said supporting structure. 
     According to some embodiments, each spacer band includes spacer elements randomly arranged on said supporting structure. 
     According to preferred embodiments, each spacer band includes spacer elements arranged on said supporting structure according to a predefined geometric pattern. 
     In some embodiments, said spacer bands are fixed to said conductor element by gluing or by means of an electrically insulating enclosure element wound around said conductor element. 
     In some embodiments, said conductor element is a continuously transposed conductor. 
     In a further aspect, the present disclosure relates to a conductor structure for manufacturing an electric winding of an electromagnetic induction apparatus according to the following claim  17 . 
     The conductor structure, according to some embodiments, comprises: 
     a conductor element extending longitudinally along a main extension direction; and 
     one or more spacer bands arranged on a corresponding lateral surface of said conductor element. Each spacer band includes a supporting structure made of electrically insulating material and spacer elements made of electrically insulating material arranged on said supporting structure. Said spacer elements are spaced one from another, along said supporting structure. 
     According to some embodiments, each turn of said electric winding is formed by a corresponding longitudinal portion of said conductor element. 
     According to some embodiments, said spacer elements are interposed between adjacent turns of said electric winding at opposite sides of said turns, when said electric winding is formed. 
     In yet a further aspect, some embodiments relate to an electric winding for an electromagnetic induction apparatus, according to the following claim  18 . 
     In yet a further aspect, some embodiments relate to an electromagnetic induction apparatus for electric power transmission and distribution grids according to the following claim  19 . 
     In some embodiments, said electromagnetic induction apparatus is an electric transformer for electric power transmission and distribution grids. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics and advantages will be more apparent with reference to the description given below and to the accompanying figures, provided purely for explanatory and non-limiting purposes, wherein: 
         FIG.  1    schematically shows a conductor element used in the manufacturing method and conductor structure, according to some embodiments; 
         FIG.  2    schematically shows an electric winding for an electromagnetic induction apparatus obtained by means of the manufacturing method, according to some embodiments; 
         FIGS.  2 A,  2 B  schematically show opposite views of a turn portion of the electric winding of  FIG.  2   ; 
         FIGS.  3 - 4    schematically show a conductor structure, according to some embodiments; 
         FIGS.  5 - 6    schematically show some details of a spacer band included a conductor structure, according to some embodiments; 
         FIG.  7    schematically shows a conductor structure, according to another embodiment; 
         FIG.  8    schematically shows some details of a spacer band included a conductor structure, according to another embodiment; 
         FIGS.  9 ,  10  and  11    schematically shows a conductor structure, according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the aforesaid figures, the present disclosure relates to a method for manufacturing an electric winding  100  of an electromagnetic induction apparatus (not shown) for electric power transmission and distribution grids. 
     Such an electromagnetic induction apparatus may be an electric transformer for electric power transmission and distribution grids, for example a power transformer or a distribution transformer. 
     The manufacturing method, according to the disclosure, comprises a step of providing a conductor structure  1  intended to form the electric winding  100 . 
     The conductor structure  1  comprises a conductor element  2  extending longitudinally along a main extension direction L ( FIG.  1   ). 
     In some embodiments, the conductor element  2  is shaped as an elongated parallelepiped including conductive material. 
     In some embodiments, the conductor element  2  has a shaped section (e.g. a rectangular or square cross section), opposite first and second lateral surfaces  2 A,  2 B and opposite third and fourth lateral surfaces  2 C,  2 D. 
     According to some embodiments of the disclosure, the conductor element  2  is a continuously transposed conductor. 
     In this case, the conductor element  2  may be manufactured according to the construction shown in  FIG.  1   . 
     According to this embodiment of the disclosure, the conductor element  2  comprises two or more stacks  21 ,  22  of conductors, which are placed side by side along the extension direction L of said conductor element. 
     Stacked conductors  20  have portions alternating between the above-mentioned stacks  21 ,  22 . In this way, portions of stacked conductors  20  alternately occupy every possible cross section position along the whole longitudinal extension of the conductor element  2 . 
     Stacked conductors  20  may be at least partially covered by electrically insulating material. 
     The conductor element  2  may include an insulating separator  23  arranged between the stacks  21 ,  22  of conductors along the extension direction L of said conductor. 
     The conductor element  2  may include an insulating band or mesh (not shown) wound around the stacked conductors  20  to maintain these latter in position during the winding operations. 
     According to other embodiments of the disclosure, however, the conductor element  2  may have different constructions (which may be of known type). 
     For example, it may include a single conductor, a plurality of conductors arranged side by side or a bundle of twisted conductors. 
     As a further example, the conductor element  2  may be formed by one or more conductive bars or by one or more conductive foils or disks. 
     According to some embodiments of the disclosure (not shown), the conductor structure  1  include one or more layers of electrically insulating material (not shown) arranged in such a way to externally cover the conductor element  2 . 
     Such an electrically insulating material may be arranged according to solutions of known type. For example, it may be selected in a group of materials comprising: paper, polyester materials, aramid or stabilized-PE materials, fiberglass materials, and the like. 
     The conductor structure  1  comprises one or more spacer bands  3  arranged on a same corresponding lateral surface  2 A or  2 B of the conductor element  2 . 
     Each spacer band  3  includes a supporting structure  30  made of electrically insulating material and a plurality of spacer elements  31  made of electrically insulating material and arranged on said supporting structure. 
     Conveniently, the spacer elements  31  of each spacer band  3  are spaced one from another along the supporting structure  30  to delimit suitable empty regions  32  ( FIG.  3 ,  4 ,  7   ). 
     According to the method of the disclosure, once the conductor structure  1  is obtained, it is carried out a step of forming the electric winding  100  by means of said conductor structure. The electric winding  100  extends axially along the winding direction DW ( FIG.  2   ). 
     In some embodiments, e.g. when the conductor structure can be bent by means of a suitable bending apparatus, the step of forming the electric winding  100  includes winding the conductor structure  1  around the winding direction DW. 
     According to alternative embodiments, e.g. when the conductor structure cannot be bent, the step of forming the electric winding  100  may include the step of mechanically connecting separated portions of the conductor structure  1  to form the electric winding  100 . 
     The electric winding  100  has a plurality of adjacent turns  101  arranged around the winding direction DW ( FIG.  2   ). 
     Each turn  101  is formed by a corresponding longitudinal portion of the conductor element  2  included in the winding structure  1 . 
     In the electric winding  100 , the first and second lateral surfaces  2 A,  2 B of the conductor element  2  are positioned perpendicular to the winding direction DW and form opposite first and second sides  101 A,  101 B of each turn  101 , which extend radially with respect to said winding direction. 
     On the other hand, the third and fourth lateral surfaces  2 C,  2 D of the conductor element  2  are positioned parallel to the winding direction DW and form third and fourth sides  101 C,  101 D of each turn  101 , which extend parallel and coaxially to said winding direction ( FIGS.  2 A,  2 B ). 
     In the electric winding  1 , due to their positioning along the first and second surfaces  2 A,  2 B of the conductor element  2 , the spacer elements  31  are interposed between adjacent turns  101  at the first and second sides  101 A,  101 B of these latter. 
     In this way, the spacer elements  31  lay on radial planes perpendicular to said the winding direction DW ( FIG.  2   ). 
     The empty regions  32  delimited by the spacer elements  31  form radial channels  104  of the electric winding  100 , which ensure the passage of an electrically insulating medium (e.g. insulating fluid or solid cast resin) among adjacent turns  101 . 
     An important aspect of the disclosure consists in that, in the electric winding  100 , the spacer elements  31 , which are interposed between each pair of adjacent turns  101  and distributed along the sides  101 A,  101 B of said turns, provide a substantially uniform mechanical support to the turns  101  and ensure a stable structural balancing of the electric winding  100 . 
     It has been seen that the solution provided greatly improves the overall resistance of the electric winding  100  to compressive forces as it ensures structural balancing. 
     It is therefore possible to prevent or remarkably mitigate the onset of deformation phenomena of the turns of the electric winding  100  during the operation of the electromagnetic induction apparatus. 
     In some embodiments, the supporting structure  30  of each spacer band  3  is formed by an elongated element of electrically insulating material having a reduced thickness (e.g. some millimeters) and two main opposite supporting surfaces  30 A,  30 B. 
     According to some embodiments, the supporting structure  30  of each spacer band  3  may be formed by a strip of electrically insulating material. 
     According to other embodiments, the supporting structure  30  of each spacer band  3  may be formed by a molded element of electrically insulating material. 
     According to yet another embodiment, the supporting structure  30  of each spacer band  3  may be formed by a mesh of electrically insulating material. 
     In some embodiments, the electrically insulating material used for the supporting structure  30  is selected in a group of materials comprising: paper, plastic materials, fiberglass materials, nylon-based materials. 
     In some embodiments, the supporting structure  30  has a holed or netting structure to favor the passage of heat during the operation of the electric winding  100 . 
     According to some embodiments ( FIGS.  3 - 4   ), the spacer bands  3  have the spacer elements  31  arranged on a same supporting surface  30 A of the supporting structure  30 . In this case, the opposite supporting surface  30 B of the supporting structure  30  is intended to lay on a lateral surface  2 A,  2 B of the conductor element  2 . 
     According to other embodiments (not shown), the spacer bands  3  have the spacer elements  31  arranged on both the opposite supporting surfaces  30 A,  30 B of the supporting structure  30 . 
     According to yet other embodiments, the spacer bands  3  have the spacer elements  31  passing through the thickness of the supporting structure  30  and protruding from the opposite supporting surfaces  30 A,  30 B of the supporting structure  30  ( FIG.  7   ). 
     In principle, the spacer elements  31  may be arranged on the supporting surfaces  30 A and/or  30 B of a supporting structure according to any desired layout. 
     According to some embodiments ( FIGS.  3 ,  7   ), the spacer bands  3  have the spacer elements  31  arranged in a random manner. 
     According to other embodiments ( FIG.  4   ), the spacer bands  3  have the spacer elements  31  arranged according to a predefined geometric pattern. 
     According to some embodiments (in particular where the spacer elements  31  are arranged on a same supporting surface  30 A of the supporting structure  30 ), the spacer bands  3  are fixed to the conductor element  2  by gluing. 
     Each spacer band  3  may be directly fixed to the conductors of the conductor element  2 , or on an insulating layer of said conductor element or on an additional insulating band or mesh surrounding said conductor element. 
     Glue may be applied to a supporting surface  30 B of a supporting structure  30  (opposite to the supporting surface  30 A on which the spacer elements are arranged) and/or to the corresponding lateral surfaces  2 A,  2 B of the conductor element  2  in a known manner, for example by spraying, brushing, dusting, by immersion or by applying a prepreg film activatable by UV radiation or heat. 
     Special glues designed to withstand high temperatures (e.g. up to 250° C.) may be used. 
     The above-describe solutions are quite advantageous. Gluing the one or more spacer bands  3  allows preventing or reducing possible undesired dislocations of these latter. Such dislocations of spacer portions  3 A,  3 B may occur due tangential forces exerted on the winding turns during the operation of the electromagnetic induction apparatus (this phenomenon is also referred to as “spiraling” of the electric winding) or during manufacturing. 
     According to other embodiments (in particular where the spacer elements  31  are arranged on both the supporting surfaces  30 A,  30 B of the supporting structure  30  or pass through it), the spacer bands  3  may be fixed to the conductor element  2  by means of an additional electrically insulating enclosure (e.g. formed by an electrically insulating band or mesh wound around the assembly formed by the conductor element  2  and the one or more spacer tapes  3 ), for example made of a glass-fiber material or polyester. 
     Also, in this case, the one or more spacer tapes  3  may be directly fixed on the conductors  20  of the electrical conductor element  2 , or on an insulating layer of said conductor or on an insulating tape or mesh surrounding said conductor. 
     In principle, the spacer elements  31  may have any shape according to the needs. As an example, they may have a circular shape, a polygonal shape or even an irregular shape. 
     In general, the selected size and distribution density of the spacer elements  31  on the supporting structure  30  depend on the type of the winding  100  to be manufactured (e.g. on the magnitude of the stress forces to which the winding  100  is subject and/or on its cooling requirements). 
     However, the spacer elements  31  may have a relatively small size with respect to the width of the supporting structure  30  on which they are arranged. As an example, they may have a width of 5-10 mm and a height of 2 mm. 
     In general, the supporting structure  30  and the spacer elements  31  are separated elements assembled through a suitable manufacturing process. 
     According to preferred embodiments, the spacer elements  31  are arranged in such a way to bond with the surface of an adjacent turn  101 , when the electric winding  100  is formed. 
     As it will be better discussed below, this solution is quite effective in preventing or reducing possible undesired dislocations due to the above-mentioned “spiraling” phenomenon. 
     According to some embodiments, the spacer elements  31  are formed by shaped pads of electrically insulating material ( FIGS.  5 - 6 ,  8   ). 
     In some embodiments, such an electrically insulating material is selected in a group of materials comprising: pressed paperboard, plastic materials, fiberglass materials, nylon-based materials. 
     In some embodiments, the shaped pads  31  of electrically insulating material are glued on the supporting structure  30 . 
     In some embodiments, when they are arranged on a supporting surface  30 A or  30 B of the supporting structure  30 , the shaped pads  31  of electrically insulating material have a base surface  31 A intended to lay on a supporting surface  30 A or  30 B of the supporting structure  30  and a top surface  31 B, opposite to the base surface  31 A ( FIGS.  5 - 6   ). 
     In some embodiments, the shaped pads  31  of electrically insulating material are glued on a supporting surface  30 A or  30 B of the supporting structure  30  at their base surface  31 A. This can be obtained by depositing a suitable layer  310 A of gluing material (e.g. an epoxy resin) on the base surface  31 A of each shaped pad  31  and/or on the corresponding region of the supporting surface  30 A,  30 B on which each shaped  31  is intended to be positioned. 
     In some embodiments, when they pass through the supporting structure  30 , the shaped pads  31  of electrically insulating material have opposite free surfaces  31 A,  31 B and a lateral surface at which they are glued with a suitable layer of gluing material  310 A with the supporting structure  30  ( FIG.  8   ). 
     In some embodiments, the shaped pads  31  comprise at least a surface  31 A,  31 B on which an additional layer of gluing material  310 B (e.g. an epoxy resin) is deposited. 
     In the embodiment of  FIG.  5   , the additional layer of gluing material  310 B is conveniently deposited on the top surface  31 B of each shaped pad  31  ( FIG.  6   ). 
     In the embodiment of  FIG.  8   , the additional layer of gluing material  310 B may be conveniently deposited on both the opposite surfaces  31 A,  31 B of each shaped pad  31  or on one of them only (in this case the surface in distal position with respect to the conductor  2 ). 
     The arrangement of an additional layer on at least a surface of the shaped pads  31  is quite advantageous as it allows obtaining (by means of a suitable thermal treatment) the bonding of each shaped pad  31  to both the adjacent turns  101  between which it is positioned, once the electric winding  100  is formed. 
     This solution thus allows further improving the overall structural strength of the electric winding  100 . In particular, this solution is quite effective in preventing or reducing possible undesired dislocations due to the above-mentioned “spiraling” phenomenon. 
     In some embodiments, the gluing material  310 A used for gluing the shaped pads  21  to the supporting structure  30  bonds at ambient temperature. 
     In some embodiments, the above-mentioned curing temperature (e.g. 100-140° C.) is higher than said bonding temperature (e.g. ambient temperature). 
     The shaped pads  31  of electrically insulating material may be placed on the supporting structure manually or by means of a suitable equipment, which may be of known type. 
     The layers of gluing material  310 A,  301 B may be arranged manually (e.g. by means a suitable tool) or by means of suitable industrial equipment, which may be of known type. 
     In some embodiments, the gluing material  310 B used for covering at least a surface  31 A,  31 B of the shaped pads  31  has a bonding temperature, at which it bonds (e.g. with the surface of adjacent turn  101 ), and a curing temperature, at which such an electrically insulating material cures. 
     According to some embodiments, the spacer elements  31  are formed by shaped regions of electrically insulating material ( FIG.  9   ). 
     In some embodiments, such an electrically insulating material is a gluing material (e.g. an epoxy resin) or, more generally, a suitable plastic material. 
     In some embodiments, the electrically insulating material used for the shaped regions  31  has a bonding temperature, at which such an electrically insulating material bonds (e.g. with the supporting surface  30 A,  30 B of the supporting structure  30  and the surface of adjacent turn  101 ), and a curing temperature, at which such an electrically insulating material cures. 
     In some embodiments, the above-mentioned curing temperature (e.g. 100-140° C.) is higher than said bonding temperature (e.g. ambient temperature). 
     it is evident that also, according to these embodiment, the spacer elements  31  (in this case formed by shaped regions of electrically insulating material) are arranged in such a way to bond with the surface of an adjacent turn  101 , when the electric winding  100  is formed. 
     In some embodiments, the shaped regions  31  of electrically insulating material are deposited on a supporting surface  30 A,  30 B of the supporting structure  30 , for example in the form of liquid drops. 
     The shaped regions  31  of electrically insulating material may be placed manually (e.g. by means of a suitable tool) or by means of suitable industrial equipment, which may be of known type. 
     Since they may have a different thickness when they are deposited on the supporting structure  30 , the shaped regions  31  of electrically insulating material may be further subject to a flattening process after the deposition. In this way, the thickness of the shaped regions  31  may be suitably equalized. 
     According to other embodiments (not shown), the supporting structure  30  and the spacer elements  31  are made in one piece, e.g. through a moulding process. 
     Also in this case, the spacer elements  31  may have comprise at least a surface on which an additional layer of gluing material (e.g. an epoxy resin) is deposited. 
     According to some embodiments ( FIG.  10   ), the conductor structure  1  comprises a single spacer tape  3  arranged on a same lateral surface  2 A,  2 B of the conductor element  2  along the entire length of this latter. In this case, the spacer elements  3  will be continuously distributed on a same lateral surface  2 A,  2 B along the entire length of the conductor element  2 . 
     According to some embodiments, the conductor structure  1  comprises a plurality of spacer bands  3  arranged on a same lateral surface  2 A,  2 B of the conductor element  2 . 
     In some embodiments, each spacer tape  3  is arranged on at least a lateral surface  2 A,  2 B of a corresponding longitudinal portion of the conductor element  2 , which is intended to form a turn  101  of the electric winding  100  ( FIG.  11   ). 
     In some embodiments, the spacer bands  3  are arranged at selected longitudinal portions  2 E of the conductor element  2 , along the main extension direction L, which are alternate with longitudinal portions  2 F, on which no spacer band is present. 
     Conveniently, each longitudinal portion  2 E,  2 F has a length (measured along the main extension direction L) equal to the length of a turn  101  of the electric winding  100 . 
     The method and the conductor structure may provide relevant advantages. 
     The method and conductor structure may allow obtaining electric windings with a high structural balancing and a high resistance to mechanical stresses, in particular to compression stresses. 
     This may allow preventing or reducing the deformation of the turns of the electric winding in operation with a consequent remarkable increase of the reliability of the electromagnetic induction apparatus in operation, even in presence of fault events or short-circuit events. 
     The method and conductor structure may be relatively easy to implement at industrial level at competitive costs with respect to known solutions of the state of the art.