Patent Publication Number: US-2022230791-A1

Title: Magnetic element

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to China Patent Application No. 202110061302.X, filed on Jan. 18, 2021, the entire contents of which are incorporated herein by reference for all purposes. 
     FIELD OF THE INVENTION 
     The present disclosure relates to a magnetic element, and more particularly to a magnetic element with uniform electric field distribution at the end part of the winding, increased partial discharge extinction voltage, reduced volume, reduced fabricating cost and simplified assembly. 
     BACKGROUND OF THE INVENTION 
     Nowadays, the existing magnetic elements such as dry-type reactors or transformers have many advantages. For example, it is not necessary to make a mold in the production process of the dry-type reactor or the transformer. In addition, the dry-type reactor or the transformer has flexible design, strong overload capability, short production cycle and low cost. Consequently, the dry-type reactor or transformer has been widely used. 
     Generally, the conventional dry-type reactor or transformer includes a magnetic core, a winding and a plurality of support strips. The winding is wound around the magnetic core. The support strips are arranged between the magnetic core and the winding. In addition, the support strips are disposed on the magnetic core to support the winding. The length of each support strip in parallel with the axial direction of the magnetic core is greater than the length between the two endpoints of the winding in parallel with the axial direction of the magnetic core. Moreover, there is no air gaps between the endpoints of the winding and the magnetic core along the radial direction of the magnetic core. Moreover, the winding is not shielded, and the endpoints of the winding are exposed to the air. Since the air breakdown field is low and the electric field strength of the endpoints of the winding is high, the endpoints of the winding are prone to partial discharges. The insulating materials covering the winding or the insulating layers in contact with the winding are readily cracked or even subjected to breakdown. Consequently, accidents possibly occur. 
     In order to solve the partial discharge problem at the endpoints of the winding, the structures of the conventional dry-type reactors or transformers need to be further improved. For example, the following three methods were used to increase the partial discharge extinction voltage to solve the partial discharge problem. In accordance with the first method, the thickness of the support strip is increased, so that the distance between the winding and the magnetic core is increased. However, this method increases the volume, cost, and power density of the dry-type reactor or transformer. In accordance with a second method, a support strip with a low permittivity constant is used. The support strip with the low permittivity constant can be made of polytetrafluoroethylene or polypropylene. However, the cost of polytetrafluoroethylene is not cost-effective, and the mechanical strength of polypropylene is not strong enough. In other words, no suitable material with low dielectric constant can be adopted. In accordance with a third method, equalizing rings are added to the endpoints of the winding. However, the process of installing and welding the winding becomes more complicated. 
     For solving the drawbacks of the conventional technologies, the present disclosure provides an improved magnetic element. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a magnetic element with uniform electric field distribution at the end part of a winding, increased partial discharge extinction voltage, reduced volume, reduced fabricating cost and simplified assembly. 
     In accordance with an aspect of the present disclosure, a magnetic element is provided. The magnetic element includes a magnetic core, at least one support strip assembly, a winding and at least one first air gap. The magnetic core includes a magnetic leg. The at least one support strip assembly is disposed on the magnetic leg. The winding is wound around the at least one support strip assembly, and includes a first end part, a second end part and a first connection part. The first end part and the second end part are respectively connected with two opposite sides of the first connection part. The first end part includes a first endpoint and a second endpoint. The second end part includes a third endpoint and a fourth endpoint. The first endpoint and the second endpoint are connected with each other. The second endpoint is connected with the first connection part. A first projection line is formed between a projection point of the second endpoint on the magnetic leg and the second endpoint. The third endpoint and the fourth endpoint are connected with each other. The fourth endpoint is connected with the first connection part. A second projection line is formed between a projection point of the fourth endpoint on the magnetic leg and the fourth endpoint. A third projection line is formed between a projection point of the first endpoint on the magnetic leg and the first endpoint. A fourth projection line is formed between a projection point of the third endpoint on the magnetic leg and the third endpoint. A connection line between the first endpoint and the third endpoint is the longest distance of the winding in parallel with an axial direction of the magnetic leg. The at least one first air gap is arranged between the magnetic leg and the winding. The at least one first air gap is at least defined by the at least one support strip assembly. A first portion of the at least one first air gap is arranged between the first projection line and the second projection line. A second portion of the at least one first air gap is beyond a region between the third projection line and the fourth projection line through at least one of the third projection line and the fourth projection line. 
     In accordance with another aspect of the present disclosure, a magnetic element is provided. The magnetic element includes a magnetic core, at least one first support strip assembly, a first winding, at least one second support strip assembly, a second winding and at least one first air gap. The magnetic core includes a magnetic leg. The at least one first support strip assembly is disposed on the magnetic leg. The first winding is wound around the at least one first support strip assembly. The at least one second support strip assembly is disposed on the first winding. The second winding is wound around the at least one second support strip assembly, and includes a first end part, a second end part and a first connection part. The first end part and the second end part are respectively connected with two opposite sides of the first connection part. The first end part includes a first endpoint and a second endpoint. The second end part includes a third endpoint and a fourth endpoint. The first endpoint and the second endpoint are connected with each other. The second endpoint is connected with the first connection part. A first projection line is formed between a projection point of the second endpoint on the magnetic leg and the second endpoint. The third endpoint and the fourth endpoint are connected with each other. The fourth endpoint is connected with the first connection part. A second projection line is formed between a projection point of the fourth endpoint on the magnetic leg and the fourth endpoint. A third projection line is formed between a projection point of the first endpoint on the magnetic leg and the first endpoint. A fourth projection line is formed between a projection point of the third endpoint on the magnetic leg and the third endpoint. A connection line between the first endpoint and the third endpoint is the longest distance of the second winding in parallel with an axial direction of the magnetic leg. The at least one first air gap is arranged between the second winding and the first winding. The at least one first air gap is at least defined by the at least one second support strip assembly. A first portion of the at least one first air gap is arranged between the first projection line and the second projection line. A second portion of the at least one first air gap is beyond a region between the third projection line and the fourth projection line through at least one of the third projection line and the fourth projection line. 
     From the above descriptions, the magnetic element of the present disclosure includes at least one first air gap. A first portion of the first air gap is arranged between the first projection line and the second projection line. A second portion of the first air gap is beyond the region between the third projection line and the fourth projection line. In other words, there are air gaps between the end parts of the winding and the magnetic leg. Consequently, the dielectric constant between the first end part of the winding and the magnetic leg and the dielectric constant between the second end part of the winding and the magnetic leg are reduced. Moreover, the electric field distribution of the first end part and the second end part will be more uniform, and the partial discharge extinction voltage will be increased. In other words, the partial discharge problem is solved. The volume and the cost of the magnetic element are both reduced. In addition, the equalizing rings are not required. Consequently, the fabricating process of the magnetic element of the present disclosure is simplified. 
     The above contents of the present disclosure will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a first embodiment of the present disclosure; 
         FIG. 2  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a second embodiment of the present disclosure; 
         FIG. 3  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a third embodiment of the present disclosure; 
         FIG. 4  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a fourth embodiment of the present disclosure; 
         FIG. 5  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a fifth embodiment of the present disclosure; 
         FIG. 6  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a sixth embodiment of the present disclosure; 
         FIG. 7  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a seventh embodiment of the present disclosure; 
         FIG. 8  is a schematic cross-sectional view illustrating the structure of a magnetic element according to an eighth embodiment of the present disclosure; and 
         FIG. 9  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a ninth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present disclosure will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this disclosure are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
     Please refer to  FIG. 1 .  FIG. 1  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a first embodiment of the present disclosure. The magnetic element  1  of this embodiment is suitably applied to a dry-type reactor or a transformer. The magnetic element  1  includes a magnetic core, at least one support strip assembly  3 , a winding  4 , at least one first air gap  5 , a first insulation layer  61  and a second insulation layer  62 . 
     For example, the magnetic core is an EI core, a UI core, an EE core or a UU core. The magnetic core includes at least one magnetic leg  2 . Preferably but not exclusively, the magnetic leg  2  has a shape of a cuboid. The magnetic leg  2  has a plurality of lateral walls  23 . The lateral walls  23  are formed on outer surfaces of the magnetic leg  2  and arranged around an axial direction Y of the magnetic leg  2 . 
     The support strip assembly  3  is used for installing and supporting the winding  4 . In an embodiment, the at least one support strip assembly  3  includes a plurality of support strip assemblies  3 . The plurality of support strip assemblies  3  are disposed on and arranged around the corresponding lateral walls  23  of the magnetic leg  2 , respectively. In another embodiment, the at least one support strip assembly  3  is a single support strip assembly  3  that is disposed on and arranged around the lateral walls  23  of the magnetic leg  2 . In an embodiment, the magnetic leg  2  has the shape of a cuboid, the magnetic leg  2  has four lateral walls  23 , and the magnetic element  1  includes at least two support strip assemblies  3 . The at least two support strip assemblies  3  are disposed on and arranged around the corresponding lateral walls  23  of the magnetic leg  2  or the corresponding edges of the magnetic leg  2 . In this embodiment, the magnetic leg  2  has the shape of a cuboid, and the magnetic leg  2  has four lateral walls  23 . The magnetic element  1  includes four support strip assemblies  3 . The four support strip assemblies  3  are disposed on and arranged around the four lateral walls  23  of the magnetic leg  2  or the four edges of the magnetic leg  2 . For succinctness, only two of the four support strip assemblies  3  in the symmetric arrangement are shown in  FIG. 1 . It is noted that the shape of the magnetic leg  2  is not restricted. For example, in another embodiment, the magnetic leg  2  has a shape of a cylinder and the magnetic leg  2  has a lateral wall  23 . Moreover, the magnetic element  1  includes more than two support strip assemblies  3 , and the support strip assemblies  3  are disposed on and arranged around the lateral walls  23  of the magnetic leg  2 . 
     In this embodiment, the winding  4  includes a first end part  41 , a second end part  42  and a first connection part  43 . The first connection part  43  includes a top side, a bottom side, an outer periphery side, and an inner periphery side. The first end part  41  and the second end part  42  of the winding  4  are connected with the top side and the bottom side of the first connection part  43 , respectively. The first insulation layer  61  is disposed on the inner periphery side of the winding  4 . However, the first insulation layer  61  is not in contact with the first end part  41  and the second end part  42  of the winding  4 . Moreover, at least a portion of the inner periphery side of the first connection part  43  is attached on the first insulation layer  61 . The first end part  41  includes a first endpoint  411  and a second endpoint  412 . The first endpoint  411  is the farthest point of the first end part  41  away from the top side of the first connection part  43 . The first endpoint  411  and the second endpoint  412  are connected with each other. The connection line between the first endpoint  411  and the second endpoint  412  is an inclined line or a curved line. Due to the incline line or the curved line, the first end part  41  has a chamfer. The second endpoint  412  is connected with the top side of the first connection part  43 . A first projection line m is formed between the projection point of the second endpoint  412  on the magnetic leg  2  and the second endpoint  412 . 
     The second end part  42  includes a third endpoint  421  and a fourth endpoint  422 . The third endpoint  421  is the farthest point away from the bottom side of the first connection part  43 . The third endpoint  421  and the fourth endpoint  422  are connected with each other. The connection line between the third endpoint  421  and the fourth endpoint  422  is an inclined line or a curved line. Due to the incline line or the curved line, the second end part  42  has a chamfer. The fourth endpoint  422  is connected with the bottom side of the first connection part  43 . A second projection line n is formed between the projection point of the fourth endpoint  422  on the magnetic leg  2  and the fourth endpoint  422 . 
     In some embodiments, the chamfers of the first end part  41  and the second end part  42  have triangular shapes, trapezoidal shapes, semi-circular shapes or fan shapes. 
     The connection line between the first endpoint  411  of the first end part  41  and the third endpoint  421  of the second end part  42  is the longest distance of the winding  4  in parallel with the axial direction Y of the magnetic leg  2 . A third projection line o is formed between the projection point of the first endpoint  411  on the magnetic leg  2  and the first endpoint  411 . A fourth projection line p is formed between the projection point of the third endpoint  421  on the magnetic leg  2  and the third endpoint  421 . The vertical distance between the third projection line o and the fourth projection line p is greater than the vertical distance between the first projection line m and the second projection line n. In this context, the direction of the vertical distance is in parallel with the axial direction Y of the magnetic leg  2 . 
     The second insulation layer  62  is disposed on and arranged around the outer periphery side of the first connection part  43  of the winding  4 . The second insulation layer  62  is used for isolating the winding  4  from the external component. The first end part  41  and the second end part  42  of the winding  4  are not in contact with the second insulation layer  62 . The outer periphery side of the first connection part  43  of the winding  4  are at least partially attached on the second insulation layer  62 . 
     Preferably but not exclusively, the first insulation layer  61  and the second insulation layer  62  are NOMEX papers or composite insulation papers. It is noted that the installation examples of the first insulation layer  61  and the second insulation layer  62  may be varied according to the practical requirements. For example, in an embodiment, the first insulation layer  61  is disposed on the inner periphery side of the first connection part  43  of the winding  4  and/or the second insulation layer  62  is disposed on the outer periphery side of the first connection part  43  of the winding  4 . Alternatively, the first insulation layer  61  is not disposed on the inner periphery side of the first connection part  43  of the winding  4  and/or the second insulation layer  62  is not disposed on the outer periphery side of the first connection part  43  of the winding  4 . That is, the winding  4  is directly disposed on and arranged around the support strip assembly  3 . 
     The number of the first air gaps  5  and the number of the support strip assemblies  3  are equal. In addition, the locations of the first air gaps  5  correspond to the locations of the support strip assemblies  3 . For example, in this embodiment, the magnetic element  1  includes four support strip assemblies  3  and four first air gaps  5 . For succinctness, only two support strip assemblies  3  and two first air gaps  5  corresponding to the two support strip assemblies  3  are shown in the drawing. Each first air gap  5  is at least defined by the adjacent support strip assembly  3 . In addition, each first air gap  5  is arranged between the winding  4  and the magnetic leg  2 . A first portion of the first air gap  5  is arranged between the first projection line m and the second projection line n. A second portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through at least one of the third projection line o and the fourth projection line p. 
     As mentioned above, the magnetic element  1  includes at least one first air gap  5 . A first portion of the first air gap  5  is arranged between the first projection line m and the second projection line n. A second portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through at least one of the third projection line o and the fourth projection line p. In other words, there are air gaps between the winding  4  and the magnetic leg  2  along the radial direction of the magnetic leg  2 . In comparison with the conventional magnetic element without the air gaps, the dielectric constant at the end parts of the winding  4  is largely reduced. Since the dielectric constant between the first end part  41  of the winding  4  and the magnetic leg  2  and the dielectric constant between the second end part  42  of the winding  4  and the magnetic leg  2  are reduced, the electric field distribution of the first end part  41  and the second end part  42  will be more uniform and the partial discharge extinction voltage will be increased. In other words, the partial discharge problem is solved. The volume and the cost of the magnetic element  1  are both reduced. In addition, the equalizing rings are not required. Consequently, the fabricating process of the magnetic element  1  of the present disclosure is simplified. 
     Please refer to  FIG. 1  again. Each first air gap  5  includes a first upper air gap part  51  and a first lower air gap part  52 . The first upper air gap part  51  is closer to the first end part  41  of the winding  4  than the first lower air gap part  52 . The first lower air gap part  52  is closer to the second end part  42  of the winding  4  than the first upper air gap part  51 . In this embodiment, each support strip assembly of the magnetic element  1  includes the first support strip  31  and the second support strip  32 . The cross section of the first support strip  31  and/or the second support strip  32  along the radial direction of the magnetic leg  2  is not restricted as long as the air gap can be defined by the first support strip  31 , the second support strip  32  and the magnetic leg  2  collaboratively. Preferably but not exclusively, the cross section of the first support strip  31  and/or the second support strip  32  along the radial direction of the magnetic leg  2  is L-shaped, rectangle, square, etc. The first support strip  31  is disposed on the magnetic leg  2  and arranged between the magnetic leg  2  and the second support strip  32 . In addition, the first support strip  31  has a top surface  31   a  and a bottom surface  31   b . The top surface  31   a  and the bottom surface  32   b  are opposed to each other. The second support strip  32  is disposed on the first support strip  31  and arranged between the first support strip  31  and the winding  4 . The second support strip  32  is used for installing and supporting the winding  4 . In addition, the second support strip  32  has a top surface  32   a  and a bottom surface  32   b . The top surface  32   a  and the bottom surface  32   b  are opposed to each other. The top surface  32   a  of the second support strip  32  is closer to the top surface  31   a  of first support strip  31  than the bottom surface  32   b  of the second support strip  32 . The bottom surface  32   b  of the second support strip  32  is closer to the bottom surface  31   b  of first support strip  31  than the top surface  32   a  of the second support strip  32 . In an embodiment, the first support strip  31  and the second support strip  32  are separate components. In some other embodiments, the first support strip  31  and the second support strip  32  are integrally formed as a one-piece structure. 
     The top surface  32   a  of the second support strip  32  is located at a level higher than the top surface  31   a  of the first support strip  31 . Consequently, the first upper air gap part  51  is defined by the magnetic leg  2 , the top surface  31   a  of the first support strip  31  and the second support strip  32  collaboratively. The first portion of the first upper air gap part  51  is arranged between the first projection line m and the top surface  31   a  of the first support strip  31 . That is, the first portion of the first upper air gap part  51  is arranged between the first projection line m and the second projection line n. The second portion of the first upper air gap part  51  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. 
     The bottom surface  32   b  of the second support strip  32  is located at a level lower than the bottom surface  31   b  of the first support strip  31 . Consequently, the first lower air gap part  52  is defined by the magnetic leg  2 , the bottom surface  31   b  of the first support strip  31  and the second support strip  32  collaboratively. The first portion of the first lower air gap part  52  is arranged between the second projection line n and the bottom  31   b  of the first support strip  31 . That is, the first portion of the first lower air gap part  52  is arranged between the first projection line m and the second projection line n. The second portion of the first lower air gap part  52  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     In this embodiment, the distance between the projection point of the first endpoint  411  of the first end part  41  on the magnetic leg  2  and the projection point of the second endpoint  412  of the first end part  41  on the magnetic leg  2  is smaller than the depth of the first upper air gap part  51 . That is, the vertical distance between the first projection line m and the third projection line o is smaller than the depth of the first upper air gap part  51 . The direction of the depth of the first upper air gap part  51  is in parallel with the axial direction Y of the magnetic leg  2 . The distance between the projection point of the third endpoint  421  of the second end part  42  on the magnetic leg  2  and the projection point of the fourth endpoint  422  of the second end part  42  on the magnetic leg  2  is smaller than the depth of the first lower air gap part  52 . That is, the vertical distance between the second projection line n and the fourth projection line p is smaller than the depth of the first lower air gap part  52 . The direction of the depth of the first lower air gap part  52  is in parallel with the axial direction Y of the magnetic leg  2 . 
     The present disclosure further provides other possible embodiments of the magnetic elements. In the following embodiments, the magnetic element also has at least one first air gap  5 . Like the first embodiment, a first portion of the first air gap  5  is arranged between the first projection line m and the second projection line n, and a second portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through at least one of the third projection line o and the fourth projection line p. The benefits of the air gap are similar, and not redundantly described herein. 
     Please refer to  FIG. 2 .  FIG. 2  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a second embodiment of the present disclosure. The magnetic element  1   a  includes a magnetic core, at least one support strip assembly  3 , a winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2  and the winding  4  of the magnetic element  1   a  in this embodiment are similar to those of  FIG. 1 , and not redundantly described herein. Component parts and elements corresponding to those of the first embodiment are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In this embodiment, the support strip assembly  3  includes a single support strip. The cross section of the support strip along the radial direction of the magnetic leg  2  is not restricted as long as the air gap can be defined by the support strip and the magnetic leg  2  collaboratively. Preferably but not exclusively, the cross section of the support strip along the radial direction of the magnetic leg  2  is L-shaped, rectangle, square, etc. The support strip has an inner surface  331 , an outer surface  332 , a top surface  333  and a bottom surface  334 . The inner surface  331  and the outer surface  332  of the support strip are opposed to each other. The top surface  333  and the bottom surface  334  of the support strip are opposed to each other. In addition, the top surface  333  and the bottom surface  334  are arranged between the inner surface  331  and the outer surface  332 . The top surface  333  of the support strip is closer to the first end part  41  of the winding  4  than the bottom surface  334  of the support strip. The bottom surface  334  of the support strip is closer to the second end part  42  of the winding  4  than the top surface  333  of the support strip. The inner surface  331  of the support strip is contacted with the magnetic leg  2 . The winding  4  is disposed on the outer surface  332  of the support strip. 
     In this embodiment, the first air gap  5  includes a first upper air gap part  51  and a first lower air gap part  52 . The first upper air gap part  51  is defined by the magnetic leg  2 , the top surface  333  of the support strip and the winding  4  collaboratively. In addition, the first lower air gap part  52  is defined by the magnetic leg  2 , the bottom surface  334  of the support strip and the winding  4  collaboratively. The first portion of the first upper air gap part  51  is arranged between the first projection line m and the top surface  333  of the support strip  31 . That is, the first portion of the first upper air gap part  51  is arranged between the first projection line m and the second projection line n. The second portion of the first upper air gap part  51  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. A first portion of the first lower air gap part  52  is arranged between the second projection line n and the bottom surface  334  of the support strip. That is, the first portion of the first lower air gap part  52  is arranged between the first projection line m and the second projection line n. The second portion of the first lower air gap part  52  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     In this embodiment, the length of the support strip is substantially equal to the distance between the top surface  333  and the bottom surface  334  of the support strip. The length of the support strip is greater than 80% of the distance between the first endpoint  411  of the first end part  41  and the third endpoint  421  of the second end part  42 . In addition, the length of the support strip is smaller than the distance between the projection point of the second endpoint  412  of the first end part  41  on the magnetic leg  2  and the projection point of the fourth end point  422  of the second end part  42  on the magnetic leg  2 . The direction of the support strip is in parallel with the axial direction Y of the magnetic leg  2 . Since the length of the strip is specially designed, the support strip can support the winding  4  and prevent the winding  4  from falling off the support strip. Due to this structure design, the dielectric constant between the first end part  41  and the second end part  42  of the winding  4  on the magnetic leg  2  is reduced. Consequently, the electric field distribution of the first end part  41  and the second end part  42  will be more uniform and the partial discharge extinction voltage will be increased. In other words, the partial discharge problem is solved. The volume and the cost of the magnetic element  1   a  are both reduced. Consequently, the fabricating process of the magnetic element  1   a  of the present disclosure is simplified. 
     Please refer to  FIG. 3 .  FIG. 3  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a third embodiment of the present disclosure. The magnetic element  1   b  includes a magnetic core, at least one support strip assembly  3 , a winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2  and the winding  4  of the magnetic element  1   b  in this embodiment are similar to those of  FIG. 1 , and not redundantly described herein. Component parts and elements corresponding to those of the first embodiment are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In this embodiment, the support strip assembly  3  includes a single support strip. The support strip has an inner surface  331 , an outer surface  332 , a top surface  333  and a bottom surface  334 . The inner surface  331  and the outer surface  332  of the support strip are opposed to each other. The top surface  333  and the bottom surface  334  of the support strip are opposed to each other. In addition, and the top surface  333  and the bottom surface  334  are arranged between the inner surface  331  and the outer surface  332 . The top surface  333  of the support strip is closer to the first end part  41  of the winding  4  than the bottom surface  334  of the support strip. The bottom surface  334  of the support strip is closer to the second end part  42  of the winding  4  than the top surface  333  of the support strip. 
     In addition, the support strip includes an upper region and a lower region. The upper region is the region of the support strip which is closer to the top surface  333  of the support strip. The lower region is the region of the support strip which is closer to the bottom surface  334  of the support strip. The inner surface  331  of the support strip is contacted with the magnetic leg  2 . The winding  4  is disposed on the outer surface  332  of the support strip. 
     In this embodiment, the first air gap  5  includes at least one vacant space. The at least one vacant space is formed by drilling the support strip from a sidewall of the support strip. Each first air gap  5  includes a single first upper air gap part  51  and a single first lower air gap part  52 . The first upper air gap part  51  is formed in the corresponding upper region of the support strip. That is, the first upper air gap part  51  is closer to the top surface  333  of the support strip. In addition, the first lower air gap part  52  is formed in the corresponding lower region of the support strip. That is, the first lower air gap part  52  is closer to the bottom surface  334  of the support strip. In this embodiment, a first portion of the first upper air gap part  51  is arranged between the first projection line m and the second projection line n. A second portion of the first upper air gap part  51  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. In addition, a first portion of the first lower air gap part  52  is arranged between the first projection line m and the second projection line n. A second portion of the first lower air gap part  52  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     In some embodiments, each of the first upper air gap part  51  and the first lower air gap part  52  includes at least one vacant space. The at least one vacant space is formed by drilling the support strip from the inner surface  331  of the support strip. Consequently, the first upper air gap part  51  is formed in the corresponding upper region of the support strip and located adjacent to the top surface  333 , and the first lower air gap part  52  is formed in the corresponding lower region of the support strip and located adjacent to the bottom surface  334 . 
     Please refer to  FIG. 4 .  FIG. 4  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a fourth embodiment of the present disclosure. The magnetic element  1   c  includes a magnetic core, at least one support strip assembly  3 , a winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2  and the winding  4  of the magnetic element  1   c  in this embodiment are similar to those of  FIG. 1 , and not redundantly described herein. Component parts and elements corresponding to those of the first embodiment are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In this embodiment, the support strip assembly  3  includes a single support strip. The length of the support strip in parallel with the axial direction Y of the magnetic leg  2  is greater than or equal to the length between the first endpoint  411  and the third endpoint  421 . The support strip includes an inner surface  331 , an outer surface  332 , a top surface  333  and a bottom surface  334 . The inner surface  331  and the outer surface  332  of the support strip are opposed to each other. The top surface  333  and the bottom surface  334  of the support strip are opposed to each other. In addition, the top surface  333  and the bottom surface  334  are arranged between the inner surface  331  and the outer surface  332 . The top surface  333  of the support strip is closer to the first end part  41  of the winding  4  than the bottom surface  334  of the support strip. The bottom surface  334  of the support strip is closer to the second end part  42  of the winding  4  than the top surface  333  of the support strip. The inner surface  331  of the support strip is contacted with the magnetic leg  2 . The winding  4  is disposed on the outer surface  332  of the support strip. 
     In this embodiment, the first air gap  5  includes at least one first upper air gap part  51  and at least one first lower air gap part  52 . 
     For example, each first upper air gap part  51  is a vacant space that is formed by drilling the support strip from the top surface  333  toward the bottom surface  334  of the support strip. The shape of the vacant space is not restricted. The at least one first upper air gap part  51  has a first depth h 1  in parallel with axial direction Y of the magnetic leg  2 . The number of the at least one first upper air gap part  51  is one or more than one. In case that the at least one first upper air gap part  51  is a single upper air gap part, the first upper air gap part  51  has the first depth h 1  in parallel with the axial direction Y of the magnetic leg  2 . In case that the at least one first upper air gap part  51  includes a plurality of first upper air gap parts, each first upper air gap part  51  has a first depth h 1  in parallel with axial direction Y of the magnetic leg  2 , or at least one of the plurality of first upper air gap parts  51  has the first depth h 1  in parallel with axial direction Y of the magnetic leg  2 . A first projection line m is formed between the projection point of the second endpoint  412  on the magnetic leg  2  and the second endpoint  412 . A third projection line o is formed between the projection point of the first endpoint  411  on the magnetic leg  2  and the first endpoint  411 . In an embodiment, the vertical length between the first projection line m and the third projection line o is smaller than the first depth h 1 . 
     Similarly, each first lower air gap part  52  is a vacant space that is formed by drilling the support strip from the bottom surface  334  toward the top surface  333  of the support strip. The at least one first lower air gap part  52  has a second depth h 2  in parallel with the axial direction Y of the magnetic leg  2 . The number of the at least one first lower air gap part  52  is one or more than one. In case that the at least one first lower air gap part  52  is a single lower air gap part, the first lower air gap part  52  has the second depth h 2  in parallel with the axial direction Y of the magnetic leg  2 . In case that the at least one first lower air gap part  52  includes a plurality of first lower air gap parts, each first lower air gap part  52  has a second depth h 2  in parallel with axial direction Y of the magnetic leg  2 , or at least one of the plurality of first lower air gap parts  52  has the second depth h 2  in parallel with axial direction Y of the magnetic leg  2 . A second projection line n is formed between the projection point of the fourth endpoint  422  on the magnetic leg  2  and the fourth endpoint  422 . A fourth projection line p is formed between the projection point of the third endpoint  421  on the magnetic leg  2  and the third endpoint  421 . The vertical length between the second projection line n and the fourth projection line p is smaller than the second depth h 2 . 
     In this embodiment, the sum of the first depth h 1  of the first upper air gap part  51  and the second depth h 2  of the first lower air gap part  52  is smaller than the length of the support strip assembly  3  in parallel with the axial direction Y of the magnetic leg  2 . In this embodiment, each first upper air gap part  51  is exposed to the top surface  333  of the support strip, and each first lower air gap part  52  is exposed to the bottom surface  334  of the support strip. 
     Please refer to  FIG. 5 .  FIG. 5  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a fifth embodiment of the present disclosure. The magnetic element  1   d  includes a magnetic core, at least one support strip assembly  3 , a winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2  and the winding  4  of the magnetic element  1   d  in this embodiment are similar to those of  FIG. 1 , and not redundantly described herein. Component parts and elements corresponding to those of the first embodiment are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In this embodiment, the support strip assembly  3  includes a single support strip. The length of the support strip in parallel with the axial direction Y of the magnetic leg  2  is greater than the length between the first endpoint  411  and the third endpoint  421  of the winding  4 . The support strip includes an inner surface  331 , an outer surface  332 , a top surface  333  and a bottom surface  334 . The inner surface  331  and the outer surface  332  of the support strip are opposed to each other. The top surface  333  and the bottom surface  334  of the support strip are opposed to each other. In addition, the top surface  333  and the bottom surface  334  are arranged between the inner surface  331  and the outer surface  332 . The top surface  333  of the support strip is closer to the first end part  41  of the winding  4  than the bottom surface  334  of the support strip. The bottom surface  334  of the support strip is closer to the second end part  42  of the winding  4  than the top surface  333  of the support strip. The inner surface  331  of the support strip is contacted with the magnetic leg  2 . The winding  4  is disposed on the outer surface  332  of the support strip. 
     In this embodiment, the first air gap  5  includes at least one first upper air gap part  51  and at least one first lower air gap part  52 . 
     For example, each first upper air gap part  51  is a vacant space that is formed by drilling the upper region of the support strip from a sidewall of the support strip. Similarly, each first lower air gap part  52  is a vacant space that is formed by drilling the lower region of the support strip from a sidewall of the support strip. 
     The at least one first upper air gap part  51  has a first depth h 1 . The direction of the first depth h 1  is in parallel with axial direction Y of the magnetic leg  2 . The number of the at least one first upper air gap part  51  is one or more than one. In case that the at least one first upper air gap part  51  includes a plurality of first upper air gap parts, each first upper air gap part  51  has a first depth h 1  in parallel with axial direction Y of the magnetic leg  2 , or at least one of the plurality of first upper air gap parts  51  has the first depth h 1  in parallel with axial direction Y of the magnetic leg  2 . A first projection line m is formed between the projection point of the second endpoint  412  on the magnetic leg  2  and the second endpoint  412 . A third projection line o is formed between the projection point of the first endpoint  411  on the magnetic leg  2  and the first endpoint  411 . The vertical length between the first projection line m and the third projection line o is smaller than the first depth h 1 . 
     The at least one first lower air gap part  52  has a second depth h 2 . The direction of the second depth h 2  is in parallel with axial direction Y of the magnetic leg  2 . The number of the at least one first lower air gap part  52  is one or more than one. In case that the at least one first lower air gap part  52  includes a plurality of first lower air gap parts, each first lower air gap part  52  has a second depth h 2  in parallel with axial direction Y of the magnetic leg  2 , or at least one of the plurality of first lower air gap parts  52  has the second depth h 2  in parallel with axial direction Y of the magnetic leg  2 . A second projection line n is formed between the projection point of the fourth endpoint  422  on the magnetic leg  2  and the fourth endpoint  422 . A fourth projection line p is formed between the projection point of the third endpoint  421  on the magnetic leg  2  and the third endpoint  421 . The vertical length between the second projection line n and the fourth projection line p is smaller than the second depth h 2 . 
     In this embodiment, the sum of the first depth h 1  of the first upper air gap  51  and the second depth h 2  of the first lower air gap  52  is smaller than the length of the support strip assembly  3  in parallel with the axial direction Y of the magnetic leg  2 . In addition, in this embodiment, each first upper air gap part  51  is not exposed to the top surface  333  of the support strip. That is, each first upper air gap  51  is arranged between the top surface  333  and the bottom surface  334  of the support strip. Similarly, each first lower air gap part  52  is not exposed to the bottom surface  334  of the support strip. That is, each first lower air gap  52  is arranged between the top surface  333  and the bottom surface  334  of the support strip. 
     Please refer to  FIG. 6 .  FIG. 6  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a sixth embodiment of the present disclosure. The magnetic element  1   e  includes a magnetic core, at least one support strip assembly  3 , a winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2  and the winding  4  of the magnetic element  1   e  in this embodiment are similar to those of  FIG. 1 , and not redundantly described herein. Component parts and elements corresponding to those of the first embodiment are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In this embodiment, the support strip assembly  3  includes a single support strip. The length of the support strip in parallel with the axial direction Y of the magnetic leg  2  is greater than or equal to the length between the first endpoint  411  and the third endpoint  421  of the winding  4 . The support strip includes an inner surface  331 , an outer surface  332 , a top surface  333  and a bottom surface  334 . The inner surface  331  and the outer surface  332  of the support strip are opposed to each other. The top surface  333  and the bottom surface  334  of the support strip are opposed to each other. In addition, the top surface  333  and the bottom surface  334  are arranged between the inner surface  331  and the outer surface  332 . The top surface  333  of the support strip is closer to the first end part  41  of the winding  4  than the bottom surface  334  of the support strip. The bottom surface  334  of the support strip is closer to the second end part  42  of the winding  4  than the top surface  333  of the support strip. The inner surface  331  of the support strip is contacted with the magnetic leg  2 . The winding  4  is disposed on the outer surface  332  of the support strip. 
     In this embodiment, the magnetic element  1   e  includes at least one first air gap  5 . The at least one first air gap  5  runs through the top surface  333  and the bottom surface  334  of the support strip. For example, the first air gap  5  is formed by drilling the support strip from the top surface  333  to the bottom surface  334 , so that at least one vacant space is formed in the support strip. 
     The number of the at least one first air gap  5  is one or more than one. In case that at least one first air gap  5  includes a single first air gap  5 , the first air gap  5  runs through the top surface  333  and the bottom surface  334  of the support strip. A first portion of the first air gap  5  is arranged between the first projection line m and the second projection line n. A second portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. In addition, a third portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     In case that at least one first air gap  5  includes a plurality of first air gaps  5 , the plurality of first air gaps  5  are formed between the inner surface  331  and the outer surface  332  of the support strip and arranged sequentially. Moreover, all of the plurality of first air gaps  5  run through the top surface  333  and the bottom surface  334  of the support strip, or at least one of the plurality of first air gaps  5  runs through the top surface  333  and the bottom surface  334  of the support strip. Moreover, in all of the plurality of first air gaps  5  or in at least one of the plurality of first air gaps  5 , a first portion of the first air gap  5  is arranged between the first projection line m and the second projection line n, a second portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o, and a third portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     Please refer to  FIG. 7 .  FIG. 7  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a seventh embodiment of the present disclosure. The magnetic element if includes a magnetic core, at least one support strip assembly  3 , a winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2  and the winding  4  of the magnetic element  1   f  in this embodiment are similar to those of  FIG. 1 , and not redundantly described herein. Component parts and elements corresponding to those of the first embodiment are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In this embodiment, the support strip assembly  3  includes two first support strips  31  and a second support strip  32 . The two first support strips  31  are discretely arranged between the magnetic leg  2  and the second support strip  32 . The first air gap  5  is defined by the two first support strips  31 , the magnetic leg  2  and the second support strip  32  collaboratively. The two first support strips  31  are disposed on two ends of the second support strip  32 , respectively. In an embodiment, the two first support strips  31  and the second support strip  32  are integrally formed as a one-piece structure. In another embodiment, one of the two first support strips  31  and the second support strip  32  are integrally formed as a one-piece structure, and the other first support strip  31  is a separate component. Alternatively, the two first support strips  31  and the second support strip  32  are three separate components. 
     The second support strip  32  is disposed on the two first support strips  31 , and the second support strip  32  is arranged between the two first support strips  31  and the winding  4 . Moreover, the winding  4  is disposed on the second support strip  32 . A first portion of the first air gap  5  is arranged between the first projection line m and the second projection line n. A second portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. A third portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     In some embodiments, the magnetic element includes a single support strip assembly and a single winding. In some other embodiments, the magnetic element includes a plurality of support strip assemblies and a plurality of windings. An exemplary magnetic element including two support strip assemblies and two windings is described as following. 
     Please refer to  FIG. 8 .  FIG. 8  is a schematic cross-sectional view illustrating the structure of a magnetic element according to an eighth embodiment of the present disclosure. The magnetic element  1   g  includes a magnetic core, at least one first support strip assembly  7 , at least one second support strip assembly  3 , a first winding  8 , a second winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2 , the second winding  4 , and the first air gap  5  in this embodiment are similar to those of  FIG. 1 , and not redundantly described herein. Component parts and elements corresponding to those of the first embodiment are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In this embodiment, the first support strip assembly  7  of the magnetic element  1   g  includes a single support strip or a plurality of support strips. The first support strip assembly  7  is disposed on the magnetic leg  2 . The first winding  8  is disposed on the first support strip assembly  7 . The first winding  8  of the magnetic element  1   g  is a low voltage winding. The first winding  8  is wound around the first support strip assembly  7 . The second support strip assembly  3  is disposed on the first winding  8 . For example, the second winding  4  is a high voltage winding. The second winding  4  is wound around the second support strip assembly  3 . It is noted that numerous modifications and alterations may be made while retaining the teachings of the disclosure. For example, in some other embodiments, the first winding  8  is a high voltage winding, and the second winding  4  is a low voltage winding. 
     In some embodiments, the number of the first air gaps  5  and the number of the second support strip assemblies  3  are equal. In addition, the locations of the first air gaps  5  correspond to the locations of the second support strip assemblies  3 . Each first air gap  5  is closer to the corresponding second support strip assembly  3 . In addition, each first air gap  5  is at least defined by the adjacent second support strip assembly  3 . The first air gap  5  is arranged between the first winding  8  and the second winding  4 . Each first air gap  5  includes a first upper air gap part  51  and a first lower air gap part  52 . The first upper air gap part  51  is closer to the first end part  41  of the second winding  4  than the first lower air gap part  52 . The first lower air gap part  52  is closer to the second end part  42  of the second winding  4  than the first upper air gap part  51 . 
     In this embodiment, the second support strip assembly  3  of the magnetic element  1   g  includes a first support strip  31 , a second support strip  32  and a third support strip  34 . The third support strip  34  is disposed on the first winding  8 . In addition, the third support strip  34  is arranged between the first support strip  31  and the first winding  8 . The first support strip  31  is disposed on the third support strip  34 . In addition, the first support strip  31  is arranged between the second support strip  32  and the third support strip  34 . The second support strip  32  is disposed on the first support strip  32 . In addition, the second support strip  32  is arranged between the first support strip  31  and the second winding  4 . The second winding  4  is disposed on the second support strip  32 . In an embodiment, at least two of the first support strip  31 , the second support strip  32  and the third support strip  34  are integrally formed as a one-piece structure. In another embodiment, the first support strip  31 , the second support strip  32  and the third support strip  34  are three separate components. 
     The first support strip  31  has a top surface  31   a  and a bottom surface  31   b . The top surface  31   a  and the bottom surface  31   b  are opposed to each other. The second support strip  32  has a top surface  32   a  and a bottom surface  32   b . The top surface  32   a  and the bottom surface  32   b  are opposed to each other. The top surface  32   a  of the second support strip  32  is closer to the top surface  31   a  of the first support strip  31  than the bottom surface  32   b . The bottom surface  32   b  of the second support strip  32  is closer to the bottom surface  31   b  of the first support strip  31  than the top surface  32   a . Moreover, the third support strip  34  has a top surface  34   a  and a bottom surface  34   b . The top surface  34   a  and the bottom surface  34   b  are opposed to each other. The top surface  34   a  of the third support strip  34  is closer to the top surface  31   a  of the first support strip  31  and the top surface  32   a  of the second support strip  32  than the bottom surface  34   b . The bottom surface  34   b  of the third support strip  34  is closer to the bottom surface  31   b  of the first support strip  31  and the bottom surface  32   b  of the second support strip  32  than the top surface  34   a.    
     The top surface  34   a  of the third support strip  34  and the top surface  32   a  of the second support strip  32  are located at a level higher than the top surface  31   a  of the first support strip  31 . Consequently, the first upper air gap part  51  is defined by the third support strip  34 , the top surface  31   a  of the first support strip and the second support strip  32  collaboratively. A first portion of the first upper air gap part  51  is arranged between the first projection line m and the top surface  31   a  of the first support strip  31 . That is, the first portion of the first upper air gap part  51  is arranged between the first projection line m and the second projection line n. A second portion of the first upper air gap part  51  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. The bottom surface  34   b  of the third support strip  34  and the bottom surface  32   b  of the second support strip  32  are located at a level lower than the bottom surface  31   b  of the first support strip  31 . Consequently, the first lower air gap part  52  is defined by the third support strip  34 , the bottom surface  31   b  of the first support strip  31  and the second support strip  32  collaboratively. A first portion of the first lower air gap part  52  is arranged between the second projection line n and the bottom surface  31   b  of the first support strip  31 . That is, the first portion of the first lower air gap part  52  is arranged between the first projection line m and the second projection line n. A second portion of the first lower air gap part  52  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     Please refer to  FIG. 8  again. In this embodiment, the magnetic element  1   g  further includes a first insulation layer  61 , a second insulation layer  62 , a third insulation layer  63  and a fourth insulation layer  64 . The first insulation layer  61  is disposed on and arranged around the inner periphery side of the second winding  4 . The first insulation layer  61  is used for isolating the second support strip assembly  3  from the second winding  4 . The second insulation layer  62  is disposed on and arranged around the outer periphery side of the second winding  4 . The second insulation layer  62  is used for isolating the second winding  4  from the external components. The third insulation layer  63  is disposed on and arranged around the inner periphery side of the first winding  8 . The third insulation layer  63  is used for isolating the first support strip assembly  7  from the first winding  8 . The fourth insulation layer  64  is disposed on and arranged around the outer periphery side of the first winding  8 . The fourth insulation layer  64  is used for isolating the second support strip assembly  3  from the first winding  8 . Moreover, the first insulation layer  61 , the second insulation layer  62 , the third insulation layer  63 , and the fourth insulation layer  64  are NOMEX papers or composite insulation papers. 
     In the embodiment of the magnetic element  1   g  as shown in  FIG. 8 , the second support strip assembly  3  includes the first support strip  31 , the second support strip  32  and the third support strip  34 . It is noted that numerous modifications and alterations may be made while retaining the teachings of the disclosure. For example, the second support strip assembly  3  may be replaced by the support strip assembly in each of the magnetic elements as shown in  FIGS. 2 to 7 . Hereinafter, some variant examples of the magnetic element  1   g  will be described. For succinctness, only the variations of the second support strip assembly  3  will be described as follows. 
     In a first variant example of the magnetic element  1   g , the second support strip assembly  3  is replaced by the support strip assembly  3  as shown in  FIG. 2 . In this embodiment, each first air gap  5  includes a first upper air gap part  51  and a first lower air gap part  52 . Each second support strip assembly  3  includes a support strip. The inner surface  331  of the support strip is disposed on the first winding  8 . The second winding  4  is disposed on the outer surface  332  of the support strip. The inner surface  331  and the outer surface  332  of the support strip are opposed to each other. The first upper air gap part  51  is defined by the first winding  8 , the top surface  333  of the support strip and the second winding  4  collaboratively. A first portion of the first upper air gap part  51  is arranged between the first projection line m and the second projection line n. A second portion of the first upper air gap part  51  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. The first lower air gap part  52  is defined by the first winding  8 , the bottom surface of the support strip  334  and the second winding  4  collaboratively. A first portion of the first lower air gap part  52  is arranged between the first projection line m and the second projection line n. A second portion of the first lower air gap part  52  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     In this embodiment, the length of the support strip is greater than 80% of the distance between the first endpoint  411  and the third endpoint  421  of the second winding  4 . In addition, the length of the support strip is smaller than the distance between the projection point of the second end part  412  of the second winding  4  on the magnetic leg  2  and the projection point of the fourth endpoint  422  of the second winding  4  on the magnetic leg  2 . The direction of the support strip is in parallel with the axial direction Y of the magnetic leg  2 . 
     In a second variant example of the magnetic element  1   g , the second support strip assembly  3  is replaced by the support strip assembly  3  as shown in  FIG. 3, 4 or 5 . In this embodiment, each first air gap  5  includes at least one first upper air gap part  51  and at least one first lower air gap part  52 . Each second support strip assembly  3  includes a support strip. That is, the at least one first upper air gap part  51  and the at least one first lower air gap part  52  are formed in the support strip. In addition, the at least one first upper air gap part  51  and the at least one first lower air gap part  52  are respectively disposed at the upper region and lower region. A first portion of the first upper air gap part  51  is arranged between the first projection line m and the second projection line n. A second portion of the first upper air gap part  51  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. A first portion of the first lower air gap part  52  is arranged between the first projection line m and the second projection line n. A second portion of the first lower air gap part  52  is at least beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     In a third variant example of the magnetic element  1   g , the second support strip assembly  3  is replaced by the support strip assembly  3  as shown in  FIG. 6 . In this embodiment, the second support strip assembly  3  includes a single support strip. In this embodiment, the length of the support strip is greater than the distance between the first endpoint  411  and the third endpoint  421  of the second winding  4 . In addition, the direction of the support strip is in parallel with the axial direction Y of the magnetic leg  2 . At least a first air gap  5  is formed in the support strip. The first air gap  5  runs through the top surface  333  and the bottom surface  334  of the support strip. 
     In a fourth variant example of the magnetic element  1   g , the second support strip assembly  3  is replaced by the support strip assembly  3  as shown in  FIG. 7 . In this embodiment, the second support strip assembly  3  includes two first support strips  31  and a second support strip  32 . The two first support strips  31  are discretely arranged between the first winding  8  and the second support strip  32 . In addition, the two first support strips  31  are disposed on two ends of the second support strip  32 , respectively. The second support strip  32  is disposed on the two first support strips  31 , and the second support strip  32  is arranged between the two first support strips  31  and the second winding  4 . Moreover, the second winding  4  is disposed on the second support strip  32 . The at least one first air gap  5  is defined by the first winding  8 , the two first support strips  31  and the second support strip  32  collaboratively. A first portion of the first air gap  5  is arranged between the first projection line m and the second projection line n. A second portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the third projection line o. A third portion of the first air gap  5  is beyond the region between the third projection line o and the fourth projection line p through the fourth projection line p. 
     Please refer to  FIG. 9 .  FIG. 9  is a schematic cross-sectional view illustrating the structure of a magnetic element according to a ninth embodiment of the present disclosure. The magnetic element  1   h  includes a magnetic core, at least one first support strip assembly  7 , at least one second support strip assembly  3 , a first winding  8 , a second winding  4  and at least one first air gap  5 . The functions and structures of the magnetic leg  2 , the second support strip assembly  3 , the second winding  4  and the first air gap  5  in this embodiment are similar to those of  FIG. 8 , and not redundantly described herein. Component parts and elements corresponding to those of the eighth embodiment as shown in  FIG. 8  are designated by identical numeral references, and detailed descriptions thereof are omitted. 
     In comparison with the magnetic element  1   g  of  FIG. 8 , the first winding  8  in the magnetic element  1   h  of this embodiment includes a third end part  81 , a fourth end part  82  and a second connection part  83 . The third end part  81  and the fourth end part  82  of the first winding  8  are connected with the top side and the bottom side of the second connection part  83 , respectively. The third end part  81  includes a fifth endpoint  811  and a sixth endpoint  812 . The fifth endpoint  811  is the farthest point of the third end part  81  away from the top side of the second connection part  83 . The fifth endpoint  811  and the sixth endpoint  812  are connected with each other. The connection line between the fifth endpoint  811  and the sixth endpoint  812  is an inclined line or a curved line. Due to the incline line or the curved line, the third end part  81  has a chamfer. The sixth endpoint  812  is connected with the second connection part  83 . A fifth projection line q is formed between the projection point of the sixth endpoint  812  on the magnetic leg  2  and the sixth endpoint  812 . 
     The fourth end part  82  includes a seventh endpoint  821  and an eighth endpoint  822 . The seventh endpoint  821  is the farthest point of the fourth end part  82  away from the bottom side of the second connection part  83 . The seventh endpoint  821  and the eighth endpoint  822  are connected with each other. The connection line between the seventh endpoint  821  and the eighth endpoint  822  is an inclined line or a curved line. Due to the incline line or the curved line, the fourth end part  82  has a chamfer. The eighth endpoint  822  is connected with the second connection part  83 . A sixth projection line r is formed between the projection point of the eighth endpoint  822  on the magnetic leg  2  and the eighth endpoint  822 . 
     The connection line between the fifth endpoint  811  of the third end part  81  and the seventh endpoint  821  of the fourth end part  82  is the longest distance of the first winding  8  in parallel with the axial direction Y of the magnetic leg  2 . A seventh projection line s is formed between the projection point of the fifth endpoint  811  on the magnetic leg  2  and the fifth endpoint  811 . An eighth projection line t is formed between the projection point of the seventh endpoint  821  on the magnetic leg  2  and the seventh endpoint  821 . 
     In this embodiment, the magnetic element  1   h  includes at least one second air gap  9 . The number of the second air gaps  9  and the number of the first support strip assemblies  7  are equal. In addition, the locations of the second air gaps  9  correspond to the locations of the first support strip assemblies  7 . Each second air gap  9  is at least defined by the adjacent first support strip assembly  7 . In addition, each second air gap  9  is arranged between the first winding  8  and the magnetic leg  2 . A first portion of the second air gap  9  is arranged between the fifth projection line q and the sixth projection line r. A second portion of the second air gap  9  is beyond the region between the seventh projection line s and the eighth projection line t through at least one of the seventh projection line s and the eighth projection line t. 
     In this embodiment, each second air gap  9  includes a second upper air gap part  91  and a second lower air gap part  92 . The second upper air gap part  91  is closer to the third end part  81  of the first winding  8  than the second lower air gap part  92 . The second lower air gap part  92  is closer to the fourth end part  82  of the first winding  8  than the second upper air gap part  91 . 
     As mentioned above, the first support strip assembly of the magnetic element  1   g  in  FIG. 8  includes a single support strip or a plurality of support strips. In compare with the magnetic element  1   g  in  FIG. 8 , the first support strip assembly  7  of the magnetic element  1   h  in this embodiment includes a fourth support strip  71 , a fifth support strip  72  and a sixth support strip  73 . The fourth support strip  71  is disposed on the magnetic leg  2 . In addition, the fourth support strip  71  is arranged between the magnetic leg  2  and the fifth support strip  72 . The fifth support strip  72  is disposed on the fourth support strip  71 . In addition, the fifth support strip  72  is arranged between the fourth support strip  71  and the sixth support strip  73 . The sixth support strip  73  is disposed on the fifth support strip  72 . In addition, the sixth support strip  73  is arranged between the fifth support strip  72  and the first winding  8 . The first winding  8  is disposed on the sixth support strip  73 . The fourth support strip  71  has a top surface  71   a  and a bottom surface  71   b . The top surface  71   a  and the bottom surface  71   b  are opposed to each other. The fifth support strip  72  has a top surface  72   a  and a bottom surface  72   b . The top surface  72   a  and the bottom surface  72   b  are opposed to each other. The top surface  72   a  of the fifth support strip  72  is closer to the top surface  71   a  of the fourth support strip  71  than the bottom surface  72   b . The bottom surface  72   b  of the fifth support strip  72  is closer to the bottom surface  71   b  of the fourth support strip  71  than the top surface  72   a . Moreover, the sixth support strip  73  has a top surface  73   a  and a bottom surface  73   b . The top surface  73   a  and the bottom surface  73   b  are opposed to each other. The top surface  73   a  of the sixth support strip  73  is closer to the top surface  71   a  of the fourth support strip  71  and the top surface  72   a  of the fifth support strip  72  than the bottom surface  73   b . The bottom surface  73   b  of the sixth support strip  73  is closer to the bottom surface  71   b  of the fourth support strip  71  and the bottom surface  72   b  of the fifth support strip  72  than the top surface  73   a . The top surface  71   a  of the fourth support strip  71  and the top surface  73   a  of the sixth support strip  73  are located at a level higher than the top surface  72   a  of the fifth support strip  72 . Consequently, the second upper air gap part  91  is defined by the fourth support strip  71 , the top surface  72   a  of the fifth support strip  72  and the sixth support strip  73  collaboratively. A first portion of the second upper air gap part  91  is arranged between the fifth projection line q and the top surface  72   a  of the fifth support strip  72 . That is, the first portion of the second upper air gap part  91  is arranged between the fifth projection line q and the sixth projection line r. A second portion of the second upper air gap part  91  is beyond the region between the seventh projection line s and the eighth projection line t through the seventh projection line s. The bottom surface  71   b  of the fourth support strip  71  and the bottom surface  73   b  of the sixth support strip  73  are located at a level lower than the bottom surface  72   b  of the fifth support strip  72 . Consequently, the second lower air gap part  92  is defined by the fourth support strip  71 , the bottom surface  72   b  of the fifth support strip  72  and the sixth support strip  73  collaboratively. A first portion of the second lower air gap part  92  is arranged between the sixth projection line r and the bottom surface  72   b  of the fifth support strip  72 . That is, the first portion of the second lower air gap part  92  is arranged between the fifth projection line q and the sixth projection line r. A second portion of the second lower air gap part  92  is beyond the region between the seventh projection line s and the eighth projection line t through the eighth projection line t. 
     From the above descriptions, the magnetic element of the present disclosure includes at least one first air gap. A first portion of the first air gap is arranged between the first projection line and the second projection line. A second portion of the first air gap is beyond the region between the third projection line and the fourth projection line through at least one of the third projection line and the fourth projection line. In other words, there are air gaps between the end parts of the winding and the magnetic leg. Consequently, the dielectric constant between the first end part of the winding and the magnetic leg and the dielectric constant between the second end part of the winding and the magnetic leg are reduced. Moreover, the electric field distribution of the first end part and the second end part will be more uniform, and the partial discharge extinction voltage will be increased. In other words, the partial discharge problem is solved. The volume and the cost of the magnetic element are both reduced. In addition, the equalizing rings are not required. Consequently, the fabricating process of the magnetic element of the present disclosure is simplified. 
     While the disclosure has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.