Patent Application
20240145127
The present disclosure is directed to a conductor for conducting electric current, in particular electric current with an AC component. The conductor may be used for conducting purely AC electric current or DC electric current with an added AC component. The conductor can be a rigid metallic conductor, and can have a substantially circular cross-section. The conductor can be suitable for conducting high AC current. The conductor can be used in in various parts of a power transmission or distribution system such as bushings, cable terminations, gas-insulated switchgear, gas-insulated lines, circuit breakers, switches, disconnectors or current bars, for example.
Known rigid conductors for currents with a significant AC component are in the form of solid metallic rods or hollow tubes. The operating current transmitted through the conductor is limited by the heat generated by the ohmic losses in the conductor, which is proportional to the electric resistance of the conductor. Due to the skin effect, the AC component of the current tends to flow only in the outer layer of the conductor of the thickness which is referred to as skin depth. Due to this limitation, full rod conductors are typically applied only with limited diameters. Large-diameter conductors are made only in a tubular form, with a wall thickness comparable to the skin depth. This requires applying conductors of very large diameters, which, for 50-60 Hz currents of some tens of kA may well reach diameters of the size of decimeters. This means that only a very small part of the total cross section of the conductor is used for transmitting current.
There are known ways of limiting the skin effect in flexible conductors comprising a core of insulated cables. In particular, segmental conductors are known, also referred to as Milliken conductors. The principles of segmental conductors are described, e.g., in U.S. Pat. Nos. 1,904,162 and 6,313,409 B1. In such Milliken conductors, stranded sub-conductors comprising thin round wires are rolled into a triangular cake-slice shape and a number of these sub-conductors are assembled to one round conductor.
Each of documents U.S. Pat. No. 2,872,501 A1, DE 11 70 486 B1, DE 82 35 154 Ul and EP 0 022 269 A1 discloses a conductor comprising conducting members being periodically transposed.
In a standard conductor comprising stranded wires, the distance of each individual wire to the conductor axis is constant along the length of the conductor. The AC magnetic flux, generated by the current in the conductor, flowing through the surface area between two wires, one running closer and another one running further from the conductor axis, induces a loop current flowing in the two wires, such that the effective current of the wire close to the axis is reduced and that of the one further from the axis is increased. Due to this mechanism, the current tends to flow only in the wires close to the surface of the conductor and is cancelled in the wires close to the conductor axis. Thus, the skin-effect occurs. In the segmental Milliken conductor, each individual wire wanders along the length of the conductor from a position close to the axis to a position far from the axis. In such a way, the magnetic flux is cancelled out and the loop current is not induced between individual wires and the skin effect is substantially reduced. However, this solution is specific for stranded-wire conductors and not applicable to rigid conductors of solid metal.
It is an object to provide an improved conductor for conducting AC current and a method for producing the conductor.
According to a first aspect, a conductor for conducting AC electric current has along its length at least two main sections and a transposing junction connecting adjacent ones of the main sections. The conductor comprises at least two partial conductors, each of the conductors running through the main sections and the transposing junction, wherein the conductors are electrically insulated from each other in the main sections and the transposing junction. Each of the partial conductors has in each of the main sections an outer diameter. For a circular cylindrical shape, the outer diameter is twice the outer radius of the partial conductor. For a shape different from a circular cylindrical shape, the outer diameter is the maximum outer diameter of the shape. As an example, for a square shape, the outer diameter is the diagonal of the square.
In the first main section, the first partial conductor has an outer diameter which is larger than the outer diameter of the second partial conductor and in the second main section, the second partial conductor has an outer diameter which is larger than the outer diameter of the first partial conductor.
Accordingly, each of the partial conductors has a different outer diameter in each of the main sections. Thereby, current flows in each of the conductors in one of the main sections closer to the center of the conductor and in the other one of the main sections at a larger distance from the center of the conductor. In this way, the current is forced to flow in both partial conductors and, in particular, once closer to the center and once at a larger distance from the center. Thereby, the skin effect can be avoided or diminished, allowing the current to be conducted at almost the entire cross section of the conductor.
The conductor may be a round conductor. Each of the partial conductors may have a round outer shape, at least in the main sections. In particular, each of the conductors may have the shape of a cylinder. The cylinder may be filled or hollow. Both conductors may be made from the same material. As an example, a material may be aluminum, copper or respective alloys.
The partial conductors may be insulated from each other by gaps along the entire length of the main sections and transposing junctions. The gaps may be air gaps or insulating inserts, for example. The insulating inserts may comprise a hardened resin, for example. Each of the partial conductors may fully enclose a longitudinal axis of the conductor in each part of the main section. Accordingly, each of the partial conductors has a closed surface in the main sections.
As an example, in the first main section, the first conductor may have a shape of a circular cylinder having a first outer radius and the second partial conductor may have a shape of a circular cylinder having a second outer radius, wherein the first outer radius is larger than the second outer radius. In the second main section, the first conductor may have a shape of a circular cylinder having the second outer radius and the second partial conductor may have a shape of a circular cylinder having the first outer radius. In the transposing junction, the shapes, in particular the radii, of the first and second conductors change. For hollow cylinders, the thicknesses of cylinder walls may be the same for all conductors and for all diameters.
In further examples, the partial conductors may have other shapes in the main sections than circular cylinders such as cylinders with elliptical or rectangular cross-sections, for example. A rectangular cross-section can also be a square cross-section.
As an example, in the main section, the first conductor may be a hollow cylinder having a first outer diameter and the second conductor may be a filled cylinder having a second outer diameter. In the second section, the second conductor may be a filled cylinder having the second outer diameter and the first conductor may be a hollow cylinder having the first outer diameter.
In each of the main sections, the partial conductors may have a constant outer diameter along the entire length of the main section. The geometry of the partial conductor is constant along the length of the main section.
The conductor may comprise more than two main sections. As an example, when the conductor comprises exactly two partial conductors, the number of main sections may be a multiple of two.
According to an embodiment, in the first main section, the first conductor may enclose the second conductor and in the second main section, the second conductor may enclose the first conductor. In particular, the respective conductor may fully enclose the respective other conductor in a main section.
The overall conductor may have an interior structure being identical in both main sections. However, in the first main section, the geometric parts are provided by a different one of the partial conductors than in the second main section. Accordingly, the conductors switch their shapes between the main sections.
The main sections may have the same lengths. Thus, the partial conductors provide the same lengths of each of the radii. Accordingly, the magnetic flux between the conductors in each of the main sections is of a similar absolute value and of the opposite sign. Hence, the magnetic flux is cancelled out in large part, thus minimizing the induced loop current which would contribute to generating a skin effect.
For enabling a change of the radii in the transposing junction, each of the partial conductors has one or more openings in its wall for allowing one or more transposing portions of the other one of the partial conductors to cross the wall of the partial conductor such that the other one of the partial conductors can change its outer diameter.
Depending on the arrangement of openings and transposing portions, a more or less homogenous current distribution in the transposing junction may be achieved. As an example, the opening and the transposing portion may take up a half-circular shape, allowing current to flow in a half-circular section. To more evenly distribute the current, the openings may take up two quarter-circular shapes, for example.
The conductor may comprise a joining junction in which the first and second conductors are electrically connected to each other.
The joining junctions may be located at each of the ends of the conductor. Accordingly, current enters the conductor in the form of a single current path, is than split up into two or more current paths provided by the partial conductors. The current paths are joined again at the other end section into a single current path.
In a further embodiment, the conductor comprises a first portion and a second portion, each of the portions comprising at least two main sections and a transposing junction between the main sections. The conductor comprises a joining junction between the portions, wherein in the joining junction the first and second conductors are electrically connected to each other. Thus, the current paths of the partial conductors are split up or joined in the joining junctions. In each of the portions, the structure of the partial conductors can be as described in the foregoing.
Thereby, the structure of each of the partial conductors in the first and second portions can be decoupled. Accordingly, the current paths in the partial conductors in one of the portions is independent from the current paths in the partial conductors in the other one of the portions. As an example, the main sections in the first portion may have different lengths than the main sections in the second portions. Also, the shape of the partial conductors in the first portion may be different from the shape of the partial conductors in the second portion.
In embodiments, the conductor has a bend. The bend may be provided in a transposing junction or in a joining junction, for example. In this case, the current path in the main sections is linear and not disturbed in the bend. The conductor may comprise several bends in transposing or joining junctions.
In some embodiments, the conductor has exactly two partial conductors and not more than the two partial conductors. Such a conductor is called double conductor in the following.
In other embodiments, the conductor has more than the two partial conductors. As an example, the conductor may comprise three partial conductors. In particular, the conductor may have exactly three partial conductors and not more than the three partial conductors. Such a conductor is called triple conductor in the following. In this case, the conductor has a third main section and a second transposing junction between the second and third main section. Each of the three partial conductors run along all of the main sections and the transposing junctions and are electrically insulated from each other in the main sections and transposing junctions. The characteristics described in the foregoing are correspondingly valid for three partial conductors.
Each of the partial conductors may have a different outer diameter in each of the main sections. As an example, the partial conductors can take up three different outer radii in the three main sections. Each one of the partial conductors takes up the first radius in one of the main sections, the second radius in another one of the main sections and the third radius in another one of the main sections. In none of the main sections, two partial conductors have the same radius.
As an example, in each of the main sections, each of the partial conductors may have a tubular shape. In this case, the conductor has a central opening running through all main sections. The central opening may also be present in the transposing junctions. As an example, the partial conductors may have in each main section the shape of concentrically arranged hollow cylinders with different radii. Each of the hollow cylinders is provided by one of the partial conductors. In a different main section, the hollow cylinders are distributed differently between the partial conductors. In a further embodiment, the inner cylinder may be a filled cylinder, instead.
Generally, the conductor may comprise two, three or more than three conductors. The number of main sections is at least the number of conductors. In particular, the number of main sections may be a multiple of the number of conductors. Adjacent ones of the main sections may be connected by transposing junctions. In case that the total number of main sections or the number of main sections between two adjacent joining junctions is equal to the number of conductors, each of the partial conductors has a different outer diameter in each of the main sections. The specifics described in the foregoing are correspondingly applicable for multiple conductors.
According to a further aspect, a use of the conductor for conducting electric current with an AC component is disclosed. In particular, the conductor can be used in various parts of a power transmission or distribution system such as bushings, cable terminations, gas-insulated switchgear, gas-insulated lines, circuit breakers, switches, disconnectors or current bars, for example. The AC current may by a large current. For example, the AC current may be a current of several kA. The frequency may be a frequency of 50-60 Hz, for example. The current may also be a DC current with an AC component.
According to a further aspect, an electric device comprises the conductor described in the foregoing. The device may be high-current device. In particular, the device may be a generator, a transformer or a switchgear, for example.
According to a further aspect, a method of manufacturing the conductor is disclosed, wherein at least a part of the conductor is manufactured by an additive manufacturing (AM) method or by a casting method. An additive manufacturing method may be a 3d-printing method. A casting method is a method in which a material in liquid form is filled into a mold.
As an example, main sections and transposing junctions may be formed by the same additive process or casting process. It is also possible to form the transposing junctions in an additive method or casting method, separately from the main sections and, after that, connect the transposing junction to the main sections.
In a casting method, an insert may be positioned in a mold. The insert may provide the gaps insulating the partial conductors from each other. Accordingly, the insert is a part of the finished conductor.
The present disclosure comprises several aspects. Every feature described with respect to one of the aspects is also disclosed herein with respect to the other aspect, even if the respective feature is not explicitly mentioned in the context of the specific aspect.
Further features, refinements and expediencies become apparent from the following description of the exemplary embodiments in connection with the figures.
In the figures, elements of the same structure and/or functionality may be referenced by the same reference numerals. It is to be understood that the embodiments shown in the figures are illustrative and are not necessarily drawn to scale.
As examples, the conductor 1 may be used in switchgears, such as gas-insulated switchgears, generators or transformers. The conductor 1 may be used in bushings, such as high-current transformer or generator bushings, in gas-insulated lines, or in insulated current bars.
The conductor 1 has a round cross-sectional shape. The conducting parts of the conductor 1 comprise metals such as copper or aluminum, for example.
Along its length, the conductor 1 comprises two main sections 2, 3 and a transposing junction 4 between the main sections 2, 3. Furthermore, the conductor 1 comprises a first end section 5 and a second end section 6.
The conductor 1 comprises two partial conductors (see
The partial conductors have structures such that in the main sections 2, 3 current flows in the direction of the length L of the conductor 1. In the transposing junction 4, current flows at least in parts of the transposing junction 4 in a thickness or radial direction R or at an angle toward the length L. In particular, current flowing in the direction of the length L in the first main section 2 is forced to flow in a thickness direction R. In the second main section 3, the current flows in the direction of the length L again, but at a different distance from the center of the conductor 1 than in the first main section 2. Accordingly, the transposing junction 4 serves to switch the distance of the current path from the center of the conductor 1.
This structure helps avoiding the skin effect and, thus, substantially the full thickness of the conductor can be used for conducting current. The skin effect leads to an AC current flowing substantially only in an outer region of a conductor, the outer region having a thickness of an order of the so-called “skin depth”.
For effectively cancelling the skin effect, the lengths 12 and 13 of the main sections 2, 3 are the same. In addition to that, the number of main sections 2, 3 for a double conductor 1 should be a multiple of two.
As can be seen in
In the first main section 2, the first partial conductor 7 has the shape of a hollow cylinder with an outer diameter d1 corresponding to twice an outer radius r1 of the first partial conductor 7. Furthermore, the second partial conductor 8 has the shape of a filled cylinder, i.e., a solid rod. In other embodiments, an inner partial conductor portion may by a hollow tube. The second partial conductor 8 has an outer diameter d2 corresponding to twice an outer radius r2 of the second partial conductor 8. The second partial conductor 8 is positioned centrally in the conductor 1.
The radius r1 is larger than the radius r2. The outer radius r1 of the first partial conductor 7 is the outer radius of the conductor 1. The first partial conductor 7 fully encloses the second partial conductor 8. The first and second partial conductors 7, 8 are arranged concentrically and have closed outer surfaces in the entirety of the main sections 2, 3.
Along the entire length of the main sections 2, 3 and the transposing junction 4, the partial conductors 7, 8 are electrically insulated from each other by one or more gaps 11. In the main sections 2, 3, the gap 11 has the shape of a hollow tube. The gap 11 may be an air gap or filled with an insulating material to uphold the insulating distance of the partial conductors 7, 8 from each other.
As can be seen from a comparison of
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As can be seen in
Following further down the length of the conductor 1 to the position shown in
As can be seen in
As can be seen in
Each of the partial conductors 7, 8 may be formed as a single, integrally formed piece. It is also possible that one or each of the partial conductors 7, 8 are formed as multiple pieces. As an example, a solid rod may be connected via a transposing junction to a hollow cylinder.
By same lengths of the first and second main sections 2, 3, and by providing two main sections 2, 3 or a number of main sections 2, 3 being a multiple of two, the current paths in the partial conductors 7, 8 run over equal portions of the conductor length at a distance closer to the center and at a distance farer away from the center. Therefore, loop currents are not generated, or at least minimized, and the current is not fully cancelled out in a central part of the conductor 1, thus significantly reducing the skin effect. In general, for the whole length of the conductor 1 there should be the same total length where the first partial conductor 7 runs at the smaller radius and the total length where the first partial conductor 7 runs at the larger radius. The same should be the case for the second partial conductor 8.
As a result, the current flows in almost the whole cross section of the conductor 1, except from the gaps 11 between the partial conductors 7, 8. This leads to a much smaller AC resistance of the conductor 1 compared to a conventional solid or tubular conductor 1 of the same outer diameter. The gaps 11 are as small as possible. In particular, the gap thickness can be much smaller than the thickness of each of the partial conductors 7, 8. Also the length of the transposing junction 4 can be much smaller than the length of each of the main sections 2, 3.
In the end section 5, the partial conductors 7, 8 are electrically connected to each other. In particular, a joining junction 9 is provided which may have the shape of a solid circular plate, a solid bolt or a threaded connector, for example. By the joining junction 9, the current is divided into the two current paths provided by the two partial conductors 7, 8 or joined together.
In the end sections 5, 6 the conductor 1 can be electrically connected to an electric contact by any known method such as clamping, a threaded connection or a plug-in connection, for example.
The conductor 1 may have the general structure as shown in
As can be seen from
In the transposing junction 4, the shapes of the partial conductors 7, 8 switch with help of a first transposing portion 12 and a second transposing portion 13, as can be seen in
Due to the transposing portions 12, 13 each comprising quarter portions being opposite to each other, the current flows more uniformly from one radial distance to the other radial distance. Furthermore, this makes the parts of the conductors 7, 8 more mechanically stable and resistant to bending. The transposing portions 12, 13 are arranged with the current running to two sides of the conductors 7, 8. It is also possible to arrange the transposing portions 12, 13 in other ways, with the current running to three, four or more sides, to distribute the current even more homogenously and to add rigidity to the construction.
The conductor 10 has three main sections 18, 19, 20. As in the foregoing embodiments, in each of the main sections 18, 19, 20, each of the partial conductors and, thus, each of the current paths runs at a fixed radial distance, homogenously along the length of the conductor 10. In the transposing junctions 21, 22 between the main sections 18, 19, 20, each of the current paths switches its radial position.
In other embodiments for a conductor 10 with three partial conductors the number of main sections can be larger than three and a multiple of three. When the number of main sections is a multiple of three (including three) and the main sections are of the same lengths, the current in each of the partial conductors flows in the same portion of the length of the conductor at the innermost radius, the intermediate radius and the outermost radius. Thereby, the loop currents induced by the magnetic flux between the conductors are minimized and the skin effect can be avoided or at least significantly reduced.
The conductor 10 has three partial conductors 15, 16, 17. As in a double conductor, the partial conductors 15, 16, 17 are electrically insulated from each other along the length of the conductor 10, except from the end sections 5, 6, where the partial conductors 15, 16, 17 are joined together.
In
As can be seen from
In the transposing junctions 21, 22, the outer radius of each of the partial conductors 15, 16, 17 changes. In particular, as can be seen from
In the shown embodiment, the conductors 15, 16, 17 have the same wall thickness in each of the main sections 18, 19, 20. It is also possible that the wall thickness is different, depending on the specific outer radius r1, r2, r3.
In the transposing junctions 21, 22 the walls of the partial conductors 15, 16, 17 are stepwise transposed from one radius to another radius. As in the double conductor, the walls of the partial conductors 15, 16, 17 open up and give room for transposing portions 23, 24, 25, 26.
As can be seen from
As can be seen from
As can be seen from
As can be seen from
In a further transposing junction 22 (see
Also, in the case of the triple conductor 10, the transposing junctions 21, 22 can be formed in a more symmetrical way, such that the walls of the partial connections open up into several symmetrically arranged parts, similar to the embodiment of the double conductor 1 shown in
The principle of the transposal in conductors with more than three partial conductors corresponds to the transposal shown for the double and triple conductors.
As for the double conductor 1 of
In the first main section 2 and the further first main section 2′, the conductor 1 has the same inner structure with the same allocation of the partial conductors to the inner structure. The same applies for the second main section 3 and the further second main section 3′. Accordingly, the first portion 27 composed by the first main section 2, the transposing junction 4 and the second main section 3 is identically repeated in the second portion 28 composed by the further first main section 2′, further transposing junction 4′ and further second main section 3′.
In the case of a triple conductor 10, two portions can be provided, with each of the portions comprising three main sections and two transposing junctions.
In further embodiments of double conductors 1 or triple conductors 10, more portions containing main sections and transposing junctions can be provided. Generally, the number of main sections should be a multiple of the number of partial conductors. In addition to that, the main sections should have lengths such that each of the partial conductors takes up each outer radius over the same total length. In this case, each of the current paths runs over equal portions of the conductor length at each of the radii, thus minimizing the loop currents and avoiding or at least reducing the skin effect. Each of the main sections can have the same length. It is also possible that the main sections 2, 3 have different lengths than the further main sections 2′, 3′.
The bend 30 is provided by a joining junction 9 joining the partial conductors in each of the adjacent main section 2′, 3. The joining junction 9 may be a portion of a rigid rod, for example. Due to the joining junction 9, the first portion 27 is decoupled from the second portion 28 with respect to the loop currents generated in each of the portions.
The main sections 2, 3 of the first portion 27 have the same lengths. The main sections 2′, 3′ of the second portion 28 have the same lengths. However, the main sections 2, 3 of the first portion 27 have a different length than the main seconds 2′, 3′ of the second portion. In further embodiments, portions 27, 28 of different lengths may be connected by a joining junction without that a bend is present.
In other embodiments, a bend 30 can be provided by a transposing junction, in which the partial conductors switch their shapes but are not electrically connected to each other.
The conductors 1, 10 of all embodiments, and in particular the partial conductors including transposing portions, can be manufactured by additive manufacturing technologies, wherein thin layers of the partial conductors are added one by one. This process can run in the direction along the length of the conductor and the shapes of the layers which have to be added in each part of the process are visible from
It is also possible to manufacture one or more transposing junctions or portions as separate components. In this case the transposing junctions can be fixed subsequently to the main sections of the conductor. The transposing junctions can be manufactured using additive manufacturing methods. Parts of the transposing junction can also be manufactured by machining, i.e., by removing material, and subsequent assembling.
In order to prevent the parts of the conductor to move with respect to each other, and coming into electrical contact, electrically insulating spacers may be inserted between the neighboring partial conductors in the main sections, especially in the areas close to the transposing junctions.
Additionally, the whole space between the partial conductors in the main sections and between separate parts of the transposing junctions can be filled with an insulating material. Suitable materials are hardenable resin such as epoxy, acrylic or silicone-based resin, for example. The resin may contain a filler, in particular a high-thermal-conductivity electrically insulating filler, such as, for example, boron nitride or aluminum nitride.
An alternative method to manufacture the conductor is a metal casting process. This is particularly suitable for conductors made of aluminum and its alloys. In this method, a core insert is prepared, for example made of a ceramic material. The core insert is in the shape of the gaps between the parts of the conductor. The shape of this empty space in the area of the transposing junction is easily derivable from the embodiments shown in
The core insert itself can be manufactured using additive manufacturing methods. After casting, the conductor is machined, so that the elements of the core insert located in the slits reaching the outer surface of the transposing junctions are exposed. In this way, the partial conductors providing the separate current paths become electrically insulated from each other.
A number of calculations have been made, in order to assess how much more current can be conducted by the conductors according to the invention in comparison to standard conductors. In particular, standard rod-shaped and tubular conductors are compared to the conductors according to the invention, with the same outer diameters. In case of the standard tubular conductors, the inner diameter of the conductor was optimized so as to minimize its AC resistance, so that the optimized standard conductor is used for the comparison.
As an example, the calculations show that replacing a 60 mm standard copper rod conductor with a double conductor of the same outer diameter, an AC resistance reduction factor of 0.69 is achieved. This provides the possibility to increase the operating current in the same device by up to 120% without increasing ohmic losses and, thus, without increasing the temperature. For a 90 mm copper rod conductor the corresponding numbers are 0.60 and 130%. When replacing the standard 90 mm conductor with a triple conductor, the AC resistance is half the AC resistance of the standard conductor and the operating current can be increased up to more than 140%.
Also for larger diameter aluminum conductors, which are commonly used in high-current applications, e.g., in components of generator circuits in power plants, such as generator bushings, LV step-up transformer bushings, generator circuit breakers, double conductors can provide operating current gains of between 130% and 140%. By using triple conductors, gains between 150% and 170% can be achieved without that the outer diameter of the conductor or the dimensions of the insulating components around the conductors is increased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21157335.7 | Feb 2021 | EP | regional |
This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/EP2022/053366 filed on Feb. 11, 2022, which in turn claims priority to European Patent Application No. 21157335.7, filed on Feb. 16, 2021, the disclosures and content of which are incorporated by reference herein in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/053366 | 2/11/2022 | WO |
