A vacuum circuit breaker contact with a built-in reverse conductor and a vacuum circuit breaker

Abstract

This invention discloses a vacuum circuit breaker contact with a built-in reverse conductor, relating to the field of vacuum circuit breaker technology. The vacuum circuit breaker contact with a built-in reverse conductor includes a contact plate, a contact cup, a conductive rod, a reverse conductor, and a support structure. The contact plate is connected to the top of the contact cup, the conductive rod is connected to the contact cup, and the reverse conductor is disposed inside the contact cup. The support structure is connected to the circuit breaker housing via an insulating rod to ensure its relatively fixed position. A through groove is formed at the bottom of the contact cup, corresponding to the support structure passing through the through groove. Several first helical grooves are formed on the sidewall of the contact cup, and several second helical grooves are formed on the sidewall of the reverse conductor. The rotation direction of the second helical grooves is opposite to that of the first helical grooves. The vacuum circuit breaker uses this vacuum circuit breaker contact with a built-in reverse conductor. This invention can solve the problem in the prior art where residual magnetism between poles affects the breaking effect during interruption in DC vacuum circuit breakers, thus improving the breaking performance and reliability of DC vacuum circuit breakers.

Description

Technical Field

[0001] This invention relates to the field of vacuum circuit breaker technology, specifically to a vacuum circuit breaker contact with a built-in reverse conductor and a vacuum circuit breaker. Background Technology

[0002] With the continuous development of new power systems, multi-terminal DC transmission systems have attracted widespread attention due to their advantages such as flexible networking, high transmission efficiency, precise control, high reliability, and intensive environmental protection. The development of DC circuit breakers is particularly important in the development of multi-terminal DC transmission systems. Among various DC circuit breakers, mechanical DC vacuum circuit breakers have become the mainstream research direction due to their low cost, strong breaking capacity, and high reliability.

[0003] Currently, arcing is unavoidable during vacuum breaking. The forced zero-crossing technology used in mechanical vacuum DC circuit breakers generates extremely strong eddy currents inside the conductor. Due to severe hysteresis in the inter-electrode magnetic field, residual magnetism between the electrodes significantly affects the effective breaking of the DC vacuum arc when the current crosses zero. Residual magnetism may even cause the arc to reignite after the current crosses zero, leading to breaking failure or even overvoltage, posing a serious threat to the equipment. To reduce residual magnetism between the electrodes when the current crosses zero, mechanical DC vacuum circuit breakers have explored contact structure optimization methods to effectively improve the magnetic field distribution characteristics in the DC breaking arc region. These methods include using laminated structures to reduce eddy current paths or using non-magnetic materials (such as stainless steel) to reduce the conductivity of the eddy current loop. However, these structural optimization methods cannot fundamentally overcome the problem of extremely high residual magnetism in DC breaking compared to AC breaking at the moment of current zero crossing.

[0004] Therefore, existing technologies need to be improved. Summary of the Invention

[0005] The technical problem to be solved by this invention is that residual magnetism in existing vacuum DC circuit breakers seriously affects the switching performance. The purpose is to provide a vacuum circuit breaker contact with a built-in reverse conductor and a vacuum circuit breaker. By adopting the corresponding technical solution, it has the beneficial effects of reducing the influence of residual magnetism and improving the performance of the circuit breaker, thereby improving the breaking performance and reliability of the DC vacuum circuit breaker.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a vacuum circuit breaker contact with a built-in reverse conductor, comprising contact plates, contact cups, conductive rods, a reverse conductor, and a support structure.

[0008] The contact piece is connected to the top of the contact cup, the conductive rod is connected to the bottom of the contact cup, the reverse conductor is disposed inside the contact cup, the support structure is connected to the circuit breaker housing via an insulating rod to ensure its position is relatively fixed, the support structure is movably connected to the reverse conductor and always maintains electrical connection, the bottom of the contact cup has a through slot for the support structure to be inserted, and the contact cup corresponds to the support structure passing through the through slot.

[0009] The sidewall of the contact cup is provided with a plurality of first spiral grooves, and the sidewall of the reverse conductor is provided with a plurality of second spiral grooves, wherein the spiral direction of the second spiral grooves is opposite to that of the first spiral grooves.

[0010] In the above technical solution, when the vacuum circuit breaker first starts to open, the moving and stationary contacts have just separated, and the breaking current is close to the peak current. At this time, the current flow path in the vacuum circuit breaker contact with the built-in reverse conductor is through the contact plate to the contact cup and then into the conductive rod. When flowing through the spiral structure of the contact cup, a clockwise eddy current is formed. This current generates a longitudinal magnetic field between the electrodes, pointing from the anode to the cathode. This longitudinal magnetic field can optimize the magnetic field distribution and achieve effective control of the arc. As the mechanism of the vacuum circuit breaker continues to operate, the vacuum circuit breaker contact with the built-in reverse conductor moves downward to a certain position. The support structure applies an upward supporting force to the reverse conductor, lifting the contact plate so that the contact plate is no longer in contact with the contact cup. At this time, the current flow path in the vacuum circuit breaker contact with the built-in reverse conductor is through the contact plate to the internal reverse conductor, then to the support structure, and finally into the conductive rod. When current flows through the internal reverse conductor, it forms counterclockwise eddy currents, generating a longitudinal magnetic field between the electrodes pointing from the cathode to the anode. This longitudinal magnetic field can effectively counteract the residual magnetic field present between the electrodes at this time. The vacuum circuit breaker significantly reduces the residual magnetic field between the electrodes when the current approaches zero crossing.

[0011] Furthermore, in this invention, an insulating sliding connector is provided between the contact cup and the contact piece.

[0012] Furthermore, in this invention, the aforementioned insulating sliding connector is configured as an insulating slide rod.

[0013] Furthermore, in this invention, the aforementioned support structure includes a sleeve fitted over the conductive rod, the top of the sleeve being provided with a support rod that inserts into the through groove and corresponds to the bottom surface of the contact cup, and the bottom of the sleeve being provided with a base plate, the base plate being provided with a through hole through which the conductive rod passes.

[0014] In the above technical solution, the structural design can ensure that the support structure stably supports the reverse conductor and achieves relative sliding with the conductive rod.

[0015] Furthermore, in this invention, the aforementioned through hole is provided with a brush that contacts the conductive rod, and the through groove is provided with a brush that contacts the supporting structure.

[0016] In the above technical solution, the brush setting can ensure a good electrical connection between the conductive rod and the support structure, and can conduct electricity stably even during relative sliding.

[0017] Furthermore, in this invention, the brush described above is configured as a graphite brush.

[0018] In the above technical solution, the graphite brush has good conductivity and wear resistance, and can meet the long-term sliding conductivity requirements.

[0019] Furthermore, in this invention, the contact piece described above is provided with a strip-shaped hole extending from the edge toward the center, and the outer end of the strip-shaped hole corresponds to the top end of the first spiral groove.

[0020] In the above technical solution, the connection between the strip hole and the first spiral groove is equivalent to extending the first spiral groove, which can improve the distribution characteristics of the magnetic field between the poles, weaken the residual magnetism between the poles at the moment when the current crosses zero, and improve the ability to break the vacuum arc.

[0021] Furthermore, in this invention, the number of the first spiral groove, the second spiral groove, and the strip-shaped holes are the same and they are all evenly distributed around the center, and the strip-shaped holes are configured as straight strip-shaped holes.

[0022] In the above technical solution, the uniformly distributed first spiral groove, second spiral groove, and strip hole can make the magnetic field distribution more uniform and improve the breaking performance.

[0023] Furthermore, in this invention, the material of the aforementioned reverse conductor is configured as a copper-chromium alloy.

[0024] In the above technical solution, copper-chromium alloy has good electrical conductivity and resistance to arc erosion, which can meet the requirements of reverse conductors under complex working conditions.

[0025] Secondly, the present invention also provides a vacuum circuit breaker that employs vacuum circuit breaker contacts with built-in reverse conductors.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] 1. By setting a reverse conductor inside the contact cup, and making the second spiral groove of the reverse conductor rotate in the opposite direction to the first spiral groove of the contact cup, reverse eddy currents can be generated when the circuit is broken. At the zero crossing, the reverse eddy currents can effectively cancel the residual magnetic field between the electrodes, greatly reducing the possibility of arc reignition and significantly improving the breaking reliability of the DC vacuum circuit breaker.

[0028] 2. The support structure, through the design of sleeves, struts, and base plates, stably supports the movement of the reverse conductor and maintains a good sliding electrical connection with the conductive rod through brushes, ensuring the stability and conductivity of the reverse conductor during operation.

[0029] 3. The strip holes on the contact plates correspond to the first spiral groove, which helps guide the arc movement. Combined with the magnetic field distribution, this improves the arc extinguishing effect and further enhances the breaking performance of the vacuum circuit breaker.

[0030] 4. Copper-chromium alloy is used as the material for the reverse conductor. Its good conductivity and resistance to arc erosion ensure the reliable operation of the reverse conductor under complex working conditions. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0032] Figure 1 This is a schematic diagram of the vacuum circuit breaker contact with a built-in reverse conductor according to the present invention;

[0033] Figure 2 This is a cross-sectional schematic diagram of the vacuum circuit breaker contact with a built-in reverse conductor according to the present invention.

[0034] Figure 3 This is a schematic diagram of the support structure of the present invention;

[0035] Figure 4 This is a schematic diagram of the end face of the contact piece of the present invention.

[0036] The attached diagram shows the markings and corresponding component names: 1-contact piece, 101-strip hole, 2-contact cup, 201-first spiral groove, 202-through groove, 3-conductive rod, 4-reverse conductor, 401-second spiral groove, 5-support structure, 501-sleeve, 502-support rod, 503-base plate, 5031-through hole. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are for explanation only and are not intended to limit the invention. The following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0038] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] Example 1

[0040] Combination Figures 1 to 4 As shown, this is a vacuum circuit breaker contact with a built-in reverse conductor provided in an embodiment of the present invention, and its specific structure is described below.

[0041] Combination Figure 1 As shown, the vacuum circuit breaker contact with built-in reverse conductor in Embodiment 1 of the present invention mainly includes five parts: contact piece 1, contact cup 2, conductive rod 3, reverse conductor 4, and support structure 5. The vacuum circuit breaker contact with built-in reverse conductor mainly serves as the moving contact in the circuit breaker and has a good breaking effect.

[0042] In some implementations of this embodiment, combined with Figure 1 As shown, contact piece 1 is a circular metal piece that serves to conduct electricity through contact.

[0043] Furthermore, in combination Figure 1 and Figure 2 As shown, the contact cup 2 is a circular cup with an internal cavity, which provides a mounting position for other components. The outer diameter of the contact cup 2 is the same as the outer diameter of the contact piece 1, and the contact piece 1 is installed at the top opening of the contact cup 2.

[0044] It should be noted that an insulating sliding connector is installed between the contact cup 2 and the contact plate 1. This insulating sliding connector can be an insulating slide rod. The top of the contact cup 2 and the contact plate 1 are provided with slots for connection to the insulating sliding connector. The insulating slide rod is fixed to the slot of the contact plate 1 and slidably connected to the slot of the contact cup 2. After the insulating sliding connector is installed, when the vacuum circuit breaker contact, which is the moving contact and has a built-in reverse conductor, moves to a certain position, the contact cup 2 and the contact plate 1 separate. After the circuit breaker completes the breaking and resets, the contact plate 1 and the contact cup 2 reassemble. The insulating sliding connector is designed to maintain the integrity of the vacuum circuit breaker contact with the built-in reverse conductor. Furthermore, during the initial period of breaking, due to the hysteresis effect, the magnetic flux density generated by the forward eddy current in the vacuum circuit breaker contact with the built-in reverse conductor will not be too high, so a reverse path is not needed to weaken it.

[0045] In some implementations of this embodiment, combined with Figure 2 As shown, the reverse conductor 4 is made of copper-chromium alloy and is installed inside the cavity of the contact cup 2. The structure of the reverse conductor 4 is similar to that of the contact cup 2, also being a circular cup shape. A first spiral groove 201 is formed on the side wall of the contact cup 2, and a second spiral groove 401 is formed on the side wall of the reverse conductor 4. The spiral direction of the second spiral groove 401 is opposite to that of the first spiral groove 201, causing the reverse conductor 4 to generate a current opposite to the direction of the eddy current inside the contact cup 2. The magnetic field generated by this current can cancel the magnetic field generated by the eddy current inside the contact cup 2, significantly reducing the residual magnetic field between the electrodes when the current approaches zero crossing.

[0046] Furthermore, in combination Figure 1 and Figure 4 As shown, a straight strip-shaped hole 101 is formed on the surface of the contact piece 1, extending from the edge of the contact piece 1 towards the center. The edge (i.e., the outer end) of the strip-shaped hole 101 is aligned with the top of the first spiral groove 201 on the contact cup 2. The strip-shaped hole 101 communicates with the first spiral groove 201, which is equivalent to extending the first spiral groove 201. This is beneficial for improving the distribution characteristics of the magnetic field between the electrodes, reducing the residual magnetism between the electrodes at the zero-crossing of the current, and improving the ability to break vacuum arcs.

[0047] Furthermore, in this embodiment, the number of the first spiral groove 201, the second spiral groove 401, and the strip hole 101 are all set to four, and they are all evenly distributed around the center of the contact cup 2. The centers of the contact piece 1, the contact cup 2, and the reverse conductor 4 are coaxial.

[0048] In this embodiment, combined with Figure 2 and Figure 3As shown, a support structure 5 is installed below the contact cup 2. The support structure 5 includes a sleeve 501 that fits over the conductive rod 3. A base plate 503 is installed at the bottom of the sleeve 501, and a through hole 5031 is opened in the center of the base plate 503. The conductive rod 3 passes through the through hole 5031. In order to allow the conductive rod 3 and the support structure 5 to slide relative to each other and maintain electrical connection, a graphite brush is installed in the through hole 5031. The graphite brush is connected to the outer wall of the conductive rod 3.

[0049] Furthermore, four through slots 202 are provided at the bottom of the contact cup 2, and the bottom surface of the reverse conductor 4 is covered by the four through slots 202. Four support rods 502 are installed on the top of the corresponding sleeve 501. The support rods 502 can be inserted into the through slots 202 and lift up the reverse conductor 4.

[0050] During installation, firstly, install the insulating slide rod between the contact cup 2 and the contact piece 1 to ensure that the insulating slide rod can properly perform its buffering function. Place the reverse conductor 4 inside the contact cup 2, with the second spiral groove 401 of the reverse conductor 4 rotating in the opposite direction to and corresponding to the first spiral groove 201 of the contact cup 2. Install the support structure 5, fitting the sleeve 501 over the conductive rod 3, inserting the support rod 502 into the through groove 202 at the bottom of the contact cup 2, and passing the through hole 5031 on the base plate 503 through the conductive rod 3, installing a graphite brush in the through hole 5031 to ensure good electrical connection and stable support between the support structure 5, the conductive rod 3, and the reverse conductor 4. Install the assembled contact assembly into the vacuum circuit breaker, connecting and fixing the support structure 5 to the circuit breaker housing using the insulating rod to ensure relative positional stability.

[0051] The working process is as follows: When the vacuum circuit breaker is in the closed state, the current forms the main current path through the conductive rod 3, contact cup 2, and contact piece 1. When it is necessary to interrupt the current, the contact piece 1 and contact cup 2 gradually separate. At the moment the current crosses zero, the reverse magnetic field generated by the reverse conductor 4 can effectively cancel the residual magnetism between the poles, greatly reducing the risk of arc reignition and ensuring that the vacuum circuit breaker can reliably interrupt the current. Throughout the interruption process, the support structure 5 maintains a good sliding electrical connection with the conductive rod 3 through graphite brushes, ensuring the stability of the reverse conductor 4. Furthermore, the support structure 5 also maintains good electrical contact with the bottom of the contact cup 2 through the brushes.

[0052] Example 2

[0053] This embodiment provides a vacuum circuit breaker that uses the vacuum circuit breaker contact with a built-in reverse conductor provided in Embodiment 1.

[0054] The working principle of the vacuum circuit breaker in this embodiment is as follows:

[0055] When the vacuum circuit breaker just starts to open, the moving and stationary contacts have just separated, and the breaking current is close to the peak current. At this time, the current flow path in the moving contact (i.e., the vacuum circuit breaker contact with a built-in reverse conductor) is through the contact piece 1 to the contact cup 2 and then into the conductive rod 3. When the current flows through the spiral structure of the contact cup 2, a clockwise eddy current will be formed. This current will generate a longitudinal magnetic field between the electrodes from the anode to the cathode. This longitudinal magnetic field can optimize the magnetic field distribution and achieve effective control of the electric arc.

[0056] The support structure 5 is in contact with the reverse conductor 4 from the beginning. To enable the support structure 5 to exert an upward force on the reverse conductor 4, it is inserted into the through hole 5031 at the bottom of the contact cup 2. Initially, the current needs to pass through the contact cup 2 and then to the conductive rod 3, so the support structure 5 needs to extend into the through hole 5031 from the beginning to maintain the integrity of the conductive path. As the vacuum circuit breaker mechanism operates, the moving contact (i.e., the vacuum circuit breaker contact with the built-in reverse conductor) moves. Since the support structure 5 remains relatively stationary, it will exert an upward supporting force on the reverse conductor 4 as the moving contact continues to move downward. Under the action of the supporting force, the internal reverse conductor 4 will contact the contact piece 1 and lift it up, so that the contact piece 1 is no longer in contact with the contact cup 2. At this time, the current flow path in the moving contact (i.e., the vacuum circuit breaker contact with the built-in reverse conductor) is through the contact piece 1 to the internal reverse conductor 4, then to the support structure 5, and finally into the conductive rod 3. When current flows through the internal reverse conductor 4, a counterclockwise eddy current is formed, generating a longitudinal magnetic field between the electrodes pointing from the cathode to the anode. This longitudinal magnetic field can effectively counteract the residual magnetic field present between the electrodes at this time, and the vacuum circuit breaker significantly reduces the residual magnetic field between the electrodes when the current approaches zero crossing.

[0057] This invention provides a vacuum circuit breaker contact with a built-in reverse conductor, comprising a contact piece 1, a contact cup 2, a conductive rod 3, a reverse conductor 4, and a support structure 5. The contact piece 1 is connected to the top of the contact cup 2, the conductive rod 3 is connected to the bottom of the contact cup 2, the reverse conductor 4 is disposed inside the contact cup 2, and the support structure 5 is connected to the circuit breaker housing via an insulating rod to ensure its relatively fixed position. The support structure 5 is movably connected to the reverse conductor 4 and always maintains an electrical connection. A through groove 202 is provided at the bottom of the contact cup 2 for the support structure 5 to be inserted. The contact cup 2 corresponds to the support structure 5 passing through the through groove 202. The side wall of the contact cup 2 is provided with a plurality of first spiral grooves 201, and the side wall of the reverse conductor 4 is provided with a plurality of second spiral grooves 401, the spiral direction of the second spiral grooves 401 being opposite to the spiral direction of the first spiral grooves 201. An insulating sliding connector is provided between the contact cup 2 and the contact piece 1. The insulating sliding connector is configured as an insulating slide rod. The support structure 5 includes a sleeve 501 fitted over the conductive rod 3. The top of the sleeve 501 has an insertion slot 202 and a support rod 502 corresponding to the bottom surface of the contact cup 2. The bottom of the sleeve 501 has a base plate 503 with a through hole 5031 through which the conductive rod 3 passes. A brush, configured as a graphite brush, is installed in the through hole 5031 to contact the conductive rod 3. The contact piece 1 has a strip-shaped hole 101 extending from the edge towards the center, with the outer end of the strip-shaped hole 101 corresponding to the top end of the first spiral groove 201. The number of the first spiral groove 201, the second spiral groove 401, and the strip-shaped holes 101 are the same and evenly distributed around the center. The strip-shaped holes 101 are configured as straight lines. The reverse conductor 4 is made of copper-chromium alloy.

[0058] The present invention also provides a vacuum circuit breaker that employs vacuum circuit breaker contacts with built-in reverse conductors.

[0059] Therefore, the vacuum circuit breaker contacts and vacuum circuit breaker with built-in reverse conductors of the present invention can solve the problem that the residual magnetism between poles affects the breaking effect when breaking in the prior art DC vacuum circuit breaker, and improve the breaking performance and reliability of DC vacuum circuit breaker.

[0060] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A vacuum circuit breaker contact with a built-in reverse conductor, characterized in that, It includes contact plate (1), contact cup (2), conductive rod (3), reverse conductor (4) and support structure (5). The contact piece (1) is connected to the top of the contact cup (2), the conductive rod (3) is connected to the bottom of the contact cup (2), the reverse conductor (4) is disposed inside the contact cup (2), the support structure (5) is connected to the circuit breaker housing through an insulating rod to ensure its position is relatively fixed, the support structure (5) is movably connected to the reverse conductor (4) and always maintains an electrical connection, the bottom of the contact cup (2) is provided with a through groove (202) for the support structure (5) to be inserted, the contact cup (2) corresponds to the support structure (5) passing through the through groove (202), The sidewall of the contact cup (2) is provided with a plurality of first spiral grooves (201), and the sidewall of the reverse conductor (4) is provided with a plurality of second spiral grooves (401). The spiral direction of the second spiral grooves (401) is opposite to that of the first spiral grooves (201). The support structure (5) includes a sleeve (501) sleeved outside the conductive rod (3). The top of the sleeve (501) is provided with a support rod (502) that is inserted into the through groove (202) and corresponds to the bottom surface of the contact cup (2). The bottom of the sleeve (501) is provided with a base plate (503). The base plate (503) is provided with a through hole (5031) through which the conductive rod (3) passes. The through hole (5031) is provided with a brush that contacts the conductive rod (3), and the through groove (202) is provided with a brush that contacts the support structure (5).

2. The vacuum circuit breaker contact with a built-in reverse conductor according to claim 1, characterized in that, An insulating sliding connector is provided between the contact cup (2) and the contact piece (1).

3. The vacuum circuit breaker contact with a built-in reverse conductor according to claim 2, characterized in that, The insulating sliding connector is configured as an insulating slide rod.

4. The vacuum circuit breaker contact with a built-in reverse conductor according to claim 1, characterized in that, The brush is configured as a graphite brush.

5. The vacuum circuit breaker contact with a built-in reverse conductor according to claim 1, characterized in that, The contact piece (1) is provided with a strip hole (101) extending from the edge toward the center, and the outer end of the strip hole (101) corresponds to the top end of the first spiral groove (201).

6. The vacuum circuit breaker contact with a built-in reverse conductor according to claim 5, characterized in that, The number of the first spiral groove (201), the second spiral groove (401), and the strip hole (101) are the same and they are all evenly distributed around the center. The strip hole (101) is configured as a straight strip hole (101).

7. The vacuum circuit breaker contact with a built-in reverse conductor according to claim 1, characterized in that, The reverse conductor (4) is made of copper-chromium alloy.

8. A vacuum circuit breaker, characterized in that, The vacuum circuit breaker contacts with a built-in reverse conductor as described in claim 1 are used.

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