WO2017028891A1

WO2017028891A1 - Damper and circuit breaker with damper

Info

Publication number: WO2017028891A1
Application number: PCT/EP2015/068831
Authority: WO
Inventors: Ara BISSAL; Ener SALINAS; Jesper Magnusson
Original assignee: Abb Schweiz Ag
Priority date: 2015-08-17
Filing date: 2015-08-17
Publication date: 2017-02-23

Abstract

The present disclosure relates to a damping device (100) comprising a first element (340) extending along an axial direction (320) and a magnetic assembly (330). The first element includes at least a first section (342) and a second section (344). The first section includes a conductive material of a first electrical conductivity and the second section includes a conductive material of a second electrical conductivity higher than the first electrical conductivity. The first section and the second section are arranged such that the magnetic assembly magnetically engages the first section prior to the second section to damp a relative displacement between the first element and the magnetic assembly along the axial direction.

Description

DAMPER AND CIRCUIT BREAKER WITH DAMPER

TECHNICAL FIELD

The present disclosure relates generally to the field of damping systems and more particularly to a magnetic damping device. The present disclosure relates also to a circuit breaker including a magnetic damping device, in particular for high voltage direct current or medium voltage direct current (HVDC or MVDC) applications or other types of actuators.

BACKGROUND

In high voltage systems such as in multi-terminal high voltage direct current (HVDC) grids, it is of great importance that the current through a transmission line can be interrupted in case of a failure event, in order to protect system equipment and system users from damage caused by the fault current. One of the key enabling technologies for such HVDC systems is therefore the existence of a circuit breaker that can operate within a few milliseconds as, otherwise, due to the low impedance of HVDC systems, fault currents would increase quickly in magnitude and become harder to interrupt unless they are interrupted promptly. One way to achieve such short interruption times is to use a circuit breaker equipped with an ultra-fast Thomson actuator. After acceleration of at least one element of the current carrying contact system for interrupting the current, it is decelerated upon the application of a controllable force within a short period of time. To decrease the speed of the moving element, a damper or damping system connected to the Thomson actuator may be used. The present disclosure is concerned with the challenge of providing a damping device, for e.g. HVDC circuit breakers, with improved damping efficiency.

SUMMARY

An object of at least some embodiments of the present disclosure is to wholly or at least partly address the above mentioned issues. In particular, it is an object of at least some embodiments of the present disclosure to provide a damping device with improved damping efficiency.

This and other objects are achieved by means of a damping device as defined in the appended independent claim. Other embodiments are defined by the dependent claims.

According to a first embodiment, there is provided a damping device comprising a first element extending along an axial direction and a magnetic assembly. The first element includes at least a first section and a second section. The first section includes a conductive material of a first electrical conductivity and the second section includes a conductive material of a second electrical conductivity. The second electrical conductivity is higher than the first electrical conductivity. The first section and the second section are arranged such that the magnetic assembly magnetically engages the first section prior to the second section to damp a relative displacement between the first element and the magnetic assembly along the axial direction.

Upon a relative displacement between the magnetic assembly and the first element comprising conductive material, a moving magnetic field is created. For example, the magnetic assembly (such as e.g. a magnet or an array of magnets) may be moving relative to the first element (e.g. an opened tube, wherein the magnetic assembly may for example travel through the tube). The moving magnetic field creates Eddy currents in the first element (e.g. the tube), thereby converting the kinetic energy into heat and hence decreasing the speed of the moving element (either one of the first element or the magnetic assembly), i.e. providing a damping effect. If there is a relative displacement between the magnet assembly (e.g. placed inside the tube) and the first element (the tube itself), an axially directed damping force is created.

In the present embodiment, there is provided a damping device in which the first element includes at least two sections of two different electrical conductivities. The damping device provides an improved damping since in a magnetic damper the generated damping force is highly dependent on the electrical conductivity of the element magnetically engaged by the magnetic assembly. For low speeds, the damping force may increase linearly with speed while, afterwards, the damping force may reach a peak at a certain speed and start decreasing. If the conductivity of the first element and the relative speed between the magnet assembly and the first element do not match, then the damping force may not be optimal. With the present embodiment, the damping efficiency is improved, or in other words a more optimal damping force is obtained, using a first element (or tube as in the example described above) having a first section with a conductive material of electrical conductivity being lower than the electrical conductivity of the second section, the second section being arranged after the first section such that the magnetic assembly first

magnetically engages the first section. In particular, the first element may include a first section having a lower electrical conductivity as it provides a larger damping force at higher velocities and a second section having a higher electrical conductivity (at least in comparison to that of the first section) as it provides a larger damping force at lower velocities.

In other words, the present embodiment provides a damping device with a hybrid first element (or hybrid tube) having different electrical conductivities based on the velocity of the moving element, i.e. the velocity of either one of the first element and/or the magnetic assembly (i.e. the velocity corresponding to the relative displacement). The first element (or tube) may be segmented into different parts or segments each made of a material having a different conductivity. The conductivity of each part may be selected in a way to match the velocity of the moving element (should it be the first element itself or the magnetic assembly, as induced by a drive or other actuating means connected to the first element or the magnetic assembly) at that position to maximize, or at least increase, the damping force. Thus, the first element, in a direction opposite to the direction of displacement of the magnetic assembly relative to the first element, includes, along its extension along the axial direction (i.e. its length or height), first a segment with a material of lower electrical conductivity and then one or more other segments of increased electrical

conductivity. The damping device provides an axially oriented damping force, i.e. a damping force along the axial direction along which the first element extends. As the amplitude of the damping force is depending on velocity, the axially oriented damping force may vary as the first element and/or the magnetic assembly is decelerated. However, the second element comprises a number of sections (or segments) which are arranged such that the damping force is optimal (or maximized) at each of these sections, i.e. the electrical conductivity of the material in a specific section is selected to increase (maximize) the damping. It will be appreciated that the length (or size) of a section of the first element will depend at least on the initial acceleration applied to the first element and/or the magnetic assembly and also on the electrical conductivity of the material forming the section in question.

By the term magnetically engage is meant that the magnetic assembly is configured to magnetically interact with the first element such that a magnetic field is created therebetween. As a result of the created magnetic field, an axially oriented repulsive force is applied on the first element, thereby providing a damping effect.

By the term section is meant a part or segment of the first element. The first element extends along the axial direction and may be divided into segments or sections along this axial direction. A segment or section therefore extends along a certain length along the axial direction. The assembly of the different sections forms the first element. By way of examples, different materials having different electrical conductivities (e.g. the different sections) may be screwed together. Alternatively, the different sections may be attached from the outside. Another possibility would also be to manufacture a tube having a varying electrical conductivity along its axial direction.

In general, with the damping device, a damping of at least the first element relative to the magnetic assembly (or vice versa) is provided to avoid any collision between the first element and any other component of the system at which the damping device is installed. This is advantageous as a collision might lead to excessive mechanical stresses exceeding the ultimate yield strength of fragile components, thereby deforming them permanently and/or reducing their lifetime.

In the present embodiment, a linear displacement of the first element relative to the magnetic field, or vice versa, is envisaged. The linear displacement is along an axial direction along which the first element extends or along which the magnetic assembly may be displaced (moved).

Referring again to the exemplifying configuration of a magnetic assembly traveling through a tube, the tube may be segmented into several sections with different electrical conductivities. The conductivity in each segment may be selected based on the relative velocity between the tube and the magnet assembly. With an appropriate choice of the electrical conductivity of the various segments, the damping force peak can be shifted to maximize it. For example, materials with lower electrical conductivity may generate a larger damping force compared with material with higher electrical conductivity at high speeds. A first section of the tube may therefore comprise material of lower electrical conductivity to improve the damping force in a first part of the damping, i.e. a first part of the relative displacement between the tube and the magnetic assembly.

Accordingly, in some embodiments, the first section and the second section may be arranged such that a first damping force is applied via the first section in a first part of the relative displacement along the axial direction and a second damping force is applied via the second section in a second part of the relative displacement along the axial direction. With such an arrangement, a more optimal first damping force is applied during the first part of the relative displacement between the magnetic assembly and the first element (corresponding to the length of the first section of the first element) since the first section of the first element has a lower electrical conductivity and a more optimal second damping force is applied during the second part of the relative displacement between the magnetic assembly and the first element (corresponding to the length of the second section of the first element) since the second section of the first element has a higher electrical conductivity . Although the above embodiments are described with reference to a first section and a second section, it will be appreciated that the first element may be divided into more than two sections. According to some embodiments, the first element may include a plurality of sections extending along the axial direction. The sections may be arranged in a successive order as a function of increased conductivity such that the magnetic assembly magnetically engages a section of higher conductivity before engaging a section of lower conductivity. In other words, from an overlapping point between the first element and the magnetic assembly or a point at which the magnetic assembly starts to magnetically engage the first element, the first element includes sections of increasing electrical conductivities.

According to some embodiments, the first element may further comprise at least a third section including a conductive material of a third electrical conductivity higher than the second electrical conductivity, the second section being arranged between the first section and the third section along the axial direction. In a more specific embodiment, the first section may be made of steel, the second section may be made of aluminum and the third section may be made of copper. According to an embodiment, the magnetic assembly may be arranged to translate within the first element. In another embodiment, the first element may be arranged to translate within the magnetic assembly (under the relative displacement along the axial direction). Different configurations may be envisaged. In a first configuration, the magnetic assembly may be inserted within the first element, such as e.g. via a shaft on which the magnetic assembly is mounted, the shaft moving within the first element (e.g. a tube). In this configuration, the motion of the magnetic assembly within the tube or the motion of the tube around the magnetic assembly creates an axially oriented damping force. In another configuration, the first element may be inserted within the magnetic assembly, such as a tube moving within a guide or other support including a magnetic assembly. In this configuration, the motion of the magnetic assembly via the guide or the motion of the tube within the guide creates an axially oriented damping force. As mentioned above, according to some embodiments, the damping device may further comprise a second element extending along the axial direction, the magnetic assembly being secured to the second element. In some embodiments, the second element may be a shaft or guide at which the magnetic assembly is disposed. Further, the first element may be a tube.

According to some embodiments, the conductive material may include copper, aluminum, titanium, steel, non-magnetic stainless steel or any combination or alloy thereof. The present embodiments are however not limited to these materials and other materials may be envisaged provided that they are electrically conductive. In some embodiments, two adjacent (or successive) sections of the first element (tube) may be made of two different materials having two different electrical conductivities. In some other embodiments, two adjacent (or successive) sections of the first element (tube) may be made of the same type of material but having two different electrical conductivities.

According to an embodiment, the magnetic assembly may include one magnet, one electromagnet or a series of magnets and/or electromagnets. In some further embodiments, the magnetic assembly may further comprise at least one ferromagnetic spacer and/or at least one polymer spacer. A spacer is arranged between two successive magnets.

According to some embodiments, the first element may be fixed and the magnetic assembly may be movable relative to the first element. Alternatively, in some other embodiments, the magnetic assembly may be fixed and the first element may be movable relative to the magnetic assembly. The relative displacement between the first element and the magnetic assembly may be obtained by either a motion of the first element and/or a motion of the magnetic assembly. In some embodiments, one of the first element and the magnetic assembly is fixed while the other one is movable. According to some embodiments, a lateral extension of the magnetic assembly along the axial direction may be less than a size of a section of the first element. With the present embodiment, the design of the damping device is facilitated as one section or part of the tube having a certain electrical conductivity will be facing the magnetic assembly at a time. It is only for a reduced part or surface of the tube, at the junctions between two adjacent sections, that materials of two different electrical conductivities may be facing the magnetic assembly simultaneously.

According to some embodiments, an actuator may be provided. The actuator may include a damping device as defined in any one of the preceding embodiments, a movable part and an energy source. The movable part may be connected to either one of the first element or the magnetic assembly of the damping device. The first element or the magnetic assembly to which the movable part is connected may be movable. Further, the energy source may be adapted to actuate the movable part in translation along the axial direction.

For example, in a damping device in which the magnetic assembly is fixed and the first element is movable, the movable part of the actuator may be connected to the first element such that, upon activation of the movable part (for e.g. disengaging two pieces of another system at which the actuator is mounted), the movable part brings the first element into motion. Once the first element is in motion and brought close to the magnetic assembly, the magnetic assembly engages magnetically with the first element such that an axially oriented damping force is applied to the first element. The energy source may be any king of energy sources providing the required energy for creating or generating a motion of the movable part of the actuator. By way of example, the energy source may comprise a coil and a capacitor bank and may be based on the Thomson effect. However, other types of energy sources may be envisaged.

It will be appreciated that the movable part of the actuator and the first element may be a single piece or two separate pieces attached together such that the first element is an extension of the movable part along the axial direction. Further, the first element and the movable part of the actuator may not necessarily be aligned along the axial direction and the movable part of the actuator may not necessarily extend along the axial direction. However, the first element may be secured to, or at least connected to, the movable part such that a motion of the movable part causes a relative

displacement between the first element and the magnetic assembly of the damping device.

According to some embodiments, a circuit breaker may be provided. The circuit breaker may include a damping device as defined in any one of the preceding embodiments and an actuator. The actuator may be arranged to disconnect at least two electrical contacts of a transmission line (for example a direct current

transmission line) by motion of a movable part upon an electrical failure event. The movable part of the actuator may be connected to the first element or the magnetic assembly of the damping device, the first element or the magnetic assembly to which the movable part is connected being movable (relative to the other one). With such a magnetic damper or damping device (based on the hybrid first element, or hybrid tube) incorporated to damp an acceleration provided by the actuator to disconnect the electrical contacts (for current interruption upon a failure event), the circuit breaker (or HVDC breaker) may have a more extended lifetime.

For example, the circuit breaker may function as an interrupter wherein, upon activation via the actuator, two electrical contacts become disconnected to interrupt the current flowing through a transmission line along which these two electrical contacts are installed. A motion of the movable part of the actuator connected to at least one of the two electrical contacts (or to any other intermediate piece) causes the disconnection of the two contacts. The present embodiments are not limited to a specific arrangement of the electrical contacts. The embodiments described herein are applicable for HVDC circuit breakers but may also be applicable to any other types of apparatuses, machines and systems for improved damping of an accelerated piece. In particular, the damping devices described herein may be suitable for circuit breakers to be used in both ac and dc systems.

It will be appreciated that other embodiments using all possible combinations of features recited in the above described embodiments may be envisaged.

BRIEF DESCRIPTION OF THE DRAWING

Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings:

Figure 1 shows a damping device in accordance with an embodiment;

Figure 2 illustrates the dependence of the damping force on the velocity for three different types of material according to some embodiments;

Figure 3 shows a damping device in accordance with an embodiment and illustrates the operation principle of such a damping device;

Figures 4 and 5 schematically show different configurations of damping devices according to some embodiments;

Figure 6 shows different arrangements of magnetic assemblies in according with some embodiments;

Figure 7 is a graph illustrating the velocity of an armature mounted with a magnet array for different initial speeds and different materials in accordance with some embodiments;

Figure 8 is a graph illustrating the velocity of an armature mounted with a magnet array for different initial speeds and different materials in accordance with yet further embodiments; and

Figure 9 is a schematic view of a circuit breaker according to some embodiments.

As illustrated in the figures, the sizes of the elements, modules and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the embodiments. Like reference numerals refer to like elements throughout. DETAILED DESCRIPTION

Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

With reference to Figure 1, a damping device 100 according to an embodiment is described.

Figure 1 shows a schematic view of a damping device 100 comprising a first element 140 extending along an axial direction 120, a second element 110 extending along the axial direction 120 and a magnetic assembly 130 secured to the second element 110.

The second element 110 may for example be a shaft or guide on which the magnetic assembly 130 is mounted. However, it will be appreciated that the magnetic assembly may be mounted on other kind of structures in order to be translated. Further, in some embodiments, the magnetic assembly is immobile (or fixed) and it is the first element 140 that is movable relative to the magnetic assembly. The magnetic assembly is arranged (or mounted on a shaft 110 extending) along the axial direction 120.

The magnetic assembly 130 may be an array of magnets disposed next to each other. Various arrangements of magnets may be used to form the magnetic assembly and examples will be described with reference to Figure 5.

In the specific embodiment shown in Figure 1, the magnetic assembly 130 is secured in translation to the shaft 110 such that a translation of the shaft 110 along the axial direction 120 causes a translation of the magnetic assembly 130 along the axial direction 120. In other words, the second element or shaft 110 acts as a guide for the magnetic assembly 130. Although not shown in Figure 1, a translation of the shaft 110 along the axial direction 120 may be induced by an actuator, or more specifically a movable part of an actuator, connected to the shaft 110. Such an actuator may for example be part of a circuit breaker such that the actuator is configured to disconnect two electrical contacts of a transmission line. In some other embodiments, the shaft 110 itself may be the movable part of the actuator.

In the embodiment shown in Figure 1, the shaft 110 with the magnetic assembly 130 are arranged to translate or glide within the first element 140. For this purpose, the shaft 110 may be equipped with one or more shaft guides 112 to facilitate the insertion of the shaft within the first element 140. In the present embodiment, the first element 140 may be a tube, in particular an opened tube within which the shaft 110 and the magnetic assembly 130 may be inserted. It will be appreciated that in other embodiments, the tube may be arranged to move along the axial direction while the shaft with the magnetic assembly are immobile.

Upon translation of the shaft 110 within the tube 140, the magnetic assembly 130 magnetically engages the tube 140 to damp a displacement of the shaft within the tube 140 with an axially oriented damping force (i.e. a damping force oriented along the axial direction 120).

The tube 140 may include at least a first section (or first segment) 142 and a second section (or second segment) 144. Each of the first and second sections extends a definite length along the axial direction 120. The first section 142 includes a conductive material of a first electrical conductivity σι and the second section 144 includes a conductive material of a second electrical conductivity σ₂ higher than the first electrical conductivity σι.

The first section 142 and the second section 144 are arranged such that the magnetic assembly 130 magnetically engages the first section 142 prior to the second section 144 to damp the displacement of the shaft 110 within the tube 140. As a result, a first damping force is applied via the first section 142 in a first part of the displacement of the shaft 110 along the axial direction 120 and a second damping force is applied via the second section 144 in a second part of the displacement of the shaft 110 along the axial direction 120. Although in the present example the damping device 100 is described to damp a displacement of the shaft 110 within the tube 140, it will be appreciated that the same principle applies for damping of a displacement of the tube 140 relative to the shaft 120. This will be further illustrated with respect to Figure 3. Thus, instead of referring to a displacement of the shaft 110 within the tube 140, reference may be made to a displacement of the shaft 110 relative to the tube 140, disregarding of whether it is the shaft 110, the tube 140 or both that are moving.

More generally, as will be explained with reference to Figure 3, the embodiments described herein rely on the relative displacement between the first element (e.g. the tube 140) and the magnetic assembly 130. With reference to Figure 2, the dependence of the damping force on velocity for three different types of material according to some embodiments (for instance for the damping device shown for example in Figure 1) is described.

Figure 2 shows the damping force of an array of magnets versus speed for three different materials of a first element (tube) having different conductivities, namely copper, aluminum and steel. Figure 2 illustrates that the copper tube has the largest damping force for velocities between 0-6 m/s while the aluminum tube has the largest damping force for velocities in the range of 6-25 m/s and the steel tube has the largest damping force for velocities exceeding 25 m/s.

Figure 2 illustrates that an electrically conductive material of a higher conductivity is more suitable for damping a moving element (should it be the magnetic assembly or the first element itself) having a lower velocity, and vice versa. Accordingly, in the damping device, a first section having a first electrical conductivity lower than the electrical conductivity of a subsequent section is used to damp the moving element in a first part of its displacement, i.e. when the moving element still has a higher velocity. Once the moving element has been decelerated and the speed reaches a lower level, then a second section of a higher conductivity is more suitable for damping.

Figure 2 is a simulation for three different materials but the embodiments described herein are not limited to the use of these three materials only. Other materials may be used to form the tube and in particular to form the various sections of the tube such that the sections are arranged in a successive order with a section of lower conductivity being used to damp a first part of the displacement (i.e. at higher velocities) while a section of higher conductivity is used to damp a subsequent part of the displacement (i.e. at lower velocities). By way of examples, the conductive material to be used to form the sections of the tube (or first element 140) may include copper, aluminum, titanium, steel, non-magnetic stainless steel or any combination or alloy thereof. With reference to Figure 3, the operation principle of a damping device 300 in accordance with an embodiment is illustrated.

Figure 3 shows a cross-sectional view of a damping device 300 including a first element 340 and a magnetic assembly 330. The damping device 300 may be equivalent to the damping device 100 described with reference to Figure 1. Figure 3 illustrates the relative positioning of the magnetic assembly 330 and the first element 340 at three time instants (ti, t₂ and t₃). In this figure, "M" denotes the magnet assembly (or the magnet), "v" the velocity and "t" the time. The first element 340 of the damping device 300 includes at least three sections 342, 344 and 346. The first section 342 includes conductive material of a first electrical conductivity σι, the second section 344 includes conductive material of a second electrical conductivity σ₂ and the third section 346 includes conductive material of a third electrical conductivity σ₃. The first electrical conductivity σι is lower than the second electrical conductivity σ₂ which itself is lower than the third electrical conductivity σ₃ (σι<σ₂< σ₃). In this arrangement, the second section 344 is arranged between the first section 342 and the third section 346 along the axial direction 320. For example, the first section 342 may be made of steel, which has an electrical conductivity σι in the range of about 2x 10⁶ S/m and thereby is adapted to damp a relative displacement between the magnetic assembly and the first element at higher speeds vi (e.g. above 25m/s such as at the beginning of the motion). Figure 3 illustrates such a scenario with the magnetic assembly 330 facing, at the time instant ti, the first section 342 of the tube 340 such that the magnetic assembly 330 magnetically engages the first section 342. The second section 344 may be made of aluminum, which has an electrical conductivity σ₂ in the range of about 3.5 ^χ 10⁷ S/m and thereby is adapted to damp a relative displacement between the magnetic assembly 330 and the first element 340 at slightly lower speeds v₂ (e.g. in the range of 6-25 m/s). Figure 3 illustrates such a scenario with the magnetic assembly 330 facing, at the time instant t₂, the second section 344 of the tube 340 such that the magnetic assembly 330 magnetically engages the first section 342. The third section 346 may be made of copper, which has an electrical conductivity σ₃ in the range of about 6^X 10⁷ S/m and thereby is adapted to damp a relative displacement between the magnetic assembly 330 and the first element 340 at even lower speeds v₃ (e.g. below 6 m/s). Figure 3 illustrates also such a scenario with the magnetic assembly 330 facing, at the time instant t₃, the third section 346 of the tube 340 such that the magnetic assembly 330 magnetically engages the third section 346.

Although Figure 3 specifically shows three sections, the first element 340 of the damping device may include a plurality of sections extending along the axial direction 320, wherein the sections are arranged in a successive order. The electrical conductivity of the sections may be selected such that the magnetic assembly magnetically engages a section of higher conductivity before engaging a section of lower conductivity.

As shown in Figure 3, a lateral extension of the magnetic assembly 330 along the axial direction 320 is less than a size of a section of the first element 340. With reference to Figures 4 and 5, different configurations of damping devices according to some embodiments are described.

Figure 4 is a cross-sectional view of a damping device in accordance with an embodiment. Figure 4 shows a first configuration of a damping device including a magnetic assembly 430 and a tube (or armature) 440 extending along an axial direction 420.

The magnetic assembly 430 is arranged along the axial direction 420 such that it can be located within the tube 440. In this configuration, either one of the magnetic assembly 430 or the tube 440 may be configured to move. In the embodiment shown in Figure 4, the magnetic assembly 430 is disposed on a shaft 410 which may be arranged to translate within the tube 440, thereby providing a relative displacement between the magnetic assembly 430 and the tube 440, which in turn creates an axially oriented damping force (along the axial direction 420). The tube 440 includes three sections 442, 444, 446, which may be designed and arranged such as described above with reference to Figures 1-3.

Figure 5 is a cross-sectional view of a damping device in accordance with another embodiment. Figure 5 shows another configuration of a damping device including magnetic assembly 530 and a tube (or armature) 540 extending along an axial direction 520.

The magnetic assembly 530 is arranged along the axial direction 520 such that it can be located around the tube or shaft 540. In this configuration, either one of the magnetic assembly 530 or the tube 540 may be configured to move. In the embodiment shown in Figure 5, the magnetic assembly 530 is disposed on a guide or tube 510 which may be arranged to translate with respect to the tube or shaft 540, thereby providing a relative displacement between the magnetic assembly 530 and the tube 540, which in turn creates an axially oriented damping force (along the axial direction 520). The tube 540 includes three sections 542, 544, 546, which may be designed and arranged such as described above with reference to Figures 1-3. In the embodiments shown in Figures 4 and 5, the magnetic assembly may in some embodiments be configured to be immobile while the first element is movable along the axial direction or, in some other embodiments, configured to be movable along the axial direction while the first element is immobile (fixed).

With reference to Figure 6, different topologies of magnetic assemblies which may be used in any of the embodiments described herein are described. Figure 6 shows different arrangements A to E of magnetic assemblies comprising axially magnetized magnets, in according with some embodiments.

Configurations A to E show five different topologies that make use of axially magnetized magnets. In configuration A, a magnet assembly 610 comprises two magnets 611 and 612 stacked on top of each other. Since the magnets 611 and 612 are magnetized in the same direction, they attract each other. Thus, this assembly is more easy to form. Two plastic spacers (or polymer spacers) 613 and 614 are arranged at the extremities of the magnetic assembly 610. In configuration B, a magnetic assembly 620 comprises two axially magnetized magnets 621 and 622 which are separated by a plastic spacer 625. The magnetic assembly 620 comprises also two plastic spacers 623 and 624 at its extremities. In configuration C, a magnetic assembly 630 comprising two axially magnetized magnets 631 and 633 oriented in opposite directions is shown. The magnets 631 and 633 may be mounted on a plastic shaft and are separated by plastic spacers 633-635. Configuration D corresponds to a magnetic assembly 640 resembling configuration B but differs in the choice of material for the spacers. The spacers 643-645 are in this case ferromagnetic.

Similarly, configuration E resembles configuration C and again differs by the choice of the spacers 653-655. Figures 7 and 8 show experimental results illustrating the concept used in the design of the damping devices according to embodiments of the invention. For this purpose, prototypes were built and tests were performed, some with a copper tube and some with an aluminum tube. An array of magnets were actuated with a Thomson drive with increasing initial speeds to verify that the velocity of the magnets inside the aluminum tube decreases faster in comparison with the copper tube for high velocities, and vice versa for lower velocities.

Figures 7 and 8 show the dependencies of the velocity of the magnets as a function of the position in the tube for different initial speeds (or different accelerations). The magnets were mounted on an armature which was accelerated via a capacitor bank. A discharge of the capacitor bank accelerates the armature at a certain initial speed. The acceleration (or initial speed) is varied by adjusting the discharge level, as represented by the different voltage levels in the figures. The armature was accelerated with voltage levels of 200, 600, 800, 1000, 1200, 1400 and 1600 Volts. For each voltage level (i.e. for each acceleration), the results obtained for the aluminum tube (Al) are shown with continuous lines in the graphs while the results for the copper tube (Cu) are shown with interrupted (or dashed) lines.

Figure 7 is a graph illustrating the velocity of an armature mounted with a magnet array for higher initial speeds corresponding to discharges of 1400 and 1600 Volts for two tubes of two different materials. As can be seen, for a discharge of 1400 V, the velocities are about the same. However, for a discharge of 1600 V, the velocity of the magnets in an aluminum tube decreases faster than in a copper tube. In other words, a larger damping force is obtained in the aluminum tube at 1600 V (i.e. for the highest velocity).

Figure 8 is a graph illustrating the velocity of an armature mounted with a magnet array for lower initial speeds corresponding to discharges of 200, 600, 800, 1000 and 1200 Volts for two tubes of two different materials (aluminum and copper). From this graph, it can be seen that as the speed increases, copper and aluminum behave almost similarly. Further, this graph shows the opposite of the previous graph in that the velocity of the magnets in the copper tube decreases faster in comparison with the velocity of the magnets in the aluminum tube. In conclusion, for low velocities, a copper tube provides a higher damping force than an aluminum tube. Once higher speeds are attained, aluminum provides a higher damping force than copper.

Referring to the damping devices described with reference to Figures 1-6 for instance, with the correct choice of electrical conductivities in the various sections of the first element (e.g. tube), the damping force peak can be shifted to be maximized, or at least increased. A material of lower electrical conductivity may generate a larger damping force compared to a material of higher electrical conductivity at higher speeds (or accelerations). A material of higher electrical conductivity may generate a larger damping force compared to a material of lower electrical conductivity at lower speeds (or accelerations).

The circuit breaker 900 includes an actuator 980 arranged to disconnect at least two electrical contacts 992, 994 of a direct current transmission line 990 by motion of a movable part 982 upon an electrical failure event.

By way of example, the actuator may be based on the Thomson effect, wherein high current time variations are generated in a coil by using a capacitive discharge delivered by a capacitor bank. Induced currents may then be developed in the movable part located proximate to the coil. The induced currents generate a magnetic flux opposed to the one that has created them and, as a consequence, a repulsion effect appears between the coil and the movable part. As the coil is fixed, the movable part is propelled along the axial direction and undergoes a high acceleration. Figure 9 schematically illustrates an actuator with a coil 984 and a capacitor bank 986 delivering a capacitive discharge to the coil 984, thereby causing a translation of the movable part 982 along the axial direction 920. It will be appreciated that Figure 9 is only a schematic illustration showing some of the components of an actuator 980 and that Figure 9 does not necessarily reflect the exact arrangement of an actuator based on the Thomson coil principle. In particular, the Thomson coil may include a spirally shaped flat coil with a conductive armature in its proximity. The armature may include an electrically conductive disc or ring. The capacitive discharge may be triggered upon detection of an electrical failure event in the DC transmission line 990, thereby disconnecting the two electric contacts 992, 994 within a few milliseconds.

As a high acceleration is applied to the movable part 982 of the actuator 980, the actuator 980 may be equipped with a damping device 950 as defined in any one of the preceding embodiments, i.e. such as described with reference to the preceding figures. In the embodiment shown in Figure 9, the movable part 982 is connected to the magnetic assembly 930 of the damping device 950 which is movable relative to the first element 940 of the damping device. The magnetic assembly 930 may be mounted on a shaft connected (or secured) in translation to the movable part 982 of the actuator. Alternatively, the magnetic assembly may be directly mounted on the movable part 982. In other words, the movable part 982 may be part of the damping device in that it provides a translation of the magnetic assembly 930 along the axial direction 920.

As in the above described embodiments, the first element 940 includes a series of segments 942-946 of increased conductivity such as to provide an improved damping force to the movable part 982.

It will be appreciated that, in other embodiments, the movable part may be connected to the first element of the damping device which is movable relative to the magnetic assembly.

Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. It will be appreciated that the claimed invention by no means is limited to a first element with only two sections. Further, the claimed invention is not limited to damping devices for circuit breakers. In principal, the damping device may be configured to operate with any actuator for damping any movable member or element of the actuator. In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

Claims

A damping device (300) comprising:

a first element (340) extending along an axial direction (320);

a magnetic assembly (330);

wherein the first element includes at least a first section (342) and a second section (344), the first section including a conductive material of a first electrical conductivity and the second section including a conductive material of a second electrical conductivity higher than the first electrical conductivity; wherein the first section and the second section are arranged such that the magnetic assembly magnetically engages the first section prior to the second section to damp a relative displacement between the first element and the magnetic assembly along the axial direction.

2. The damping device of claim 1, wherein the first section and the second section are arranged such that a first damping force is applied via the first section in a first part of the relative displacement along the axial direction and a second damping force is applied via the second section in a second part of the relative displacement along the axial direction.

3. The damping device of claim 1 or 2, wherein the first element is arranged to translate within the magnetic assembly or wherein the magnetic assembly is arranged to translate within the first element under the relative displacement along the axial direction.

4. The damping device of any one of the preceding claims, wherein the first

element is a tube.

5. The damping device of any one of the preceding claims, further comprising a second element (110) extending along the axial direction, the magnetic assembly (130) being secured to the second element.

6. The damping device of claim 5, wherein the second element is a shaft, or guide, at which the magnetic assembly is disposed.

7. The damping device of any one of the preceding claims, wherein the

conductive material includes copper, aluminum, titanium, steel, non-magnetic stainless steel or any combination or alloy thereof.

8. The damping device of any one of the preceding claims, wherein the first element further comprises at least a third section (346) including a conductive material of a third electrical conductivity higher than the second electrical conductivity, the second section being arranged between the first section and the third section along the axial direction.

9. The damping device of claim 8, wherein the first section is made of steel, the second section is made of aluminum and the third section is made of copper.

10. The damping device of any one of the preceding claims, wherein the magnetic assembly includes one magnet, one electromagnet or a series of magnets and/or electromagnets.

11. The damping device of claim 10, wherein the magnetic assembly further comprises at least one ferromagnetic spacer and/or at least one polymer spacer.

12. The damping device of any one of the preceding claims, wherein the first element is fixed and the magnetic assembly is movable relative to the first element or wherein the magnetic assembly is fixed and the first element is movable relative to the magnetic assembly.

13. The damping device of any one of the preceding claims, wherein the first element includes a plurality of sections extending along the axial direction, the sections being arranged in a successive order as a function of increased conductivity such that the magnetic assembly magnetically engages a section of higher conductivity before engaging a section of lower conductivity.

14. The damping device of any one of the preceding claims, wherein a lateral extension of the magnetic assembly along the axial direction is less than a size of a section of the first element.

15. An actuator (980) including:

a damping device as defined in any one of the preceding claims; and a movable part connected to either one of the first element or the magnetic assembly of the damping device, the first element or the magnetic assembly to which the movable part is connected being movable; and

an energy source adapted to actuate the movable part in translation along the axial direction.

16. A circuit breaker (900) including:

an actuator arranged to disconnect at least two electrical contacts of a transmission line by motion of a movable part upon an electrical failure event; and

a damping device as defined in any one of claims 1-14;

wherein the movable part of the actuator is connected to the first element or the magnetic assembly of the damping device, the first element or the magnetic assembly to which the movable part is connected being movable.