WO2014198313A1

WO2014198313A1 - Switch element and armature for use in a switch element

Info

Publication number: WO2014198313A1
Application number: PCT/EP2013/062203
Authority: WO
Inventors: Bissal ARA; Ener SALINAS; Thomas Eriksson
Original assignee: Abb Technology Ltd
Priority date: 2013-06-13
Filing date: 2013-06-13
Publication date: 2014-12-18

Abstract

An at least partially conductive armature (100) for use in a switch element (10) is disclosed, where operation of the switch element (10) is based on generation of a magnetic force on the armature (100), e.g. between the armature (100) and a magnetic field generator (200),so as to effect movement of the armature (100). The armature (100) comprises an elongated member(101) having a longitudinal axis (A) and an armature head (102) arranged at one end of the elongated member (101). According to embodiments of the present invention the armature (100) has a shape similar to that of a mushroom, which allows for quick acceleration of the armature (100) with a relatively high efficiency in operation of the switch element(10). By the particular shape or form of the armature(100), tensile stresses in the armature(100) can be redistributed into compressive stresses, reducing or minimizing any deformation of the armature(100).

Description

SWITCH ELEMENT AND ARMATURE FOR USE IN A SWITCH ELEMENT

FIELD OF THE INVENTION

The present invention generally relates to switch devices or elements, e.g. for use in circuit breakers. Specifically, the present invention relates to an armature for use in a switch element where operation of the switch element is based on generation of a magnetic force on the armature, e.g. between the armature and a magnetic field generator, e.g. including a coil, so as to effect movement of the armature.

BACKGROUND OF THE INVENTION

Power systems such as electrical power distribution or transmission systems generally include a protection system for protecting, monitoring and controlling the operation and/or functionality of other components included in the power system. Such a protection system may for example detect short-circuits, over-currents and over-voltages in power lines, transformers and/or other parts or components of the power system. The protection system can include protection equipment such as circuit breakers for isolating any possible faults for example occurring in power transmission and distribution lines by opening or tripping the circuit breakers. After the fault has been cleared, e.g. by performing repairs and/or maintenance on the component in which the fault has been detected, the power flow can be restored by closing the circuit breakers. Alternatively or optionally, the protection system can be arranged to, upon detection of a fault in a particular route for power flow, isolate the route in which the fault has been detected and select an alternative route for the power flow.

Considering as an example a multi-terminal voltage source converter based High Voltage Direct Current (HVDC) power system, faults on a DC cable or DC overhead line (OHL) are typically isolated from the rest of the power system or another part of the power system by temporarily shutting down the DC line, or temporarily taking the DC line out of operation, using DC circuit breakers. Operation of the circuit breakers may be responsive to detection of a fault condition or fault current. Upon detection of a fault condition or fault current, a mechanism may operate the circuit breaker so as to interrupt the current flowing there through. Once a fault has been detected, contacts within the circuit breaker may separate in order to interrupt the current therethrough. Spring arrangements, pneumatic arrangements or some other means utilizing mechanically stored energy may be employed to separate the contacts. Hence, mechanical current interrupters may for example be employed in circuit breakers. In alternative or in addition, solid-state interrupters based on semiconductor devices may be employed in the circuit breakers. When interrupting the current flowing in the electrical circuit, an arc is in general generated. Such an arc may be referred to as a fault current arc. In order to break the current in the electrical circuit, it may be required or desired to extinguish such an arc. Once the fault condition has been mitigated or eliminated the contacts can be closed so as to resume flow of current through the circuit breaker.

HVDC power transmission is becoming increasingly important due to the increasing need for power supply or delivery and interconnected power transmission and distribution systems. An HVDC grid or a DC grid may comprise multiple alternating current (AC)/DC converter terminals interconnected by transmission lines, e.g., underground cables and/or OHLs. Within the grid, a terminal may be connected to multiple terminals resulting in different types of topologies. DC circuit breakers can be used for isolating faulty components, such as transmission lines, in HVDC and DC grids. Unlike AC circuit breakers, there are no natural current zeros at which a fault current arc may be extinguished in DC circuit breakers. Instead, it may be desired or even required to create a current zero when utilizing DC circuit breakers. Due to the absence of natural current zeros as in AC circuit breaker systems and due to the relatively low impedance in HVDC or DC grids or networks, DC circuit breakers may be desired or required to be able to interrupt fault currents relatively quickly, e.g. on the order of a few microseconds, before the fault current has increased too much in magnitude. As a result, it is in general desired or required to be able to relatively quickly open DC circuit breakers, for example as compared to AC circuit breakers.

Mechanical circuit breakers are relatively inexpensive but are relatively slow in operation time. Solid-state based circuit breakers have a faster operation time that may be on the order of microseconds, but they are in general relatively expensive. It would be desirable with an actuator, or actuating mechanism, that could be used to e.g. separate contacts within a circuit breaker in order to interrupt current therethrough relatively quickly, e.g. within 10-100 microseconds or even faster. Such fast operation of separation of contacts may not be limited only to circuit breaker applications, but may be desired or required in other switching applications as well. In order to achieve separation of contacts within a circuit breaker in order to interrupt current therethrough within 10-100 microseconds or even faster, use of so called Thomson drives has been proposed. According to one example, the Thomson drive comprises a plunger, or armature, which is displaceable along a displacement direction and which is driven by a Thomson coil, i.e. a drive where a conducting member adjacent to a coil is subjected to a repulsive force upon application of a current pulse to the coil. The current pulse in the coil generates a varying magnetic flux, which in turn generates a current with opposite direction in the plunger, which generates a magnetic force between the coil and the plunger for effecting movement of the plunger relatively to the coil. Thomson drives are not limited to actuation of linear movement of the plunger but may in alternative or addition be configured so as to effect or actuate rotational movement of the plunger.

SUMMARY OF THE INVENTION

Some factors which may decrease the efficiency of such drives are mechanical losses, electromechanical losses, and deformation, e.g. elongation and/or bending, of the plunger or armature. For achieving high actuation speeds for relatively heavy loads, an electromagnetic impulsive force can be used. Both the magnitude and the time constant of such an impulse force impulse may be required or desired to be tailored so as to achieve the required steady state speed of actuation within specified time constraints or requirements. The relatively large forces which are generated in relatively short time may result in relatively large accelerations of the plunger or armature, which accelerations may cause deformation, e.g. bending and/or elongation, of the plunger or armature, which may decrease the efficiency of the drive. It would be desirable with a drive having an increased efficiency as compared to known drives.

In view of the above, an concern of the present invention is to provide an armature for use in a switch element where operation of the switch element is based on generation of a magnetic force on the armature, e.g. between the armature and a magnetic field generator, e.g. including a coil, so as to effect movement of the armature, which armature allows for an increased efficiency in operation of the switch element as compared to known armatures.

A further concern of the present invention is to provide a switch element where operation of the switch element is based on generation of a magnetic force on an armature, e.g. between the armature and a magnetic field generator, e.g. including a coil, so as to effect movement of the armature, which switch element has an increased efficiency of operation as compared to known switch elements.

To address at least one of these concerns and other concerns, an armature for use in a switch element and a switch element in accordance with the independent claims are provided. Preferred embodiments are defined by the dependent claims.

According to a first aspect, there is provided an at least partially conductive armature for use in a switch element, which switch element has at least a first contact and a second contact which can be selectively connected and disconnected such that when the first and second contacts are connected the switch element is closed, and when the first and second contacts are disconnected the switch element is opened. The switch element is arranged such that the armature is movable along a displacement path between at least a first position and a second position. The switch element is further arranged such that when the armature is in the first position, the first and second contacts are connected, and when the armature is in the second position, the first and second contacts are disconnected. The switch element comprises a magnetic field generator, which is adapted to, preferably controllably and/or selectively, generate a magnetic field. The armature comprises an elongated member, or shaft, or stem, which has a longitudinal axis. The armature further comprises an armature head which is arranged at one end of the elongated member. The armature head may for example be fixated, or secured, to the elongated member at one end of the elongated member. The armature head is arranged such that in presence of a magnetic field generated by the magnetic field generator, current is induced within at least a portion, or current induction portion, of the armature head. By means of the induced current, a magnetic force on the armature head, e.g. between the armature head and the magnetic field generator, can be generated so as to move the armature along the displacement path to the second position such that the first and second contacts are disconnected so as to open the switch element. The armature comprises at least one force-redistributing portion, or stress-redistributing portion, having an area of its cross section in a plane perpendicular to the longitudinal axis which varies along the longitudinal axis. Thereby, tensile stresses within the armature head caused by movement of the armature responsive to the generation of a magnetic force on the armature head, e.g. between the armature head and the magnetic field generator, can be redistributed into compressive stresses within the armature, which in turn may reduce any deformation of the armature, e.g. caused by forces on the armature due to relatively large accelerations of the armature when it is moved along the displacement path e.g. to the second position.

Embodiments of the present invention are based on a choosing or selecting the design, shape and/or arrangement of an armature for use in a switch element where operation of the switch element is based on generation of a magnetic force on the armature, e.g. between the armature and a magnetic field generator, e.g. including a coil, so as to effect movement of the armature, so as to minimize or reduce any deformation of the armature, e.g. by bending and/or elongation thereof, caused by forces on the armature due to relatively large

accelerations of the armature when it is moved.

Forces on a solid resulting from electromagnetic fields may, if large enough, cause structural deformation of the solid. If the deformations of the solid are large enough, the electromagnetic fields may be affected. Modeling of such interaction may involve e.g. the coupling between structural mechanics and electromagnetism. Embodiments of the present invention described herein are based on comprehensive multi-physics finite element modeling based simulation models for the electromechanical forces in the armature when movement of the armature is effected based on generation of a magnetic force on the armature, e.g. between the armature and a magnetic field generator.

Such multi-physics finite element modeling based simulations have shown or indicated that by arranging the armature such that it has at least one portion having an area of its cross section in a plane perpendicular to the longitudinal axis which varies along the longitudinal axis, tensile stresses within the armature caused by movement of the armature responsive to the generation of a magnetic force on the armature can be redistributed into compressive stresses within the armature, which in turn may reduce any deformation of the armature, e.g. caused by forces on the armature due to relatively large accelerations of the armature when it is moved along the displacement path e.g. to the second position. As will be discussed further in the following, the at least one portion of the armature (referred to in the foregoing and in the following as 'force-redistributing portion' of the armature), which at least one portion is arranged so that the area of its cross section in a plane perpendicular to the longitudinal axis varies along the longitudinal axis, may be situated at least in part in the armature head, and/or at least in part in the elongated member. According to embodiments of the present invention, the force-redistributing portion of the armature and the current induction portion of the armature head may be the same, or they may be different and possibly at least partly overlapping.

In the context of the present application, by the term 'force-redistributing portion' is it meant in principle any portion of the armature which has an area of its cross section in a plane perpendicular to the longitudinal axis which varies along the longitudinal axis, and which allows for tensile stresses within the armature head caused by movement of the armature responsive to the generation of a magnetic force on the armature head, e.g. between the armature head and the magnetic field generator, to be redistributed into compressive stresses within the armature, which in turn may reduce any deformation of the armature, e.g. caused by forces on the armature due to relatively large accelerations of the armature when it is moved along the displacement path e.g. to the second position.

In the context of the present application, by at least one (force-redistributing) portion of the armature being arranged so that the area of its cross section in a plane perpendicular to the longitudinal axis varies along the longitudinal axis, it is generally meant that at least one portion of the armature is arranged so that the area of its cross section in a plane perpendicular to the longitudinal axis varies along a predefined or selected length of the longitudinal axis.

According to embodiments of the present invention, the armature has a shape similar to that of a mushroom, with the armature head exhibiting a shape similar to the shape of a 'top' of a mushroom. Such a shape of the armature may allow for quick acceleration of the armature with a relatively high efficiency in operation of the switch element. Multi- physics finite element modeling such as mentioned in the foregoing have shown that by such a shape of the armature, tensile stresses in the armature can be redistributed into compressive stresses, reducing or minimizing any deformation of the armature, e.g. in the form of elongation and/or bending thereof, resulting e.g. from relatively high acceleration of the armature. The armature may be arranged such that it is formed substantially in one piece, i.e. such that the armature head and the elongated member are constituted by different portions of the same element or member. However, the armature head and the elongated member may be separate elements, and the armature head may for example be fixated, or secured, to the elongated member at one end of the elongated member.

According to an embodiment of the present invention, the area of the cross section of the at least one force-redistributing portion of the armature in a plane perpendicular to the longitudinal axis decreases monotonically or substantially monotonically along the longitudinal axis away from the elongated member.

According to another embodiment of the present invention, the at least one force-redistributing portion of the armature has an inclined, e.g. outer, surface which is at an angle to a direction perpendicular to the longitudinal axis, with the angle being between 5 ° to 60 °.

For example in case the at least one force-redistributing portion of the armature is situated at least in part in the armature head, the at least one force-redistributing portion of the armature may define a frustoconical tip.

In the context of the present application, by the term "frustoconical" it is in general meant a shape of a part of a solid, such as a cone, pyramid, etc., between two planes, which may be either parallel or inclined to each other, or a shape of a frustum of a cone, or a shape of a cone having its tip, or narrow end, removed.

According to another embodiment of the present invention, the armature head may comprise a disc-shaped or cylindrical portion, and a tip portion which is disposed on, or arranged next to or adjacent to, the disc-shaped or cylindrical portion. The tip portion may constitute an end portion of the armature. The area of the cross section of the tip portion in a plane perpendicular to the longitudinal axis may vary along the longitudinal axis.

The tip portion may for example be tapered in a direction parallel to the longitudinal axis away from the elongated member.

The tip portion may for example be arranged such that it has a smaller cross sectional area in a plane perpendicular to the longitudinal axis as compared to the disc-shaped or cylindrical portion.

According to an embodiment of the present invention, the tip portion defines a frustoconical tip.

As mentioned in the foregoing, the at least one force-redistributing portion of the armature, which at least one force-redistributing portion is arranged so that the area of its cross section in a plane perpendicular to the longitudinal axis varies along the longitudinal axis, may in alternative or in addition be situated at least in part in the elongated member.

The at least one force-redistributing portion of the armature may for example comprise a fillet portion by means of which the elongated member is coupled, or fixated, to the armature head. The fillet portion may be tapered in a direction parallel to the longitudinal axis away from the from the armature head. The fillet portion may for example have a radius between about 0.5 mm and 25 mm, preferably between about 0.5 mm and 10 mm, though deviations from this range is possible.

In the context of the present application, by the term "fillet" it is in general meant something that connects or couples two (filleted) objects with an arc that is tangent to the objects and which has a certain radius, or a rounding of an interior or exterior corner of a part or portion of an element. "Fillets" are sometimes referred to as "rounds". In the context of the present application, by a radius of a fillet it is meant a radius of the arc that connects or couples filleted objects.

Preferably, the armature head comprises a conductive material, e.g. a metallic material including Al or Al-based alloys, or reinforced Al, or Cu or Cu-based alloys, or another metal or alloy, etc. The armature head may be solid or substantially solid. According to an embodiment of the present invention, the armature head may comprise at least one through-hole or the like.

Preferably, the elongated member comprises an insulating material.

The elongated member may for example comprise a cylindrical member.

According to an embodiment of the present invention, the cylindrical member has a radius defined by at least one of a mass of a load attached to the armature, a maximum desired acceleration of the armature when the armature is moved along the displacement path to the second position, and a length along the longitudinal axis of the elongated member.

The larger the elongation of the elongated member, caused e.g. by forces on the armature due to relatively large accelerations of the armature when it is moved along the displacement path e.g. to the second position, the greater the reduction in efficiency in operation of the switch element may become. As will be further described in the following with reference to the accompanying drawings, by appropriate selection of the radius of the elongated member any elongation of the elongated member can be reduced or even minimized.

According to a second aspect, there is provided a switch element which comprises at least a first contact and a second contact which can be selectively connected and disconnected such that when the first and second contacts are connected the switch element is closed, and when the first and second contacts are disconnected the switch element is opened. The switch element further comprises an at least partially conductive armature. The armature comprises an elongated member, or shaft, or stem, having a longitudinal axis, and an armature head which is arranged at one end of the elongated member. The armature head may for example be fixated, or secured, to the elongated member at one end of the elongated member. The switch element further comprises a magnetic field generator adapted to generate a magnetic field. The switch element is arranged such that the armature is movable along a displacement path between at least a first position and a second position. The switch element is further arranged such that when the armature is in the first position, the first and second contacts are connected, and when the armature is in the second position, the first and second contacts are disconnected. The armature head is arranged such that in presence of a magnetic field generated by the magnetic field generator, current is induced within at least a portion, or current induction portion, of the armature head. By means of the induced current, a magnetic force on the armature head, e.g. between the armature head and the magnetic field generator, can be generated so as to move the armature along the displacement path to the second position such that the first and second contacts are disconnected so as to open the switch element. The armature comprises at least one force-redistributing portion having an area of its cross section in a plane perpendicular to the longitudinal axis which varies along the longitudinal axis. Thereby, tensile stresses within the armature head caused by movement of the armature responsive to the generation of the magnetic force on the armature head, e.g. between the armature head and the magnetic field generator, can be redistributed into compressive stresses within the armature, which in turn may reduce any deformation of the armature, e.g. caused by forces on the armature due to relatively large accelerations of the armature when it is moved along the displacement path e.g. to the second position.

The armature head may comprise a disc-shaped or cylindrical portion and a tip portion which is disposed on the disc-shaped or cylindrical portion, wherein the area of the cross section of the tip portion in a plane perpendicular to the longitudinal axis varies along the longitudinal axis.

The tip portion may be arranged such that it has a smaller cross sectional area in a plane perpendicular to the longitudinal axis as compared to the disc-shaped or cylindrical portion

The disc-shaped or cylindrical portion may have a radius r and the tip portion may at a boundary between the disc-shaped or cylindrical portion and in a plane perpendicular to the longitudinal axis have a radius /¾.

The magnetic field generator may for example comprise a coil having a plurality of turns or windings, e.g. N turns or windings, where N is a positive integer, arranged substantially in one plane. The coil may have an outer radius r_oc and an inner radius r_lc.

According to an embodiment of the present invention, the armature may be arranged such that the radii r and comply with the following requirements:

r_h = r_oc ± c, and

n = r_ic + a (N-t_w),

where 0.5 < a < 1.0, c is a selected or predefined length, and t_w is a dimension, e.g. a width, of a turn or winding.

According to a third aspect, there is provided a circuit breaker including a switch element according to the second aspect, wherein the circuit breaker is adapted to interrupt a current in a transmission line arranged to carry current, e.g. direct current, when the switch element is opened.

According to a fourth aspect, there is provided a power system including a transmission line arranged to carry current and a circuit breaker according to the third aspect coupled to the transmission line for controllably effecting discontinuation of flow of current in the transmission line. The power system may for example comprise a HVDC power transmission system. The transmission line may for example be arranged to carry direct current.

Further objects and advantages of the present invention are described in the following by means of exemplifying embodiments.

It is noted that the present invention relates to all possible combinations of features recited in the claims. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplifying embodiments of the invention will be described below with reference to the accompanying drawings.

Fig. 1 is a schematic sectional side view of a switch element, including an at least partially conductive armature, according to an embodiment of the present invention.

Fig. 2 is a schematic sectional side view of a switch element according to an embodiment of the present invention.

Fig. 3 is a schematic block diagram of a power system in accordance with an embodiment of the present invention.

In the accompanying drawings, the same reference numerals denote the same or similar elements throughout the views.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments of the present invention are shown. The present 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 by way of example so that this disclosure will convey the scope of the invention to those skilled in the art. Furthermore, like numbers refer to the same or similar elements or components throughout. Referring now to Fig. 1 , there is shown a schematic sectional side view of a switch element, or device, 10, including an at least partially conductive armature 100, according to an embodiment of the present invention.

Hence, according to the depicted embodiment, the at least partially conductive armature 100 is for use in a switch element 10. The switch element 10 has at least a first contact and a second contact (not shown in Fig. 1) which can be selectively connected and disconnected such that when the first and second contacts are connected the switch element 10 is closed, and when the first and second contacts are disconnected the switch element 10 is opened.

The switch element 10 comprises a magnetic field generator 200, which is adapted to, preferably controllably and/or selectively, generate a magnetic field. In accordance with the embodiment depicted in Fig. 1, the magnetic field generator 200 may for example comprise a coil having a plurality of turns or windings 202, e.g. N turns or windings 202, where N is a positive integer such as two, four, six, eight or ten or higher. Note that only some of the turns or windings 202 are indicated by a reference numeral 202 in Fig. 1. The following description will mainly refer to the example where the magnetic field generator 200 comprises a coil 200 having a plurality of windings 202. However, this is merely for describing principles of embodiments of the present invention and is not to be interpreted in a limiting manner. The magnetic field generator 200 may be coupled to a power storage device (not shown in Fig. 1) adapted to store power which can be conveyed, e.g. to the coil, preferably in a selective and/or controllable manner. The power storage device may for example include a capacitor bank or the like.

The switch element 10 is arranged such that the armature 100 is movable along a displacement path between at least a first position and a second position. The switch element 10 is arranged such that when the armature 100 is in the first position, the first and second contacts are connected, and when the armature 100 is in the second position, the first and second contacts are disconnected.

For example, the armature 100 may be attached to one of the first and second contacts, with the one of the first and second contacts being movable and the other stationary, such that by moving the armature 100 into the first position the first contact and the second contact are brought into contact with each other. According to another example, the armature 100 may be attached to a third contact (not shown in Fig. 1), which third contact when the armature 100 is in the first position causes connection or coupling between the first contact and the second contact, e.g. so as to form a conducting path for carrying a current between the first contact and the second contact, for example by bridging a contact gap between the first contact and the second contact, and which third contact when the armature 100 is in the second position causes disconnection or decoupling between the first contact and the second contact. The armature 100 comprises an elongated member 101, or shaft, or stem, which elongated member 101 has a longitudinal axis A.

The displacement path may for example be arranged along or substantially along the longitudinal axis A, or arranged along or substantially along an axis parallel or substantially parallel to the longitudinal axis A. However, the displacement path is not necessarily straight but may be at least in part curved, and is not necessarily linear but may conform to or define a rotational movement of the armature 100 when the armature 100 is moved along the displacement path.

The armature 100 comprises an armature head 102. The armature head 102 is arranged at one end of the elongated member 101, e.g. such as illustrated in Fig. 1. The armature head 102 may for example be fixated, or secured, to the elongated member 101 at one end of the elongated member 101.

The armature head 102 is arranged such that in presence of a magnetic field, e.g. generated at least in part by the magnetic field generator 200, current is induced within at least a portion, or current induction portion, of the armature head 102. By means of the induced current, a magnetic force between the armature head 102 and the member which generated the magnetic field, e.g. the magnetic field generator 200, can be generated so as to move the armature 100 along the displacement path to the second position such that the first and second contacts are disconnected, thereby opening the switch element 10.

In a similar manner, current may be induced in the armature head 102 in presence of a magnetic field, e.g. generated at least in part by the magnetic field generator 200, so as to effect movement of the armature 100 e.g. out of the second position, for example along the displacement path to the first position such that the first and second contacts are connected, thereby closing the switch element 10.

Following discharge of the power storage device, e.g. including a capacitor bank or the like, into the coil 200, relatively high current densities may be created in the coil 200 cross section, thereby increasing the coil's 200 temperature and resistance. Within a relatively short time, e.g. within one or a few milliseconds or less, relatively large magnetic flux densities, e.g. on the order of 5 T or more, can build up in the coil 200. Currents in the presence of a magnetic field result in electromagnetic forces. The time derivative of the axial component of the magnetic flux density can induce eddy currents in the armature 100, and as a result, the azimuthal eddy currents and the radial component of the magnetic flux density create a magnetic force or forces that moves the armature 100. The magnetic force(s) may be defined by the product of the azimuthal eddy current density and the radial magnetic flux density. The currents in the coil 200 and in the armature 100 are in general different. In case no external currents are applied to the armature 100, the only currents in the armature 100 may be due to the induced eddy currents. The currents in the armature 100 may be induced e.g. based on the time derivative of the current pulse supplied to the coil 200 and the distance between the armature 100 and the coil 200.

The armature 100 is arranged such that it comprises at least one portion having an area of its cross section in a plane perpendicular to the longitudinal axis A which varies along the longitudinal axis A. Thereby, tensile stresses within the armature head 102 which are caused by movement of the armature 100 responsive to the generation of the magnetic force on the armature 100 can be redistributed into compressive stresses within the armature 100, which in turn may reduce any deformation of the armature 100, e.g. caused by forces on the armature 100 due to relatively large accelerations of the armature 100 when it is moved along the displacement path e.g. to the second position. Hence, the at least one portion of the armature 100 may be referred to as at least one 'force-redistributing portion' of the armature 100.

The shape of the armature 100 can be chosen or selected so as to minimize or reduce any deformation of the armature 100, e.g. by bending and/or elongation thereof. Forces on a solid resulting from electromagnetic fields may, if large enough, cause structural deformation. If the deformations of the solid are large enough, the electromagnetic fields may be affected. Modeling of such interaction may involve e.g. the coupling between structural mechanics and electromagnetism. Embodiments of the present invention are based on comprehensive multi-physics finite element modeling based simulation models for the electromechanical forces in the armature 100 when movement of the armature 100 is effected based on generation of a magnetic force between the armature 100 and e.g. a magnetic field generator 200. Hence, the design, shape and/or arrangement of the armature 100 as described in the following and in the foregoing have in general been determined based on such multi- physics finite element modeling, e.g. using COMSOL Multiphysics™ produced by Cortisol AB based in Stockholm, Sweden.

With further reference to Fig. 1, the at least one force-redistributing portion of the armature 100, which at least one force-redistributing portion is arranged so that the area of its cross section in a plane perpendicular to the longitudinal axis A varies along the longitudinal axis A, can in general be situated at least in part in the armature head 102 and/or at least in part in the elongated member 101.

For example according to the embodiment of the present invention depicted in Fig. 1, the armature head 102 may have an inclined, outer, surface 106 which is at an angle a to a direction perpendicular to the longitudinal axis A, such that a portion of the armature head 102 defines a frustoconical tip. As can be seen in Fig. 1, the area of the cross section of the portion of the armature head 102 defining a frustoconical tip in a plane perpendicular to the longitudinal axis A decreases monotonically along the longitudinal axis A away from the elongated member 101. Based on multi-physics finite element modeling such as described in the foregoing, the armature head 102 is preferably arranged such that the angle a is between about 5 ° to about 60 °, in order to minimize or reduce any deformation of the armature 100, e.g. by bending thereof, caused by forces on the armature 100 due to relatively large accelerations of the armature 100 when it is moved along the displacement path e.g. to the second position.

As illustrated in Fig. 1, the armature head 102 may comprise a disc-shaped or cylindrical portion 103, with a radius /¾, and a tip portion 104. As further illustrated in Fig. 1, the tip portion 104 may constitute an end (or top) portion of the armature 100. As can be seen in Fig. 1, the area of the cross section of the tip portion 104 in a plane perpendicular to the longitudinal axis A varies along the longitudinal axis A. Hence, the tip portion 104 may constitute or be included in the force-redistributing portion of the armature.

As illustrated in Fig. 1, the tip portion 104 may be arranged such that it has a smaller cross sectional area in a plane perpendicular to the longitudinal axis A as compared to the disc-shaped or cylindrical portion 103. As further illustrated in Fig. 1, the largest cross sectional area in a plane perpendicular to the longitudinal axis A of the tip portion may be defined by the radius r .

In accordance with the embodiment of the present invention depicted in Fig. 1, the coil 200 may for example comprise a spiral coil 200 having N coil turns or windings arranged substantially in one plane and having an outer radius r_oc and an inner radius r_lc.

Based on multi-physics finite element modeling such as described in the foregoing, in order to minimize or reduce any deformation of the armature 100, e.g. by bending thereof, caused by forces on the armature 100 due to relatively large accelerations of the armature 100 when it is moved along the displacement path e.g. to the second position, the armature 100 may be arranged such that the radii r and comply with the following requirements:

r_h = r_oc ± c, and

n = r_ic + a (N-t_w),

where 0.5 < a < 1.0, c is a selected or predefined length (c may for example be about 10 mm), and t_w is a dimension, e.g. a width, of a coil turn or winding 202.

The at least one force-redistributing portion of the armature 100, which at least one force-redistributing portion is arranged so that the area of its cross section in a plane perpendicular to the longitudinal axis A varies along the longitudinal axis A, may, in accordance with the embodiment depicted in Fig. 1, in addition or in alternative comprise or be constituted by a fillet portion 105 (as shown in greater detail in the inset in Fig. 1). By means of the fillet portion 105 the elongated member 101 can be coupled, or fixated, to the armature head 102. As illustrated in Fig. 1, the fillet portion 105 may be tapered in a direction parallel to the longitudinal axis A away from the armature head 102. By arranging the (fillet) radius of the fillet portion 105 appropriately such that the area of the fillet portion's 105 cross section in a plane perpendicular to the longitudinal axis A varies along the longitudinal axis A, any deformation of the armature 100, e.g. by bending thereof, caused by forces on the armature 100 due to relatively large accelerations of the armature 100 when it is moved along the displacement path e.g. to the second position, can be minimized or reduced.

Based on multi-physics finite element modeling such as described in the foregoing, according to example embodiments of the present invention the fillet portion 105 preferably has a (fillet) radius between about 0.5 mm and about 25 mm, preferably between about 0.5 mm and about 10 mm, in particular for the case where r and comply with the equations presented in the foregoing, and/or for the case where the total weight of the armature 100 and a load attached thereto (e.g. the third contact as described in the foregoing) is about 1.5 kg, with the weight of the armature 100 being about 1 kg and the weight of the attached load being about 0.5 kg. However, the radius of the fillet portion 105 may be smaller than 0.5 mm or larger than 10 mm or 25 mm depending on, e.g., the magnitude and/or direction of forces on the armature 100 when in use, the weight of a load attached to the armature 100, and/or the particular dimensions and/or weight of other components or portions of the armature 100, such as the size and/or dimensions of the armature head, e.g. a radius r thereof, and/or the elongated member 101 , e.g. a radius r_s thereof.

According to embodiments of the present invention, the force-redistributing portion of the armature 100, e.g. including the tip portion 104, and the current induction portion of the armature head 102 may be the same, or they may be different and possibly at least partly overlapping.

According to one example, the armature 100 can be arranged such that it is formed substantially in one piece, i.e. such that the armature head 102 and the elongated member 101 are constituted by different portions of the same element or member. However, the armature head 102 and the elongated member 101 may be separate elements, with the armature head 102 for example being fixated, or secured, to the elongated member 101 at one end of the elongated member 101.

Preferably, the armature head 102 comprises a conductive material, e.g. a metallic material including Al or Al-based alloys, or reinforced Al, or Cu or Cu-based alloys, or another metal or alloy, etc.

Preferably, the elongated member 101 comprises an insulating material.

Thereby, it can be avoided to induce current within the elongated member 101 in presence of a magnetic field used for inducing current within at least a portion of the armature head 102 in order to generate a magnetic force on the armature head 100.

In accordance with the embodiment of the present invention depicted in Fig. 1 , the elongated member 101 may for example comprise a cylindrical member, which has a radius r_s defined by at least one of a mass m of a load (not shown in Fig. 1 ; e.g. including or constituting the third contact as described in the foregoing) attached to the armature 100 (e.g. to the elongated member 101 of the armature 100), a maximum desired acceleration acc_max of the armature 100 when the armature 100 is moved along the displacement path to the second position, and a length L_s along the longitudinal axis A of the elongated member 101.

According to one example, r_s can be defined as:

r_s = [ (m-acc_max-L_s) I ( -E- L) f ⁵,

where E is the Young's modulus of the material of the elongated member 101 , and AL is an elongation of the elongated member 101 caused by forces on the armature 100 due to relatively large accelerations of the armature 100 when it is moved along the displacement path e.g. to the second position, which elongation of the elongated member 101 of the armature 100 is tolerable (e.g., 0.1 mm < AL < 1.0 mm). The larger the elongation of the elongated member 101 , caused e.g. by forces on the armature 100 due to relatively large accelerations of the armature 100 when it is moved along the displacement path e.g. to the second position, the greater the reduction in efficiency in operation of the switch element 10 may become.

In alternative or in addition, preferably r_s « r_lc.

It is to be noted that only some of the components or constituents of the switch element 10 are shown in Fig. 1. However, the switch element 10 may further comprise, for example, one or more of electrical couplings for providing power to the magnetic field generator 200, a chamber or the like e.g. for housing and/or guiding the armature 100 (e.g. for guiding the armature 100 for moving along the displacement path), a (bistable) suspension mechanism or device, e.g. comprising hydraulic and/or pneumatic means such as pistons or the like, for at least momentarily holding the armature 100 e.g. in the first position and/or the second position, etc. Since such additional possible components of the switch element 10 are not necessary for the implementation of the present invention, detailed description of such additional possible components of the switch element 10 is therefore omitted. Such additional possible components of the switch element 10 are not shown in Fig. 1.

Referring now to Fig. 2, there is shown a very schematic sectional side view of a switch element 10 according to an embodiment of the present invention.

The switch element 10 has a first contact 1 1 and a second contact 12. The first and second contacts 1 1 , 12 can be selectively connected and disconnected such that when the first and second contacts 1 1 , 12 are connected, the switch element 10 is closed, and when the first and second contacts are disconnected, the switch element 10 is opened.

The switch element 10 comprises an at least partially conductive armature 100, and is arranged such that the armature 100 is movable along a displacement path between at least a first position and a second position. The switch element 10 is arranged such that when the armature 100 is in the first position, the first and second contacts 1 1 , 12 are connected, and when the armature 100 is in the second position, the first and second contacts 1 1 , 12 are disconnected. For example, according to the embodiment depicted in Fig.2, the armature 100 can be attached to a third contact 13 which when the armature 100 is in the first position causes connection or coupling between the first contact 11 and the second contact 12, e.g. so as to form a conducting path for carrying a current between the first contact 11 and the second contact 12. The situation where the armature 100 is in the first position in which the third contact 13 causes connection or coupling between the first contact 11 and the second contact 12 is depicted in Fig. 2. As shown in Fig. 2, the first contact 11 and the second contact 12 can be connected to ends of transmission lines 15, 16 (of which only portions are shown in Fig. 2) arranged to carry current, which transmission lines 15, 16 for example may be part of a power system. When the armature 100 is brought into the second position, the third contact 13 is moved away from the first and second contacts 11, 12, e.g., upwards in Fig. 2 from the position of the third contact 13 shown in Fig. 2, by the armature 100 being pulled upwards in Fig. 2 with respect to the position of the armature 100 shown in Fig. 2 (indicated by the dashed arrow in Fig. 2), so as to cause disconnection or decoupling between the first contact 11 and the second contact 12, thereby interrupting current between the first and second contacts 11, 12 (and thereby also current between transmission lines 15, 16).

According to another example (not illustrated in Fig. 2), the armature 100 may be attached to one of the first and second contacts 11, 12, with the one of the first and second contacts 11, 12 being movable and the other stationary, such that by moving the armature 100 into the first position the first contact 11 and the second contact 12 are brought into contact with each other, and by moving the armature 100 into the second position the first contact 11 and the second contact 12 are brought out of contact with each other.

Hence, connection or coupling between the first contact 11 and the second contact 12 does not necessarily imply that there is a direct contact between the first contact 11 and the second contact 12, but may instead imply that there is an indirect contact between the first contact 11 and the second contact 12, e.g. via a functional connection having one or more intermediate components.

According to the embodiment depicted in Fig. 2, the armature 100 is attached to the third contact 13 at an end of an elongated member 101, or shaft, or stem, of the armature 100.

The elongated member 100 has a longitudinal axis A. The displacement path of the armature 100 may for example be arranged along or substantially along the longitudinal axis A, or arranged along or substantially along an axis parallel or substantially parallel to the longitudinal axis A. However, the displacement path do not necessarily have to be straight but may be at least in part curved, and do not necessarily have to be linear but may conform to or define a rotational movement of the armature 100 when the armature 100 is moved along the displacement path. Movement of the armature 100 along the displacement path can be based on generation of a magnetic force on the armature 100, e.g. between the armature 100 and a magnetic field generator (not shown in Fig. 2) adapted to induce current within at least a portion, or current induction portion, of an armature head 102 of the armature 100, which magnetic field generator may be included in the switch element 10, such as described in the foregoing e.g. with reference to Fig. 1.

Referring now to Fig. 3, there is shown a schematic block diagram of a power system 300 in accordance with an embodiment of the present invention. The power system 300 includes a transmission line 302 (of which only a portion is shown in Fig. 3) which is arranged to carry direct current between terminals 303, and a circuit breaker 301 coupled to the transmission line 302 for contra llably effecting discontinuation of flow of direct current in the transmission line 302. The circuit breaker 301 includes a switch element 10 according to an embodiment of the present invention, e.g. configured in accordance with the switch element 10 described in the foregoing with reference to Fig. 1 or Fig. 2. With further reference to Fig. 3, the circuit breaker 301 is adapted to interrupt a current in the transmission line 302 when the switch element 10 is opened (i.e. on a condition that the switch element 10 is opened, a current in the transmission line 302 is interrupted). The power system 300 may for example comprise a HVDC power transmission system, and/or a (portion of) a DC or HVDC grid.

In conclusion, there is disclosed an at least partially conductive armature for use in a switch element, where operation of the switch element is based on generation of a magnetic force on the armature, e.g. between the armature and a magnetic field generator, so as to effect movement of the armature. The armature comprises an elongated member having a longitudinal axis and an armature head arranged at one end of the elongated member.

According to embodiments of the present invention the armature has a shape similar to that of a mushroom, which allows for quick acceleration of the armature with a relatively high efficiency in operation of the switch element. By the particular shape or form of the armature, tensile stresses in the armature can be redistributed into compressive stresses, reducing or minimizing any deformation of the armature.

While the present invention has been illustrated and described in detail in the appended drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplifying and not restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An at least partially conductive armature (100) for use in a switch element (10) having at least a first contact (11) and a second contact (12) which can be selectively connected and disconnected such that when the first and second contacts are connected the switch element is closed, and when the first and second contacts are disconnected the switch element is opened, wherein the switch element is arranged such that the armature is movable along a displacement path between at least a first position and a second position, and wherein the switch element is arranged such that when the armature is in the first position, the first and second contacts are connected, and when the armature is in the second position, the first and second contacts are disconnected, the switch element comprising a magnetic field generator (200) adapted to generate a magnetic field, the armature comprising:

an elongated member (101) having a longitudinal axis (A); and an armature head (102) arranged at one end of the elongated member;

wherein the armature head is arranged such that in presence of a magnetic field generated by the magnetic field generator, current is induced within at least a current induction portion of the armature head, wherein by means of the induced current a magnetic force on the armature head is generated so as to move the armature along the displacement path to the second position such that the first and second contacts are disconnected so as to open the switch element;

wherein the armature comprises at least one force-redistributing portion (104;

105) having an area of its cross section in a plane perpendicular to the longitudinal axis which varies along the longitudinal axis, whereby tensile stresses within the armature head caused by movement of the armature responsive to the generation of a magnetic force on the armature head are redistributed into compressive stresses within the armature, thereby reducing any deformation of the armature.

2. An armature according to claim 1, wherein the at least one force-redistributing portion of the armature is situated at least in part in the armature head.

3. An armature according to claim 2, wherein the area of the cross section of the at least one force-redistributing portion of the armature in a plane perpendicular to the longitudinal axis decreases monotonically along the longitudinal axis away from the elongated member.

4. An armature according to claim 2 or 3, wherein the at least one force- redistributing portion of the armature has an inclined surface at an angle (a) to a direction perpendicular to the longitudinal axis between 5 ° to 60 °.

5. An armature according to any one of claims 2-4, wherein the at least one force- redistributing portion of the armature defines a frustoconical tip.

6. An armature according to any one of claims 2-5, wherein the armature head comprises a disc-shaped or cylindrical portion (103) and a tip portion (104) which is disposed on the disc-shaped or cylindrical portion, wherein the area of the cross section of the tip portion in a plane perpendicular to the longitudinal axis varies along the longitudinal axis.

7. An armature according to claim 6, wherein the tip portion is tapered in a direction parallel to the longitudinal axis away from the elongated member.

8. An armature according to claim 6 or 7, wherein the tip portion is arranged such that it has a smaller cross sectional area in a plane perpendicular to the longitudinal axis as compared to the disc-shaped or cylindrical portion.

9. An armature according to any one of claims 6-8, wherein the tip portion defines a frustoconical tip.

10. An armature according to any one of claims 1-9, wherein the at least one force- redistributing portion of the armature is situated at least in part in the elongated member.

1 1. An armature according to claim 10, wherein the at least one force- redistributing portion of the armature comprises a fillet portion (105) by means of which the elongated member is coupled to the armature head.

12. An armature according to claim 1 1 , wherein the fillet portion is tapered in a direction parallel to the longitudinal axis away from the armature head.

13. An armature according to claim 1 1 or 12, wherein the fillet portion (105) has a radius (r_f) between 0.5 mm and 25 mm.

14. An armature according to any one of claims 1-13, wherein the armature head comprises a conductive material.

15. An armature according to any one of claims 1-14, wherein the elongated member comprises an insulating material.

16. An armature according to any one of claims 1-15, wherein the elongated member comprises a cylindrical member having a radius defined by at least one of a mass of a load attached to the armature, a maximum desired acceleration of the armature when the armature is moved along the displacement path to the second position, and a length along the longitudinal axis of the elongated member.

17. A switch element (10) comprising:

at least a first contact (11) and a second contact (12) which can be selectively connected and disconnected such that when the first and second contacts are connected the switch element is closed, and when the first and second contacts are disconnected the switch element is opened;

an at least partially conductive armature (100) comprising:

an elongated member (101) having a longitudinal axis (A); and an armature head (102) arranged at one end of the elongated member; and

a magnetic field generator (200) adapted to generate a magnetic field;

wherein the switch element is arranged such that the armature is movable along a displacement path between at least a first position and a second position, and wherein the switch element is arranged such that when the armature is in the first position, the first and second contacts are connected, and when the armature is in the second position, the first and second contacts are disconnected;

wherein the armature comprises at least one force-redistributing portion (104; 105) having an area of its cross section in a plane perpendicular to the longitudinal axis which varies along the longitudinal axis, whereby tensile stresses within the armature head caused by movement of the armature responsive to the generation of the magnetic force on the armature head are redistributed into compressive stresses within the armature, thereby reducing any deformation of the armature.

18. A switch element according to claim 17, wherein the armature head comprises a disc-shaped or cylindrical portion (103) and a tip portion (104) which is disposed on the disc-shaped or cylindrical portion, wherein the area of the cross section of the tip portion in a plane perpendicular to the longitudinal axis varies along the longitudinal axis, and wherein the tip portion is arranged such that it has a smaller cross sectional area in a plane perpendicular to the longitudinal axis as compared to the disc-shaped or cylindrical portion, wherein the disc-shaped or cylindrical portion has a radius r and the tip portion at a boundary between the disc-shaped or cylindrical portion and in a plane perpendicular to the longitudinal axis has a radius r .

19. A switch element according to claim 17 or 18, wherein the magnetic field generator comprises a coil having a plurality of windings (202) arranged in a plane, wherein the coil has an outer radius r_oc and an inner radius r_lc.

20. A switch element according to claims 18 and 19, wherein:

r_h = r_oc ± c; and

n = r_ic + a (N-t_w);

wherein N is the number of windings, 0.5 < a < 1.0, c is a predefined length, and t_w is a width of a winding.

21. A circuit breaker (301) including a switch element (10) according to any one of claims 17-20, wherein the circuit breaker is adapted to interrupt a current in a transmission line (302) arranged to carry current when the switch element is opened.

22. A power system (300) including a transmission line (302) arranged to carry current and a circuit breaker (301) according to claim 21 coupled to the transmission line for controllably effecting discontinuation of flow of current in the transmission line.

23. A power system according to claim 22, wherein the power system comprises a High Voltage Direct Current, HVDC, power transmission system.