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Title:
ELECTROMAGNETIC CIRCUIT BREAKER FOR LOW VOLTAGE DC APPLICATIONS
Document Type and Number:
WIPO Patent Application WO/2015/110156
Kind Code:
A1
Abstract:
An electromagnetic circuit breaker (1) comprising fixed contacts (11), moveable contact bridges (13) arranged to electrically connect the fixed contacts(11), a magnetic core (3), a coil (4) electrically connected to the fixed contacts (11) and arranged to magnetise the magnetic core (3), an actuator (5) arranged to actuate the moveable contact bridges (13) between a closed circuit position in which the moveable contact bridges (13) are in mechanical connection with the fixed contacts (11) and the actuator (5) is in a first actuator position and an open circuit end position in which the actuator (5) is in a second actuator position, a magnetic member (7) arranged to move to the magnetic core (3) when the coil (4) is fed with a current greater than a threshold value, wherein the magnetic member (7) is arranged to initiate an initial motion of the actuator (5) when the magnetic member (7) moves towards the magnetic core (3) to break the mechanical connection between the moveable contact bridges (13) and the fixed contacts (11).The electromagnetic circuit breaker (1) further comprises a resilient arrangement (17), an energy accumulating member (19), and a bi-stable linkage (9) which in a first equilibrium state is arranged to maintain the resilient arrangement in an energised state, forcing the actuator (5) into the first actuator position, wherein bi-stable linkage (9) is arranged to be released from the first equilibrium state by the initial motion of the actuator (5), wherein the energy accumulating member (19) is arranged to provide a continued motion of the actuator (5) to the second actuator position.

Inventors:
BREDER, Henrik (Kaserngatan 221, Västerås, S-723 47, SE)
SCHAEFFER, David (Västra Ringvägen 21 A, Västerås, S-724 61, SE)
JONSSON, Lars (Anundsgatan 6, Västerås, S-723 51, SE)
ZHANG, Zichi (Regementsgatan 93, Västerås, S-723 45, SE)
VALDEMARSSON, Stefan (Kungsbacken Strö, Lidköping, S-531 98, SE)
Application Number:
EP2014/051304
Publication Date:
July 30, 2015
Filing Date:
January 23, 2014
Export Citation:
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Assignee:
ABB AG (Kallstadter Str. 1, Mannheim, 68309, DE)
International Classes:
H01H71/24; H01H5/06; H01H73/04; H01H77/06; H01H1/20; H01H1/50
Foreign References:
US5587861A
US6013889A
EP1498926A2
US8373523B2
Attorney, Agent or Firm:
VOGEL, Albrecht (ABB AG/ GF-IP, Wallstadter Strasse 59, Ladenburg, 68526, DE)
Download PDF:
Claims:
l8

CLAIMS

1. An electromagnetic circuit breaker (1) comprising: fixed contacts (11), moveable contact bridges (13) arranged to electrically connect the fixed contacts (11), a magnetic core (3), a coil (4) electrically connected to the fixed contacts (11) and arranged to magnetise the magnetic core (3), an actuator (5) arranged to actuate the moveable contact bridges (13) between a closed circuit position in which the moveable contact bridges (13) are in mechanical connection with the fixed contacts (11) and the actuator (5) is in a first actuator position and an open circuit end position in which the actuator (5) is in a second actuator position, a magnetic member (7) arranged to be moved to the magnetic core (3) when the coil (4) is fed with a current greater than a threshold value, wherein the magnetic member (7) is arranged to initiate an initial motion of the actuator (5) when the magnetic member (7) moves towards the magnetic core (3) to break the mechanical connection between the moveable contact bridges (13) and the fixed contacts (11), a resilient arrangement (17; 17'), an energy accumulating member (19), and a bi-stable linkage (9) which in a first equilibrium state is arranged to maintain the resilient arrangement (17; 17') in an energised state, forcing the actuator (5) into the first actuator position, wherein bi-stable linkage (9) is arranged to be released from the first equilibrium state by the initial motion of the actuator (5), wherein the energy accumulating member (19) is arranged to provide a continued motion of the actuator (5) to the second actuator position.

2. The electromagnetic circuit breaker (1) as claimed in claim 1, wherein the resilient arrangement (17; 17') and the energy accumulating member (19) are springs, and wherein the resilient arrangement (17; 17') has a greater stiffness than the energy accumulating member (19).

3. The electromagnetic circuit breaker (1) as claimed in any of the preceding claims, wherein the bi-stable linkage comprises a lever (9a) , a first arm (9c) and a second arm (9d), wherein the lever (9a) has a pivotal connection with the first arm (9c) and the first arm (9c) has a pivotal connection with the second arm (9d).

4. The electromagnetic circuit breaker (1) as claimed in claim 3, wherein the lever (9a) is arranged to bias the energy accumulating member (19) when the bi-stable linkage is in the first equilibrium state to force the actuator (5) into the first position.

5. The electromagnetic circuit breaker (1) as claimed in claim 3 or 4, wherein an axis (A2) defined by the pivotal connection of the lever (9a) and the first arm (9c) is moveable in a first direction.

6. The electromagnetic circuit breaker (1) as claimed in any of claims 3-5, wherein an axis (A3) defined by the pivotal connection of the first arm (9c) and the second arm (9d) is moveable in a second direction.

7. The electromagnetic circuit breaker (1) as claimed in any of claims 3-6, wherein the lever (9a) has a fixed pivot axis (Ai).

8. The electromagnetic circuit breaker (1) as claimed in any of claims 3-7, wherein the second arm (9d) at one end thereof has a fixed pivot axis (A4).

9. The electromagnetic circuit breaker (1) as claimed in any of the preceding claims, wherein the actuator (5) comprises moveable contact bridge through- openings (sd), wherein the moveable contact bridges (13) are arranged in a respective moveable contact bridge through-opening (sd).

10. The electromagnetic circuit breaker (1) as claimed in any of the preceding claims, wherein the actuator (5) comprises a magnetic member through- opening (5a) in which the magnetic member (7) is arranged, wherein a first wall (5b) of the magnetic member through-opening (5a), closest to the magnetic core (3), is arranged to interact with the magnetic member (7) when the magnetic member (7) is moved towards the magnetic core (3).

11. The electromagnetic circuit breaker (1) as claimed in claim 10, wherein the magnetic member (7) and a second wall (5c) of the magnetic member through-opening (5a), farthest from the magnetic core (3), defines a play (P) to enable continued motion of the actuator (5) when the magnetic member (7) has reached the magnetic core (3).

12. The electromagnetic circuit breaker (1) as claimed in any of the preceding claims, wherein the magnetic member (7) is arranged at a distance (d) of approximately 0.6 mm from the magnetic core (3) under normal operating currents.

13. The electromagnetic circuit breaker (1) as claimed in any of the preceding claims, wherein the resilient arrangement (17') comprises a plurality of springs, each spring being arranged to provide resiliency to a respective fixed contact (11) to enable the bi-stable linkage to be set in its first equilibrium state.

14. The electromagnetic circuit breaker (1) as claimed in any of the preceding claims, wherein the electromagnetic circuit breaker (1) is a low voltage DC circuit breaker adapted to handle voltages up to 1000 V.

Description:
ELECTROMAGNETIC CIRCUIT BREAKER FOR LOW VOLTAGE DC APPLICATIONS

TECHNICAL FIELD

The present disclosure generally relates to circuit breakers. In particular, the present disclosure relates to an electromagnetic circuit breaker for low voltage direct current (DC) applications.

BACKGROUND

Electromagnetic trip and installation switching devices are typically electromechanical devices. The point of electrical connection includes a fixed contact member and a moveable contact member which is held by a moveable contact arm or contact bridge. In the closed position, the moveable contact member is pressed against the fixed contact member, influenced by the force of a contact spring. Such trip devices and installation switching devices can also include a mechanical gear mechanism with a latch and a spring force based energy storage assembly.

In case of a tripping condition, a tripping device is known to act on the latch, which then releases the energy from the energy storage assembly so that the gear mechanism can act upon the contact lever or contact bridge in order to break the electrical connection.

US 8,373,523 discloses an electromagnetic trip device which comprises a magnetic core around which a coil is wound. The core has a base portion which has a narrow gap, about 0.6 mm. In this gap a contact lever or bridge is arranged contacting the coil and which under normal conditions provides a flow path for current. When a fault current passes through the coil, the magnetic flux in the magnetic core, which is substantially perpendicular to the direction of current flow through the contact bridge, a Lorentz force acts on the contact bridge, pulling it vertically upwards into the central opening of the magnetic core. The Lorentz force acts against the repelling force of the contact spring. An increasing current flow increases the Lorentz force, a result of two cumulating effects: the magnetic flux is increased, and the current itself is increased. The absolute value of the Lorentz force is proportional to the product of current times flux, so the Lorentz force increases strongly on an increase of current flow through the current path. In case of a short circuit current, the current flow increases quickly. As soon as the Lorentz force surpasses the repelling force of the contact springs the contact bridge is torn away in the upward direction, separating the fixed contact pieces from the moveable contact pieces. A short circuit interruption of the current path is thereby achieved. SUMMARY

There may however sometimes be drawbacks with utilising the Lorentz force to break an electrical connection. The actuating device which breaks the electrical connection includes the moveable contact. The moveable contact arranged in the space between the base portion or legs of the magnetic core may therefore only be arranged to carry current in a unidirectional manner because the Lorentz force of each pair of moveable contact providing current flow in opposing directions would cancel out. Moreover, it is more difficult to series connect several contacts in the small space between the magnetic core legs, to reduce voltages between contact points upon tripping, resulting in that fewer moveable contacts can be used, and in that the dimension of the moveable contacts must be reduced resulting in a higher risk that they burn off /melt due to high currents.

In view of the above, a general object of the present disclosure is to provide a circuit breaker that solves or at least mitigates these problems. According to a first aspect of the present disclosure there is provided an electromagnetic circuit breaker comprising: fixed contacts; moveable contact bridges arranged to electrically connect the fixed contacts; a magnetic core; a coil electrically connected to the fixed contacts and arranged to magnetise the magnetic core; an actuator arranged to actuate the moveable contact bridges between a closed circuit position in which the moveable contact bridges are in mechanical connection with the fixed contacts and the actuator is in a first actuator position and an open circuit end position in which the actuator is in a second actuator position; a magnetic member arranged to move to the magnetic core when the coil is fed with a current greater than a threshold value, wherein the magnetic member is arranged to initiate an initial motion of the actuator when the magnetic member moves towards the magnetic core to break the mechanical connection between the moveable contact bridges and the fixed contacts; a resilient arrangement; an energy accumulating member; and a bi-stable linkage which in a first equilibrium state is arranged to maintain the resilient arrangement in an energised state, forcing the actuator into the first actuator position, wherein bi-stable linkage is arranged to be released from the first equilibrium state by the initial motion of the actuator, wherein the energy accumulating member is arranged to provide a continued motion of the actuator to the second actuator position.

The electromagnetic circuit breaker thus provides bi-stable functionality between a closed and open position without the utilisation of the Lorentz force. In the first equilibrium state, the bi-stable linkage maintains the energy in the resilient arrangement and forces the actuator to maintain the first actuator position. This energy has initially been provided to the resilient arrangement by the bi-stable linkage when the actuator manually is set into its first actuator position and the bi-stable linkage attains its first equilibrium state. Mechanical connection of the moveable contact bridges and the fixed contacts may thereby be maintained under normal operating conditions. By means of the very fast initial acceleration and movement of the actuator due to a fault current, the bi-stable linkage is released from the first equilibrium state. This results in that the resilient arrangement is no longer energised by the bi-stable linkage, and thus the actuator is no longer forced into the first actuator position. The energy accumulating member may thereby provide a continued motion of the actuator to the second actuator position to further increase the distance between the moveable contact bridges and the fixed contacts.

The electromagnetic circuit breaker presented herein hence enables bidirectional current flow in the electromagnetic circuit breaker. Moreover, the dimensions of the moveable contacts do not depend on the space between the magnetic core base portion/legs to the same extent as in the prior art.

According to one embodiment the resilient arrangement and the energy accumulating member are springs, wherein the resilient arrangement has a greater stiffness than the energy accumulating member. The resilient arrangement is hence able to provide a stronger load force to the actuator than the energy accumulating member, which is arranged to apply a force to the actuator in the opposite direction compared to the force applied by the resilient arrangement. The moveable contact bridges may hence be maintained in mechanical contact with the fixed contacts until the bi-stable linkage is released from the first equilibrium state.

According to one embodiment the bi-stable linkage comprises a lever, a first arm and a second arm, wherein the lever has a pivotal connection with the first arm and the first arm has a pivotal connection with the second arm. According to one embodiment the lever is arranged to bias the energy accumulating member when the bi-stable linkage is in the first equilibrium state to force the actuator into the first position.

According to one embodiment an axis defined by the pivotal connection of the lever and the first arm is moveable in a first direction. According to one embodiment an axis defined by the pivotal connection of the first arm and the second arm is moveable in a second direction.

According to one embodiment the lever has a fixed pivot axis.

According to one embodiment the second arm at one end thereof has a fixed pivot axis. According to one embodiment the actuator comprises moveable contact bridge through-openings, wherein the moveable contact bridges are arranged in a respective moveable contact bridge through-opening. According to one embodiment the actuator comprises a magnetic member through-opening in which the magnetic member is arranged, wherein a first wall of the magnetic member through-opening, closest to the magnetic core, is arranged to interact with the magnetic member when the magnetic member is moved towards the magnetic core.

According to one embodiment the magnetic member and a second wall of the magnetic member through-opening, farthest from the magnetic core, defines a play to enable continued motion of the actuator when the magnetic member has reached the magnetic core. According to one embodiment the magnetic member is arranged at a distance of approximately 0.6 mm from the magnetic core under normal operating currents.

According to one embodiment the resilient arrangement comprises a plurality of springs, each spring being arranged to provide resiliency to a respective fixed contact to enable the bi-stable linkage to be set in its first equilibrium state.

According to one embodiment the electromagnetic circuit breaker is a low voltage DC circuit breaker adapted to handle voltages up to 1000 V

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise. BRIEF DESCRIPTION OF THE DRAWINGS

The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. l schematically shows a perspective of an example of an electromagnetic circuit breaker;

Fig. 2a shows a close-up view of a lateral portion of the electromagnetic circuit breaker in Fig. l; Fig. 2b shows a top view of moveable contact bridges and fixed contact bridges;

Figs 3a-b show close-up views of the interaction between the magnetic member and the magnetic core;

Figs 4a-b show close-up views of the bi-stable linkage in a first equilibrium state and a second stable state respectively;

Fig. 5 depicts a close-up view of the actuator when it has reached its second actuator position; and

Fig. 6 depicts a portion of an electromagnetic circuit breaker having a variation of the resilient arrangement. DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying

embodiments are shown. The inventive concept 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 be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

Fig. l depicts an example of an electromagnetic circuit breaker ι for low voltage DC applications. With low voltage is here meant voltages up to 1000 V, for example 400 V. The electromagnetic circuit breaker is a passive electromagnetic circuit breaker, meaning that no external control is necessitated for tripping operations. The electromagnetic circuit breaker 1 comprises a magnetic core 3, an actuator 5, a coil 4, a magnetic member 7, a bi-stable linkage 9, fixed contacts 11, moveable contact bridges 13, a resilient arrangement 17 and an energy accumulating member 19. These components may for example be mounted to a frame 21. Other variations of the resilient arrangement are however also possible, as will later be made clear with reference to Figs 3a and 6.

The moveable contact bridges 13 are arranged to electrically connect the fixed contacts 11, which are spaced apart. The moveable contact bridges 13 hence act as bridge members arranged to mechanically connect with the fixed contacts 11. The fixed contacts 11 are arranged to be connected to terminals of a circuit that the electromagnetic circuit breaker 1 is to protect.

The moveable contact bridges 13 are moveably arranged relative to the fixed contacts 11. In a closed circuit position, as shown in Fig. 1, the moveable contact bridges 11 are arranged in mechanical connection with the fixed contacts 11. Current may thereby flow through the electromagnetic circuit breaker 1. The moveable contact bridges 13 may in particular be arranged to be connected in series with the fixed contacts 11 such that bidirectional current flow may be provided in the electromagnetic circuit breaker 1, as will be further elaborated upon in connection with the discussion of Fig. 2b. The moveable contact bridges 13 may also be set in an open circuit end position, in which the moveable contact bridges 13 are spaced apart from the fixed contact bridges 11. When the moveable contact bridges are in the open circuit end position current is unable to flow through the electromagnetic circuit breaker 1 and the electromagnetic circuit breaker has thus tripped. The magnetic core 3 may for example be made of solid isotropic magnetic material or laminated metal sheets, such as iron sheets. The magnetic core 3 has a yoke 3a and legs 3b and 3c which are connected to a respective end of the yoke 3 a.

According to one variation the legs 3b, 3c have end portions with inclined inner surfaces. These inner surfaces define a respective plane which intersects the inner surfaces of the remaining portion of the legs 3b, 3c. The width of the end portion of each leg 3b, 3c may for example increase linearly as a function of the distance from the yoke. This particular shape may be advantageous in that the magnetic flux may be optimised for circuit breaking for low DC voltages. It should however be noted that other shapes of the legs are also possible within the scope of the present disclosure, as would be apparent to the skilled person.

The coil 4 is arranged to magnetise the magnetic core 3. The coil 4 may thus be wound around the magnetic core 3. The coil 4 may for example be wound with 1-6 turns around the magnetic core 3, e.g. the yoke 3a. The coil 4 may be connected to the fixed contacts 11. The coils 4 could however be connected in other manners too, as would be apparent to the skilled person.

The magnetic member 7 is arranged to be moved, i.e. pulled by magnetic force, to the magnetic core 3 when a current flowing through the

electromagnetic circuit breaker 1 reaches above a threshold value. In this case, the coil 4 provides such magnetisation of the magnetic core 3 that the magnetic flux in the magnetic core 3 forces the magnetic member 7 towards the magnetic core 3. According to one variation the magnetic member 7 is pulled towards the legs 3b, 3c of the magnetic core 3. Depending on the magnitude of the current, the magnetic member 7 may be lifted only slightly, or it may be moved such that it actually reaches the magnetic core 3.

The magnetic member 7 may according to one variation be made of iron, for example soft iron. According to another variation the magnetic member may be a laminated stack of individually insulated electrical steel-sheets glued or seemed together.

The electromagnetic circuit breaker 1 may according to one variation comprise a magnetic member support 15 arranged to support the magnetic member 7. The magnetic member support 15 may be arranged adjacent the magnetic core 3, such that the magnetic member 7 resting on the magnetic member support 15 is able to interact with the magnetic flux provided by the magnetic core 3. The magnetic member support 15 may be fixedly arranged in the frame 21, disconnected from any other component of the

electromagnetic circuit breaker 1.

The actuator 5 is arranged to actuate the moveable contact bridges 13. The actuator 5 may thus be actuated between a first actuator position in which the moveable contact bridges 13 are in mechanical connection with the fixed contacts 11, and a second actuator position in which the moveable contact bridges 13 are in the open circuit end position.

The actuator 5 is arranged to interact with the magnetic member 7, with the magnetic member 7 being arranged to initiate an initial motion of the actuator 5 when the magnetic member 7 moves towards the magnetic core 3. This results in an initial movement of the moveable contact bridges 13 to break the mechanical connection with the fixed contacts 11.

The resilient arrangement 17 may be a spring, such as a helical spring. The energy accumulating member 19 may be a spring, such as a helical spring.

The bi-stable linkage 9 is arranged to obtain a first equilibrium state and a second equilibrium state. In the first equilibrium state the bi-stable linkage 9 is arranged to energise the resilient arrangement 17 and to maintain the energy in the resilient arrangement^, such that the energy accumulating arrangement 17 provides a continuous load force to the actuator 5 in the first actuator position. Thus, when exemplified by a spring, the bi-stable linkage 9 compresses the spring such that the spring applies a spring force to the actuator 5 forcing the moveable contact bridges 13 into mechanical connection with the fixed contacts 11. Furthermore, the resilient arrangement enables the bi-stable linkage to be set into its first equilibrium state, in particular by means of the resilience provided by the resilient arrangement.

The energy accumulating member 19 is arranged to provide a continuous load force to the actuator 5 when the bi-stable linkage 9 is in the first equilibrium state. As a result of the bi-stable linkage 9 being released from the first equilibrium state due to the initial motion of the actuator 5, the energy accumulating member 19 can provide continued motion of the actuator 5 to the second actuator position.

When exemplified by springs, the resilient arrangement 17 has a greater stiffness than the energy accumulating member. In other words, the spring constant of the resilient arrangement is greater than the spring constant of the energy accumulating member. The load force provided to the actuator 5 by the resilient arrangement 17 may thereby prevail over the load force of the energy accumulating member 19, which is directed in the opposite direction.

The electromagnetic circuit breaker 1 hence provides a two stage tripping mechanism, with a very fast initial motion of the actuator 5 and thus the moveable contact bridges 13 upon a circuit failure, limiting the current in the circuit protected by the circuit breaker 1, and a continued motion of the actuator by means of the energy accumulating member 19 when the magnetic member 7 is moving towards the magnetic core 3. The initial motion provided by the actuator 5 is faster than the continued motion provided by the energy accumulating member 19, but the total motion is faster than what has previously been possible.

Turning now to Fig. 2a, a lateral view of a portion of the electromagnetic circuit breaker 1 is shown. According to the depicted example, the actuator 5 comprises moveable contact bridge through-openings 5d. Each through- opening is arranged to receive a moveable contact bridge 13. In operation of the electromagnetic circuit breaker 1, each moveable contact bridge 13 is arranged in a respective moveable contact bridge through-opening sd. The dimension of each moveable contact bridge through-opening sd is preferably essentially equal to the cross-sectional dimension of the moveable contact bridges 13. By means of this design, linear movement of the actuator 5 hence actuates the moveable contact bridges 13 concurrently with the motion of the actuator, between their closed position and their open circuit end position.

The actuator 5 may also have a magnetic member through-opening 5a. The magnetic member through-opening 5a has a first wall 5b, which is located closest to the magnetic core 3, and a second wall 5c which is that wall of the magnetic member through-opening 5a which is farthest away from the magnetic core 3. The first wall 5b and the second wall 5c hence face each other. The magnetic member through-opening 5a is arranged to receive the magnetic member 7. The magnetic member 7 is thus arranged in the magnetic member through-opening 5a when the electromagnetic circuit breaker 1 is in operation. The magnetic member 7 is arranged to abut the first wall 5b during normal operation, i.e. when the current through the coil 4 is below a threshold value. The magnetic member 7 is in this situation arranged at a distance d from the magnetic core 3. The distance d may for example be between 0.05 mm to 1 mm, preferably 0.6 mm. It is however to be noted that this distance in general is dependent of the size of the electromagnetic circuit breaker, and more specifically on parameters such as the effective iron length of the magnetic core, the distance between the legs of the magnetic core, thickness and width of the legs, and the thickness of the magnetic member. The effective iron length of the magnetic core is the average magnetic flux circuit length in the magnetic core.

The magnetic member 7 is arranged to rest on the magnetic member support 15 when the current through the coil 4 is below a threshold. The surface of the magnetic member support 15 on which the magnetic member 7 rests, is hence arranged at a distance from the magnetic core 3 corresponding to the thickness of the magnetic member 7 and the distance d. The magnetic member support 15 may comprise a first support portion and a second support portion which are spaced apart and arranged at a respective side of the actuator 5. The magnetic member 7 is thus arranged to rest on the first support portion and the second support portion and to extend through the magnetic member through-opening 5a.

Since the magnetic member 7 abuts the first wall 5b, movement of the magnetic member 7 towards the magnetic core 3 provides movement of the actuator 5. The actuator 5 will thus also move towards the magnetic core 3 when the magnetic member 7 moves towards the magnetic core 3 and thus provide an initial motion to the actuator 5.

The distance between first wall 5b and the second wall 5c is greater than the thickness of the magnetic member 7. There is hence a play P between the magnetic member 7 and the second wall 5c when the magnetic member 7 rests on the magnetic member support 15. The play P allows the actuator to move further, i.e. in a continued motion, when the magnetic member 7 has travelled the distance d and thus reached the magnetic core 3. The moveable contact bridges 13 may thereby be distanced further from the fixed contacts 11 during tripping, with a total distance which amounts to the initial distance d between the magnetic core 3 and the magnetic member 7 and the play P. This continued motion is, as previously explained, obtained by means of the energy accumulating member 19. The play P may for example be of such a magnitude that the total possible movement of the actuator is about 5 mm. Thus in the example in which the distance d is 0.6 mm, the play P may be 4.4 mm.

Fig. 2b depicts a top view of an example of electrical connections between the moveable contact bridges 13 and fixed contacts 11. The number of moveable contact bridges and fixed contact bridges may depend on the particular application. Fig. 2b is thus only one example of a plurality of possibilities; Fig. 2b merely illustrates the basic concept of series connected moveable contact bridges 13 and fixed contacts 11. The current path is illustrated by means of the arrows. By means of this construction, the number of contact points between moveable contact bridges and fixed contact bridges is two times the number the moveable contact bridges. Upon breaking of the mechanical connection between the moveable contact bridges and the fixed contact bridges, the voltage at each contact point is the total voltage divided by the number of contact points. The moveable contact bridges and the fixed contact bridges may be made of metal such as copper, or any other suitable conductive material. The operation of the electromagnetic circuit breaker 1 will now be described in more detail with reference to Figs 3a-5.

Fig. 3a depicts the upper part of the electromagnetic circuit breaker 1 shown in Fig. 1. The magnetic member 7 rests on the first support portion and the second support portion of the magnetic member support 15. The magnetic member 7 is thus located at a distance d from the magnetic core 3. The actuator 5 is in the first actuator position, and the moveable contact bridges 13 are in mechanical connection with the fixed contacts 11.

It may here be noted that in Fig. 3a, the depicted example of an

electromagnetic circuit breaker comprises a resilient arrangement^'. This resilient arrangement^' may replace the energy accumulating member 17 arranged at the actuator 5. Thus, instead of energy accumulating member 17, energy accumulating member 17' may be utilised. Alternatively, both energy accumulating arrangements 17 and 17' may be utilised in one variation of the electromagnetic circuit breaker. In case only the resilient arrangement^' is utilised, the upper spring defining the resilient arrangement^, as shown in for example Fig. 5, may be discarded.

In case the electromagnetic circuit breaker comprises resilient

arrangement^' the fixed contacts 11 may have a counter weight portion 11a at their distal end with respect to their fixed ends. The counter weight portions 11a are thus arranged essentially in vertical alignment with the movable contacts 13. Each counterweight portion 11a provides a higher weight to the distal end of its fixed contact 11 to prevent the fixed contacts to follow the movable contacts 13 towards the magnetic member upon the initial movement of the movable contacts in the case of a circuit breaking operation. Mechanical contact breaking can thereby be ensured. Since the fixed contacts 11 are made of a highly electrically conductive material such as copper, which is a non-resilient material, the resilient arrangement provides resilience to the fixed contacts 11. According to the example in Fig. 3a, the resilient arrangement^' comprises springs, e.g. leaf springs or plate springs. Each fixed contact 11 is associated with a respective spring and each such spring extends in parallel with its fixed contact 11, in the longitudinal direction thereof, as shown in Fig. 3a. The resilience provide by the resilient

arrangement^', i.e. the leaf or plate springs, allows for setting the bi-stable linkage 9 into its first equilibrium state, as will be described in more detail below.

In Fig. 3b, a fault has occurred in the circuit which the electromagnetic circuit breaker 1 is arranged to protect. For the sake of clarity, the magnetic member support is not shown in this figure. A current which exceeds the threshold value flows through the coil 4 which thus magnetises the magnetic core 3. The magnetic flux in the magnetic core is thus increased and the magnetic member 7 is attracted and pulled towards the magnetic core 3. In Fig. 3b, it can be seen that the magnetic member 7 has almost reached the magnetic core 3. The actuator 5 has thus been set in an initial motion and has therefore been moved in the same direction as the magnetic member 7. The mechanical connection between the moveable contact bridges 13 and the fixed contacts 11 has thus been broken.

Fig. 4a depicts the lower portion of the electromagnetic circuit breaker 1 shown in Fig. 1. In particular, the bi-stable linkage 9, the actuator 5, resilient arrangement 17 and the energy accumulating member 19 are shown. In Fig. 4a the bi-stable linkage 9 is in the first equilibrium state, and corresponds to the situation shown in Fig. 3a when the moveable contact bridges are in mechanical connection with the fixed contacts.

The bi-stable linkage 9 comprises a lever 9a, a first arm 9c arranged in pivotal connection with the lever 9a, and a second arm 9d arranged in pivotal connection with the first arm 9c. The lever 9a is pivotally arranged around a fixed axis Ai, and has a first arm connecting portion 9b offset from the fixed axis Ai and arranged in pivotal connection with the first arm 9c, defining a moveable axis A2. The pivotal connection between the first arm 9c and the second arm 9d forms a knee, which is arranged to rest against an arm support 23 when the bi-stable linkage is in the first equilibrium state. The pivotal connection between the first arm 9c and the second arm 9d defines an axis A3 which is moveable. The second arm 9d is at its other end arranged to pivot around a fixed axis A4.

The actuator 5 may have a resilient arrangement through-opening 5e in which the resilient arrangement 17 may be arranged. In case the resilient arrangement is a spring, the spring may be arranged around an axial protrusion extending from the lower portion of the resilient arrangement through-opening 5e. Other means for causing mechanical interaction between the actuator and the resilient arrangement are also possible. The resilient arrangement could for example be arranger around the actuator, wherein the actuator could be provided with a collar for holding the resilient arrangement in position.

The lever 9a is arranged to energise the resilient arrangement 17 when the bistable linkage 9 is set in its first equilibrium state, and to maintain the resilient arrangement 17 in an energised state when the bi-stable linkage 9 has attained its first equilibrium state. The lever 9a hence compresses the resilient arrangement 17. In particular, the lever 9a may have a finger 9e, shown in Fig. 4b for hooking into the resilient arrangement 17 in the first equilibrium state. The actuator 5 is thereby pressed in a direction away from the magnetic core 3, such that the moveable contact bridges 13 are forced into mechanical connection with the fixed contacts 11.

In case of an embodiment comprising an resilient arrangement^', the bistable linkage 9 actuates the actuator 5 by means of the finger 9e, which in turn moves the movable contacts 13 towards the distal ends of the fixed contacts 11. In particular, the movable contacts 13 are pressed against the fixed contacts 11, wherein the resilient arrangement^', in the form of leaf or plate springs, is bent and provides the necessary resilience to the fixed contacts 11 to allow the bi-stable linkage 9 to be set into its first equilibrium state, and thus the actuator into the first actuator position.

Fig. 4b illustrates the case when the bi-stable linkage 9 has been released from the first equilibrium state due to the initial motion of the actuator 5 provided by the magnetic member 7, as shown in Fig. 3b. The initial motion of the actuator 5 causes the knee to collapse from its resting position on the arm support 23, causing the bi-stable linkage to be released from the first equilibrium state. The lever 9a hence pivots around the fixed axis Ai such that the finger 9e is released from the resilient arrangement 17 and the energy accumulating member 19 provides a continued motion of the actuator 5, even when the magnetic member 7 has reached the magnetic core 3, until the second wall of the magnetic member through-opening reaches the lower portion of the magnetic member 7. Fig. 5 illustrates the situation when the magnetic member 7 has reached the second wall sd, the actuator 5 has reached its second actuator position and the moveable contact bridges 13 have reached their open circuit end position. As can be seen, the play P has now moved to the other side of the magnetic member 7, i.e. the play P is defined between the first wall 5b and the magnetic member 7. Re-close operation of the circuit breaker is typically made manually.

Fig. 6 depicts an example of an electromagnetic circuit breaker comprising a resilient arrangement^", which is a variation of resilient arrangement^ and 17'. According to this variation, the resilient arrangement^" comprises a plurality of springs 17" fixed to a structure 18 which may be an

electromagnetic circuit breaker housing in which the components of the electromagnetic circuit breaker is arranged. Each spring is mechanically coupled to a respective fixed contact 11, in particular the distal end thereof, thus providing resilience to the distal ends of each fixed contact 11. Thereby, the movable contacts and the actuator may be moved in a direction away from the magnetic member in a resilient manner when the movable contacts are in physical contact with the fixed contacts, allowing the bi-stable linkage to be set in its first equilibrium state, wherein the actuator 5 is set in the first actuator position. The bi-stable linkage hence energises and maintains this energy in the resilient arrangement^", i.e. the springs when the bi-stable linkage is in the first equilibrium state. This is in particular obtained via the actuator 5 which is actuated by means of the finger 9e shown in Fig. 5. Thus, when the finger 9e provides the necessary force to the actuator 5, the actuator 5 moves the movable contacts 13, which in turn provide pressure to the fixed contacts 11 and thus to the resilient arrangement^".

The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.