GB2596085A

GB2596085A - Circuit breaker with delayed reclosing function

Info

Publication number: GB2596085A
Application number: GB2009155.9A
Authority: GB
Inventors: Guaschino Mirko; Heins Volker
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2020-06-16
Filing date: 2020-06-16
Publication date: 2021-12-22
Also published as: GB202009155D0; DE102021115059A1

Abstract

A circuit breaker 1 comprises a rotatable contact arm 6, a supporting surface 9a,b running along a control curve, and a tension spring arrangement 10a,b having a first end C1,C2 connected to the contact arm and a second end D1,D2 slidably supported by the supporting surface (9a,b, figure 5). The tension spring pulls the contact arm towards a closed arm position in which it is separated from the second end of the tension spring. Upon an opening rotation, the contact arm contacts the second end at an intermediate arm position while the second end is at a first spring position or depression b1. Upon a further opening rotation, the contact arm pushes the second end into a second spring position b2 over a convex elevation E. The second end may be pulled into the first spring position by the tension of the spring during a closing rotation of the contact arm. The circuit breaker may comprise a rotatable switching shaft 8 as a secondary slow opening mechanism which rotates at a higher threshold current than that of the contact arm. The sliding of the second end between the two spring positions delays the reclosing time of the contact arm and allows the switching shaft to permanently open the contacts.

Description

Circuit breaker with delayed reclosing function TECHNICAL FIELD The invention relates to a circuit breaker, which comprises a housing as well as a first electrical terminal and a second electrical terminal, which reach through the housing and which are provided for switching the circuit breaker in a current path of an electric circuit. Furthermore, the circuit breaker comprises a first fixed switching contact, which is electrically connected to the first electrical terminal within the housing (by means of a first electrical conductor). Moreover, the circuit breaker comprises a contact arm, which is pivotally mounted around a first axis within the housing and which has a first movable switching contact, which contacts the first fixed switching contact in a closed arm position of the contact arm and which is lifted off the first fixed switching contact in open arm positions of the contact arm (or in more detail upon an opening rotation of the contact arm). In addition, the circuit breaker comprises at least one supporting surface, which is arranged within the housing and which intersects a virtual plane perpendicular to the first axis along a control curve. Finally, the circuit breaker comprises at least one tension spring arrangement, wherein a first end of the tension spring arrangement is pivotally connected to the contact arm (e.g. by means of a first bolt) at a first supporting point and wherein a second end of the tension spring arrangement is slidably supported by said at least one supporting surface and wherein the tension spring arrangement generates a tension force in a direction causing a closing rotation of the contact arm.

BACKGROUND ART

A delayed reclosing function of a contact arm of a circuit breaker basically is needed because of two reasons. First, contact arms are often combined with (secondary) slower opening mechanisms such as switching shafts. The contact arm has comparably low inertia and thus opens the switching contacts very fast in an overcurrent condition. Besides that, the slower opening mechanism triggers as well. One condition for a proper function is that the slower opening mechanism opens faster than the contact arm bounces back and recloses the switching contacts. So the aim is that the switching contacts stay open from the very first point in time of an overcurrent. One approach is to slow down the contact arm what is a bit of a -2 -contradiction, because on the one hand it shall open as fast as possible, on the other hand it shall reclose as slow as possible.

A second application is chaining of selective devices. In an illustrative example one can assume that there is an upstream circuit breaker with a delayed reclosing and several fast downstream circuit breakers in different branches of an electric circuit. If there is an overcurrent event (e.g. a short circuit) in one of the branches, both the fast downstream circuit breaker of the associated branch and the upstream circuit breaker detect an overcurrent. That is why both switch off the dangerous current instantaneously. However, while the downstream circuit breaker stays in its OFF-state after having opened, the upstream circuit breaker recloses. In that way it is ensured that branches, which are not faulty, are not unnecessarily switched off by the upstream circuit breaker, but are cut off just for the delay time of the contact arm. Only if there is a very high overcurrent, the upstream circuit breaker permanently switches of the electric circuit. To achieve this function, the upstream circuit breaker and the downstream circuit breakers have different nominal current capacity and thus turn off the current at different thresholds. Moreover, the slower opening mechanism of the upstream circuit breaker should not be triggered at a current level which is slightly above the switch off current threshold of the downstream circuit breaker. If these conditions are fulfilled, upstream circuit breaker recloses its switching contacts so as to keep the remaining branches of the electric circuit alive.

US 5,310,971 A and US 7,005,594 B2 disclose circuit breakers providing the aforementioned function. However, they suffer from a poor performance of the contact arms, meaning that the do open too slow and/or do reclose too fast.

DISCLOSURE OF INVENTION

Accordingly, an object of the invention is the provision of an improved electric circuit breaker. In particular, the contact arm shall open very fast, but reclose very slow.

The object of the invention is solved by an electric circuit breaker as defined in the opening paragraph, wherein the contact arm is lifted off the second end of the tension spring arrangement in the closed arm position (that means that the contact arm is decoupled from the second end of the tension spring arrangement there),

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the contact arm is designed to contact the second end of the tension spring arrangement at an intermediate open arm position of the contact arm and at a first spring position of the second end of the tension spring arrangement upon an opening rotation of the contact arm (hence the contact arm is rigidly motion coupled to the second end of the tension spring arrangement there) and the contact arm is designed to further contact the second end of the tension spring arrangement and to push it along the at least one supporting surface at least in a section between the intermediate open arm position of the contact arm and a full open arm position of the contact arm and to cause a movement of the second end of the tension spring arrangement into a second spring position upon a further opening rotation of the contact arm (and thus the contact arm at least temporarily is rigidly motion coupled to the second end of the tension spring arrangement during a further opening rotation).

By the above measures, the contact arm opens very fast, but it recloses very slow. In detail, the contact arm may freely move when it opens because it is lifted off the second end of the tension spring arrangement in positions ranging from the closed arm position until its intermediate open arm position. So, the tension spring arrangement does not hinder (and thus does not slow down) a rotation of the contact arm. That is why the switching contacts are separated very fast. In addition, the contact arm is slowed down from the intermediate open arm position onwards. That means that from the point in time the contact arm passes the intermediate open arm position, a comparably high retarding force acts on the contact arm, which slows the same down and which in turn increases the time until the switching contacts reclose. The total time from opening the switching contacts until reclosing the same is denoted as "delay time" in this disclosure. In particular, the intermediate open arm position is the position where arcs burning between the switching contacts are quenched when the circuit breaker is operated at its nominal voltage, or the intermediate open arm position is even located beyond this position (meaning that the intermediate open arm position is closer to the open arm position in the latter case).

In accordance with an improved delay time, the proposed circuit breaker offers advantages in a situation, in which a secondary slow opening mechanism is triggered, as well as in selectivity applications. In the first case, the increased delay -4 -fime helps to avoid reclosing of the switching contacts before the secondary opening mechanism keeps the same permanently open, and in the second case it helps that the switching contacts are not reclosed before the downstream circuit breaker keeps its switching contacts permanently open. Basically, in both cases the proposed measures help to bridge the time, which a slow opening mechanism needs to keep the switching contacts permanently open. In the first case, the slow opening mechanism in question is situated in the same circuit breaker, in which the delayed contact arm is located, and in the second case it is the slow opening mechanism of a downstream circuit breaker.

Although, the advantages of the proposed solution get transparent in particular in the context of a secondary slow opening mechanism, it should be noted that the same is no necessary condition, but the proposed measures are also useful without having such a secondary slow opening mechanism.

Generally, a "closed position" of the contact arm may also be denoted as an "ON position" of the contact arm, and an "open position" of the contact arm may also be denoted as an "OFF position" of the contact arm. In the closed position, a current may flow between the first and the second electrical terminal, whereas in the open position, if at all, a current may just flow over an arc. Because the contact arm is pivotally mounted, positions of the contact arm in a more detailed sense are "angular positions". The "intermediate position" of the contact arm is located between its closed position and its open position.

The "control curve" controls the torque, which is generated by the spring force and acts on the contact arm. In this way, basically any desired graph of the torque over a rotation angle of the contact arm can be achieved. It is noted that the term "curve" in the given context does not necessarily imply a curved course of the control curve, but the control curve may also comprise straight sections or may be straight as a whole.

"Lifted off' in the context of this disclosure does not necessarily mean that one part is arranged above another part or even arranged vertically above another part, but means "moved away from" or "distant from" independent of a special orientation of said parts to each other. In addition, "lifted off' may both mean the state as well as the action or transition as the case may be. -5 -

It should be noted that in the phase where the contact arm pushes the second end of the tension spring arrangement along the at least one supporting surface into the second spring position between the intermediate open arm position and the full open arm position, there may be sections where the second end lifts off the contact arm after their initial contact. This can happen if the second end temporarily moves faster than the contact arm, in particular if there is an elevation in the at least one supporting surface. Generally, the movement of the second end of the tension spring arrangement depends on the shape of the at least one supporting surface and the orientation of the tension spring arrangement relative to said supporting surface. However, in any case the contact arm catches up at the second spring position and contacts the same again in the full open arm position at the latest. But this second contact can also take place earlier. Of course, the contact arm can also stay in contact with second end of the tension spring arrangement the whole way between the intermediate open arm position and the full open arm position of the contact arm and between the first spring position and the second spring position of the tension spring arrangement.

Further advantageous embodiments are disclosed in the claims and in the description as well as in the figures.

Advantageously, the contact arm is designed to be lifted off the second end of the tension spring arrangement at the second spring position of the tension spring arrangement or at the first spring position of the tension spring arrangement or at a lift off point between said first spring position and said second spring position and it is designed to be kept lifted off until the closed arm position of the contact arm upon a closing rotation of the contact arm (i.e. until the contact arm reaches its closed arm position). In particular, the contact arm is designed to be lifted off the second end of the tension spring arrangement at the full open arm position of the contact arm upon a closing rotation of the contact arm. That means that the lift off point coincides with the second spring position. In other words this means that the second end of the tension spring arrangement stays in its second spring position when the contact arm reverses its movement towards its closed position, and it never catches up with the same. In this way, the spring force acting on the contact arm in its closing direction is kept low and thus the acceleration and speed of the contact arm in its closing direction is kept low. In turn, this also means the contact arm needs a comparably -6 -long time to return from its open arm position to its closed arm position. Because the return time is part of the total delay time as well, the same can be increased by the proposed measures. However, the lift off point can also be shifted towards the first spring position if the second end of the tension spring arrangement follows the contact arm at its back rotation. Nonetheless, the contact arm lifts off the second end of the tension spring arrangement at its first position at the latest. In those cases, the above effects may occur to a less extent.

Beneficially, the second end of the tension spring arrangement is pulled into its first spring position by the tension force generated by the tension spring arrangement during a closing rotation of the contact arm. So there can be a closing force acting on the contact arm besides of dynamic effects. That means that the contact arm is pulled into its closed arm position in any case. That is why the reclosing function of the circuit breaker is particularly reliable. Nevertheless, it is also possible that there is no closing spring force during a closing rotation of the contact arm, and the contact arm is forced into its closed arm position only by dynamic effects (e.g. it rebounds at a stopper by elastic deformation of the stopper or by elastic bending to the tension spring arrangement).

Beneficially, the first axis of the contact arm is fixedly arranged relative to or in the housing. For example, friction bearings may be used for this reason.

But it is also beneficial if the circuit breaker comprises a switching shaft, wherein the first axis is arranged in the switching shaft and wherein the switching shaft is rotatably mounted around a second axis, which is fixedly arranged relative to the housing, and wherein the switching shaft is designed to stand still during a contact arm movement, which is caused by an overcurrent between the first electrical terminal and a second electrical terminal, or to rotate slower than the contact arm in case of such an overcurrent. In particular, the switching shaft can be designed to stand still below a current threshold and designed to be rotated by an overcurrent actor into an opening direction above said current threshold, wherein said current threshold is above a current causing a rotation of the contact arm. The switching shaft is one embodiment of a secondary opening mechanism, and generally, the switching shaft can be rotated by any kind of actuator which is sensitive to an overcurrent and/or can be turned manually by means of a handle. An overcurrent -7 -situation can be detected by directly measuring the current through the circuit breaker and/or by measuring an increase of temperature caused by the current through the circuit breaker. The circuit breaker can also comprise a latch, on which a overcurrent actor and/or a handle acts. The overcurrent actor can be a temperature sensitive overcurrent actor (e.g. a bimetal actor) or an electrodynamic overcurrent actor. Of course, both a temperature sensitive overcurrent and an electrodynamic overcurrent actor can act on the latch so as to trigger the switching shaft in case of a comparably low but long lasting overcurrent (temperature sensitive overcurrent actor) or in case of a comparably high overcurrent (electrodynamic overcurrent actor). In addition, the handle can act on the latch so that in total there may be three possibilities to trigger the switching shaft. In contrast to the comparably slow switching shaft, the contact arm can be opened by electrodynamic forces very fast. It opens faster even in case that the switching shaft is triggered by its electrodynamic overcurrent actor. So generally, there is the possibility that the switching shaft stands still, and the contact arm opens, or it slowly moves and the contact arm opens fast. As disclosed above, a current threshold for a movement of the switching shaft preferably is above a current causing a rotation of the contact arm. So, below this current threshold just the contact arm rotates (and the switching shaft stands still), and above this current threshold both the contact arm and the switching shaft rotate (but the switching shaft rotates slower). It is particularly advantageous, if the switching contacts do not reclose in case of a rotation of the switching shaft. This means, that the delay time of the contact arm is longer than it takes to open the switching contacts by means of the switching shaft. In other words, the switching contacts reclose below the above current threshold, but they do not above said current threshold. This behavior is particularly advantageous in applications where selectivity is needed.

Coming back to the illustrative example of selectively chained circuit breakers, advantageously the current threshold for the switching shaft of the upstream circuit breaker should be higher than a current, which causes switching off the downstream circuit breaker, but lower than a current, which may cause serious damage in the electric circuit between the upstream circuit breaker and the downstream circuit breaker. So, the (upstream) circuit breaker of the disclosed kind provides a fast cut off of any dangerous current by means of the contact arm and in particular faster -8 -than it was possible with its switching shaft (because the contact arm rotates faster), but it also provides a controlled reclosing in case it turns out that a permanent cutting off is not necessary. In other words, If there is an overcurrent event (e.g. a short circuit) in one of the branches, both the fast downstream circuit breaker of the associated branch and the upstream circuit breaker detect an overcurrent. That is why both switch off the dangerous current instantaneously. However, while the downstream circuit breaker stays in its OFF-state after having opened, the upstream circuit breaker recloses. In that way it is ensured that branches, which are not faulty, are not unnecessarily switched off by the upstream circuit breaker, but are cut off just for the delay time of the contact arm. Only if there is a very high overcurrent, the upstream circuit breaker permanently switches of the electric circuit.

Advantageously, the contact arm is forced into the direction of the closing rotation between its full open arm position and an over rotation arm position, which is beyond the full open arm position (i.e. farther away from the closed arm position), by deformation of an elastic element. In particular, said force is generated by the elastic element (arranged) between a) the contact arm and the second end of the tension spring arrangement, b) the contact arm and a rigid stop in the housing, c) the contact arm and a rigid stop in the switching shaft, d) the second end of the tension spring arrangement and a rigid second spring position stop in the housing, e) between the second end of the tension spring arrangement and a rigid second spring position stop in the switching shaft.

Accordingly, the elastic element assists the back rotation of the contact arm and if it acts on the second end of the tension spring arrangement (which is true in cases d and e) also the back movement of the second end of the tension spring arrangement from its second spring position to its first spring position. Accordingly, an elastic element acting on the second end of the tension spring arrangement is useful if said second end without such an elastic element generally or occasionally tends to stay or stick in its second spring position when the contact arm rotates back to its closed arm position. By the proposed measures, the second end of the tension spring arrangement reliably moves back to its first spring position when the contact arm rotates back to its closed arm position. So, the second end of the tension spring -9 -arrangement reliably is in its first spring position when the contact arm is in its closed arm position. The elastic element can be made of rubber or an elastomer or may be embodied as a spring for example.

In a very advantageous embodiment, the circuit breaker comprises a spring stopper, which in the full open arm position of the contact arm is in contact with the spring arrangement in a limited region between the first end and the second end of the tension spring arrangement. In particular, the spring stopper can act as a bending point, around which the tension spring arrangement bends transverse to its longitudinal spring axis. In detail, the bending of the longitudinal spring axis of the tension spring arrangement occurs, when the first end and the second end of the tension spring arrangement by the movement of the contact arm are moved beyond a position where a straight shape of the longitudinal spring axis between said first end and said second end is no longer possible. Hence, the longitudinal spring axis of the tension spring arrangement becomes arc shaped upon a further opening rotation of the contact arm. In this state, the tension spring arrangement does not only generate a tension force between its first end and its second end, but also a force transverse to the longitudinal spring axis of the tension spring arrangement (and hence in a direction which is usually not intended by a tension spring). This transverse force assists to bring back the second end of the tension spring arrangement from the second spring position to the first spring position when the contact arm rotates back to its closed arm position. Accordingly, the spring stopper is useful if the second end of the second tension spring arrangement without such a spring stopper generally or occasionally tends to stay or stick in its second spring position when the contact arm rotates back to its closed arm position. By the proposed measures, the second end of the tension spring arrangement reliably moves back to its first spring position when the contact arm rotates back to its closed arm position. So, the second end of the tension spring arrangement reliably is in its first spring position when the contact arm is in its closed arm position.

It should be noted that the position and the height of the bending point defines the shape of the longitudinal spring axis of the tension spring arrangement and thus also how the second end behaves when the contact arm rotates back towards its closed arm position. Said height defines how far the bending point protrudes into a virtual (straight) connection line between the first end and the second end at the -10 -maximum bending of the tension spring arrangement. It is advantageous in the above context if the bending point is closer to the second end of the tension spring arrangement than to its first end, and it is particularly advantageous if the distance between the bending point and the second end of the tension spring arrangement is in a range of 20% to 40% of the distance between the first end and the second end of the tension spring arrangement. By these measures the curvature of the longitudinal spring axis of the tension spring arrangement is higher in the region of the second end than in the region of the first end. Hence, also the back force is higher for the second end than for the first end. The second end can also stay in contact with the contact arm for a while during the back rotation of the contact arm and even push back the contact arm to a certain extent. The second end of the tension spring arrangement may stay in contact with the contact arm until the first spring position or until a lift off point between the first spring position and the second spring position of the tension spring arrangement. However, the contact arm may also be lifted off the second end of the tension spring arrangement at the second spring position, if the contact arm moves back faster than said second end.

It should also be noted, that the spring stopper may be embodied as rigid or elastic element, and that both a spring stopper and a separate elastic element acting on the second end of the tension spring arrangement may be provided. Accordingly, both effects can be combined so that the back movement of the contact arm and the back movement of the second end of the tension spring arrangement can be controlled in a better and more sophisticated way. Further on, one or both of the above variants can be combined with the embodiment where the tension spring arrangement is pulled into its first spring positions by the tension force generated by the tension spring arrangement during a closing rotation of the contact arm. So any one of the three disclosed effects can be used alone or in any combination.

Beneficially, the circuit breaker comprises a second fixed switching contact, which is electrically connected to the second electrical terminal within the housing, and beneficially the contact arm has a second movable switching contact, which contacts the second fixed switching contact in the closed arm position of the contact arm and which is designed to synchronously move with the first movable switching contact. In this way, the voltage to be switched off at one switching contact pair can be halved. Accordingly, the angle, which the contact arm has to rotate before arcing stops is halved, too. In turn, the intermediate open arm position can be set to lower angles and retarding can start earlier. Hence, the delay time can be increased even further by the proposed measures.

In an advantageous embodiment of the circuit breaker, the control curve of the at least one supporting surface an the virtual plane perpendicular to the first axis) comprises a convex elevation at an intermediate spring position between the first spring position and the second spring position and comprises lower sections on both sides thereof.

In particular, an advantageous course of the torque, which acts on the contact arm in a direction of a closing rotation of the contact arm and which is generated by a tension force of the tension spring arrangement over a rotation angle of the contact arm starting in the closed arm position can be obtained with the above convex elevation. In detail, the graph a) upon an opening rotation of the contact arm comprises al) first differential changes between the closed arm position and the intermediate open arm position of the contact arm, a2) a step up at the intermediate open arm position of the contact arm (which during an opening rotation of the contact arm is the first spring position), a3) second differential changes between the first spring position and the intermediate spring position, which are above the first differential changes, a4) a drop after the intermediate spring position and a5) third differential changes between the intermediate spring position and the second spring position, which are below the second differential changes and b) upon a closing rotation of the contact arm comprises bl) fourth differential changes in a first section between the second spring position and the intermediate spring position, b2) fifth differential changes in a second section between the second spring position and the intermediate spring position, which are above the fourth differential changes, b3) a drop after the intermediate spring position and b4) sixth differential changes until the closed arm position, which are below the fifth differential changes. In this way, a comparably high retarding force or a comparably high retarding torque -12 -acts on the contact arm during its opening movement between the first spring position and the intermediate spring position. In turn, the rotational motion of the contact arm is slowed down very much in this region. However, at the same time a closing force or closing torque acting on the contact arm during its closing movement is very low. So there is not much acceleration and not much speed of the contact arm in its closing movement. Both effects contribute to a comparably high delay time.

Alternatively, a graph of the torque, which acts on the contact arm in a direction of a closing rotation of the contact arm and which is generated by a tension force of the tension spring arrangement over a rotation angle of the contact arm starting in the closed arm position a) upon an opening rotation of the contact arm comprises al) first differential changes between the closed arm position and the intermediate open arm position of the contact arm, a2) a step up at the intermediate open arm position of the contact arm (which during an opening rotation of the contact arm is the first spring position), a3) second differential changes between the first spring position and the second spring position, which are below the first differential changes, b) upon a closing rotation of the contact arm comprises bl) third differential changes in a first section between the second spring position and the intermediate spring position, b2) fourth differential changes in a second section between the intermediate spring position and the first spring position, which are above the third differential changes.

As can be seen, there is no distinct drop after the intermediate spring position as it was the case in the preceding example. This torque graph can be obtained by omitting a distinct convex elevation. Instead, a less curved supporting surface is used.

Beneficially the at least one supporting surface comprises a second spring position stop acting on the second end of the tension spring arrangement in its second spring position (i.e. in the full open arm position of the contact arm). In this way, a defined second spring position is provided so that a particular delay time of the contact arm is reliably achieved. In case that at least one supporting surface has a convex -13 -elevation, the second spring position stop is located at distance from said convex elevation.

It is also beneficial if the control curve of the at least one supporting surface comprises a first spring position stop acting on the second end of the tension spring arrangement in its first spring position an the intermediate open arm position of the contact arm). Accordingly, a defined first spring position is provided what helps to reliably achieve a particular delay time of the contact arm, too. In case that the at least one supporting surface has a convex elevation, the first spring position stop is located vis-a-vis of the second spring position stop at distance from said convex elevation.

BRIEF DESCRIPTION OF DRAWINGS

The invention now is described in more detail hereinafter with reference to particular embodiments, which the invention however is not limited to.

Fig. 1 shows a schematic cross sectional side view of an exemplary embodiment of a circuit breaker in its ON-state; Fig. 2 shows a schematic cross sectional side view of the switching arrangement of the circuit breaker in more detail and in a state in which it is taken out of the circuit breaker; Fig. 3 shows a detailed oblique view of the switching shaft; Fig. 4 shows a cross sectional view of the switching shaft in a first cross sectional plane; Fig. 5 shows a cross sectional view of the switching shaft in a second cross sectional plane; Fig. 6 shows a detailed view of the supporting surface for the tension spring arrangement; Fig. 7 shows a detailed oblique view of the contact arm; -14 -Fig. 8 shows a schematic view of the switching arrangement, wherein the contact arm is in a overrotating closed arm position at a rotation angle of (x..=0°, Fig. 9 shows a schematic view of the switching arrangement, wherein the contact arm is in a closed arm position at a rotation angle of a=8°; Fig. 10 shows a schematic view of the switching arrangement, wherein the contact arm is in an intermediate open arm position at a rotation angle of ot=28° during an opening movement; Fig. 11 shows a schematic view of the switching arrangement, wherein the contact arm is in a full open arm position at a rotation angle of a=45°; Fig. 12 shows a schematic view of the switching arrangement, wherein the contact arm is at a rotation angle of o=21° during a closing movement, Fig. 13 shows a schematic view of the switching arrangement, wherein the contact arm has returned to its closed arm position at cx=8°; Fig. 14 shows a graph of the torque acting on the contact arm over its rotation angle u. and

Fig. 15 shows an elastic element arranged at the second spring position.

DETAILED DESCRIPTION

Generally, same parts or similar parts are denoted with the same/similar names and reference signs. The features disclosed in the description apply to parts with the same/similar names respectively reference signs. Indicating the orientation and relative position (up, down, sideward, etc) is related to the associated figure, and indication of the orientation and/or relative position has to be amended in different figures accordingly as the case may be.

Fig. 1 shows a schematic cross sectional side view of an exemplary embodiment of a circuit breaker 1 in its ON-state. The circuit breaker 1 comprises a housing 2 as well as a first electrical terminal 3a and a second electrical terminal 3b, which reach through the housing 2 and which are provided for switching the circuit breaker 1 in a current path of an electric circuit. Further on, the circuit breaker 1 comprises a first -15 -fixed switching contact 4a electrically connected to the first electrical terminal 3a within the housing 2 by means of a first electrical conductor 5a and a optional second fixed switching contact 4b electrically connected to the second electrical terminal 3b within the housing 2 by means of a second electrical conductor 5b In addition, the circuit breaker 1 comprises a contact arm 6, which is pivotally mounted around a first axis A within the housing 2 and which has a first movable switching contact 7a, which contacts the first fixed switching contact 4a in a closed arm position of the contact arm 6 and which is lifted off the first fixed switching contact 4a in open arm positions of the contact arm 6, i.e. upon an opening rotation of the contact arm 6. In this example, the contact arm 6 also comprises the optional second movable switching contact 7b, which contacts the second fixed switching contact 4b in a closed arm position of the contact arm 6 and which is lifted off the second fixed switching contact 4b in open arm positions of the contact arm 6, i.e. upon an opening rotation of the contact arm 6.

The contact arm 6 has a symmetric design in this example. However, it is also possible in principle that the second fixed switching contact 4b and the second movable switching contact 7b are omitted. In this case, the first movable contact 7a can be connected to the second electrical conductor 5b by means of a flexible cable.

In this embodiment, the circuit breaker 1 moreover comprises a switching shaft 8, wherein the first axis A of the contact arm 6 is arranged in the switching shaft 8 and wherein the switching shaft 8 is rotatably mounted around a second axis B, which is fixedly arranged in or relative to the housing 2. In this example, the first axis A coincides with the second axis B which, however, is no necessary condition. It may also be that the first axis A is located at a position which is different from the position of the second axis B. Furthermore it is imaginable, that there is no switching shaft 8 at all. In this case, the first axis A of the contact arm 6 is fixedly arranged in or relative to the housing 2.

Note that in the particular embodiment shown in Fig. 1, both the first axis A and the second axis B are fixedly arranged relative to the housing 2 because the coincide. If they do not, just the second axis B is arranged relative to the housing 2 in this embodiment.

-16 -The circuit breaker 1 also comprises supporting surfaces 9a, 9b, which are arranged within the housing 2 and which intersect a virtual plane perpendicular to the first axis A along control curves. In Fig. 1, said virtual plane is parallel to the plane of the drawing sheet or coincides with the same. Refer to Figs. 1 to 6 for a detailed pictures of the supporting surfaces 9a, 9b or their control curves.

Furthermore, the circuit breaker 1 comprises tension spring arrangements 10a, 10b, which are arranged between the contact arm 6 and the switching shaft 8 in this example. The contact arm 6, the switching shaft 8 and the spring arrangements 10a, 10b are part of a switching arrangement 11, which is shown in Fig. 2 in more detail.

Finally, the circuit breaker 1 comprises optional arcing chambers 12a, 12b, the function of which is known in principle and hence not explained in detail at this point.

Fig. 2 shows a schematic cross sectional side view of the switching arrangement 11 in more detail and in a state in which it is taken out of the circuit breaker 1.

First ends Cl, C2 of the tension spring arrangements 10a, 10b are pivotally connected to the contact arm 6 by means of first bolts 13a, 13b at first supporting points. Second ends D1, D2 of the tension spring arrangements 10a, 10b are slidably supported by the supporting surfaces 9a, 9b. For this reason, the second ends D1, D2 comprise second bolts 14a, 14b in this example, which slide on the supporting surfaces 9a, 9b, wherein the second bolts 14a, 14b are arranged within yokes of the spring arrangements 10a, 10b. Generally, the tension spring arrangements 10a, 10b generate a tension force in a direction causing a closing rotation of the contact arm 6. Note that the springs as such are not visible in Fig. 2 because just their envelopes are drawn.

In addition, the contact arm 6 comprises optional pushers 15a, 15b which are mounted to the base body of the contact arm 6 by means of screws 16. The pushers 15a, 15b may also be omitted, and they may also be integral part of the main body of the contact arm 6.

-17 -Fig. 3 shows a detailed oblique view of the switching shaft 8. Fig. 3 particularly shows a first recess 17 for the contact arm 6 and a second recess 18 for the spring arrangements 10a, 10b In addition, Fig. 3 shows a first cross sectional plane 1, which is relevant for Fig. 4, and a second cross sectional plane II, which is relevant for Fig. 5. Fig. 4 shows a cross sectional view of the switching shaft Bin the first cross sectional plane I, and Fig. 5 shows a cross sectional view of the switching shaft 8 in the second cross sectional plane II. Fig. 5 particularly shows a first spring stopper 19a for the first spring arrangement 10a and a second spring stopper 19b for the second spring arrangement 10b. The spring stoppers 19a, 19b may be embodied as rigid parts or may be made by an elastic material (e.g. an elastomer). In particular, the spring stoppers 19a, 19b may be formed by screws like this is depicted in Fig. 5 or may be integral part of the switching shaft 8 or the part, in which the tension spring arrangements 10a, 10b are arranged. The function of the spring stoppers 19a, 19b is explained in more detail later in combination with Fig. 14.

Fig. 6 shows a detailed view of the second supporting surface 9b, in detail its control curve, which is generated by intersecting the second supporting surface 9b with a virtual plane perpendicular to the first axis A or here with the plane of the drawing sheet. The control curve of the second supporting surface 9b comprises a convex elevation E at an intermediate spring position bm between a first spring position bi and a second spring position b2 and comprises lower sections Fl, F2 on both sides thereof in this example.

Further on, the control curve comprises a first spring position stop G1 acting on the second end 02 of the tension spring arrangement 10b in its first spring position bi in this example. The control curve in addition comprises a second spring position stop G2 acting on the second end D2 of the tension spring arrangement 10b in its second spring position b2 in this example. In detail, the first spring position stop G1 is located at distance from said convex elevation E and vis-a-vis of the second spring position stop G2, and the second spring position stop G2 is located at distance from said convex elevation E and vis-a-vis of the first spring position stop G1. In this embodiment the spring position stops G1, G2 are part of the second supporting -18 -surface 9b. However, there may also separate parts for the spring position stops G1, G2.

Fig. 7 shows a detailed oblique view of the contact arm 6. In particular, Fig. 7 shows the recesses 20a, 20b for the first bolts 13a, 13b.

The function of the circuit breaker 1 is now explained by reference to Figs. 8 to 13, which show the switching arrangement 11 in different states, and by reference to Fig. 14, which shows a graph of the torque T acting on the contact arm 6 at a particular rotation angle a. It should be noted that the torque T acts in counterclockwise direction here. In other words, positive values of the torque T force the contact arm 6 in closing direction.

Fig. 8 shows the contact arm 6 in a overrotating closed arm position at a rotation angle of a=0°, and Fig. 9 shows the contact arm 6 in a closed arm position al at a rotation angle of a=8°. This overrotation reserve of 8° is used for compensation of contact erosion which occurs during use of the circuit breaker 1. That means in a unused or new condition, the closed arm position ai is at a=8° whereas it moves towards the overrotating closed arm position a=0° during use. That is why the closed arm position ai is at a=8° in the unused or new condition of the circuit breaker 1 whereas the closed arm position al moves towards a=0° during use. For the concerns of this disclosure, a=8° is considered to be the closed arm position al hereinafter. In other words, a new or unused circuit breaker 1 is described.

Fig. 9 particularly discloses that the contact arm 6 is lifted off the second ends D1, D2 of the tension spring arrangements 10a, 10b (i.e. it is decoupled from the second ends D1, D2 of the tension spring arrangement 10a, 10b) in the closed arm position al. This also counts for a=0° as depicted in Fig. 8.

It is assumed now that the contact arm 6 is forced towards its open position during an overcurrent event by electrodynamic forces. That means it starts to rotate in clockwise direction.

Fig. 10 shows the contact arm 6 in an intermediate open arm position am at a rotation angle of a=28°. Fig. 10 particularly discloses that the contact arm 6 contacts the second ends D1, D2 of the tension spring arrangements 10a, 10b there and thus is -19 -rigidly motion coupled to the second ends D1, D2 of the tension arrangements 10a, 10b at the intermediate open arm position am of the contact arm 6 and at the first spring position b, of the second ends D1, 02 of the tension spring arrangements 10a, 10b.

The diagram shown in Fig. 14 discloses first differential changes of the torque T between the closed arm position ai and the intermediate open arm position az of the contact arm 6 (step al).

The following notes should be taken into consideration. The rotation angle a denotes the rotation angle of the contact arm 6 and is no rotation angle of the second ends D1, 02 of the tension spring arrangements 10a, 10b. The movement of the second ends D1, D2 of the tension spring arrangements 10a, 10b during an opening movement of the contact arm 6 (i.e. during switching off the circuit breaker 1) is indicated in the uppermost section of Fig. 14 which is denoted with "-> off'. The movement of the second ends D1, D2 of the tension spring arrangements 10a, 10b during a closing movement of the contact arm 6 (i.e. during switching on the circuit breaker 1) is indicated below the uppermost section and is denoted with "on <-". Sections, in which the second ends D1, D2 move are indicated with "->" or "<-", wherein the starting point and the end point are indicated, too. Because the second ends D1, 02 stay in the first spring position bi during a rotation of the contact arm 6 between a=0° and a=28°, the associated range is denoted with "b1".

Fig. 11 shows the contact arm 6 in an full open arm position az at a rotation angle of a=45°. Fig. 11 particularly discloses that the contact arm 6 starting at the intermediate open arm position am further contacts the second ends D1, D2 of the tension spring arrangement 10a, 10b (and thus is further rigidly motion coupled to the second ends D1, D2 of the tension spring arrangements 10a, 10b). Thus, the contact arm 6 pushes the second ends D1, D2 along the supporting surfaces 9a, 9b between the intermediate open arm position an, of the contact arm 6 and a full open arm position az of the contact arm 6. In turn, the second ends D1, 02 of the tension spring arrangements 10a, 10b are pushed into a second spring position bz by a further opening rotation of the contact arm 6.

-20 -The diagram shown in Fig. 14 discloses a step up of the torque T at the intermediate open arm position am of the contact arm 6 at a=28°, which during an opening rotation of the contact arm 6 corresponds to the first spring position bi (step a2). The reason is that the free movement of the contact arm 6 ends at the intermediate open arm position am stops and any further movement of the contact arm 6 is hindered by the second ends D1, D2 sliding on the supporting surfaces 9a, 9b.

There are second differential changes of the torque T between the first spring position bi and the intermediate spring position bm, which are above the first differential changes (step a3). The reason is that the second ends D1, D2 from the lower section Fl move towards the convex elevation E. In illustrative words, the second ends D1, D2 move "uphill" driven by the contact arm 6. The corresponding moving range of the second ends D1, D2 is denoted with "bi-*bm".

Moreover, the diagram shown in Fig. 14 discloses a drop after the intermediate spring position bm (step a4). The reason is that the second ends D1, D2 from the convex elevation E move towards the lower section F2. In illustrative words, the second ends D1, D2 fall "downhill" at the intermediate spring position bm.

In addition, the diagram shown in Fig. 14 discloses third differential changes between the intermediate spring position bm and the second spring position b2, which are below the second differential changes (step a5). Here the second ends D1, D2 of the tension spring arrangements 10a, 10b are moved along the lower section F2 driven by the contact arm 6. The corresponding moving range of the second ends D1, D2 is denoted with "bm->b2".

It should be noted that in the above example the assumption has been made that the contact arm 6 stays in contact with the second ends D1, D2 of the tension spring arrangements 10a, 10b during the whole movement between the intermediate open arm position am and the full open arm position a2 and correspondingly between the first spring position bi and the second spring position b2 of the second ends D1, D2 of the tension spring arrangements 10a, 10b. However, this is no necessary condition, and the second ends D1, D2 can immediately move into the second spring position b2 and lift of the contact arm 6 after the intermediate spring position bm. In this case, the contact arm 6 catches up with the second ends D1, D2 at the second -21 -spring position b2 and contacts the same again in the full open arm position a2. But this second contact can also take place earlier, that means somewhere between the intermediate spring position bin and the second spring position b2. So, the second ends D1, D2 temporarily can move faster than the contact arm 6. Generally, the movement of the the second ends D1, D2 of the tension spring arrangements 10a, 10b depends on the shape of the supporting surfaces 9a, 9b and the orientation of the tension spring arrangements 10a, 10b relative to said supporting surfaces 9a, 9b.

Further on, the diagram shown in Fig. 14 discloses a steep increase of the torque T, which is caused by elastic deformation when the contact arm 6 and the second ends D1, D2 of the tension spring arrangements 10a, 10b are finally stopped at the second spring position stop G2.

After the contact arm 6 has stopped, it reverses its rotational movement. That means it starts to rotate in counterclockwise direction.

Fig. 12 shows a state in which the contact arm 6 has returned to a rotation angle of a=21°. Actually, the contact arm 6 moved through the intermediate open arm position am of the contact arm 6 during its return movement. So, the position of the contact arm 6 in Fig. 12 shall not be confused with the intermediate open arm position am, where the contact arm 6 gets in contact with the second ends D1, 02 of the tension spring arrangements 10a, 10b during its opening movement.

The second ends D1, D2 do not stay still during back rotation of the contact arm 6, but move back from the second spring position b2 to the intermediate spring position bm On this context also refer to the explanation of the optional spring stoppers 19a, 19b further below). The diagram shown in Fig. 14 discloses fourth differential changes between the second spring position b2 and the intermediate spring position bm in a first section (step b1). There are also fifth differential changes between the second spring position b2 and the intermediate spring position bm, which are above the fourth differential changes in a second section (step b2). These are caused by the second ends D1, D2 moving "uphill" the convex elevation E coming from the lower section F2. This movement is denoted by "bm4-b2" in Fig. 14.

-22 -At the intermediate spring position bm there is a drop (step b3). This is caused by the second ends D1, 02 falling "downhill" the convex elevation E towards the lower section Fl. Basically, the second ends D1, D2 of the tension spring arrangements 10a, 10b instantaneously fall back to their first spring position bi in this example. However, they do not catch up with the contact arm 6 in this example, because the contact arm 6 already has moved on to a rotation angle of a=21°, whereas a contact between the contact arm 6 and the second ends D1, D2 of the tension spring arrangements 10a, 10b is only possible in a range of a28° to 45° in this example.

Fig. 13 finally shows a state in which the contact arm 6 has returned to its closed arm position ai at a=8°. Fig. 14 shows sixth differential changes until the closed arm position al, which are below the fifth differential changes (step b4). Basically, the torque T is the same during the opening movement of the contact arm 6 and its closing movement in a range of a=8° to 21° in this example because during both movements, the second ends D1, D2 of the tension spring arrangements 10a, 10b stay in the first spring position bi. In contrast, there is a step down of the torque T when the contact arm 6 reverses its movement at a=45°. The reason is the direction of the friction force between the second bolts 14a, 14b and the supporting surfaces 9a, 9b which change their direction, too. Whereas the friction force acts in closing direction during an opening movement of the contact arm 6, it acts in opening direction during a closing movement of the contact arm 6 thus lowering the torque T acting in closing direction.

It should be noted, that the movement of the the second ends D1, 02 of the tension spring arrangements 10a, 10b depends on the shape of the supporting surfaces 9a, 9b and the orientation of the tension spring arrangements 10a, 10b relative to said supporting surfaces 9a, 9b. So, the second ends D1, D2 can stay in contact with the contact arm 6 for a while during its back rotation. It can also be the case that the tension spring arrangements 10a, 10b do not instantaneously fall back to their first spring position bi. Instead, they can stay in a region behind the convex elevation E for a while and move back to the first spring position bi later. Also a continuous movement of said second ends D1, 02 is no necessary condition, but they can stop once or more often during their movement from the second spring -23 -position b2 to the first spring position bi. Remember that there is no stringent motion coupling between the contact arm 6 and the second ends D1, D2 of the tension spring arrangements 10a, 10b during the back rotation of the contact arm 6.

The circuit breaker 1 takes benefit of a comparably high retarding force in a range of a=28° to 37° during opening so that the time, until the contact arm 6 reaches its full open arm position az, is comparably long. Moreover, the circuit breaker 1 takes benefit of a comparably low accelerating force during closing so that the time, until the contact arm 6 reaches its closed arm position al, is comparably long, too. Both effects lead to a comparably long delay between opening the switching contacts 4a, 4b, 7a, 7b and reclosing the same. This is of general advantage in view of a secondary opening mechanisms such as a switching shaft 8, but it is also particularly advantageous in applications where selectivity of different circuit breakers 1 is needed. In the first situation, the increased delay time helps to avoid that the switching contacts 4a, 4b, 7a, 7b are not reclosed before the switching shaft 8 keeps the switching contacts 4a, 4b, 7a, 7b open permanently, and in the second situation it helps that the switching contacts 4a, 4b, 7a, 7b are not reclosed before a downstream circuit breaker keeps its switching contacts open permanently. For example, there can be an upstream circuit breaker 1 of the proposed kind and a downstream circuit breaker of different kind in one of the sub-branches.

Generally, the switching shaft 8 can stand still during a movement of the contact arm 6, which is caused by an overcurrent between the first electrical terminal 3a and a second electrical terminal 3b, or can rotate slower than the contact arm 6 in case of such an overcurrent. In particular, the switching shaft Scan be designed to stand still below a current threshold and can be designed to be rotated by an overcurrent actor into an opening direction above said current threshold, wherein said current threshold is above a current causing a rotation of the contact arm 6. The switching shaft 8 is one embodiment of a secondary opening mechanism, and generally, the switching shaft 8 can be rotated by any kind of actuator which is sensitive to an overcurrent and/or can be turned manually by means of a handle. An overcurrent situation can be detected by directly measuring the current through the circuit breaker 1 and/or by measuring an increase of temperature caused by the current through the circuit breaker 1. The circuit breaker 1 can also comprise a latch, on which a overcurrent -24 -actor and/or a handle acts. The overcurrent actor can be a temperature sensitive overcurrent actor (e.g. a bimetal actor) or an electrodynamic overcurrent actor. Of course, both a temperature sensitive overcurrent and an electrodynamic overcurrent actor can act on the latch so as to trigger the switching shaft 8 in case of a comparably low but long lasting overcurrent (temperature sensitive overcurrent actor) or in case of a comparably high overcurrent (electrodynamic overcurrent actor). In addition, the handle can act on the latch so that in total there are three possibilities to trigger the switching shaft 8 in this example. In contrast to the comparably slow switching shaft 8, the contact arm 6 can be opened by electrodynamic forces very fast. It opens faster even in case the switching shaft 8 is triggered by its electrodynamic overcurrent actor.

A current threshold for a movement of the switching shaft 8 preferably is above a current causing a rotation of the contact arm 6. So, below this current threshold just the contact arm 6 rotates (and the switching shaft 8 stands still), and above this current threshold both the contact arm 8 and the switching shaft 6 rotate (but the switching shaft 8 rotates slower). In case of selectively chained circuit breakers, advantageously the current threshold for the switching shaft 8 of the upstream circuit breaker 1 should be higher than a current, which causes switching off the downstream circuit breaker, but lower than a current, which may cause serious damage in the electric circuit between the upstream circuit breaker 1 and the downstream circuit breaker.

As disclosed in Fig. 5, the circuit breaker 1 may comprise optional spring stoppers 19a, 19b. In the full open arm position az of the contact arm 6, the second spring stopper 19b is in contact with the second tension spring arrangement 10b in a limited region between the first end C2 and the second end D2 of the second tension spring arrangement 10b. In other words, the second spring stopper 19b contacts the second tension spring arrangement 10b at a point between the first end C2 and the second end D2 in this example. In more detail, the second spring stopper 19b gets in contact with the second tension spring arrangement 10b even before the contact arm 6 reaches its full open arm position az, concretely when the first end C2 and the second end 02 of the second tension spring arrangement 10b by the movement of the contact arm 6 are moved beyond a position where the longitudinal spring axis H between said first end C2 and said second end D2 cannot be straight any longer.

-25 -Beyond this position, the longitudinal spring axis H starts to bend and becomes arc shaped upon a further opening rotation of the contact arm 6. Hence, in particular, the second spring stopper 19b can act as a bending point, around which the second tension spring arrangement 10b bends transverse to its longitudinal spring axis H. In this state, the second tension spring arrangement 10b does not only generate a tension force between its first end C2 and its second end 02, but also a force transverse to the longitudinal spring axis H of the second tension spring arrangement 10b (and hence in a direction which is usually not intended by a tension spring). This transverse force assists to bring back the second end 02 of the second tension spring arrangement 10b from the second spring position b2 to the first spring position bi when the contact arm 6 rotates back to its closed arm position al. Accordingly, the second spring stopper 19b is useful if the second end D2 of the second tension spring arrangement 10b without such a second spring stopper 19b generally or occasionally tends to stay or stick in its second spring position b2 when the contact arm 6 rotates back to its closed arm position al. By the proposed measures, the second end D2 of the second tension spring arrangement 10b reliably moves back to its first spring position bi when the contact arm 6 rotates back to its closed arm position ai. So, the second end 02 of the second tension spring arrangement 10b reliably is in its first spring position bi when the contact arm 6 is in its closed arm position al. It should be noted that the position and the height of the bending point! second spring stopper 19b defines the shape of the longitudinal spring axis H of the second tension spring arrangement 10b and thus also how the second end 02 behaves when the contact arm 6 rotates back towards its closed arm position ai. Said height defines how far the bending point / second spring stopper 19b protrudes into a virtual (straight) connection line between the first end C2 and the second end D2 at the maximum bending of the second tension spring arrangement 10b. It is advantageous in the above context if the bending point! second spring stopper 19b is closer to the second end D2 of the second tension spring arrangement 10b than to its first end C2, and it is particularly advantageous if the distance between the bending point! second spring stopper 19b and the second end D2 of the second tension spring arrangement 10b is in a range of 20% to 40% of the distance between the first end 02 and the second end 02 of the second tension spring -26 -arrangement 10b. By these measures the curvature of the longitudinal spring axis H is higher in the region of the second end D2 than in the region of the first end 02. Hence, also the back force is higher for the second end 02 than for the first end 02. The second end 02 can also stay in contact with the contact arm 6 for a while during the back rotation of the contact arm 6 and even push back the contact arm 6 to a certain extent. The second end D2 of the second tension spring arrangement 10b may stay in contact with the contact arm D2 until the first spring position bi or until a lift off point between the first spring position bi and the second spring position bz of the second tension spring arrangement 10b. However, the contact arm 6 may also be lifted off the second end D2 of the second tension spring arrangement 10b at the second spring position bz, if the contact arm 6 moves back faster than said second end 02.

It should be noted that the lift off point shall not confused with the intermediate spring position bm. Both points can coincide, but this is no necessary condition.

Furthermore, one should note that the contact arm 6 lifts off the second ends D2 of the second tension spring arrangement 10b at the first spring position bi at the latest because of the first spring position stop G1.

It should also be noted at this point that the considerations which have been made hereinbefore for the second tension spring arrangement 10b and the advantages resulting thereof equally apply to the first tension spring arrangement 10a.

In the above example, the rebound of the contact arm 6 and/or of the second end 02 of the second tension spring arrangement 10b is assisted by the elastic transversal deformation of the second tension spring arrangement 10b. However, this is not the only possibility.

Alternatively or in addition to the elastic transversal deformation of the second tension spring arrangement 10b, the contact arm 6 and/or the second end D2 of the second tension spring arrangement 10b can be forced into the direction of the closing rotation / towards the first spring position bi between the full open arm position az of the contact arm 6 and an over rotation arm position, which is beyond the full open arm position az (i.e. farther away from the closed arm position ai), by deformation of an elastic element. In particular, said force is generated by the elastic element -27 -between a) the contact arm 6 and the second end D1, 02 of the tension spring arrangement 10a, 10b, b) the contact arm 6 and a rigid stop in the housing 2, c) the contact arm 6 and a rigid stop in the switching shaft 8, d) the second end D1, D2 of the tension spring arrangement 10a, 10b and a rigid second spring position stop in the housing 2, e) between the second end D1, 02 of the tension spring arrangement 10a, 10b and a rigid second spring position stop in the switching shaft 8.

By way of an example showing case e) in Fig. 15, the above function is explained. In detail an elastic element 21 is arranged between the second end 02 of the second tension spring arrangement 10b and a rigid second spring position stop in the switching shaft 8. So from the point in time when the second end 02 of the second tension spring arrangement 10b contacts the elastic element 21 (which is the case in the full open arm position az of the contact arm 6 and in the second spring position bz of the second tension spring arrangement 10b), the elastic element 21 is compressed and generates a back force acting on the second end D2 of the second tension spring arrangement 10b and thus also on the contact arm 6. So the movement of the contact arm 6 and said second end 02 is decelerated and reversed at the over rotation arm position of the contact arm 6.

Accordingly, the elastic element 21 assists the back rotation of the contact arm 6 and the back movement of the second end D2 of the second tension spring arrangement 10b. Accordingly, the elastic element 21 acting on said second end 02 is useful if it without such an elastic element 21 generally or occasionally tends to stay or stick in its second spring position bz when the contact arm 6 rotates back to its closed arm position al. Again, the second end 02 of the second tension spring arrangement 10b reliably moves back to its first spring position bi when the contact arm 6 rotates back to its closed arm position al by the proposed measures.

The example depicted in Fig. 15 refers to case e). However, by variation of the position of the elastic element 21 different effects can be obtained. In cases d) and e) both the contact arm 6 and the second end 02 of the second tension spring -28 -arrangement 10b are pushed back by the elastic element 21, whereas in cases a) to c) just the contact arm 6 is pushed back by the elastic element 21.

It should be noted that both a spring stopper 19b and a separate elastic element 21 acting on the second end D2 of the second tension spring arrangement 10b may be provided. Accordingly, both effects can be combined so that the back movement of the contact arm 6 and the back movement of the second end D2 of the second tension spring arrangement 10b can be controlled in a better and more sophisticated way.

It should also be noted that although a spring stopper 19b and/or an elastic element 21 assist a back movement of the second end D2 of the second tension spring arrangement 10b, their existence is no necessary condition. The reason is that the second end D2 of the second tension spring arrangement 10b can also be pulled into its first spring positions bi by the tension force generated by the tension spring arrangements 10b during a closing rotation of the contact arm 6. So any one of the three disclosed effects can be used alone or in any combination.

Again the considerations, which have been made hereinbefore for the second tension spring arrangement 10b and the advantages resulting thereof, equally apply to the first tension spring arrangement 10a.

Although the use of a convex elevation E is beneficial, its use its not mandatory. Instead, the second ends D1, D2 of the tension spring arrangements 10a, 10b can continuously move on the supporting surfaces 9a, 9b. In this case a graph of the torque T, which acts on the contact arm 6 in a direction of a closing rotation of the contact arm 6 and which is generated by a tension force of the tension spring arrangements 10a, 10b over a rotation angle of the contact arm 6 starting in the closed arm position ai a) upon an opening rotation of the contact arm 6 comprises al) first differential changes between the closed arm position ai and the intermediate open arm position am of the contact arm 6, a2) a step up at the intermediate open arm position am of the contact arm 6 which during an opening rotation of the contact arm 6 corresponds to the first spring position lot -29 -a3) second differential changes between the first spring position bi and the second spring position b2, which are below the first differential changes, b) upon a closing rotation of the contact arm 6 comprises b1) third differential changes in a first section between the second spring position b2 and the intermediate spring position bm, b2) fourth differential changes in a second section between the intermediate spring position bm and the first spring position lot which are above the third differential changes.

It should be noted that although the circuit breaker 1 has been explained by use of two tension spring arrangements 10a, 10b hereinbefore, it is also possible to build the circuit breaker 1 with a different number of spring arrangements 10a, 10b, in particular with just a single spring arrangements 10a or with four spring arrangements 10a, 10b. In the latter case, the spring arrangements 10a, 10b are arranged on each side of the contact arm 6 in a pairwise way. In fact, the switching shaft 6 shown in the Figs. comprises recesses for four spring arrangements 10a, 10b so that it can be equipped with one to four spring arrangements 10a, 10b.

Furthermore, it is noted that the invention is not limited to the embodiments disclosed hereinbefore, but combinations of the different variants are possible. In reality, the circuit breaker 1 may have more or less parts than shown in the figures. Moreover, the description may comprise subject matter of further independent inventions.

It should also be noted that the term "comprising" does not exclude other elements and the use of articles "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

LIST OF REFERENCE NUMERALS

1 circuit breaker 2 housing 3a, 3b electrical terminal 4a, 4b fixed switching contact 5a, 5b electrical conductor 6 contact arm 7a, 7b movable switching contact 8 switching shaft 9a, 9b supporting surface 10a, 10b tension spring arrangement 11 switching arrangement 12a, 12b arcing chamber 13a, 13b first bolt 14a, 14b second bolt 15a, 15b pusher 16 screw 17 first recess 18 second recess 19a, 19b spring stopper 20a, 20b recess for the first bolt 21 elastic element closed arm position am intermediate open arm position az full open arm position bi first spring position bz second spring position bm intermediate spring position -30 - -31 -A first axis second axis Cl, C2 first end of the tension spring arrangement D1, D2 second end of the tension spring arrangement convex elevation F2 lower sections G1, G2 spring position stop longitudinal spring axis torque a rotation angle

Claims

-32 -CLAIMS1. Circuit breaker (1), comprising a housing (2), a first electrical terminal (3a) and a second electrical terminal (3b), which reach through the housing (2) and which are provided for switching the circuit breaker (1) in a current path of an electric circuit, a first fixed switching contact (4a) electrically connected to the first electrical terminal (3a) within the housing (2), a contact arm (6), which is pivotally mounted around a first axis (A) within the housing (2) and which has a first movable switching contact (7a), which contacts the first fixed switching contact (4a) in a closed arm position (ai) of the contact arm (6) and which is lifted off the first fixed switching contact (4a) in open arm positions (at am) of the contact arm (6), at least one supporting surface (9a, 9b), which is arranged within the housing (2) and which intersects a virtual plane perpendicular to the first axis (A) along a control curve, at least one tension spring arrangement (10a, 10b), wherein a first end (Cl, C2) of the tension spring arrangement (10a, 10b) is pivotally connected to the contact arm (6) at a first supporting point and wherein a second end (D1, 02) of the tension spring arrangement (10a, 10b) is slidably supported by said at least one supporting surface (9a, 9b) and wherein the tension spring arrangement (10a, 10b) generates a tension force in a direction causing a closing rotation of the contact arm (6), characterized in that the contact arm (6) is lifted off the second end (D1, D2) of the tension spring arrangement (10a, 10b) in the closed arm position (al), the contact arm (6) is designed to contact the second end (D1, D2) of the tension spring arrangement (10a, 10b) at an intermediate open arm position (am) of the contact arm (6) and at a first spring position (bi) of the second end (D1, 02) of the tension spring arrangement (10a, 10b) upon an opening rotation of the contact arm (6) and the contact arm (6) is designed to further contact the second end (D1, D2) of -33 -the tension spring arrangement (10a, 10b) and to push it along the at least one supporting surface (9a, 9b) at least in a section between the intermediate open arm position (am) of the contact arm (6) and a full open arm position (a2) of the contact arm (6) and to cause a movement of the second end (D1, 02) of the tension spring arrangement (10a, 10b) into a second spring position (b2) upon a further opening rotation of the contact arm (6).
2. Circuit breaker (1) as claimed in claim 1, characterized in that the contact arm (6) is designed to be lifted off the second end (D1, D2) of the tension spring arrangement (10a, 10b) at the second spring position (b2) of the tension spring arrangement (10a, 10b) or at the first spring position (bi) of the tension spring arrangement (10a, 10b) or at a lift off point between said first spring position (bi) and said second spring position (b2) and is designed to be kept lifted off until the closed arm position (ai) of the contact arm (6) upon a closing rotation of the contact arm (6).
3. Circuit breaker (1) as claimed in claim 1 or 2, characterized in that the second end (D1, D2) of the tension spring arrangement (10a, 10b) is pulled into its first spring position (bi) by the tension force generated by the tension spring arrangement (10a, 10b) during a closing rotation of the contact arm (6).
4. Circuit breaker (1) as claimed in any one of claims 1 to 3, characterized in that the first axis (A) is fixedly arranged relative to the housing (2).
5. Circuit breaker (1) as claimed in any one of claims 1 to 4, characterized in a switching shaft (8), wherein the first axis (A) is arranged in the switching shaft (8) and wherein the switching shaft (8) is rotatably mounted around a second axis (B), which is fixedly arranged relative to the housing (2), and wherein the switching shaft (8) is designed to stand still during a contact arm (6) movement, which is caused by an overcurrent between the first electrical terminal (3a) and the second electrical terminal (3b), or to rotate slower than the contact arm (6) in case of such an overcurrent.
6. Circuit breaker (1) as claimed in claim 5, characterized in that the switching shaft (8) is designed to stand still below a current threshold and designed to be rotated by an overcurrent actor into an opening direction above said current threshold, wherein said current threshold is above a current causing a rotation of the contact arm (6).
7. Circuit breaker (1) as claimed in any one of claims 1 to 6, characterized in that the contact arm (6) is forced into the direction of the closing rotation between its full open arm position (a2) and an over rotation arm position, which is beyond the full open arm position (a2), by deformation of an elastic element (21).
8. Circuit breaker (1) as claimed in claim 7, characterized in that said force is generated by the elastic element (21) between a) the contact arm (6) and the second end (D1, 02) of the tension spring arrangement (10a, 10b), b) the contact arm (6) and a rigid stop in the housing, c) the contact arm (6) and a rigid stop in the switching shaft (8), d) the second end (D1, D2) of the tension spring arrangement (10a, 10b) and a rigid second spring position stop in the housing (2), e) between the second end (D1, D2) of the tension spring arrangement (10a, 10b) and a rigid second spring position stop (G2) in the switching shaft (8).
9. Circuit breaker (1) as claimed in any one of claims 1 to 8, characterized in a spring stopper (19a, 19b), which in the full open arm position (a2) of the contact arm (6) is in contact with the tension spring arrangement (10a, 10b) in a limited region between the first end (Cl, C2) and the second end (D1, D2) of the tension spring arrangement (10a, 10b).
10. Circuit breaker (1) as claimed in any one of claims 1 to 9, characterized in that the circuit breaker (1) comprises a second fixed switching contact (4b) electrically connected to the second electrical terminal (3b) within the housing (2) and in that the contact arm (6) has a second movable switching contact (7b), which contacts the -35 -second fixed switching contact (4b) in the closed arm position (al) of the contact arm (6) and which is designed to synchronously move with the first movable switching contact (4a).
11. Circuit breaker (1) as claimed in any one of claims 1 to 10, characterized in that the control curve of the at least one supporting surface (9a, 9b) comprises a convex elevation (E) at an intermediate spring position (b.) between the first spring position (bi) and the second spring position (b2) and comprises lower sections on both sides thereof.
12. Circuit breaker (1) as claimed in any one of claims 1 to 11, characterized in that the control curve of the at least one supporting surface (9a, 9b) comprises a second spring position stop (G2) acting on the second end (D1, D2) of the tension spring arrangement (10a, 10b) in its second spring position (b2).
13. Circuit breaker (1) as claimed in any one of claims 1 to 12, characterized in that the control curve of the at least one supporting surface (9a, 9b) comprises a first spring position stop (G1) acting on the second end (D1, D2) of the tension spring arrangement (10a, 10b) in its first spring position (bi).
14. Circuit breaker (1) as claimed in any one of claims 11 to 13, characterized in that a graph of the torque (T), which acts on the contact arm (6) in a direction of a closing rotation of the contact arm (6) and which is generated by a tension force of the tension spring arrangement (10a, 10b) over a rotation angle (a) of the contact arm (6) starting in the closed arm position (ai) a) upon an opening rotation of the contact arm (6) comprises al) first differential changes between the closed arm position (al) and the intermediate open arm position (a.) of the contact arm (6), a2) a step up at the intermediate open arm position (a.) of the contact arm (6) and at the first spring position (bi), a3) second differential changes between the first spring position (bi) and the intermediate spring position (b.), which are above the first differential changes, a4) a drop after the intermediate spring position (b.) and -36 -a5) third differential changes between the intermediate spring position (bm) and the second spring position (b2), which are below the second differential changes and b) upon a closing rotation of the contact arm (6) comprises bi) fourth differential changes in a first section between the second spring position (b2) and the intermediate spring position (bm), b2) fifth differential changes in a second section between the second spring position (b2) and the intermediate spring position (bm), which are above the fourth differential changes, b3) a drop after the intermediate spring position (bm) and b4) sixth differential changes until the closed arm position (a1), which are below the fifth differential changes.
15. Circuit breaker (1) as claimed in any one of claims 1 to 10, characterized in that a graph of the torque (T), which acts on the contact arm (6) in a direction of a closing rotation of the contact arm (6) and which is generated by a tension force of the tension spring arrangement (10a, 10b) over a rotation angle (a) of the contact arm (6) starting in the closed arm position (al) a) upon an opening rotation of the contact arm (6) comprises al) first differential changes between the closed arm position (al) and the intermediate open arm position (am) of the contact arm (6), a2) a step up at the intermediate open arm position (am) of the contact arm (6), a3) second differential changes between the first spring position (bi) and the second spring position (b2), which are below the first differential changes, b) upon a closing rotation of the contact arm (6) comprises bi) third differential changes in a first section between the second spring position (b2) and the intermediate spring position (bm), b2) fourth differential changes in a second section between the intermediate spring position (bm) and the first spring position (bi), which are above the third differential changes.