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Title:
METHOD FOR DRIVING AN ACTUATOR OF A CIRCUIT BREAKER, AND ACTUATOR FOR A CIRCUIT BREAKER
Document Type and Number:
WIPO Patent Application WO/2013/013984
Kind Code:
A1
Abstract:
During the opening process of an actuator (12) of a circuit breaker (10), the polarity of a DC power supply (54) for a coil (28) of the actuator (12) is reversed to achieve a deceleration effect before the armature and the stator of the actuator (12) impact on each other.

Inventors:
REUBER, Christian (Lendersweg 35, Willich, 47877, DE)
MECHLER, Günther (Verlängerte Kirchbaumstr. 2, Heddesheim, 68542, DE)
CHLADNY, Ryan (S84w12628 Blue Heron Ln, Muskego, Wisconsin, 53150, US)
STENGEL, Gregor (Haldenwangstr. 2, Karlsruhe, 76227, DE)
DERKX, Jeroen (Fogdegatan 6a, Västerås, S-72219, SE)
Application Number:
EP2012/063597
Publication Date:
January 31, 2013
Filing Date:
July 11, 2012
Export Citation:
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Assignee:
ABB TECHNOLOGY AG (Affolternstrasse 44, Zurich, CH-8050, CH)
REUBER, Christian (Lendersweg 35, Willich, 47877, DE)
MECHLER, Günther (Verlängerte Kirchbaumstr. 2, Heddesheim, 68542, DE)
CHLADNY, Ryan (S84w12628 Blue Heron Ln, Muskego, Wisconsin, 53150, US)
STENGEL, Gregor (Haldenwangstr. 2, Karlsruhe, 76227, DE)
DERKX, Jeroen (Fogdegatan 6a, Västerås, S-72219, SE)
International Classes:
H01H47/22; H01H3/30; H01H47/32
Domestic Patent References:
WO1995000960A1
Foreign References:
US5633779A
EP0424280A1
Other References:
None
Attorney, Agent or Firm:
DE SANTIS, Giovanni (ABB S.p.A, Via L. Lama 33, Sesto San Giovanni, I-20099, IT)
Download PDF:
Claims:
CLAIMS

A method for driving an actuator (12) of a circuit breaker (10), the method comprising the steps of:

Supplying a coil (48) of the actuator (12) with a first voltage (60), such that the coil (48) generates a magnetic field which causes an armature (32) to move relative to a stator (40) of the actuator from a closed position to an opened position,

supplying the coil (48) with a second voltage (62) of reverse polarity with respect to the first voltage (60), while the armature (32) is moving relative to the stator (40), such that the coil (48) generates a reverse magnetic field which decelerates the relative movement of the stator (40) and the armature (32).

The method of claim 1 ,

wherein the first voltage (60) is almost constant during a first time period (ti) and the second voltage (62) is almost constant during a second time period (t2).

The method of one of the preceding claims,

wherein the first voltage (60) is supplied to the coil (48) during a first time period (ti) after which the second voltage (62) is supplied to the coil (48) for a second time period (t2), wherein after the second time period the second voltage (62) may be switched off or a third voltage (71 ) with same polarity as the first voltage (60) may be supplied for a third time period and then switched off.

The method of claim 3,

wherein the first time period (ti) and the second time period (t2) and in case the third time period are optimized, such that a movement speed (66) of the armature (32) relative to the stator (40) approaches a specified value, when the actuator is approaching the opened position.

The method of claim 3 or 4,

wherein the first time period (ti) and the second time period (t2) and in case the third time period are optimized such that the time period, during which the armature is moving relative to the stator, is minimized.

The method of claim 3, 4 or 5,

wherein the first time period (t1 ) and or the second time period (t2) and or the third time period are chosen individually for every operation basing on an assessment of the actual motion of the actuator. This assessment may base on the information of sensors.

An actuator (12) for a circuit breaker (10), the actuator comprising:

a stator (40) and an armature (32), which are movable with respect to each other between a closed position and an opened position, a coil (48) for generating a magnetic field, which is adapted to cause a relative movement of the stator (40) and the armature (32),

a switch circuit (26) connected to a voltage source (54) for supplying the coil (48) with a voltage,

wherein the switch circuit (26) is adapted for supplying a first voltage (60) and a second voltage (62) and a third voltage (71 ) to the coil (48), wherein the second voltage has a reverse polarity with respect to the first and the third voltage.

The actuator (12) of claim 7, further comprising:

a controller (30) for executing the method according to one of the claims 1 to 6, wherein the controller (30) is adapted to control switches (56a, 56b, 56c, 56d) of the switch circuit (26), such that the first voltage and second voltage and optional also the third voltage are supplied to the coil (48).

The actuator (12) of claim 7 or 8, further comprising:

a permanent magnet (44) for generating a force acting mainly on the main armature disk (34) in a closing direction of the actuator (12) while the actuator (12) is in closed position,

a spring element (52) for generating a force acting on the main armature disk (34) in an opening direction opposite to the closing direction while the actuator (12) is in closed position,

wherein in the closed position, the force of the permanent magnet (44) is bigger than the force of the spring element (52),

wherein in the opened position, a magnetic force caused by the permanent magnet (44) acting on the small armature disk (38) is sufficient to hold the armature (32) in an open position, while the force of the spring element (52) may support this magnetic force,

wherein in the closed position a sum of a magnetic force caused by the coil (48) supplied with the first voltage and the force of the spring element (52) becomes bigger than the force of the permanent magnet (44) once the current in the coil has reached a certain value.

0. A circuit breaker (10), comprising:

an actuator (12) according to one of the claims 7 to 9,

a switching chamber (14) with a first terminal (18) and a second terminal (20), wherein the actuator (12) is mechanically connected to the first terminal (18) of the switching chamber (14), such that the actuator (12) is adapted to move the first terminal (18) between a closed position, in which the first terminal (18) is electrically connected with the second terminal (20), and an opened position, in which the first terminal (18) is electrically disconnected from the second terminal (20).

Description:
METHOD FOR DRIVING AN ACTUATOR OF A CIRCUIT BREAKER, AND ACTUATOR FOR A CIRCUIT BREAKER

FIELD OF THE INVENTION

The invention relates to the field of high power circuit breakers. In particular, the invention relates to a method for driving a terminal of a circuit breaker, and to an actuator for the operation of a circuit breaker.

BACKGROUND OF THE INVENTION

An automatic circuit breaker usually comprises a switching chamber in which two terminals are connected or disconnected for opening and closing an electric path between the two terminals, and an actuator which is used for generating a relative movement of the two terminals.

For example, an actuator for generating a linear movement may comprise an armature and a stator that are adapted to move relative to each other and a coil in which a magnetic field may be induced that causes the movement of the stator and the armature from a closed into an opened position or from an open to a closed position.

The armature is accelerated relative to the stator of the actuator, if it has to be moved from the closed position into the opened position. The movement stops, when the armature hits mechanical components of the stator that limit its movement in the open position. Due to the abrupt stop of the moving components of the actuator, the components of the actuator are subjected to large mechanical stress. Additionally, once the armature reaches the final position relative to the stator, it may have a high kinetic energy and the collision with the stationary structure may cause a mechanical bouncing according to the structural properties of the frame of the device.

This bouncing effect may generate an over-travel and/or a back-travel of the actuator components, for example the stator and the armature, as well as of the moving terminal of the circuit breaker. This may degrade the switching properties of the circuit breaker.

DESCRIPTION OF THE INVENTION

It may be an objective of the invention to provide a circuit breaker with well-defined switching properties.

This objective may be achieved by the subject-matter of the independent claims. Further exemplary embodiments are evident from the dependent claims and the following description.

A first aspect of the invention relates to a method for driving the terminals of a circuit breaker relative to each other, thus providing an actuator of a circuit breaker. In particular, the circuit breaker may be a medium voltage circuit breaker, wherein a medium voltage may be a voltage between 1 kV and 50 kV.

According to an embodiment of the invention, the method comprises the steps of: supplying a coil of the actuator with a first voltage, such that the coil generates a magnetic field which directly or indirectly causes an armature of the actuator starting to move relative to a stator of the actuator from a closed position of the actuator to an opened position of the actuator. The method further comprises the step of: supplying the coil with a second voltage of reverse polarity with respect to the first voltage, while the armature is moving relative to the stator, such that the coil generates a reverse magnetic field which decelerates the movement of the armature relative to the stator.

In other words, during the opening process of the actuator, the polarity of the DC power supply, i.e. the first voltage, may be reversed to achieve a deceleration effect before the impact of the armature onto the stator in the opened position. Since the armature may be decelerated with respect to the stator, it has a lower kinetic energy compared to the situation when it is not decelerated, and in this way, the energy which has to be absorbed by the other components of the actuator and/or the circuit breaker may be reduced. Due to this, the bouncing effect may be reduced, in particular, such that a well-defined over-travel and back- travel value of the actuator is reached.

In order to limit the deceleration of the armature in a way that the armature will not stop its movement before it arrives at the closed position, the second voltage may be switched off after a certain time period or a third voltage may be applied for a third time period and then the voltage may be switched off.

There are several alternatives, how the coil may move the armature relative to the stator. A first possibility is that the coil induces a magnetic field in the stator and/or the armature which counteracts a further magnetic field, for example generated by a permanent magnet, thus causing a force which separates the stator from the armature.

Another possibility is that the actuator comprises a permanent magnet that generates a magnetic field which generates a force that pulls the armature in the closed position, and a spring that produces a counterforce to the magnetic force. The spring and the permanent magnet are chosen such that the magnetic force is bigger than the spring force, if the actuator shall be held in the closed position. With such a setup, the coil may generate a magnetic field that counteracts the magnetic field of the permanent magnet and such reduces the overall magnetic field in a way that the magnetic force is smaller than the spring force. Altogether this leads to an overall force causing the armature moving away from closed position. In this situation, the magnetic field of the coil may indirectly cause the movement of the armature relative to the stator.

According to an embodiment of the invention, the first voltage is applied during a first time period and the second voltage is applied during a second time period. Such voltages may be produced with a very simple circuit that is used to connect the coil with a constant DC voltage source.

According to a further embodiment of the invention, the second voltage has the negative polarity of the first voltage. In this case, the circuit may be constructed very simple, since the coil only has to be connected in a first direction to the voltage source to supply the first voltage and in the opposite direction to supply the second voltage.

According to a further embodiment of the invention, the second voltage may be switched off after a certain time period or a third voltage with same polarity as the first voltage may be applied for a certain time period in order to limit the deceleration.

According to an embodiment of the invention, the first voltage is supplied to the coil during a first time period after which the second voltage is supplied to the coil for a second time period. After the second time period, the second voltage may be switched off, i. e. set to 0 or a third voltage may be applied with same polarity as the first voltage. It has to be understood, that the switching of the voltage to the third voltage or 0 may be before the stator and the armature reach the opened position of the actuator. With the first time period, the length of the acceleration period of the movement may be set. Further, with the second time period, the length of the deceleration period of the movement may be set. In such a way, the first time period and the second time period may be chosen such that the movement of the stator and the armature with respect to each other is optimized with respect to specific objects. According to an embodiment of the invention, the first voltage, the second voltage, the first time period and the second time period are optimized, such that a movement speed of the armature approaches zero, when the armature is approaching the opened position. In this case, also the kinetic energy of the armature approaches zero, when both components approach the opened position. In such a way, there may be nearly no mechanical stress on the components of the actuator and/or nearly no bouncing effect.

According to an embodiment of the invention the first voltage, the second voltage, the first time period and the second time period are optimized such that a movement time during which the stator and the armature are moving is minimized. This optimization might be done under the condition that the movement speed of the armature when arriving at the opened position is not bigger than a predefined value. In this situation, there may be a small bouncing effect, but the circuit breaker may switch faster as in a situation when there is nearly no bouncing effect.

For reliability reasons another condition might be that the speed of the armature when approaching the open position is not smaller than a predefined value in order to prevent the situation that unexpected friction forces stop the movement before the open position is reached. However, it may be also possible, that the above-mentioned time periods are optimized in such a way, that the movement speed just before reaching the opened position is adjusted to a well defined value and the movement time is minimized concurrently.

It is also possible, that the first voltage and the second voltage are functions over time, of a DC voltage source, while the values of the second function have the opposite sign of the first function, and that with these voltage functions, the first time period and the second time period are optimized in the above mentioned ways.

E.g. if the DC voltage source is a loaded capacitor, the absolute value of the voltage function will reduce over time.

The voltages applied to the coil may be pulse with modulated.

A further aspect of the invention relates to an actuator for a circuit breaker.

According to an embodiment of the invention, the actuator comprises a stator and an armature, which are movable with respect to each other between a closed position and an opened position, a coil for generating a magnetic field which causes a relative movement of the stator and the armature, a switch circuit connected to a voltage source for supplying the coil with a voltage, wherein the switch circuit is adapted for supplying a first voltage and a second voltage to the coil, wherein the second voltage has a reverse polarity with respect to the first voltage. With such an actuator, it is possible to execute the method as described in the above and in the following.

For example, the actuator may comprise a controller which is adapted to execute the method as described in the above and in the following. For example, the switch circuit may comprise switches, for example semiconductor switches, that are adapted to connect the coil to the voltage source in two directions. After the controller has received a switch signal, the controller may open the switches of the switch circuit in such a way, that during a first time period, the coil is connected to the voltage source in a first direction. When the first time period has elapsed, the controller may switch the switches of the switch circuit in such a way, that the coil is connected to the voltage source in the other direction, such that the reverse voltage is supplied to the coil. At the end of the second time period, the controller may switch the switches of the switch circuit in such a way, that the coil is disconnected from the voltage source, such that no voltage is supplied to the coil. In such a way, the controller may execute the method as described in the above and the following and an actuator with such a controller may be adapted to perform such a method.

As already said, the actuator may be constructed in such a way, that the coil directly causes the movement of the armature relative to the stator. However, it may be also possible, that the coil causes the movement in an indirect way as explained above.

According to an embodiment of the invention, the actuator comprises a permanent magnet for generating a force in a closing direction of armature relative to the stator. For example, the permanent magnet may be a part of the stator and the armature may comprise a ferromagnetic material that is attracted by the magnetic field that is induced by the permanent magnet in the material of the stator.

According to an embodiment of the invention, the actuator comprises a spring element for generating a force in an opening direction opposite to the closing direction. In other words, the force generated by the spring element may counteract the force caused by the permanent magnet. The permanent magnet and the spring element may be chosen, such that the actuator has two stable positions, i.e. the opened position and the closed position. To achieve this, the force of the permanent magnet may be bigger than the force of the spring in the closed position. Starting from closed position the magnetic force between the stator and the armature may decrease when the two components of the actuator are moved away from each other and the spring element may be a helical spring that has a nearly linearly changing force when being compressed or extended.

In the open position the spring force in open direction is small or zero. The armature is mainly held in open position by magnetic forces on a part of the armature that are caused by the permanent magnet.

According to an embodiment of the invention, an open operation can be started if the coil causes a magnetic field that reduces the magnetic field caused by the permanent magnet. Thus the magnetic force on the armature is reduced, that it becomes smaller than the opening force of the spring element. In other words, the coil is located in the actuator in such a way and the winding is excited with current in a direction, that the magnetic field of the coil caused by the first voltage counteracts the magnetic field of the permanent magnet. For example, the coil may be wound around a yoke of the stator in such a way, that it generates a magnetic field in the opposite direction as the permanent magnet.

A further aspect of the invention relates to a circuit breaker.

According to an embodiment of the invention, the circuit breaker comprises an actuator as described in the above and the following, and a switching chamber with a first terminal and a second terminal, wherein the actuator is mechanically connected to the first terminal of the switching chamber, such that the actuator is adapted to move the first terminal between a closed position, in which the first terminal is electrically connected with the second terminal, and an opened position in which the first terminal is electrically disconnected from the second terminal. For example, the first terminal of the switching chamber is movable with respect to the switching chamber, which may be a vacuum interrupter, and the second terminal is fixed with respect to the switching chamber. Since such a circuit breaker has an actuator with a well-defined moving behaviour and with well-defined over-travel and back-travel, such a circuit breaker may have a well-defined switching behaviour, and in particular a very well- defined switching time.

It has to be noted, that the closed and opened position of the switching chamber of the circuit breaker may be reached, when the actuator reaches its closed position and opened position, respectively. However, it may also be possible, that the switching chamber reaches its closed position, when the actuator is in its opened position and vice versa. In other words, the above-mentioned method may be used for either opening the circuit breaker but also for closing the circuit breaker.

According to an embodiment of the invention, a coil that moves an armature relative to a stator of an actuator, is supplied by a well defined coil voltage signal. The current in the coil may be measured by an observing apparatus that may determine from the shape of the current signal the position of the armature relative to the stator as a function of time (position signal).

According to an embodiment of the invention, a coil that moves an armature relative to a stator of an actuator, is supplied by a well defined coil current signal. The voltage between the terminals of the coil may be measured by an observing apparatus that may determine from the shape of the voltage signal the position of the armature relative to the stator as a function of time (position signal).

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the invention will be explained in more detail in the following text with reference to exemplary embodiments which are illustrated in the attached drawings.

Fig. 1 schematically shows a circuit breaker according to an embodiment of the invention.

Fig. 2 shows an actuator invention in a closed position according to an embodiment of the invention.

Fig. 3 shows the actuator of Fig. 2 in an opened position.

Fig. 4 shows a switch circuit according to an embodiment of the invention.

Fig. 5A shows the relative position of the stator and the armature during a switching operation of the actuator according to an embodiment of the invention.

Fig. 5B shows the relative velocity of the stator and the armature during a switching operation of an actuator according to an embodiment of the invention.

Fig. 5C shows a voltage signal to be supplied to a coil of an actuator according to an embodiment of the invention.

Fig. 5D shows the coil current in the coil of an actuator according to an embodiment of the invention.

The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Fig. 1 schematically shows a circuit breaker 10 which comprises an actuator 12 and a switching chamber 14. The circuit breaker 10 may be any switching device in particular any medium voltage switching device. The actuator 12 is adapted to generate a linear movement of a rod 16 that is mechanically connected to a first terminal 18 of the switching chamber 14, which is movable connected to the switching chamber 14. The first terminal 18 may be pushed onto the second terminal 20 by the actuator 12, thus bringing the switching chamber 14 or respective the circuit breaker 10 into a closed position, in which the contacts 22 of the circuit breaker are in electrical contact. Further, the terminal 18 may be moved away from the terminal 20 by the actuator 12, thus bringing the switching chamber 14 of the circuit breaker 10 into an opened position, in which the contacts 22 are electrically disconnected from each other.

The actuator 12 is an electromagnetic actuator that is connected over an electrical line 24 with a voltage source 54. The actuator 12 has a switch circuit 26 that is adapted to connect an electromagnetic coil 28 with the voltage source 54 and a controller 30 for controlling the switches of the switch circuit 26. When the controller 30 receives a switch signal, it opens and closes the switches of the switch circuit 26 in such a way, that a magnetic field is induced in the coil 28 which causes the actuator 12 to move from a closed into an opened position as will be explained in the following.

Fig. 2 schematically shows a longitudinal cross-section through an actuator 12. The actuator 12 has an armature 32 comprising a main armature disk 34, a shaft 36 and a small armature disk 38. The armature disks 34 and 38 are parallel to each other and are mechanically connected by the shaft 36 which is used for guiding the armature 32 relative to the stator 40 of the actuator 12 in a linear movement between the positions when the two armature disks 34 and 38 touch the stator 40. The stator 40 comprises an inner yoke 42 which has a hole through which the shaft 36 can move as a part of the armature 32.

The stator 40 further comprises two permanent magnets 44 attached to side faces of the inner yoke 42 and two outer yokes 46 attached to the permanent magnets 44. The yokes 42, 46 and the permanent magnets 44 form a comb-like structure with teeth defined by the end of the yokes pointing into the direction of the armature disk 34. Between the teeth there are two gaps in which a coil 48 is situated, which is wound around the inner yoke 42.

The actuator 12 shown in Fig. 2 is an actuator with two stable positions, i.e. a closed position shown in Fig. 2 and an opened position shown in Fig. 3. In the closed position shown in Fig. 2, the stator 40 and the armature 32 form a magnetic circuit with a closed air gap 50 between the stator 40 and the armature components 42 and 46. The permanent magnets 44 are placed in series into the magnetic circuit to provide a static magnetic flux that causes sufficiently strong magnetic forces holding the air gap 50 closed. A spring element 52 is applied as a counterforce to the magnetic force generated by the permanent magnets 44. In the closed position shown in Fig. 2, the magnetic force generated by the permanent magnets 44 is larger than the spring force generated by the spring element 52. Thus, the closed position is stable even in the case of external mechanical excitations like earthquakes.

The opening process of the actuator 12 is started by excitation of the magnetic coil 48 in a way that the magnetic flux in the magnetic circuit is reduced until the magnetic force is smaller than the spring force of the spring element 52. Once the total force on the armature 32 has a zero crossing, a net acceleration of the armature 32 will start the opening process. The more the gap between stator 40 and armature 32 has increased, the more the spring force will dominate the magnetic force. During the relaxation of the spring element 52 the spring force will decrease nearly linearly or stepwise linearly. When the armature 32 approaches the open position, the spring force may be close to zero. A magnetic force caused by the magnetic flux of the permanent magnets 44 acting on the small disk 38 shall hold the armature 32 in a stable open position.

Fig. 3 shows schematically a longitudinal cross-section through the actuator 12 in the opened position. In the closed position, the stator 40 is abutting the armature disk 34 with the side that houses the coil 48. In the open position, the stator 40 is abutting the armature disk 38 with the opposite side. Thus, in the open position, the air gap 50 is maximal.

The more the air gap 50 between the stator 40 and the disk 34 has increased, the more the spring force will dominate the magnetic force between stator and disk 34 until the spring force is supported by the attractive magnetic force between disk 38 and the stator 40. Due to this attractive force the open position shown in Fig. 3 is also a stable position of the actuator 12. However as long as the magnetic flux of the coil 48 is reducing the magnetic force, the armature 32 is getting faster when leaving the closed position. As long as the coil 48 is connected to the power supply in such a (conventional) way, that it increasingly compensates the magnetic flux of the permanent magnet, the current in the coil 48 will rise, thus reducing the magnetic counterforce of the spring force, thus accelerating the armature 32 even more. Once the armature 32 reaches its final opened position relative to the stator, shown in Fig. 3, it will have a certain kinetic energy, when the relative velocity is not zero. This kinetic energy will cause a mechanical bouncing due to the collision of the components of the actuator 12 which causes the above-mentioned degrading of the switching properties of the circuit breaker.

This bouncing effect is reduced by supplying a reverse voltage to the coil 48 during the relative movement of the armature 32 and the stator 40. In particular, once the armature 32 has reached a position relative to the stator 40, where the separation of the circuit breaker terminals 18, 20 has happened and after the kinetic energy of the armature 32 has exceeded the amount needed to reach the opened position, the polarity of the power supply may be reversed by the switch circuit 26 which is controlled by the controller 30. Thus, the current in the coil 48 is reduced with maximal change rate and finally also the current in the coil 48 changes its polarity thus increasing the total magnetic force and hence decelerating the relative movement of armature 32 and stator 40.

Fig. 4 shows a diagram with a switch circuit 26 that is adapted to change the polarity of the voltage supplied to the coil 48. The switch circuit 26 comprises four switches 56a, 56b, 56c, 56d that, for example, may be thyristors, and that are opened and closed by the controller 30. For connecting the coil 48 in a first direction to the DC voltage source 54, the controller 30 opens the switches 56a and 56b and closes the switches 56c and 56d. In such a way a positive voltage is supplied to the coil 48. For connecting the coil 48 in the other direction with the DC voltage source 54, the controller 30 closes the switches 56a, 56b and then opens the switches 56c, 56d. In such a way, a negative voltage is supplied to the coil 48. For disconnecting the coil 48 from the voltage source 54, the controller 30 opens all switches 56a, 56b, 56c, 56d.

The Figs. 5A to 5D show diagrams which depict certain parameters of the switching operation of the actuator 12 over time. The lines 68, 66, 58, 64 in the diagrams show the parameters for the inventive solution. The lines 68', 66', 58', 64' show the parameters for a conventional actuator. In the diagrams, time is running from left to right and the values are given in seconds.

Fig. 5C shows the voltage signal 58 applied to the coil 48 and generated by the switch circuit 26 controlled by the controller 30. During a first time period ti of about 4 ms, a first constant voltage 60 is applied to the coil 48. As may be seen from Fig. 5D absolute value of the coil current 64 increases (see Fig. 5D), the absolute value of the velocity 66 between the armature 32 and the stator 40 increases (see Fig. 5B) and the relative position 68 between the armature 32 and the stator 40 decreases (see Fig. 5A).

After the first time period ti , the voltage 58 supplied to the coil 48 is reversed for a second time period t 2 , which lasts about 10 ms. As may be seen from Fig. 5C, a constant second voltage 62, which has the negative value of the first voltage 60 is applied to the coil 48. After the time period t 2 , the voltage 58 is switched to 0.

The earlier the polarity of the DC voltage source 54 is reversed, the higher is the deceleration effect. However, if the time ti of the voltage reversal is chosen too early, the armature 32 and the stator 40 will not reach their opened position and the opening operation may fail. If the voltage reversal ti is chosen too late, the influence on the bouncing behaviour may be very small. Figs. 5A to 5D show, that a range of voltage reversal time can be determined, where a significant influence on the impact velocity at the armature 32 at the opened position can be achieved and thus the bouncing effect may be reduced.

For an optimal switching behaviour, it may be advantageous to assess the movement of the armature 32 by any kind of sensor, e.g. a position-, velocity- or acceleration sensor. Then the time t1 can be adapted to the actual travel curve that may differ due to external influences like friction of temperature. In particular, due to the switching from the first voltage 60 to the second voltage 62, the absolute value of the coil current 64 starts to decrease. The coil current 64 changes its sign a short time after the voltage reversal ti . Due to this, a reverse magnetic field is induced in the coil 48 which starts to decelerate the movement of the stator 40 and the armature 32. As may be seen from Fig. 5B, after about 8 ms, the absolute value of the velocity 66 has reached its maximum value and decreases after that.

The time periods ti and t 2 are chosen in such a way, that the velocity 66 reaches nearly zero, when the relative position 68 reaches the opened position after about 16 ms. In such a way, nearly no bouncing of the components occurs compared to the situation in which the voltage is not changed to a reverse voltage.

This situation is shown with the lines 68', 66', 58' and 64' in Fig. 5A to 5D. If a constant voltage 58' is applied to the coil 48, the absolute value of the coil current 64' is increasing more and more and the absolute value of the velocity 66 is increasing until the armature 32 and the stator 40 impact on each other, which causes a back-bouncing 70.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or controller or other unit may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

LIST OF REFERENCE SYMBOLS

10 circuit breaker

12 actuator

14 switching chamber

16 rod

18 first terminal

20 second terminal

22 electrical contact

24 electrical line

26 switch circuit

28 coil

30 controller

32 armature

34 main armature disk

36 shaft

38 small armature disk

40 stator

42 inner yoke

44 permanent magnet

46 outer yoke

48 coil

50 air gap

52 spring element

54 DC voltage source

56a-56d switch

58, 58' voltage signal

60 first voltage

61 , 61 ' coil voltage signal

62 second voltage

63, 63' coil current signal

64, 64' coil current

65, 65' observing apparatus

66, 66' velocity

68, 68' position

69, 69' armature position signal

70 back bouncing

71 third voltage