Field of the invention

The invention relates to a magnetic actuator unit for a circuit breaker, particularly for a medium voltage vacuum circuit breaker, a circuit breaker and a magnetic actuator unit for switching the circuit breaker, the use of a magnetic actuator for switching a circuit breaker, and a method of assembling a magnetic actuator for a circuit breaker.

For the operation of a circuit breaker, especially a medium voltage vacuum circuit breaker, it may be necessary to generate a high force to press the first moving electrical contact to a second corresponding fixed electrical contact. The force may be generated by a magnetic actuator. The magnetic actuator comprises a coil for generating an electrical field, a core for forming this field and a first movable plate which is attracted by the core. When being attracted by the core, the movable plate generates the force used for closing the circuit breaker. WO 01/46968 A1 discloses a variable reluctance solenoid which includes an armature and a yoke located axially beyond one end of the armature. Magnetic attraction across an axial gap between the armature and yoke causes the armature to move axially and close the gap. The armature includes ferromagnetic laminations lying in a plane perpendicular to the axial direction. These laminations may include slots, proportioned and directed to combat eddy currents and reduce moving mass while avoiding creation of flux bottlenecks. The solenoid may have two yokes on opposite sides of the armature, providing reciprocating armature motion. EP 1 843 375 A1 relates to an electro-magnetic actuator, such as for a medium voltage switch, having a first movable plate in form of a round yoke, an actuating shaft and a lower smaller second movable plate in form of a lower smaller yoke which is fixedly spaced apart from the first movable plate and arranged at an opposite end of the core. A damping pad for mechanical damping is inserted between the core of the magnetic actuator and the small yoke.

However, the thickness of damping pads is generally too large to generate the required force to keep the system, for example the magnetic actuator and external devices like one or more vacuum interrupters, fixed in OPEN or OFF position. Typically, the required force in the OFF position is generated by the opening spring. The opening spring will generate the highest force in ON position. Since the magnetic actuator is generally not able to magnetically generate its own locking force for the OFF position, the opening spring has to be designed in a way that it also helps to generate the locking force in the OFF position. Consequently, the mechanical energy for charging the opening spring during the closing operation is relatively high, and higher than required for obtaining the desired opening speed.

Summary of the invention

It is an object of the invention to provide a compact, flexible and efficient magnetic actuator for a circuit breaker.

The subject is achieved by the subject matter of the independent claims. Further exemplary embodiments are evident from the dependent claims.

According to an aspect of the invention, a magnetic actuator unit for a circuit breaker is provided, in particular for a medium voltage vacuum circuit breaker, wherein the magnetic actuator unit is adapted for switching the circuit breaker ON and OFF by moving a first movable plate on an actuating shaft through the core of the magnet between an ON position and an OFF position. The magnetic actuator unit comprises a non-magnetic flat insert arranged between the core and a second movable plate, which is mounted onto said actuating shaft at a defined distance to the first moving plate, wherein the non-magnetic flat insert and the second movable plate are adapted for adjusting a holding force of the magnetic actuator unit provided by the second movable plate at the OFF position, wherein the holding force is sufficiently strong for holding the actuator unit in the OFF position against the outer forces that are acting on the magnetic actuator unit. No additional spring element is necessary for generating the holding force in the OFF position.

The non-magnetic flat insert and / or the second movable plate may be adapted for adjusting the holding force of the magnetic actuator provided by the second movable plate at the OFF position by adjusting the thickness of the non-magnetic flat insert and / or the thickness and / or width or diameter of the second movable plate.

In other words, the present invention proposes according to this embodiment a relatively flat non-magnetic insert instead of a damping layer wherein, by the thickness of the non-magnetic insert the holding force of the magnetic actuator in an OFF position or disconnected position may be adjusted according to the requirements of the system that is operated by said magnetic actuator. An opening spring may be omitted for holding the OFF position as the required holding force in the OFF position is generated by the second movable plate. The holding force may increase when decreasing the thickness of the non-magnetic flat insert and the holding force may decrease when increasing the thickness of the non-magnetic flat insert.

Further adjustment of the holding force in OFF position can be made with a variation of the thickness and / or the width or diameter of the second movable plate.

According to a preferred embodiment of the invention, the magnetic actuator further comprises a fixing device for fixing the non-magnetic flat insert to the core, in particular a screw. It may be advantageous to use existing screws to fix the layer in a reliable way to the core. The fixing device may comprise at least one screw.

In a preferred embodiment of the invention, the non-magnetic flat insert is made of stainless steel. The non-magnetic flat insert may have the form of a layer that can be optionally made of different non-magnetic materials as long as they comply with the expected number of operations and corrosion resistance of the magnetic actuator. Stainless steel is fulfilling both of these above-mentioned aspects.

Depending on the specific application, the non-magnetic flat insert is adapted for adjusting a holding force of the magnetic actuator, provided by the second movable plate at the OFF position, based on the distance between the second movable plate and the core, i.e. based on the adjustment of the thickness of the non-magnetic flat insert. Generally, this dependency has a hyperbolic character.

In a preferred embodiment of the invention the magnetic actuator unit further comprises a core element, at least two flanks surrounding the core element, and at least two permanent magnets arranged between the core element and the flanks, wherein the second movable plate is adapted for adjusting a holding force of the magnetic actuator provided by the second movable plate at the OFF position based on a relation of the width of the second movable plate to the distance between the outer ends of the permanent magnets.

Due to the distribution and concentration of the magnetic flux and due to saturation effects in the iron parts, such as the core, the flanks and the second movable plate, the holding force has a maximum value when the width of the second movable plate is a little bit larger than the distance between the outer ends of the permanent magnets.

For wider second movable plates the holding force decreases as the magnetic flux is less concentrated.

For narrower second movable plates the holding force also decreases as the amount of magnetic flux is reduced due to the low content of iron and the high content of air in the magnetic circuit including the second movable plate.

In case, the first movable plate is not rectangular but round, there is also a maximum holding force in OFF position for a certain diameter of the second movable plate, but with a less accentuated peak due to the superposition of regions of the round second movable plate that are wider than the width between the outer ends of the permanent magnets, and other regions of the round second movable plate that are less wide.

In a further embodiment of the invention, the holding force of the magnetic actuator unit provided by the second movable plate at the OFF position is adapted based on the thickness of the second movable plate. In case the second movable plate is relatively thin, it may happen that the magnetic flux saturates areas of the second movable plate to such an extent that the magnetic resistance is increased significantly. Then the amount of magnetic flux is reduced, and therefore also the magnetic locking force in the OFF position.

In order to reach a more compact design of the magnetic actuator, a circuit breaker and a magnetic actuator for switching the circuit breaker according to any one of the above- and below-mentioned embodiments is provided, wherein the magnetic actuator may be integrated in the circuit breaker. The use of such a magnetic actuator in a circuit breaker is provided according to another preferred embodiment of the invention.

According to a further aspect of the invention, a method of assembling a magnetic actuator for a circuit breaker is provided the method comprising the steps of arranging a coil at a core of the magnetic actuator unit such that the coil generates a magnetic flux in the core, movably arranging a first movable plate on an actuating shaft that goes through said core such that the first movable plate is movable between an ON position and an OFF position of the circuit breaker, arranging a non-magnetic flat insert at the other side of the core, opposite to the first movable plate, and then arranging a second movable plate below the non-magnetic flat insert and on the same actuating shaft where the first movable plate is arranged so that the non-magnetic flat insert lies between the core and the second movable plate of the magnetic actuator unit. The flat insert and the second movable plate are adapted for adjusting a holding force of the magnetic actuator unit provided by the second movable plate at the OFF position.

These and other aspects of the invention will be apparent from and elucidated with reference to the exemplary embodiments described herein after. Brief description of the drawings

Below, the most preferred embodiments of the present invention are described in more detail with reference to the attached drawings.

Figure 1 shows a cross-sectional view of a magnetic actuator unit for a circuit breaker in ON position according to an embodiment of the invention.

Figure 2 shows a perspective view of a magnetic actuator unit for a circuit

breaker in ON position according to another embodiment of the invention.

Figure 3 shows a cross sectional view of a magnetic actuator unit for a circuit breaker according to Figure 2.

Figure 4 shows a diagram describing the relation of the width of a second

movable plate of the magnetic actuator unit according to figures 1 to 3 to the distance between the outer ends of the permanent magnets of the core of the magnetic actuator unit.

Figure 5 shows a flow chart of a method of assembling a magnetic actuator unit for a circuit breaker according to an embodiment of the invention.

All drawings are schematic.

Detailed description of the drawings

In Figure 1 a magnetic actuator unit 100 for a circuit breaker, particularly for a medium voltage vacuum circuit breaker is shown comprising a core 101 with a core element 109, at least two flanks 102 surrounding the core element 109, and at least two permanent magnets 106 arranged between the core element 109 and the flanks 102. The magnetic actuator unit 100 is adapted for switching the circuit breaker ON and OFF by moving a first movable plate 103 between an ON position and an OFF position. A non-magnetic insert 110 is arranged between a core 101 of the magnetic actuator unit 100 and a second movable plate 107.

The first movable plate 103 is attracted by the core 101 to a first position P1 at a first side of the core 101 when the magnetic field is generated by the coil 105, the coil 105 generating a magnetic flux 112 in the core 101. The first movable plate 103 is moving towards the core 101 when being attracted by the core 101. The first movable plate 103 and the second movable plate 107 are spaced apart from one another in a fixed position at a distance d1 , such that, if the first movable part 103 lifts off from the core 101 with a desired stroke of the magnetic actuator unit 100 in an OFF position, the second movable plate 107 bears against the non-magnetic flat insert 110 at a second side of the core 101 at a second position P2, opposite of the first position P .

Figure 2 shows a magnetic actuator unit 100 for a circuit breaker according to another exemplary embodiment of the invention. The actuator is in position P1 , i.e. the ON or closed position of a not show circuit breaker that is to be driven by the magnetic actuator unit. The non-magnetic flat insert 110 may comprise stainless steel and is arranged between the core 101 and the second movable plate 107 and may be fixed to the core or the second movable plate 107, for example by a fixing device 111.

The flat insert 110 is, together with the second movable plate 107, adapted for adjusting a holding force of the magnetic actuator unit 100 provided by the second movable plate 107 at the OFF position, in particular if the first movable plate 103 lifts off from the core 101 with a desired stroke of the magnetic actuator unit 100, possibly by adjusting the thickness T of the non-magnetic flat insert 110. An actuating shaft 104 is adapted to guide the first movable plate 103 and the second movable plate 107 through the core 101.

Figure 2 shows a magnetic actuator unit 100 for a circuit breaker, wherein the first movable plate 103 is fixed to an actuating shaft 104. The magnetic actuator unit 100 of Figure 2 comprises a coil, a core 101 with a core element, at least two flanks 102 surrounding the core element, and at least two permanent magnets arranged between the core element and the flanks according the magnetic actuator unit of Figure 1 , with the difference, that the second movable plate 107 is a round plate with a diameter 201 , and a non-magnetic flat insert 110 is provided which is fixed to the core by a screw 111.

Figure 3 shows a cross-sectional view of the magnetic actuator unit 00 of Figure 2. The thickness of the non-magnetic flat insert 110 is adapted for adjusting a holding force of the magnetic actuator unit 100 provided by the second movable plate 107 at the OFF position. The holding force decreases when increasing the thickness T of the non-magnetic flat insert 110, and an adjustment of the holding force based on a relation of the width 201 of the second movable plate 107 to the distance between the outer ends 202, 203 of the permanent magnets becomes less sensitive to the value of this relation. The round second movable plate 107 provides a maximum holding force for a certain diameter 201 , but with a less accentuated peak compared to a rectangular second movable plate 107 as shown in Figure 1 , due to the fact that some regions of the round second movable plate 107 are wider than the width 200 between the outer ends 202, 203 of the permanent magnets 106, and other regions of the round second movable plate 107 are less wide.

The magnetic locking force or holding force in OFF position may also depend on the thickness T2 of the second movable plate 107. The magnetic flux that is generated by the permanent magnets 106 and guided by the core 101 respectively the core element 109 and the flanks 102 passes finally through the plate 107 and thereby generates the holding or locking force. In case the second movable plate 107 is relatively thin, it may happen that the magnetic flux saturates areas of the second movable plate 107 to such an extent, that the magnetic resistance is increased significantly. Then the amount of magnetic flux is reduced, and therefore also the magnetic holding force in OFF position.

The magnetic holding force in OFF position may depend also on the thickness T of the non-magnetic layer or non-magnetic flat insert 110. Generally, this dependence is of hyperbolic character. The iron in the second movable plate 107 may saturate if both, the second movable plate 107 and the non-magnetic flat insert 10 are thin, because in this case the magnetic holding or locking force in OFF position will be reduced due to said saturation.

Figure 4 shows a diagram with a vertical holding force axis 402 depicting the principal shape of the holding or locking force, provided by the second movable plate in an OFF position, and a horizontal axis 401 depicting the width - or the diameter in case the second movable plate is round - of the second movable plate.

Graph 404 shows the principal shape of the holding force or magnetic locking force of a second movable plate and a non-magnetic flat insert with a relatively small thickness in relation to the dimensions of the other parts of the magnetic circuit, like the core 101 , the permanent magnets 106, the flanks 102 and the second movable plate 107. The vertical line 403 shows the width 200 between the outer ends 202, 203 of the permanent magnets (see also Figure 3). Graph 405 shows the holding force of the second movable plate and a non-magnetic flat insert with a larger thickness.

Due to the distribution and concentration of the magnetic flux and due to the saturation effects in the iron parts (the core, the flanks, the second movable plate) the holding force has a maximum value when the width of the second movable plate is a little bit larger than the distance between the outer ends of the permanent magnets.

For wider second movable plates the holding force decreases as the magnetic flux is less concentrated.

For narrower second movable plates the holding force also decreases as the amount of magnetic flux is reduced due to the low content of iron and the high content of air in the magnetic circuit including the second movable plate.

For a higher thickness of the non-magnetic insert, as shown in graph 405, the locking force in OFF position will be generally lower. Further, the peak force over the width of the second movable plate will be less distinctive, and it will occur with wider second movable plates. Figure 5 depicts a flow chart of a method 500 of assembling a magnetic actuator unit for a circuit breaker with the steps of arranging 501 a coil at a core of the magnetic actuator unit such that the coil generates a magnetic flux in the core, movably arranging 502 a first movable plate on an actuating shaft such that the first movable plate is movable between an ON position and an OFF position of the circuit breaker which is switched ON and OFF by the magnetic actuator unit, such that the first movable plate is attracted by the core to a first position of the core when a magnetic field is generated by the coil. The next step is arranging 503 a non-magnetic flat insert at the other side of the core, i.e. opposite to the first moving plate. The last step ot the method 500 is arranging 504 a second movable plate below the non-magnetic flat insert and on the same actuating shaft where the first movable plate is arranged so that the non-magnetic flat insert lies between the core and the second movable plate. The flat insert is adapted for adjusting a holding force of the magnetic actuator unit provided by the second movable plate at the OFF position, and wherein the first movable plate and the second movable plate are spaced apart from one another in a fixed position at a distance, such that, if the first movable plate lifts off from the core with the desired stroke of the magnetic actuator at an OFF position, the second movable plate bears against a non-magnetic flat insert at a second position at the core opposite of the first position generating a holding force of the magnetic actuator unit at the OFF position.

While the invention has been illustrated and described in detail in the drawings and the 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 practicing the claimed invention, from 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. 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 symbols in the claims should not be construed as limiting the scope. Reference signs

100 magnetic actuator unit

101 core

102 flanks

103 first movable plate

104 actuating shaft

105 coil

106 permanent magnets

107 second movable plate

109 core element

110 non-magnetic flat insert

111 fixing device, screw

112 magnetic flux

200 distance (between the outer ends of the permanent magnets)

201 width or diameter (of the first movable plate)

202 outer end (of the permanent magnet)

203 outer end (of the permanent magnet)

400 diagram of holding force in relation to the width of the second movable plate to the distance between the outer ends of the permanent magnets

401 width of second movable plate axis

402 holding force axis

403 distance between the outer ends of the permanent magnets

404 graph of relatively thin non-magnetic flat insert

405 graph of relatively thick non-magnetic flat insert

d1 distance between first movable plate and second movable plate

d2 distance between second movable plate and core

P1 first position = ON

P2 second position = OFF

T thickness of non-magnetic flat insert

T2 thickness of second movable plate