EP3218915A1

EP3218915A1 - Electromagnetic actuator and circuit breaker including such an actuator

Info

Publication number: EP3218915A1
Application number: EP15793787.1A
Authority: EP
Inventors: Philippe Schuster
Original assignee: Schneider Electric Industries SAS
Current assignee: Schneider Electric Industries SAS
Priority date: 2014-11-12
Filing date: 2015-11-10
Publication date: 2017-09-20
Anticipated expiration: 2035-11-10
Also published as: US10283301B2; US20170263404A1; WO2016075118A1; FR3028349A1; EP3218915B1; FR3028349B1

Abstract

The invention relates to an electromagnetic actuator (2) including a magnetic housing (20), a coil (22) that is rigidly connected to the housing and is capable of being connected to an electric circuit, a magnetic core (26) that is arranged in the coil and can move along a central axis (X2) defined by the coil and according to the strength of the current flowing in the coil, and a shunt (28) that is arranged in the coil and includes a magnetocaloric material (29) the magnetisation of which is temperature-dependent. The shunt is arranged in the coil along the central axis along a length (L) so as to create an air gap (E) between the shunt and the magnetic core. The actuator further includes means (31) for attaching the shunt to the housing that are designed to adjust said length.

Description

ELECTROMAGNETIC ACTUATOR AND CIRCUIT BREAKER COMPRISING

AN ACTUATOR

The invention relates to an electromagnetic actuator, as well as a circuit breaker comprising such an actuator.

In the field of protection of electrical circuits, it is known to use a circuit breaker including a thermal actuator for detecting an overload current or including a magnetic actuator in order to recognize a short circuit current. By way of example, mention may be made of document FR-A-2 772 981 in which the circuit breaker is equipped with a thermal actuator. In particular, the actuator comprises a straight bimetal and a plunger electromagnet

It is also known to combine in a single actuator the two thermal and magnetic functions, so as to combine in a single circuit breaker the detection of overload and short-circuit currents. As such, it is known, for example from EP-A-1 001 444, to equip an actuator with a bimetallic bimetallic strip. It is also known, for example from US-A-2,690,528, to equip an actuator with a dashspots system which operates differently during an overload or short-circuit current. The actuators mentioned above have the advantage of reducing the size and the number of parts. However, the dynamic opening of the contacts of such actuators does not allow to hit the contacts. It follows that the opening speed is relatively low compared to the necessary breaking capacity.

Furthermore, it is known, from DE-A-3,028,900, and WO-A-2014/087073, to use an actuator equipped with a shunt device which includes a magnetocaloric material and a plunger core. Such an actuator makes it possible to increase the opening speed of the contacts by percussion or extraction thereof. On the other hand, the structure of this actuator fixes the tripping thresholds for circuit protection. The thresholds are not adaptable to the different electrical circuits, which limits the areas of use of such a device.

It is this disadvantage that the invention intends to remedy more particularly by proposing a new electromagnetic actuator whose triggering thresholds are adjustable, for example depending on the context of use.

In this spirit, the invention relates to an electromagnetic actuator comprising a magnetic carcass and a coil integral with the carcass and connectable to an electrical circuit. The actuator also comprises a magnetic core, arranged in the coil and movable, along a central axis defined by the coil, as a function of the intensity of the current flowing in the coil, and a shunt device, arranged in the coil and comprising a magnetocaloric material whose magnetization is a function of the temperature. According to the invention, the shunt device is arranged in the coil for a length, along the central axis, and so as to form an air gap between the shunt device and the magnetic core. In addition, the actuator comprises means for fixing the shunt device to the carcass, designed to adjust this length.

Thanks to the invention, the actuator combines the advantages of the thermal and magnetic functions with those of an actuator with adjustable thresholds. In other words, such an actuator comprises a reduction in the size and number of parts, as well as a reduction in the heat dissipation and the number of variants to be considered. In addition, the actuator improves in particular its sensitivity and thermal efficiency, as it increases or decrease its sensitivity to harmonic currents depending on the field of use. Finally, such an actuator also has economic advantages, that is to say a decrease in the amount of active materials required and easier realization of the actuator.

According to advantageous but non-obligatory aspects of the invention, such an electromagnetic actuator may comprise one or more of the following characteristics, taken in any technically permissible combination:

- The actuator further comprises a heat-conducting sleeve disposed in the coil and in that the magnetic core and the shunt device are arranged in the sleeve.

- The shunt device is in contact with the thermo-conductive sleeve.

- A spring is interposed between the shunt device and the magnetic core. - The shunt device is provided with a pole piece arranged between the spring and a portion of the shunt device, constituted by the magnetocaloric material.

- The thermo-conductive sleeve is solid wall.

- The thermo-conductive sleeve includes a slot which extends parallel to its central axis.

- The fixing means comprise a laser weld or a mechanical locking device.

- The magnetocaloric material is an alloy of nickel, cobalt, manganese and a fourth element selected from aluminum, indium, antimony and tin.

The invention also relates to a circuit breaker comprising a housing housing an actuator as described above, the coil being coupled to a current line. The circuit breaker also comprises a pair of movable contacts relative to each other, a first contact being in mechanical connection with the movable core of the actuator.

The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows, given solely by way of nonlimiting example and with reference to the appended drawings, in which:

- Figure 1 is a schematic view of an actuator according to the invention;

FIG. 2 is a perspective view of a thermo-conductive sleeve of the actuator of FIG. 1;

- Figure 3 is a schematic view of a circuit breaker according to the invention, comprising an actuator according to the invention;

FIG. 4 is a schematic representation of the actuator of FIG. 1 when a nominal current feeds the coil, which is omitted for the sake of clarity;

- Figure 5 is a view similar to Figure 4 when an overcurrent feeds the coil;

- Figure 6 is a view similar to Figure 4 when a short-circuit current feeds the coil;

- Figure 7 is a view similar to Figure 2 according to an alternative embodiment of the invention; and

- Figure 8 is a diagram showing the magnetization of a shunt device according to the invention as a function of its temperature and the magnetic field.

In Figure 1 is shown an electromagnetic actuator 2 comprising a magnetic housing 20 which defines a central axis X2 of the actuator. The central axis X2 is fixed and constitutes a central axis for all the elements of the actuator 2. The magnetic casing 20 is, for example, tubular and has two axially opposed bases 20A and 20B. In each of these bases 20A and 20B, is formed a bore, respectively 21A and 21B. The bores 21A and 21B provide access to a volume 200 internal to the carcass 20.

The actuator 2 also comprises a coil 22, arranged in the volume 200 of the casing 20 and integral with the casing 20. The coil 22 is able to be connected, in a manner known per se, to an electrical circuit which is not shown in Figure 1.

The actuator 2 further comprises a thermo-conductive sleeve 24. As shown in Figure 2, the sleeve 24 has a hollow cylindrical shape with a solid wall. The sleeve 24 is disposed in the coil 22 and in radially contact along the axis X2 with it. On the side of the base 20A, the sleeve 24 passes through the bore 21 A. Part end of the sleeve 24 is projecting with respect to the base 20A and outside the carcass 20.

The main function of the sheath is to transmit the heat. It is so metal.

The actuator 2 also comprises a magnetic core 26 of cylindrical shape, arranged in the sleeve 24 and movable in translation along the central axis X2 as a function of the intensity of the current flowing in the coil 22.

The actuator 2 further comprises a shunt device 28 comprising a magnetocaloric material 29, in the form of a corresponding piece, whose magnetization is a function of the temperature. The shunt device 28 is of cylindrical shape and is partially arranged in the sheath 24 for a length L, along the central axis X2, forming along the axis X2 an air gap E between the shunt device 28 and the core 26. Therefore, the shunt device 28 is arranged in part in the bore 21 B of the carcass 20, the remaining portion being positioned outside the carcass 20 projecting from the base 20B. The shunt device 28 is further in contact with the thermo-conductive sleeve 24.

In practice, in a state prior to use, typically during the manufacture of the actuator 2, the shunt device 28 is movable in translation along the axis X2 relative to the sleeve 24 and the carcass 20. Thus, it is possible to choose the value of the length L and, as described below, a switching threshold of the actuator 2 due to the corresponding variation of the gap E. The actuator also comprises means 31 for fixing from the shunt device 28 to the carcass 20, the fixing means 31 being designed to adjust this length L. In particular, the fixing means 31 are made by a laser weld or by a mechanical locking device.

The magnetocaloric material 29 of the shunt device 28 is an alloy of nickel, cobalt, manganese and a fourth element selected from aluminum, indium, antimony and tin. The shunt material 29 is chosen for its magnetocaloric properties. More precisely, as represented in FIG. 8, the magnetocaloric material 29 is such that its magnetization has a peak as a function of the temperature T. In particular, at low temperature, the material is little, if any, magnetic. When the temperature T increases, beyond a first temperature T0, the magnetization of the magnetocaloric material 29 increases rapidly, reaching a maximum at a second temperature T1, beyond which the magnetization decreases until it cancels out. the curie temperature Te of the material magnetocaloric 29. For further explanation, the reader will refer to WO-A-2014/087073.

In a preferred embodiment of the invention, the shunt device 28 is provided with a pole piece 30 arranged in the sheath 24 and disposed between the piece constituted by the magnetocaloric material 29 of the shunt device 28 and the core 26, the air gap E thus being delimited between this pole piece 30 and the magnetic core 26. As shown in FIG. 1, the pole piece 30 bears, in the axis X2, against the magnetocaloric material 29 of the shunt device 28.

Finally, the actuator 2 comprises a spring 32 arranged, along the axis X 2, between the pole piece 30 and the magnetic core 26.

In Figure 3, a circuit breaker 4 comprises a housing 40 which houses the actuator 2. In the circuit breaker 4, the coil 22 of the actuator 2 is connected to a current line 41 of an electrical circuit. The current line 41 has two first pellets 42 fixed. The circuit breaker 4 also comprises a bridge 44 secured to the magnetic core 26 of the actuator 2 and equipped with two second pellets 46. The bridge 44 is, consequently, movable in translation along the axis X2 of the actuator 2 with the core 26 and is able to move between a first position, shown in FIG. 3, where the second pellets 46 are in contact with the first pellets 42 and a second position where the second pellets 46 are separated from the first pellets 42. first position corresponds to the closed configuration of the circuit-breaker 4 while the second position corresponds to the open configuration of the circuit-breaker 4.

The operation of the electromagnetic actuator 2 and the circuit breaker 4 is as follows. Before the installation of the actuator 2 in the circuit breaker 4, in particular during the manufacture of the actuator, the shunt device 28 is inserted into the thermo-conductive sleeve 24 for the length L and is then fixed to the carcass 20 by the fixing means 31 above. This length L is chosen as a function of the field of use of the circuit breaker 4. Indeed, as is explained below, the length L makes it possible to choose the switching threshold of the actuator 2 and therefore the tripping threshold of the circuit breaker 4 .

In the assembled and closed configuration of the circuit breaker 4, as represented in FIG. 3, the spring 32 exerts against the core 26 a force E32, shown in FIG. 1, so as to pull the movable pellets 46 from the bridge 44 to remove them from the pellets fixed 42 and ensure the opening of the electrical circuit. In a normal use condition, as shown in FIG. 4, a so-called nominal current flows in the circuit to which the coil 22 is connected. In a manner known per se, the coil 22 then creates a magnetic flux Fn.

The actuator 2 is thus configured to constitute a magnetic circuit. In particular, the magnetic circuit is composed of the parts 30, 28, 20, 24, 26 and the air gap E between the core 26 and the pole piece 30 of the shunt device 28. In the magnetic circuit, the pole piece 30a the function, on the one hand, to channel the magnetic flux Fn between the movable core 26 and the magnetocaloric material 29 and, on the other hand, to protect the latter from shocks during the closure of the gap E.

All the aforementioned parts have a fixed magnetic reluctance excluding the shunt device 28. In the temperature range where the magnetization of the device 28 increases, its reluctance decreases by facilitating the passage of the magnetic flux.

The magnetic core 26 traversed along the central axis X2 by the magnetic flux Fn is subject to a magnetic force En, depending on the magnetic flux Fn and, in a manner known per se, in close correlation with the current flowing in the coil 22 The magnetic core 26 thus exerts its force against the spring 32.

The coil 22 generates heat dissipation, in particular by Joule effect. The sheath 24 is responsible for transmitting this dissipated heat to the other parts of the actuator and in particular to the shunt device 28 whose magnetization depends on its temperature. In addition, the sleeve 24 is itself responsible for heat dissipation due to currents flowing in its surfaces and which are induced by the magnetic flux Fn.

In a normal use condition, the overall heat dissipation due to the nominal current induces an increase in temperature T, which however remains lower than the first temperature T0 mentioned above. The magnetization of the shunt device 28 remains zero or very low. Thus, during a nominal current, the force En is less than or equal to the force E32 of the spring 32, so that the magnetic core 26 does not move and the closed configuration of the circuit breaker 4 is maintained.

When an overload current flows in the electric circuit, as shown in FIG. 5, a magnetic flux Fs surrounds the coil 22, as described above. Consider, for example, the current flowing as having a value greater than or equal to 1.5 times the value of the nominal current. Thus, the magnetic flux Fs generated by such an overload current is strictly greater than the magnetic flux Fn generated by the nominal current. In addition, this overload current causes an increase in the heat dissipation by the Joule effect of the coil 22. heat dissipation is transmitted via the thermo-conductive sleeve 24 to the shunt device 28. The shunt device 28 is therefore raised to increase temperature and to acquire a temperature T between the first and second aforementioned temperatures. This temperature thus allows greater magnetization of the shunt device 28 and thus a decrease in its magnetic reluctance. In practice, the magnetic circuit for the overload current has a lower overall magnetic reluctance than in the case of the nominal current. The magnetic flux Fs then exerts on the magnetic core 26 a force Es. The core 26 compresses the spring 32 which opposes its effort E32. In this case, the force Es is greater than the force E32 of the spring and the core 26 is translated along the axis X2 and reduces the gap E. At the circuit breaker 4, the displacement of the core 26 causes the movable bridge 44 and its pellets 46, away from the fixed pellets 42. The circuit breaker 4 is then in its open configuration.

Heat transfer depends in particular on the weather. The temperature increase is not instantaneous but occurs gradually. In other words, the magnetization of the device 28 increases in time with the temperature. The force Es exerted by the core 26 on the spring 32 also increases progressively in time in parallel with the increase in the temperature of the shunt device 28. It is possible to consider a threshold temperature beyond which the stress E is greater than the force E32 of the spring 32. The displacement of the core 26 and the opening of the pellets 42 and 46 of the circuit breaker 4 will be possible when the temperature T of the device 28 exceeds the threshold temperature.

When a short-circuit current flows in the electric circuit, as shown in Figure 6, a magnetic flux Fc is generated. Considering, for example, the short-circuit current as greater than or equal to five times the nominal current, the magnetic flux Fc is significantly greater than the magnetic flux Fn. In other words, the short-circuit current causes a large increase in the magnetization of the shunt device 28 whatever its temperature and the magnetic flux Fc exerts on the core 26 a force Ec which is immediately greater than the force E32 of the spring 32. In this case, the magnetic flux Fc is able to move the core 26 without waiting for heat transmission between the coil 22 and the shunt device 28. As a result, the short-circuit current causes almost instantaneously a displacement of the core 26 along the axis X2 so as to reduce the gap E and compress the spring 32 and, at the circuit breaker 4, open the pellets 42 and 46.

In the case where the actuator 2 intervenes to open the pellets 42 and 46 when a short-circuit current flows in the electrical circuit, the magnetic force generated by the coil 22 is such that it causes the opening very quickly: this causes a limitation of the short-circuit current.

The reluctance of the shunt device 28, and therefore of the entire magnetic circuit, is a function of the length L of the device 28 relative to the sleeve 24. The length L plays an important role in the operation of the circuit breaker 4. This length L defines the part of the shunt device 28 which is part of the magnetic circuit. The length L thus defines the part of the shunt device 28 which is in contact with the sheath 24 and thus directly exposed to the heat transfer.

By considering as fixed the position of the core 26, when the length L is reduced, the gap E increases and therefore the overall reluctance of the magnetic circuit increases. So that the force of the core 26 is greater than the force E32 of the spring 32, it will be necessary to achieve a degree of magnetization of the upper device 28, that is to say a higher threshold temperature. In other words, by reducing the length L, it is possible to delay the tripping threshold of the circuit breaker 4.

On the contrary, by increasing the length L, the gap E is reduced, as well as the overall reluctance of the magnetic circuit. The threshold temperature is then lower. In other words, by increasing the length L, it is possible to advance the tripping threshold of the circuit breaker 4.

Various arrangements and variants of the actuator 2 are also possible. As examples:

- The pole piece 30 is hollow cylindrical shape including a bore in which is partially arranged the spring 32 which bears against the magnetocaloric material 29 of the shunt device 28 and the magnetic core 26;

the heat-conducting sleeve 24 includes a slot 240, as shown in FIG. 7, which extends parallel to the central axis X2. The slot 240 makes a cut for the currents generated by electromagnetic induction in the sheath 24. The presence of the slot 240 thus allows to delay the triggering threshold. The choice to use or not a sheath 24 with the slot 240 is therefore depending on the field of use of the circuit breaker 4.

The embodiment and variants envisaged above can be combined with one another to generate new embodiments.

Claims

1 .- Electromagnetic actuator (2), comprising a magnetic carcass (20), a coil (22) integral with the carcass and connectable to an electrical circuit, a magnetic core (26) arranged in the coil and movable, along a central axis (X2) defined by the coil, as a function of the intensity of the current flowing in the coil, and a shunt device (28), arranged in the coil and comprising a magnetocaloric material (29) whose magnetization is a function of the temperature, the actuator being characterized in that the shunt device (28) is arranged in the coil (22) for a length (L), along the central axis (X2), so as to form a gap (E) between the shunt device and the magnetic core (26), the actuator further comprising means (31) for attaching the shunt device to the carcass (20), adapted to adjust that length (L).

2. An actuator according to claim 1, characterized in that the actuator (2) further comprises a heat-conducting sleeve (24) disposed in the coil (22) and in that the magnetic core (26) and the device shunt (28) are arranged in the sheath.

3. Actuator according to claim 2, characterized in that the shunt device

(28) is in contact with the heat-conducting sleeve (24).

4. - actuator according to one of the preceding claims, characterized in that a spring (32) is interposed between the shunt device (28) and the magnetic core (26).

5. - actuator according to claim 4, characterized in that the shunt device (28) is provided with a pole piece (30) arranged between the spring (32) and a portion (29) of the shunt device, constituted by the magnetocaloric material.

6. Actuator according to one of claims 2 to 5, characterized in that the thermo-conductive sleeve (24) is solid wall.

7. Actuator according to one of claims 2 to 5, characterized in that the heat-conducting sleeve (24) includes a slot (240) which extends parallel to its central axis (X2).

8. - actuator according to one of the preceding claims, characterized in that the fastening means (31) comprise a laser weld or a mechanical locking device.

9. - Actuator according to one of the preceding claims, characterized in that the magnetocaloric material is an alloy of nickel, cobalt, manganese and a fourth element selected from aluminum, indium, antimony and tin.

10. - Circuit breaker (4), comprising a housing (40) housing an actuator (2) according to one of the preceding claims, the coil (22) of the actuator being connected to a line (41) of current, and a pair of contacts (42, 46) movable relative to each other, a first (46) of the contacts being in mechanical connection with the magnetic core (26) of the actuator.