ES2221798B1 - AUTOMATIC REARME DEVICE FOR MODULAR APPLIANCES OF GOVERNMENT PROTECTION. - Google Patents

Abstract

Automatic reset device for modular protection devices to govern. The invention refers to an automatic reset and remote control device for modular protection devices to be governed, presenting a shape corresponding to a group of modular devices (2), to which it must be coupled, characterized in that it is constituted by means mechanical (1 '') of assembly and opening, capable of being coupled to the group of modular devices that are to be governed (2) by means of a detachable device (3) and by an electromagnetic means (4) for governing the medium mechanical (1 '') of arming and opening, applicable to electrical installations, of protection of different circuits against overloads, such as circuit breakers and contacts directly or indirectly, by means of electrical safety devices, such as circuit breakers, circuit breakers differentials or differential switches, and especially to remote control devices of these devices.

Description

Automatic reset device Modular protection to govern.

The present invention refers to the scope of electrical installations, in particular to the protection of the different circuits against overloads such as short circuits and direct or indirect contacts, by means of electrical safety devices such as circuit breakers, differential circuit breakers or differential switches, and especially to the remote government devices of these devices and aims at an automatic reset device and of telegovernment for modular protection devices.

In some of these circuits, putting out voltage as a result of a defect may represent a significant inconvenience to the user, for example, in the case of a circuit that feeds a freezing installation, of heating, or fire protection devices or even when the governed device is located in a room not monitored, for example, in an industrial facility.

The trip of a protection device does not come always caused by a frank and permanent defect. In effect, the triggering may be caused by transient defects, such such as a current or transient voltage wave due to the lightning strike on the transport line of current, a condensation that generates significant humidity liable to cause a ground leak and disappears after to dry, etc.

In these cases, there are rearming devices automatic that carry out one or more successive tests of reassembly to increasingly longer time intervals. The devices of these types are mainly used in urban facilities of lighting, public shelters, light ads, etc.

The conception of these electrical appliances of Safety is based on electronics for differential function. In addition, these devices are frequently equipped with simple contact means that tolerate only currents relatively weak nominal and present some possibilities of Short circuit limited.

The problem of a repetition of the redisparo or rearmament of these devices and level overload of the means of contact .. Indeed, in case of persistence of a defect is advantageous to be able to avoid an excessive number of rearmed, limiting them, in order to guarantee the perenniality of the contacts

For this purpose, through the request of French patent number 00 15029, a device of automatic reassembly for modular protection devices that must be governed, which presents a general form that corresponds to the of the modular devices to which it must be coupled and which it is provided, on the one hand, with fixing means and indexing on the equipment to be governed by another part, of actuating means of a steering hand or analogous element of said apparatus to govern and, finally, of display means of the operating status of the devices and defects detected by it.

It is true that this device allows to govern distance a wide range of products from the point of view of admissible nominal currents and of performance, by means of its juxtaposition to a modular product designed to protect classic electrical installations in the domestic environment as well as in the industrial field, but it is a device only suitable to work based on all or nothing, that is, to determine the crimping or re-crimping or reassembly of the modular or similar protective equipment or tripping or opening of contacts of such a device.

The present invention aims to alleviate the drawbacks of currently known devices proposing an automatic reset and telegovernment device for modular protection devices that allows, on the one hand, govern a wide range of products from the point of view of the nominal and allowable nominal currents and, on the other  part of not disturbing the normal operation of the product associated.

For this purpose, the reset device automatic and telegovernment for modular protection equipment to govern, which presents a general form that corresponds to that of the modular equipment to which it must be coupled, is characterized for being essentially constituted by a mechanical means of arming and opening that can be coupled to the modular device to be governed by means of a detachable device and by  an electromagnetic means of governing the mechanical means of assembly and opening.

The invention can be more easily understood. thanks to the description that follows, which refers to a form preferred embodiment, given by way of example no limiting, and that is explained by referring to the drawings schematic annexes, in which:

- Figure 1 is a perspective view of the device according to the invention in the assembly phase, being the box in the open position;

- Figure 2 is a perspective view of the device in combination with a modular device govern;

- Figures 3 and 4 are partial views in side elevation of the mechanism, on a larger scale, representing the mechanical means of arming and opening and electromagnetic of government, respectively in armed position and in position of opening;

- Figure 5 is a perspective view, to larger scale, of the referred mechanical arming devices and of opening and electromagnetic government;

- Figure 6 is an exploded view in device perspective;

- Figures 7a to 7h and 8a to 8g are, respectively, partial views in side elevation representing the kinematics of assembly and opening of the mechanical device of armed and opening, and

- Figure 9 is an electrical diagram of the feeding of an electromagnet that constitutes the medium 4 electromagnetic government.

In Figures 1 and 2 of the attached drawings it has been represented an automatic reset device 1 and of telegovernment for modular protection devices to govern, which presents a general form that corresponds to that of modular equipment 2 to which it must be coupled. A device this type is especially intended to be mounted on a rail of assembly of an electrical cabinet or cabinet.

According to the invention, this device automatic rearmament and telegovernment is essentially constituted by a mechanical means 1 'of assembly and opening that can be coupled to the modular device 2 that is about governing through a clutch device 3 and by a means electromagnetic control 4 of the mechanical means 1 'of assembly and opening.

The mechanical means 1 'of assembly and opening is a set that, as shown in figures 1 and 3 to 6 of the attached drawings, is constituted by a government hand 5 pivotally mounted on the case 6 of the device and whose lever or arm 5 'protrudes from this box, by one: connecting rod or maneuvering hook 7 articulated to the hand 5, by a finger of maneuver 8 also articulated to the hand 5 and by a fork 9 of hand drag 5. This hand of government 5 presents a central part of the swingarm assembly on the  box 6 of the device by means of pivots 10 integral with the same and is provided, on the opposite side of the lever 5 ' with respect to axis 10, of two bearings 11 and 12, displaced radially, intended, respectively, for the finger joint of maneuver 8 and of the connecting rod or hook 7 (figures 3 and 4).

The fork 9 of the handle 5 advantageously present the shape of an independent lever behaving two arms substantially aligned on either side of a shaft 9 'through which its tilting assembly is carried out on the box 6 of the device, cooperating one of these arms by its tip with the connecting rod or maneuver hook 7 by means of drag protrusions 29, to determine a crimp, while the opposite arm cooperates on its limb with the middle electromagnetic steering 4. This fork 9 is provided, also, substantially in its central part, of a drag cam 13 intended to operate the maneuvering finger 8 to determine a opening (figures 4, 7 and 8).

The connecting rod or maneuver hook 7 is mounted with the possibility of tilting, by one of its extremities, on the articulation bearing 12 of the steering hand 5 by middle of an axis 14, the opposite extremity being constituted by two elements each of which is provided with a peak of internal retention 15, determining a central emptying of the connecting rod and allowing the insertion of the corresponding limb of the fork 9, one of whose elements is provided with a outer guide bumper 16 arranged to cooperate with a guide 17 provided in box 6 of the device, which extends at least partially around the central part of the hand 5 (Figures 1 to 3 and 8). In this way, when a crimping or reassembling movement, the tip of the fork 9 can snag on retaining peaks 15 and make a traction on the connecting rod or hook 7 in the direction corresponding to determine the tilting of the hand 5.

On the other hand, the connecting rod or maneuver hook 7 is provided, at its mounting end on the bearing 12 of the hand 5, of a cam 7 'intended to cooperate with the maneuvering finger 8 during arming or reassembly operations. A 7 'cam of this type allows, by means of its support against the finger 8, determine the partial tilting of the latter around its axle on the bearing 11 to prevent its engagement with the fork 9, on the drive cam 13, during an operation of armed or reengatillado.

Maneuvering finger 8 is guided by a tip on the corresponding bearing 11 of the hand 5 by middle of a link axis and presents at its opposite end, by one part, a support zone 18 intended to cooperate with the cam of drag 13 of the fork 9 drag of the hand 5 and, by another part, a guide element 19 that takes the form of a rib intended to cooperate with a guide 20 provided in the box 6 of the device (figures 1, 3, 4 and 6). This maneuvering finger 8, as well as the connecting rod or maneuver hook 7, it is driven by another part, by a double acting recovery spring, not represented, consisting of two spiral springs joined between yes and acting for its free limb, respectively, on the connecting rod or maneuver hook 7 and over maneuvering finger 8 to push them clockwise towards the central part of assembly of the hand 5, tending to retrace the hook 7 in direction towards guide 17 and to apply finger 8 against cam 7 ' of the hook 7. In this way, the connecting rod or maneuvering hook 7. and the  maneuvering finger 8 are automatically separated, respectively, of the range of action of the drag fork 9 and of the electromagnetic means 4 of government, so that these two elements remain firmly dedicated to their sole function, avoiding  any risk of snagging the first during the phase of opening, while the second is kept hooked with the drag cam 13 of the fork 9 during said phase of opening, the spring opposing the force of inertia during the arming or opening phase to avoid, in cooperation with the guide 20, that the finger collides with the electromagnetic medium 4. On the other hand, the guide 20 guarantees that the finger 8 does not enter collision with the medium 4.

The electromagnetic medium 4 is constituted by an electromagnet fixed through its housing in box 6 and whose mobile core 4 'is provided with a means 4' 'intended for cooperate with the corresponding fork end of drag 9. Preferably, the medium 4 '' of the core 4 'is presented  in the form of a circumferential throat arranged to cooperate with the 9 '' lugs provided on the corresponding arm of the drag fork 9.

On the other hand, the fork part 9 that supports the 9 '' lugs delimits an internal wall between its branches of toric surface. In this way, the fork 9, through its support against the 4 'core, when it adopts its position Extreme outstanding, ensures the effect of guidance on the referred core 4 '.

The forecast of the 9 '' studs allows a axial distribution of the forces transmitted by the core 4 ' of the electromagnet, so that, in combination with the support represented by the fork 9, the risk of bowing

Preferably, the 9 '' studs will adopt the diamond shape, so they will have a degree of resistance increased mechanics.

The clutch device 3 is presented under the shape of a guided cursor on the lever of the hand 5 which protrudes outside box 6 and cooperates identically with the hand of the modular device that is to govern 2 (figure 2). This cursor can move to the right or to left with respect to box 6 and with respect to the government hand 5, depending on the position taken by the modular equipment that is about governing 2.

According to a characteristic of the invention, the constituent cursor of the clutch device 3 is it is also provided, on the one hand, with a transverse drain intermediate 3 'and, on the other hand, on either side of this emptying 3 'and next to each other, of 3' 'stops arranged to cooperate with 6 'extreme nails. The 3 'housing is intended to allow the placement of a locking means in the intermediate position, such as a padlock or analog element, while the 3 '' stops have been planned to limit the possibilities of displacement of the cursor, avoiding disassembly, so that it results safety pin.

On the other hand, the constitutive cursor of the clutch device 3 will be advantageously provided, in its internal face cooperating with the external surface of the lever of the hand 5, of at least one hard point, preferably several of these points, which rely heavily against the corresponding lever surface. These hard points allow the device 3 to be locked in a certain position of drag of the equipment that in each case is to govern.

In the central position of device 3 with with respect to the hand of government 5, the device that constitutes object of the invention is decoupled from the apparatus in question to govern 2 and can be locked in this position by placement of a padlock that cooperates with the 3 'emptying and with a corresponding drilling provided on the lever of the hand 5.

According to another feature of the invention, the constituent cursor of the clutch system 3 is  provided, in addition, in each of its extremities with an index 3 '' 'ready to cooperate with a corresponding 6' 'recess of the 6 'fingernails in order to lock in rotation the hand of Government 5 in an intermediate position.

The device that is the subject of the invention is maintained in mechanical coupling with the device 2 to govern by at least one, and preferably three, clips of coupling 21 cooperating, through pins 22, with about corresponding accommodations. provided respectively on the less one of the faces of the devices that are to be coupled. This coupling clip 21 may preferably be presented. in the form of a small bar capable of deforming to Pressure. Thus, this bar may have a slightly domed and two end pins 22 arranged to cooperate can corresponding housings, allowing the application to press the pinching of the pins while another pressure exerted, on the central part of the bar will allow a slight translation to the right or to the left in views to the removal of one of the pins, and then the disassembly of the clip set.

Okay, with another feature of the invention, the hand of government 5, in the part that involves the bearings 11 and 12, it is provided with a tongue 23 (figures 1 and 3 to 6) positioning, intended to cooperate with some position detectors (not shown), these being arranged detectors in alignment with said tab 23 respectively in the armed and opening positions.

In this way, said tongue 23 allows know at any time the exact position adopted by the hand 5, both in their extreme positions, in which they are activated the corresponding detectors, as in the position intermediate, in which no detector is activated.

The indicated intermediate position corresponds, already either to a locked position, or to a position where contacts of the governed device 2 are connected. This way the user can detect instantly, either a intervention on the protected circuit, either an anomaly that affect a protective device attached to the device government.

The operation of the reset device automatic for modular protection equipment that is about govern, according to the invention, will be described below referring to figures 7 and 8 of the attached drawings.

To move the hand of a device governed 2 from its service position to a position of opening, the core 4 'of the electromagnetic medium 4, which, in the resting position, protrudes from the armor of said means 4, under the combined effect of gravity and momentum of a spring (not shown), is attracted to said armor (figure 4) and determine the tilt of the fork 9 (figures 7a and 7b) by middle of the nipples 9 '' that cooperate with the throat 4 ''.

In the course of fork rotation 9 around its axis, during core 4 'retraction, the cam drag 13 comes into contact with the support part 18 of the finger of maneuver 8 and exerts on the latter a pressure transmitting a tilting movement to the government hand 5 (figure 7c). During the entire approach movement, the finger of maneuver 8 is applied against the fork arm 9 opposite to the arm that cooperates with the 4 'core of the electromagnet to through its spiral recovery spring.

When, in the course of its movement of tilt, fork 9 reaches the maximum end point 8 finger displacement and, consequently, onset of the rotation of the hand 5, the latter exceeds its point of stability, which corresponds to that of the government hand of the governed equipment, and is dragged by the device hand governed, being forced to swing towards its opening position (figure 7d). Being the government of the electromagnet constituting the electromagnetic medium 4 a government by impulse, the core 4 ' quickly recovers its initial position under the effect of gravity and momentum of a spring not shown. In this movement, the fork 9, with its arm opposite the core 4 'of the electromagnet, passes between the elements provided with peaks of internal retention 15 and the central emptying of the connecting rod or hook 7, then outlining its drag protrusions 29 the peaks of interior retention 15, passing over these. last and crossing the central emptying that corresponds to the set with its support arm (figures 7e and 7h).

When this recovery movement occurs towards the initial position of the core 4 'and of the fork 9, this last causes a slight tilt of the hook or connecting rod 7 around its bearing 12 on the hand 5, without acting on this on the position adopted by the latter, determining the recovery spring of the hook or connecting rod 7 that the latter is apply against said hand 5, when the end of career (figures 7g and 7h).

The reengatillado or armed, that is, the step from an opening position of the hand 5 towards a position of closing, is also carried out by means of a drive of 4 'core recoil towards the electromagnet armor constituting the electromagnetic means 4 of government (figures 4 and 8).

In this case, the fork 9 is engaged in through its drag protrusions 29 at the retention peaks interior 15 of the hook or connecting rod 7 (figure 8a), so that this last is dragged by the fork 9 and determines a corresponding rotation of the hand 5 in the opposite direction to of the fork 9 (figures 8b to 8e). During this movement of rotation of the fork 9 and the hand 5, the finger 8 has tendency to approach cam 13 of fork 3 and enter contact with it. To avoid this contact, it would prevent device operation in the direction of arming, cam 7 ' of the hook or rod 7 rests against the corresponding edge of the finger 8 and partially separates it from the hand 5. In it movement, the limb of the support part 18 is displaced out of contact with cam 13 (figure 8d) to develop outwardly an impulse on the latter.

When the fork 9, in the course of its tilting movement, reaches the point of stability of the associated device hand, hand 5 continues its Race until you are in position.

Upon reaching the end of the race, the 4 'core it automatically recovers its initial position, as it has been explained above and as represented in the Figures 8e to 8g and 7a.

In the crimping and opening positions, the hand 5 can be perfectly operated independently of the electromagnetic means of government 4, so that the operation of the associated equipment 1 to govern is not in absolute disturbed, the fork being disengaged in this case 9.

The position detectors (not shown), which are intended to cooperate with the positioning tab 23 of the hand of government 5, allow, not only to detect the arming and opening positions, but also, by default, a intermediate position of hand 5, not being detected by no captor the position adopted by the tongue 23, or a cut of current, when the two detectors indicate the same signal of presence, which must necessarily be considered wrong.

According to another feature of the invention, in order to avoid assembly failures, the electromagnet constituting the electromagnetic means 4 will be advantageously provided with a multi-level power supply 24 (Figure 9). A feed of this type allows the electromagnet to be subjected successively, which is a very fast, weak, medium and high power actuator, so that its acceleration, which is usually important, can be
modulated

This staggered feeding at various levels 24 it is established by levels of government 27, 28 of the same type, provided with two switching elements 29, 30 and a series resistance 25, 26 for the current limitation of electromagnet supply, the number of feeding levels by the formula 2 Nb -1, in which Nb represents the number of levels. A high number of levels of government allows a finer management of electromagnet.

The value of resistors 25, 26 is regressive from a first level 27 to the other 28. In this way, when the electromagnet drive occurs, these two levels 27, 28 represented in figure 9 of the attached drawings are successively governed in binary form, in the manner next :

-

First level 27 closed and second level 28 open = limited current by resistance 25

-

First level 27 open and second level 28 closed = current limited by resistance 26

-

First level 27 closed and second level 28 closed = current limited by \ frac {25x26} {25 + 26}

As a consequence that resistance 25 is more strong than resistance 26, the power developed by the electromagnet corresponds to a minimum when only closed the first level 27 and to a maximum when they are closed the two levels 27, 28.

The first level 27 may be used, for example, to ensure compensation of mechanical clearances, in order to suppress shocks, while the following levels 28 will provide acceleration according to the product needs Indeed, a difficult product to assemble is  will be in the top position at the end of the race, being consequently subjected to acceleration, when It will provide the second impulse.

The switching elements 29, 30 may be of type triac, thyristor, IGBT, transistor or relay depending on the voltage and electromagnet characteristics in each case used.

Thanks to the invention, it is possible to perform a rearming device that allows to govern a range of very broad products from the point of view of the currents Nominal and yield ratings. This device can perfectly juxtapose to a modular product designed to protect electrical installations of classic type in the field domestic as well as in the industrial field, without requiring any coupling or any special type tool.

In addition, the device allows you to perform closing maneuvers of the governed device without arming failures or untimely openings, while ensuring a career of complete arm assembly.

As understood, the invention is not limited. to the embodiment described and represented in the drawings annexes It is possible to introduce modifications, especially from the point of view of the constitution of the different elements or by replacing technical equivalents, without that this means departing from the scope of the invention.

Claims (23)

1. Automatic rearmament and remote control device for modular protection equipment to be governed, presenting a general form that corresponds to that of a modular device (2) to which it must be coupled and essentially constituted by a mechanical means (1 ') of arming and opening, arranged to be coupled to the modular device that is to be governed (2) by means of a clutch device (3) and by an electromagnetic means (4) for governing the mechanical means (1 ') of assembly and opening, characterized in that the mechanical means (1 ') for arming and opening is a set consisting of a steering handle (5) swiveling mounted on a box (6) of the device, whose lever (5') protrudes from this box (6), by a connecting rod or maneuver hook (7) articulated to the hand (5), by a maneuvering finger (8) also articulated on the hand (5) and by a fork (9) dragging the hand (5). 2. Device according to claim 1, characterized in that the steering hand (5) has a central part through which it is swiveled on the case (6) of the device by means of pivots (10) of the latter and it is provided, on the opposite side to the lever (5 ') with respect to the axis (10) of two bearings (11 and 12), displaced radially and intended, respectively, for the articulation of the operating finger (8) and the connecting rod or maneuver hook (7). Device according to claim 1, characterized in that the fork (9) for driving the handle (5) is in the form of an independent lever equipped with two arms substantially aligned on either side of an axis (9 ') a through which its tilting assembly is carried out on the box (6) of the device, cooperating one of said arms by its end with the connecting rod or maneuver hook (7) through drag projections (29), to determine a crimp , while the opposite arm cooperates through its limb with the electromagnetic means of government (4). Device according to claim 3, characterized in that the fork (9) is also provided, in its central part, with a drive cam (13) intended to drive the operating finger (8) to carry out an opening Device according to claim 2, characterized in that the connecting rod or maneuvering hook (7) is mounted with the possibility of tilting, through one of its extremities, on the articulation bearing (12) of the steering hand ( 5) by means of an axis (14), the limb being constituted. opposite by two elements each of which is provided with an inner retention spout (15), between which a central emptying of the connecting rod is defined that allows the insertion of the corresponding tip of the fork (9), being provided one of the elements of an external guide pin (16) intended to cooperate with a guide (17) provided in the case (6) of the device, which extends at least partially around the central part of the hand (5). Device according to claim 5, characterized in that the connecting rod or maneuvering hook (7) is provided, at its end through which the mounting on the bearing (12) of the hand (5), of a cam (7 ') intended to cooperate with the maneuvering finger (8) in the course of an arming or reassembly operation. Device according to any one of claims 2 to 4, characterized in that the maneuvering finger (8) is guided by a limb in the corresponding bearing (11) of the hand (5) by means of a coupling shaft and it has on its opposite end, on the one hand, a support area (18) intended to cooperate with the drag cam (13) of the fork (9) of the hand drag (5) and, on the other hand, an element of guide (19) in the form of a rib intended to cooperate with a guide (20) provided in the box (6) of the arrangement
tivo. Device according to any one of claims 2 to 5 and 8, characterized in that the maneuvering finger (8), as well as the connecting rod or maneuvering hook (7), is further driven by a double-acting recovery spring , constituted by two spiral spring elements joined together, acting through their free extremities, respectively, on the connecting rod or maneuver hook (7) and on the maneuvering finger (8) to propel them clockwise in the direction towards the central mounting part, tending to retrace the hook (7) towards the guide (17) and apply the finger (8) against the cam (7 ') of the hook (7). Device according to claim 1, characterized in that the electromagnetic means (4) is constituted by an electromagnet fixed through its housing to the housing (6) and whose mobile core (4 ') is provided with a means ( 4 '') intended to cooperate with the corresponding tip of the drag fork (9). Device according to claim 9, characterized in that the means (4 '') of the core (4 ') are presented in the form of a circumferential throat arranged to cooperate with lugs (9'') provided in the corresponding arm of the drag fork (9). Device according to claim 3, characterized in that the part of the fork (9) having the lugs (9 '') delimits between its branches an internal wall of toric surface. 12. Device according to claim 10, characterized in that the studs (9 '') have the shape of diamonds. 13. Device according to claim 1, characterized in that the clutch device (3) is in the form of a cursor guided on the lever of the hand (5) protruding from the case (6) and arranged to cooperate so identical with the handle of the modular device that is to govern (2). 14. Device according to claim 13, characterized in that the constituent cursor of the clutch device (3) is further provided, on the one hand, with an intermediate transverse emptying (3 ') and, on the other hand, on both sides. side of this drain (3 ') and close to each other, of stops (3'') intended to cooperate with some extreme projections (6'). 15. Device according to claim 13, characterized in that the constitutive cursor of the clutch device (3) is provided, on its inner face cooperating with the outer face of the lever of the steering hand (5), of at least a hard point, preferably several of these points, which press against the corresponding face of the lever. 16. Device according to claim 13, characterized in that the cursor constituting the clutch means (3) is also provided, on each of its extremities, with an index (3 '') intended to cooperate with a corresponding housing ( 6 '') of the projections, (6 ') in order to determine the rotation lock of the steering hand (5) in an intermediate position. 17. Device, according to claim 1, characterized in that it is maintained in mechanical coupling with the apparatus that is to be governed (2) by at least one, and preferably three, coupling clips (21) which, through pins (22), cooperate with corresponding housings provided respectively on at least one of the faces of the devices that must be coupled. 18. Device according to claim 17, characterized in that the coupling clip (21) is in the form of a small bar capable of elastically deforming under pressure. 19. Device according to claim 1, characterized in that the steering hand (5), in the part that comprises the bearings (11 and 12), is provided with a positioning tab (23) intended to cooperate with some detectors of position, these detectors being arranged in alignment with the said tab (23) respectively in the positions corresponding to the assembly and the opening. 20. Device according to claim 1, characterized in that the electromagnetic constituent of the electromagnetic means (4) is provided with a stepped supply. 21. Device according to claim 20, characterized in that the staggered feeding at several levels (24) is constituted by levels of government (27, 28) of the same type each provided with a switching element (29, 30) and of a series resistor (25, 26) for limiting the supply current of the electromagnet, the number of power levels being determined by the formula 2 Nb -1, in which Nb represents the number of levels . 22. Device according to claim 21, characterized in that the value of the resistors (25, 26) is degressive from a first level (27) to the remaining ones (28). 23. Device according to claim 21, characterized in that the switching elements (29, 30) are of the triac, thyristor, IGBT, transistor or relay type depending on the characteristics of the voltage and the electromagnet used.