EP2750158B1 - Thermal, magnetic subassembly for a selective circuit-breaker - Google Patents

Description

The present invention relates to a magnetic and thermal subassembly for use in a protection circuit breaker of lines and / or electrical apparatus against over-currents and short-circuits, which is selective with respect to protection against overcurrents and short circuits possibly connected upstream and / or downstream.

This type of circuit breaker is particularly used as a group circuit breaker installed upstream of different circuits each protected by a line circuit breaker in distribution facilities.

The selectivity of circuit breakers connected in series in a distribution system is necessary or at least desirable, so that in the event of a short circuit or overcurrent, the smallest possible part of the distribution system, the one in which the short circuit is located. -circuit or the cause of the overcurrent, be turned off.

This type of circuit breaker comprises a main current circuit in which are arranged a magnetic actuator responding to a short circuit and acting directly on the opening of contacts placed in an arc extinguishing chamber, and a thermal actuator responding to a overcurrent and acting on an unlocking lock that can in turn open the contacts.

This main circuit can be temporarily supplemented by an auxiliary current circuit comprising another thermal actuator acting also on the unlock lock which can in turn open the contacts, a current limiting resistor being placed in said auxiliary circuit to ensure the time delay.

Normal flow of current flows through the main circuit when operation is normal. It passes simultaneously through the auxiliary circuit but is very weak because of the resistance. If a short circuit occurs, a magnetic trip occurs which cuts the main current circuit temporarily by opening a main movable contact, while the auxiliary circuit passes a current considerably reduced by the resistance.

This makes it possible to continue supplying the downstream devices safely and this leaves time for the breaker of the line in which the problem occurred to cut it without all the lines being impacted. If the fault persists, the current, although limited by the resistance, will provoke, after a certain time delay which depends in particular on the resistor, a thermal tripping of the auxiliary circuit, and thus unlock the lock of the circuit-breaker and cut the current in all of the circuit. installation. The reset of the circuit breaker must then be done manually after identification and repair of the fault, or even isolation of the fault line. In the case where the fault is only of very short duration, for example when a downstream circuit breaker trips in the meantime, the magnetic device of the selective circuit-breaker returns to its rest position and the main circuit is restored without it. triggered its unlock lock.

Such a selective circuit breaker is known in particular by DE 102008021768 and allows, when a fault is detected, for example in the case of a short circuit, a temporary opening of the main circuit contacts by action of the magnetic device and switching on the auxiliary circuit. More specifically, the magnetic device is conventionally constituted of a fixed core assembly, a core movable in translation in a magnetic yoke actuated magnetically under the effect of a solenoid traveled by the short-circuit current, said movable core driving a striker in translation, from striking a rocker which pivots by driving a movable contact carrier, thus causing the opening of said movable contact relative to the fixed contact.

This circuit breaker, however, has many disadvantages, particularly in terms of insulation. Indeed, the internal arrangement of the magnetic and thermal actuators creates in practice two groups of components having two different potentials, the components being connected to each other electrically within each group to form a current path.

On the one hand, the first group consisting of magnetic yoke, rocker, spring, moving contact and braid forms a current path at a first potential.

On the other hand, the second group, composed of the fixed contact, the solenoid and a terminal, forms a current path at a second potential.

This potential difference between these two current paths is problematic because it requires in principle electrical isolation between the components belonging to different groups. However, the components being mixed within the circuit breaker and located close to each other, with current paths that cross de facto repeatedly, it is very difficult to ensure such insulation within the circuit breaker.

The solution adopted in this document DE 102008021768 consists of integrating many pieces of plastic insulation between the components of the two groups. These parts are very complex and require a tedious development to present forms for enclosing the components to be protected while being easily integrated within the circuit breaker, within which the available volume is limited, and compactness therefore required.

These complex plastic parts also induce manufacturing and assembly costs which are not negligible in an approach overall economy of the circuit breaker, and they also do not allow to eliminate certain risks of breakdown. The document " DE 957 321 C "discloses an electrical line protection apparatus according to the preamble of claim 1.

The present invention proposes to remedy the various disadvantages mentioned by proposing a compact technical solution, simple to manufacture, and guaranteeing the absence of risk of breakdown.

To do this, the idea behind the proposed solution is to design a new arrangement within the circuit breaker, according to which all the components belonging to the thermal and magnetic actuators of the main circuit form a single current path and are therefore the same. potential.

• d'un actionneur magnétique apte à séparer au moins un contact mobile d'un contact fixe lors de l'apparition d'un court-circuit dans la ligne à protéger, et comportant une culasse magnétique fixe ;
• d'un déclencheur thermique composé d'un bilame apte à déverrouiller une serrure mécanique de l'appareil lors de l'apparition d'une surcharge dans la ligne à protéger.

The invention thus relates to an electric line protection apparatus, of the selective circuit breaker type, which comprises a subset consisting of:

• a magnetic actuator adapted to separate at least one movable contact from a fixed contact when a short circuit occurs in the line to be protected, and comprising a fixed magnetic yoke;
• a thermal trip device composed of a bimetallic device able to unlock a mechanical lock of the device when an overload occurs in the line to be protected.

• un porte-contact fixé de manière pivotante à la culasse et portant le contact mobile ;
• une bobine entourant une partie de la culasse et connectée en série avec le bilame ;
• une palette mobile en rotation par rapport à la culasse, apte à venir au contact d'au moins une surface polaire de la culasse lors d'un court-circuit, la culasse étant dotée de moyens de positionnement et de guidage de la palette mobile ;
• des moyens de rappel de la palette et du porte-contact établissant un calibrage du seuil de déclenchement de l'actionneur magnétique ;
• des moyens d'entraînement entre la palette et le porte-contact, établissant une correspondance directe entre au moins une fraction du mouvement de rotation de la palette et au moins une fraction du mouvement de rotation du contact mobile.

The magnetic actuator according to the invention also comprises:

• a contact carrier pivotally attached to the cylinder head and carrying the movable contact;
• a coil surrounding a portion of the yoke and connected in series with the bimetallic strip;
• a pallet movable in rotation with respect to the yoke, able to come into contact with at least one polar surface of the yoke during a short-circuit, the yoke being provided with means for positioning and guiding the movable pallet;
• means for returning the pallet and the contact carrier establishing a calibration of the trigger threshold of the magnetic actuator;
• drive means between the pallet and the contact carrier, establishing a direct correspondence between at least a fraction the rotational movement of the pallet and at least a fraction of the rotational movement of the movable contact.

For this specific arrangement, in which all the components are electrically connected to each other and are at the same potential, there are no longer any constraints related to electrical insulation. The insulating plastic parts used in the solutions of the prior art are then no longer necessary.

This magnetic and thermal subset is further considerably simplified compared to the prior art, since it has about half of the components. This is particularly true, compared to the prior art cited, since the movable core, the striker and the rocker have been replaced by a single piece, the movable pallet.

It also has the advantage of being transportable in the state, and to integrate in one block in all the selective circuit breakers of the range.

Particular attention has been paid to the design of the components which is relatively uncluttered, so that they are simple to manufacture. The assembly of the magnetic subassembly of the invention is ultimately easy, and moreover automatable, these possibilities helping to make it economically very attractive.

According to one possible configuration, said return means may consist of a spring, of the pull-up coil spring type, connecting a first protuberance protruding from the end of the proximal pallet of its pivot axis to a second protruding protrusion of the contact carrier.

This spring thus makes it possible both to return the pallet to the rest position and to return the contact carrier to the closed position of the contacts. This spring also ensures the maintenance of the pallet in position relative to the cylinder head, and the contact pressure between the fixed and movable contacts.

Furthermore, said drive means may consist of an arm of the pallet extending the proximal end of its pivot axis and bent towards the contact carrier, adapted to come into contact and to rest on a tab protruding from the contact carrier.

In normal operation, when a nominal current flows through the coil, the magnetic field it induces ducted in the magnetic yoke produces a magnetic attraction force of the pallet to the cylinder head which is not sufficient to counterbalance the spring force holding the pallet and attracting it in contact with the polar surface. The pallet is thus in a state of rest and positioned slightly recessed with respect to the polar surface of the magnetic yoke, while the moving contact is in contact with the fixed contact. In these respective positions of the pallet and the contact carrier, a game is present between the arm of the pallet and the paw of the contact carrier.

When a short circuit current passes through the coil, it induces a magnetic field in the magnetic yoke which is obviously sufficient to attract the pallet to the cylinder head against the force of the spring. The attraction force of the pallet then being greater than the force of the spring, the pallet begins to pivot in the direction of the polar surface of the cylinder head. His arm comes into contact with the bracket of the contact-carrier, the fixed and mobile contacts being still closed. The paddle continues to pivot until it comes to rest against the polar surface of the breech. During this pivoting movement, the arm of the pallet, via its contact with the bracket of the contact carrier, causes rotation of the contact carrier clockwise, and therefore the static opening of the contacts. The moving contact is moved away from the fixed contact and brought to a static opening distance with respect to the fixed contact. The moving contact then continues to rotate clockwise under the effect of its inertia to a dynamic opening distance relative to the fixed contact, his tab therefore no longer in contact with the arm of the pallet. Finally, because of the tensile force of the spring exerted on the contact carrier, the latter rotates counterclockwise until its leg comes into contact, and therefore in abutment, against the arm of the pallet, the contact mobile being again positioned at the static opening distance with respect to the fixed contact. The magnetic actuator remains in this position triggered until the short circuit or unlocking of the device is released by the mechanical unlocking lock.

In this case, the force of attraction of the pallet towards the yoke, induced by the coil, is again lower than the force of the spring, and the pallet returns to its rest position, thus allowing the contact carrier to pivot in the counterclockwise direction by action of the tensile force of the spring, until the movable contact abuts against the fixed contact. The magnetic actuator is then in the initial position again.

The choice of the spring is therefore essential to ensure the tripping of the circuit breaker in a specific current range. Indeed, the resistive force of the spring opposite the closing of the pallet is critical to define the trigger threshold.

According to a possible configuration, the contact carrier comprises a fixing surface of the moving contact and a braid connecting it to the bimetal, being extended by said second protrusion and by two lateral flanks coming to cover the part of the yoke supporting the axis of pivoting of the contact carrier, said flanks having two orifices inside which is introduced the axis of pivoting of the contact carrier, one of the flanks having said tab for interfacing with the pallet and the other side having a form for interfacing with the lock of the device.

A major advantage of the present invention also lies in the fact that the cylinder head is provided with a phase shift ring, crimped on one end of the cylinder head.

This phase shift ring, also called Frager turn, plays a key role in the movements of the pallet when the coil is traversed by an alternating current. During a short-circuit, without a phase shift ring, the magnetic attraction force of the pallet towards the cylinder head, produced by the coil supplied with alternating current, will be lower than the restoring force of the spring in the vicinity of each passage to 0 between two half-periods, causing brief openings of the pallet, and therefore unwanted vibrations unacceptable for the structure of the subassembly, and premature wear of the components. To reduce these fluctuations of the force of attraction, a phase shift ring is placed near the polar surface of the yoke, and produces a specific magnetic force out of phase with the original magnetic attraction force and counteracting the force of the force. recall of the spring at each passage to 0 between two half-periods, thereby removing any short opening of the pallet. Therefore, during a short circuit, the pallet will be held continuously against the polar surface of the cylinder head.

According to a possible configuration, the yoke is U-shaped, the end of the first arm has an upper edge corresponding to the axis of pivoting of the pallet, the coil being wound around an insulating core plugged into the second arm of the cylinder head via a central orifice and being locked in translation by the phase shift ring partially surrounding the end of the second arm. The phase shift ring therefore also acts as a stop for the core.

• prolongeant l'extrémité du premier bras de la culasse ;
• disposées de part et d'autre dudit chant de la culasse servant au pivotement de la palette ;
• et venant s'insérer dans deux évidements prévus à cet effet dans la palette.

So that the pallet can pivot correctly with respect to the cylinder head, without decentering in particular following the different forces applied to the pallet both by the force of the spring and by the magnetic attraction force, means for positioning and guiding the movable pallet with respect to the cylinder head are provided, and consist of two legs:

• extending the end of the first arm of the breech;
• disposed on either side of said edge of the breech for pivoting the pallet;
• and being inserted into two recesses provided for this purpose in the pallet.

Specifically, the section of the second arm is of rectangular shape with stepped corners in the vicinity of the circular periphery of the core of the coil. The end of the second arm of the cylinder head has a transverse groove in which is inserted the phase shift ring. The latter surrounds a lower cut made in the second arm, whose upper end portion retains the original shape. This shape specific with bearings allows to maximize the section of the polar surface relative to the nucleus surrounding it.

Preferably, the yoke is made by an assembly of sheets of the same thickness but different profiles so as to vary the outer shape of the yoke.

• raccorder électriquement un bilame à un porte-contact mobile via une tresse ;
• raccorder le bilame à une tôle d'arc permettant d'accompagner le déplacement de l'arc électrique à l'ouverture des contacts ;
• fixer le porte-contact à une culasse magnétique de manière pivotante au moyen d'un axe de pivotement ;
• enficher un noyau isolant dans un bras de la culasse magnétique ;
• entourer une partie de l'extrémité dudit bras de la culasse magnétique par une bague de déphasage ;
• enrouler autour dudit noyau une bobine reliée électriquement d'une part à la tôle d'arc, et d'autre part à une borne de raccordement de l'appareil ;
• centrer et positionner, sur des plans d'allure parallèle, une palette par rapport à un autre bras de la culasse, les deux bras étant eux-mêmes parallèles ;
• accrocher un ressort entre une extrémité de la palette et le porte-contact ;
• faire pivoter la palette par rapport à la culasse magnétique jusqu'à ce que son extrémité libre vienne au voisinage du bras muni de la bague de déphasage.

The invention also relates to a method of assembling a magnetic and thermal subassembly intended to be integrated into a line protection apparatus as described above, and comprising the following steps:

• electrically connecting a bimetallic strip to a movable contact carrier via a braid;
• connect the bimetallic strip to an arc sheet to accompany the movement of the electric arc at the opening of the contacts;
• fastening the contact carrier to a magnetic yoke pivotally by means of a pivot pin;
• plug an insulating core into an arm of the magnetic yoke;
• surrounding a portion of the end of said arm of the magnetic yoke by a phase shift ring;
• winding around said core a coil electrically connected on the one hand to the arc sheet, and on the other hand to a connection terminal of the apparatus;
• centering and positioning, on parallel planes, a pallet with respect to another arm of the bolt, the two arms being themselves parallel;
• hooking a spring between one end of the pallet and the contact carrier;
• rotate the pallet with respect to the magnetic yoke until its free end comes in the vicinity of the arm provided with the phase shift ring.

Such a subassembly can be manufactured in a fully automated manner, and can be easily integrated into all the selective circuit breakers of the range, since it is transportable as such.

• la figure 1 est une vue tridimensionnelle du sous-ensemble magnétique et thermique selon l'invention ;
• les figures 2 à 6 montrent les différentes étapes lors d'un déclenchement de l'actionneur magnétique ;
• la figure 7 représente la culasse de l'actionneur magnétique ;
• la figure 8 illustre la palette de l'actionneur magnétique ;
• la figure 9 montre le porte-contact avec le contact mobile ;
• les figures 10 et 11 représentent le noyau de l'actionneur magnétique en vue de profil et en vue de face respectivement ;
• la figure 12 illustre la bague de déphasage de l'actionneur magnétique.

The invention will now be described in more detail, with reference to the appended figures, for which:

• the figure 1 is a three-dimensional view of the magnetic and thermal subassembly according to the invention;
• the Figures 2 to 6 show the different steps when triggering the magnetic actuator;
• the figure 7 represents the yoke of the magnetic actuator;
• the figure 8 illustrates the palette of the magnetic actuator;
• the figure 9 shows the contact carrier with the moving contact;
• the Figures 10 and 11 represent the core of the magnetic actuator in profile and in front view respectively;
• the figure 12 illustrates the phase shift ring of the magnetic actuator.

The subassembly according to the invention, illustrated in figure 1 , comprises a magnetic actuator and a thermal actuator, all of whose components are electrically connected to each other so as to be at the same potential. This subassembly is intended to be integrated in a line protection device of the type selective circuit breaker.

The thermal actuator consists mainly of a bimetallic strip (1) whose fixed end (2) is connected to an arc plate (3) and the free end (4) is able to undergo a deflection when a current overload on the line so as to unlock a lock (not shown) of the apparatus.

The magnetic actuator consists mainly of a U-shaped magnetic yoke (5) whose first arm (8) supports a movable pallet (7) and a movable contact carrier (6) to which the movable contact is attached ( 14), and the second arm (9) (see figure 7 ) supports an insulating core (10) around which a coil (11) is wound. The breech (5), the pallet (7), the contact carrier (6) and the movable contact (14) are thus all electrically connected and are at the same potential.

The coil (11) is connected, at a first end (12) of its wire, to the arc sheet (3), thereby making a first electrical connection with the thermal actuator. The second end (13) of the coil wire (11) is electrically connected to a terminal (not shown) of the apparatus.

A second electrical connection with the thermal actuator is provided by means of a braid (39) connecting the bimetal (1) to the movable contact (14). Therefore, the thermal actuator and the magnetic actuator are also at the same potential, and make up a subset that does not require any piece of insulation between the various parts of the component.

• une surface plane (17) apte à venir en contact avec les surfaces polaires (18, 19) de la culasse (5), illustrée en figure 7 ;
• deux évidements (20) pratiqués dans la surface plane (17) et dans lesquels sont insérées deux pattes (21) prolongeant l'extrémité du premier bras (8) de la culasse (5) et disposées de part et d'autre du chant (16) supérieur de pivotement de la palette (7), permettant à cette dernière d'être correctement centrée et positionnée par rapport à la culasse (5) ;
• une protubérance (15) saillant du milieu de l'extrémité de la palette (7) proximale des évidements (20), recourbée à 90° en direction opposée à la culasse (5) ;
• un bras (22) prolongeant une portion latérale de l'extrémité de la palette (7) proximale des évidements et recourbée à 90° en direction de la culasse (5).

The pallet (7) is rotatable about a pivot axis corresponding to an upper edge (16) of the end of the first arm (8) of the yoke (5). The pallet (7), represented in figure 8 , includes:

• a flat surface (17) adapted to come into contact with the polar surfaces (18, 19) of the yoke (5), illustrated in FIG. figure 7 ;
• two recesses (20) formed in the flat surface (17) and in which are inserted two tabs (21) extending the end of the first arm (8) of the yoke (5) and arranged on either side of the edge ( 16) upper pivoting the pallet (7), allowing the latter to be correctly centered and positioned relative to the yoke (5);
• a projection (15) protruding from the middle of the end of the pallet (7) proximal recesses (20), curved at 90 ° in the direction opposite to the cylinder head (5);
• an arm (22) extending a lateral portion of the end of the pallet (7) proximal to the recesses and bent at 90 ° towards the yoke (5).

• une surface plane (25) à laquelle est fixé le contact mobile (14), qui est entraîné contre ou à distance d'un contact fixe (38) de l'appareil ;
• une protubérance (31) saillant de la surface plane (25) ;
• deux flancs latéraux (26, 27) venant recouvrir la partie de la culasse (5) supportant l'axe de pivotement du porte-contact (6), et présentant deux orifices (28) coaxiaux à l'orifice (24) de la culasse (5) et supportant le tourillon (23) ;
• une patte (29) saillant de l'extrémité libre du premier flanc (26) et présentant une surface d'appui pour le bras (22) de la palette (7) ;
• un bras (30) prolongeant l'extrémité libre du second flanc (27) et coopérant avec la serrure de l'appareil.

The contact carrier (6), visible more precisely in figure 9 , is also rotatable about a pivot axis corresponding to a pin (23) inserted in a hole (24) provided for this purpose in the first arm (8) of the yoke (5), as illustrated in FIG. figure 7 . This contact carrier (6) comprises:

• a flat surface (25) to which is fixed the movable contact (14), which is driven against or at a distance from a fixed contact (38) of the apparatus;
• a projection (31) protruding from the flat surface (25);
• two lateral flanks (26, 27) covering the portion of the yoke (5) supporting the pivot axis of the contact carrier (6), and having two orifices (28) coaxial with the orifice (24) of the cylinder head (5) and supporting the trunnion (23);
• a tab (29) projecting from the free end of the first sidewall (26) and having a bearing surface for the arm (22) of the pallet (7);
• an arm (30) extending the free end of the second sidewall (27) and cooperating with the lock of the apparatus.

A pulling spring (33) connects the protuberance (15) of the pallet (7) to the protuberance (31) of the contact carrier (6).

The cylindrical insulating core (10) supporting the coil (11) and shown in Figures 10 and 11 , has a central orifice (32) allowing it to be plugged into the second arm (9) of the yoke (5). The outer contour of the second arm (9) matches the inner shape of the central hole (32) of the core (10). To maximize the polar surface (19) of the yoke (5), the thickness of the cylindrical wall of the core (10) must be as thin as possible, and the section of the second arm (9) as large as possible. The yoke (5) being constituted by an assembly of aligned plates, it is difficult to obtain a circular section. Therefore, the section of the second arm (9) is of rectangular shape with stepped corners. The shape of the inner wall of the central hole (32) of the core (10) is therefore also of rectangular shape with stepped corners, as illustrated in FIG. figure 11 .

The end of the second arm (9) of the yoke (5) has a groove (36) in which is inserted a phase shift ring (37). as represented in figure 12 . This ring (37) surrounds a lower cutout (35) formed in the second arm (9), whose upper end portion (34) retains the original shape, and is crimped on the yoke (5). It is wider than the central orifice (32), and therefore constitutes a stop limiting any translational movement of the core (10) along the second arm (9).

The operation of this subset at the occurrence of a short circuit will now be detailed, with reference to Figures 2 to 6 .

The figure 2 shows the magnetic actuator at rest, that is to say when a nominal current passes through the coil (11). In this case, the contacts (14, 38) are closed and the pallet (7) is slightly recessed relative to the polar surfaces (18, 19) and retained by the spring (33). Indeed, the magnetic attraction force exerted by the yoke (5) on the pallet (7) is in this case less than the restoring force of the spring (33). Due to this rest position of the pallet (7), its arm (22) is at a distance from the lug (29) of the contact carrier (6), and the only mechanical link between the pallet (7) and the carrier contact (6) is the spring (33). The latter exerts a restoring force on the contact carrier (6) which urges it counterclockwise. However, the movable contact (14) abuts against the fixed contact (38), thereby preventing the contact carrier (6) from rotating in this direction.

In figure 3 a short-circuit current passes through the coil (11) which then generates a large magnetic field in the cylinder head (5). The magnetic attraction force exerted by the yoke (5) on the pallet (7) is then greater than the restoring force of the spring (33), thus causing the pallet (7) to pivot in the direction of the polar surfaces ( 18, 19). During this pivoting movement, the arm (22) of the pallet (7) comes into contact with the bearing surface of the lug (29) of the contact carrier (6), the contacts being still closed.

In figure 4 , while the pallet (7) terminates its pivoting and abuts against the pole surfaces (18, 19), the arm (22) bears on the tab (29) and drives the contact carrier (6) in rotation clockwise, against the restoring force of the spring (33), thus bringing the contact mobile (14) at a static opening distance from the fixed contact (38). The circuit is then cut.

In figure 5 , the movable contact (14) continues its stroke under the effect of its inertia to a dynamic opening distance relative to the fixed contact (38). In this case, the contact carrier (6) follows its rotational movement clockwise and its lug (29) is moved away from the arm (22) of the pallet (7).

In figure 6 , the contact carrier (6), biased by the spring (33), pivots counterclockwise until its lug (29) abuts against the arm (22) of the pallet (7), the movable contact (14) then being brought back to a static opening distance with respect to the fixed contact (38). The magnetic actuator then remains in this position until the disappearance of the short circuit or until the unlocking of the device by the lock of the auxiliary circuit.

Claims (13)

1. Electrical device for line protection in the form of a selective circuit breaker, comprising a subassembly comprising:

   - a magnetic actuator capable of separating at least one moving contact (14) of a fixed contact (38) when a short circuit occurs in the line being protected, and comprising a fixed magnetic yoke (5);

   - a thermal release comprising a bimetal strip (1) capable of unlatching a mechanical lock of the device when an overload occurs in the line being protected;
   characterised in that the magnetic actuator also comprises:

   - a contact support (6) attached, so that it can pivot, to the yoke (5) and carrying the moving contact (14);

   - a coil (11) surrounding a part of the yoke (5) and connected in series to the bimetal strip (1);

   - a blade (7) able to move in rotation with respect to the yoke (5), capable of coming into contact with at least one polar surface (18, 19) of the yoke (5) when a short circuit occurs, the yoke (5) being provided with means to position and guide the moving blade (7);

   - means of returning the blade (7) and the contact support (6) providing the threshold level at which the magnetic actuator is triggered;

   - driving means between the blade (7) and the contact support (6), establishing a direct correspondence between at least one part of the rotational movement of the blade (7) and at least one part of the rotational movement of the moving contact (14).
2. Electrical device for line protection according to the preceding claim, characterised in that the said returning means consist of a spring (33) in the form of a helical tension spring, connecting a first protuberance (15) protruding from the end of the blade (7) near its pivotal axis (16) with a second protuberance (31) protruding from the contact support (6).
3. Electrical device for line protection according to one of the preceding claims, characterised in that the said driving means consist of an arm (22) of the blade (7), extending the end near its pivotal axis (16) and bent towards the contact support (6), capable of coming into contact and resting on a lug (29) extending from the contact support (6).
4. Electrical device for line protection according to the preceding claim, characterised in that the contact support (6) comprises a surface (25), to attach to the moving contact (14) and a flexible braid (39), connecting it to the bimetal strip (1), being extended by said second protuberance (31) and two lateral flanks (26, 27), positioned so as to cover the part of the yoke (5) carrying the pivotal shaft (23) of the contact support (6), said flanks (26, 27) having two openings (28) inside which the pivotal shaft (23) of the contact support (6) is inserted, one of the flanks (26, 27) having said lug (29) to interface with the blade (7) and the other flank (27) having a shape (30) to interface with the lock of the device.
5. Electrical device for line protection according to one of the preceding claims, characterised in that the yoke (5) is provided with a shading ring (37).
6. Electrical device for line protection according to the preceding claim, characterised in that said shading ring (37) is crimped on one end of the yoke (5).
7. Electrical device for line protection according to one of the claims 5 and 6, characterised in that the yoke (5) is U-shaped, the end of the first arm (8) having an upper edge corresponding to the pivotal axis (16) of the blade (7), the coil (11) being wound around an insulating core (10) plugged into the second arm (9) of the yoke (5) by means of a central opening (32) and being stopped in translation by the shading ring (37) partially surrounding the end of the second arm (9).
8. Electrical device for line protection according to the preceding claim, characterised in that said positioning and guiding means of the moving blade (7) consist of two lugs (21):

   - extending the end of the first arm (8) of the yoke (5);

   - arranged on both sides of said edge (16) of the yoke (5), providing the pivoting point for the blade (7);

   - and being inserted in two cut-out areas (20) provided for this purpose in the blade (7).
9. Electrical device for line protection according to one of the claims 7 and 8, characterised in that the section of the second arm (9) has a rectangular appearance with stepped corners located in the vicinity of the circular periphery of the core (10) of the coil (11).
10. Electrical device for line protection according to one of the claims 7 to 9, characterised in that the end of the second arm (9) of the yoke (5) has a transverse groove (36) in which the shading ring (37) is inserted.
11. Electrical device for line protection according to the preceding claim, characterised in that the shading ring (37) surrounds a lower cut-out (35) formed in the second arm (9), while the upper part of end (34) retains the initial shape.
12. Electrical device for line protection according to any one of the preceding claims, characterised in that the yoke (5) is constructed as an assembly of sheet metal plates of the same thickness but differing in profile in order to vary the external shape of the yoke (5).
13. Method of assembling a magnetic and thermal subassembly, intended to be incorporated in an electrical device for line protection as described in claims 1 to 12, characterised in that it comprises the following steps:

    - electrical connection of a bimetal strip (1) to a moving contact support (6) by means of a braid (39);

    - connection of the bimetal strip (1) to an arc metal sheet (3);

    - attachment of the contact support (6) to a magnetic yoke (5) such that said contact can pivot by means of a pivoting shaft (23);

    - plugging an insulating core (10) into one arm (9) of the magnetic yoke (5);

    - encirclement of a part (35) of the end of said arm (9) of the magnetic yoke (5) with a shading ring (37);

    - surrounding said core (10) with a coil (11) connected electrically on the one hand to the arc metal sheet (3), and on the other hand to a connecting terminal of the device;

    - centring and positioning a blade (7) on parallel-running planes in relation to another arm (8) of the yoke (5), the two arms (8, 9) themselves remaining parallel;

    - hooking a spring (33) between one end (15) of the blade (7) and the contact support (6);

    - allowing the blade (7) to pivot with respect to the magnetic yoke (5) until its free end is brought into the vicinity of the arm (9) provided with the shading ring (37).

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