AU2013224790B2

AU2013224790B2 - Electromagnetic actuator having a high unlocking force

Info

Publication number: AU2013224790B2
Application number: AU2013224790A
Authority: AU
Inventors: Vincent BOITEUX; Edouard Dezille; Pascal FRITSCH
Original assignee: Hager Electro SAS
Current assignee: Hager Electro SAS
Priority date: 2012-02-29
Filing date: 2013-02-28
Publication date: 2016-07-07
Anticipated expiration: 2033-02-28
Also published as: AU2013224790A1; PL2820664T3; FR2987493B1; ES2621667T3; CN104246957A; IN2014MN01908A; EP2820664A1; FR2987493A1; PT2820664T; WO2013128125A1; EP2820664B1; CN104246957B

Abstract

The invention relates to an electromagnetic trigger, of the differential relay type, comprising: a U-shaped armature (1), the ends of the two legs (4, 5) of which form two coplanar polar surfaces; a pivoting plate (2) that pivots between two positions, in which it, respectively, is at distance, i.e. there is a gap between it and said armature (1) and, in the armed position of the trigger, it makes contact with said polar surfaces and thus closes the magnetic circuit formed by said armature (1) and said plate (2), the hinge (3) of the plate (2) being located in the immediate vicinity of the end of one of the legs (4) of the armature (1); a permanent magnet (6) for biasing the magnetic circuit, placed between the legs (4, 5) of the armature (1) and creating a permanent magnetic force attracting the plate (2) toward the polar surfaces, which magnetic force acts against a return force exerted by a spring (13); and an inductive coil (16) encircling the magnetic circuit, connected, for example, to a circuit to be controlled, with a view to modifying the initial balance between the magnetic force and the return force of the spring (13). The magnet (6) is positioned in the vicinity of the leg (5) of the armature (1) opposite the leg (4) proximate the hinge (3) of the plate (2).

Description

ELECTROMAGNETIC ACTUATOR HAVING A HIGH UNLOCKING FORCE

The present invention relates to an electromagnetic actuator of the differential relay type, capable of providing a sufficient unlocking force in order to for example trigger a differential switch lock. It more specifically relates to an actuator device with high sensitivity, notably used in the field of differential protection, when the latter is contemplated independently of the mains voltage.

This type of electromagnetic actuator conventionally comprises: - a fixed armature, generally U-shaped, for which the ends of the two legs form two coplanar polar surfaces; - a plate between two positions respectively at a distance, i.e. leaving an air gap to subsist with the armature and, in an armed position of the trigger, in contact with said polar surfaces, thus closing the magnetic circuit formed by said armature and said plate, the hinge of the plate being located in close vicinity to the end of one of the legs of the armature; - a permanent magnet for biasing the magnetic circuit, positioned between the legs of the armature and generating a permanent magnetic force attracting the plate towards the polar surfaces, a magnetic force which acts against a return force exerted by a spring. - an induction coil surrounding the magnetic circuit, for example connected to a circuit to be controlled, with view to modifying the initial balance between the magnetic force and the return force exerted by the spring.

Practically, the torque transmitted to the plate by the permanent magnet opposes the torque exerted by the spring on the plate. The permanent magnet further allows finer control of the fluxes passing in the magnetic circuit and higher sensitivity of the actuator.

When a current crosses the coil, for example signaling an incident of a differential order on lines, the flux generated in this case in the magnetic circuit by the coil is combined with the flux generated by the magnet, destroying the initial mechanical balance and causing the plate to pivot, attracted to the contact of the end polar surfaces of the armature. The displacement of the plate causes that of a mechanical member, for example a rod able to unlock the lock of a differential switch placed in proximity to the electromagnetic actuator, so that said rod may act on a trigger.

Such an electromagnetic trigger in its principal is described in patent FR 2 630 256. In this document, the permanent magnet is approximately localized in the middle of the armature, parallel to the legs of the U. The drawback is then that the lever arm between the magnet and the hinge of the plate is relatively short, and the magnetic force generated by the permanent magnet is not optimally used since the torque applied to the hinge is not maximized. The antagonistic torque due to the spring can consequently only be of the same order, and the actuator only provides a moderate unlocking force. This type of trigger may therefore only operate with locks capable of being unlocked with a relatively strong force.

In order to surmount this problem, it is then sometimes necessary to introduce additional means between the relay and the lock, which has the function of reducing the force required for unlocking the lock.

This solution is however not advantageous, neither structurally since it requires the addition of components and therefore a larger volume in the casing of the circuit breaker (furthermore jeopardizing the reliability of the whole), nor economically since it adds additional steps during the manufacturing of the appliance.

The object of the present invention therefore consists of finding a remedy to the drawbacks of the solutions of the prior art, by proposing an electromagnetic actuator capable of providing a large unlocking force, which is furthermore simple to apply and the design of which remains compact.

The targeted object furthermore is not to increase the volume of the magnet, or those of the plate and of the armature, which is already undesirable from a congestion point of view, and obviously has incidences on the operation and the behavior of the magnetic circuit.

Moreover, obtaining a higher unlocking force should be possible without increasing the triggering power.

To achieve these objects, and other ones which will appear subsequently, the invention is mainly characterized in that the magnet is positioned in the vicinity of the leg of the armature opposite to the proximal leg of the hinge of the plate.

The force generated by the magnet may remain identical with what was known, the torque attracting the plate towards the polar surfaces of the armature being substantially larger because of the increase of the lever arm between the magnet and the hinge of the plate.

It is then possible to dimension the spring means generating, when the balance is broken by the occurrence of a current in the coil, a much larger force being applied to the mechanical member provided for actuating an outer device.

Such a positioning of the magnet is not a solution which is imposed to experts of this technical field, and should therefore be considered as quite original in such an electromagnetic actuator for several reasons, the most important being: - an adjustment of the electromagnetic trigger is always necessary, and is especially accomplished by adjusting the induction of the magnet. Now, the closer the magnet is to the hinge, the easier is the adjustment since only a small portion of the flux of the magnet is used in the useful portion of the electromagnetic circuit, the one which comprises the largest air gap opposite to the hinge of the plate.

The remainder is somewhat short-circuited by passing into the leg in the vicinity of the hinge. Thus, if 70% of the flux is in this case, and that only 30% of the flux is useful, a variation of 0.01 T of the magnet has a repercussion of 0.3 x 0.01 T, i.e. 0.003 T. The adjustment is then easy to obtain, much more than in the opposite assumption, when the magnet is positioned far away from the hinge. - demagnetization: the magnets used in this type of actuator or for example those which are known under the name of AINiCO magnets considered as easy to adjust and which have a drift of the magnetic characteristics compatible with that of the magnetic materials of the armature and of the plate. However they demagnetize relatively easily for example when the magnetic circuit changes.

Now, this is specifically what occurs in such an actuator, since the magnet does not see the same magnetic circuit depending on whether the plate is open or closed. This, however, is much less true and/or much less significant when the magnet is closer to the hinge, since the short-circuited portion of the magnetic circuit hardly changes, and the larger flux portion passes through it: under these conditions, the global magnetic circuit does not change much when it is seen from the magnet. On the other hand this is no longer true when the magnet is placed close to the leg opposite to the hinge. - If the magnet is brought too close to this leg, its flux will directly pass laterally in said leg, without passing through the plate, and there is a risk of saturation of said leg of the armature.

In these three perspectives, the reflex of one skilled in the art is therefore to rather move the magnet away from the leg opposite to the hinge, this position generating too many drawbacks/potential problems.

The present solution will therefore go against the constraints which are imposed and which in principle dictate to one skilled in the art the attitude to adopt in terms of the design of such an assembly according to customary knowledge on this technical field.

The positioning of the magnet relatively to the armature, according to the invention, results from a fine compromise which aims at maximizing the torque for attracting the plate towards the polar surfaces of the armature while avoiding saturation of the leg of the armature opposite to the hinge on the one hand, and demagnetization of the permanent magnet on the other hand.

To do this, the distance A between the magnet and the leg of the armature opposite to the proximal leg of the hinge of the plate is intended to be less than half of the distance D separating both legs of the armature.

Moreover, preferably, the distance A may be intended to be larger than the distance B between the magnet and the plate in the closed position added to the distance C between the magnet and the base of the armature. Still preferably, the distance A is selected to be greater than 0.3 mm. According to other characteristics of the magnetic circuit specific to the invention and which allow optimum operation of the trigger, it should be noted that the polar surface of the magnet facing the plate is intended to be greater than 6 mm2.

Moreover, the plate preferably covers: - at least 75% of the polar surface of the magnet which faces it, and - between 30% and 80% of the polar surface of the proximal leg of the magnet which faces it.

Still for meeting the conditions of a compromise as best as possible, it is provided according to the invention that the aperture angle of the plate be limited, in practice comprised between 0° and 15°.

Other advantages and features will become more clearly apparent from the description which follows, of a particular embodiment of the invention, given as a non-limiting example, and illustrated in the appended drawings wherein: - Fig. 1 very schematically illustrates a possible configuration for a magnetic circuit according to the invention, and - Fig. 2 illustrates an actuator, the magnetic circuit of which meets the criteria of the invention.

With reference to Fig. 1, the magnetic circuit of a conventional actuator according to the invention includes a U-shaped fixed armature (1), a pivotally mounted plate (2) along an axis (3) in the vicinity of the upper end of a leg (4) of the armature (1), and which is in this case illustrated as closed, i.e. its free end is in contact with the upper end of the other leg (5). A permanent magnet (6) is placed in the close vicinity of the leg (5), the distance A separating them having been artificially increased for improving the clarity of the figure, but being less significant than the illustration which is made of it in the reality.

In this configuration, D is the distance separating said legs (4, 5), A is therefore the distance separating the permanent magnet (6) from the leg (5), and B and C are the distances separating the permanent magnet (6) from the plate (2) and from the base (7) of the magnetic armature (1), respectively.

These are the distances which are dealt with by the conditions which were mentioned beforehand, more specifically: - A < D/2

- A > B + C - A > 0.3 mm

The polar surfaces (20) and (21) of the magnet (6) and of the leg (5) respectively, which face the plate (2) meets the surface conditions mentioned earlier, notably as regards the covering level of the surfaces (20, 21) by the plate (2). Many tests have actually shown that these conditions, when they 5 are met, allow optimum operation of the trigger.

Fig. 2 illustrates in a more detailed way a configuration example of an electromagnetic actuator according to the invention with, in a casing (10), the armature (1) and the plate (2) connected to a plate metal sheet (11) which is rotatably mounted in the casing in (3). This metal sheet (11) further includes 10 a tab (12) on which is attached an end of a helical spring (13), the other end of which is secured to an armature metal sheet (14) extending along the leg (4) .

The plate code operates with a pusher (15), the free end of which juts out from the casing (10), and which is moved by it between two positions 15 corresponding to the two positions which the plate (2) may assume, respectively in contact with and at a distance from the armature (1), depending on whether the coil (16) has a current flowing through it or not. This coil (16) is mounted on a support (17) surrounding the base (7) of the armature (1), and for this purpose passing through a window (18) made in 20 the casing (10).

The permanent magnet (6) is positioned in close proximity to the leg (5) , and its positioning meets the length and distance conditions laid down beforehand.

Conventionally, in the case of occurrence of a current in the coil (16) 25 for example caused by a differential fault in a circuit, the flux generated by the coil (16) unbalances the assembly, previously mechanically balanced, as long as the torque generated by the spring (13) is equal to the one generated by the permanent magnet (6).

The plate (2) moves relatively to the armature (1), it in fact pivots from 30 its position in contact with the end of the leg (5) pulled back by the spring (13), driving the pusher (15), the end of which cooperates with a triggering system, for example of a circuit breaker (not shown).

Of course, the example above should not be considered as exhaustive of the invention, which on the contrary includes the whole of the alternatives of shape and configurations which are within the reach of one skilled in the art.

Claims

1. An electromagnetic trigger, of the differential relay type, comprising: - a U-shaped armature, the ends of the two legs of which form two coplanar polar surfaces; - a plate pivoting between two positions, respectively at a distance, i.e. leaving an air gap with the armature and in an armed position of the trigger, in contact with said polar surfaces, thus closing a magnetic circuit formed by said armature and said plate, the hinge of the plate being located in the close vicinity of the end of one of the legs of the armature; - a permanent magnet for biasing the magnetic circuit, positioned between the legs of the armature and generating a permanent magnetic force attracting the plate to the polar surfaces, a magnetic force which acts against a return force exerted by a spring; - an introduction coil surrounding the magnetic circuit, for example connected to a circuit to be controlled, with view to modifying the initial balance between the magnetic force and the return force exerted by the spring; wherein the magnet is positioned in the vicinity of the leg of the armature opposite to the leg of the armature proximal to the hinge of the plate; and wherein the plate covers at least 75% of the polar surface of the magnet which faces the plate; and wherein the plate covers between 30% and 80% of the polar surface of the leg of the armature opposite to the leg of the armature proximal to the hinge, which faces the plate.

2. The electromagnetic trigger according to claim 1, wherein the distance A between the magnet and the leg of the armature opposite to the leg of the armature proximal to the hinge of the plate is less than half of the distance D separating both legs of the armature.

3. The electromagnetic trigger according to any one of the preceding claims, wherein the distance A is greater than the distance B between the magnet and the plate in the closed position, added to the distance C between the magnet and the base of the armature.

4. The electromagnetic trigger according to any one of the preceding claims, wherein the distance A is greater than 0.3 mm.

5. The electromagnetic trigger according to any one of the preceding claims, wherein the polar surface of the magnet facing the plate is greater than 6 mm2.

6. The electromagnetic trigger according to any one of the preceding claims, wherein the aperture angle of the plate lies between 0° and 15°.