ELECTROMAGNETIC ACTUATOR HAVING MAGNETIC GENERATOR FIELD OF THE INVENTION [0001] The present invention relates to an electromagnetic actuator having a magnetic generator at least preferred forms of which strengthen immunity to electrical shocks. Disclosed are electromechanical actuators that are used in combination with locks for activating electrical apparatuses for protecting lines, for example differential and/or circuit breaker products. BACKGROUND OF THE INVENTION [0002] These apparatuses must activate under very specific conditions, typically when an imbalance occurs between the sum of the incoming currents and the sum of the outgoing currents of the line protected by the apparatus in question, or when the intensity of the current is abnormally high. The actuators integrated into such apparatuses traditionally include a yoke made from a magnetic material, at least one coil surrounding a mobile magnetic core forming a magnetic circuit with said yoke, said core being guided between an inoperative position and operative positions caused by the appearance of current in the coil. The core, with a generally elongated configuration, then serves as a striker for a mechanical lock, the activation of which results in quickly separating one or more movable contacts from corresponding stationary contact(s). The base device of the actuator also includes return means for returning the mobile core to its inoperative position, making it possible to reset the actuator in a way if the conditions necessary to move the mobile core are not met, or after the return to normal. [0003] The problem at least preferred forms of aim to resolve is as follows: the circuits protected by electrical apparatuses such as those mentioned above may be subject to impulse waves resulting from electrical phenomena outside the protected line or circuit, for example due to lightning, which may then create sharp overvoltages, with no direct relationship to the status and/or operation of said protected line and/or circuit. Such phenomena are additionally not among the issues for which the protection device is initially provided.
2 [0004] The traditional electrical apparatuses for protecting lines must in principle be activated only in case of an imbalance of the incoming/outgoing currents, or voltage overloads or short-circuits in the lines that they equip. The aim of the present invention primarily pertains to the fact that shocks caused by brief overvoltages not due to a malfunction of the circuit strictly speaking, for example caused by lightning, do not activate the product. [0005] To that end, the electromagnetic actuator according to the invention is primarily characterized in that it includes at least two coils connected to first and second independent control means, respectively, at least one primary coil being managed by the first control means with a view to controlling the movement of the mobile core, and at least one secondary coil being positioned relative to the primary coil(s) and actuated by the second control means in order to modify the magnetic field generated by the primary coil(s). [0006] One aspect of the invention provides an electromagnetic actuator having a magnetic generator including a coil surrounding a mobile magnetic core capable of moving by means of the magnetic field generated by the coil, said core being guided between an inoperative position to which it is returned by return means and operative positions of a lock for activating electrical apparatuses for protecting lines, the actuator including at least two coils connected to first and second independent control means, respectively, at least one primary coil being managed by the first control means with a view to controlling the movement of the mobile core, and at least one secondary coil being positioned relative to the primary coil(s) and actuated by the second control means in order to modify the magnetic field generated by the primary coil(s); the primary coil is activated in a normal operating mode and allows for a movement of the mobile core in case of a short circuit in the line; the secondary coil is deactivated in the normal operating mode and activated in case of very significant overvoltage due to phenomenon outside the line in order to maintain the core in its inoperative position when the line is not subjected to short-circuit. [0007] In a preferred form of the invention the coils share the same magnetic circuit, are controlled independently, and perform different functions. At least one is assigned to the actuator function, whereas at least one other, not sharing the same control 3 means, is used to interact with the first actuator function, under certain conditions that are in practice managed by the second control means. [0008] Said primary and secondary coil(s) are arranged relative to one another such that the effect of the field generated by one group opposes the effect of the field generated by the other group for the mobile core, the resulting magnetic flow applied to said core being the result of the subtraction of the flows of the primary coils and secondary coils. [0009] More specifically, according to one possibility, the actuator according to the invention may include a primary coil serially connected to a secondary coil, which are wound so as to generate opposing magnetic fields. [0010] In practice, the control means are provided such that only the primary coil(s) is (are) activated in a normal operating mode, the secondary coil(s) only being activated in case of very significant overvoltage due to phenomena outside the line, so as to compensate the force generated in the mobile core by the overall magnetic field created by the normal operation of the line and by such phenomena. [0011] The primary coil may correspond to the rated coil of the actuator, to which a winding is added that is intended to strengthen the immunity of the product by absorbing the consequences of the transient overvoltages on the mobile core. To date, this problem, which clearly has already been identified, has been resolved by the use of large varistors, the bulk of which is nevertheless a drawback, as it is often incompatible with the increasingly imperative constraints of space management, which impose a continuous requirement to reduce bulk. [0012] However, the varistors used to date, positioned separate from the actuator strictly speaking, have a bulk that assumes taking their installation in the available space into account separately. The solution according to the invention makes it possible to manage the problem, i.e., improving immunity to shocks generated by overvoltages, at the actuator itself, in connection with the winding with which the latter is always equipped. [0013] A varistor may certainly remain, under the conditions specified hereafter: the secondary coil is in fact, according to one possible configuration of the invention, 4 connected to second threshold control means provided to make it operative once a predetermined voltage value is reached across its terminals. [0014] Said threshold means can then for example consist of such a varistor, but the bulk of which is then much smaller than that of the varistors used in the prior art, as it is simply intended to make the portion of the coil turn on, inducing a force in the mobile core opposite that induced by the turns of the first "rated" portion, beyond a certain threshold value. The function is therefore not performed in the same way. [0015] Alternatively, the threshold component may be an avalanche diode, the characteristic of which is comparable to that of a varistor. Said characteristic, which determines the choice of the component, depends only on the selected voltage threshold. [0016] More generally, said second control means may consist of means for eliminating the transient voltage. [0017] The primary coil may also be connected to a control stage, consisting of a voltage or current threshold control component. The latter is preferably selected from among the following components: transient voltage suppressor component of the varistor or avalanche diode type, Zener diode, IGBT transistors, bipolar transistor, thyristor, triac, MOSFET transistor and relays. [0018] The invention will now be described in reference to the sole appended figure, which diagrammatically shows one embodiment of an electromechanical actuator equipped with the system according to the invention. Hereafter, it has been considered that the primary and secondary coils in reality make up a single coil segmented into two portions, which may be seen as strictly technically equivalent, using a different explanatory approach. [0019] The actuator includes a yoke (1) surrounding a coil made up of two portions, a portion (2) with NI turns, which is dimensioned such that it can act as the rated coil, and a portion (3) with N2 turns, surrounding a mobile core (4) biased in its inoperative position by a spring (5) positioned at one of its ends (it should be noted that this return system could be replaced by a technical equivalent of the permanent magnet or 5 permanent current type circulating in the turns N2 in order to recall the mobile core to its inoperative position when the magnetic force drops back below a certain level). At its other end, the core (4) is guided in an orifice (5) of the yoke (1) allowing it to move in the direction of the arrow F toward a mechanical lock (not shown) that can be activated in case of contact with the straight end of the mobile core (4). [0020] The two coils are connected serially in the protected line, i.e., typically between phase Ph and neutral N, a control component (6) of the threshold type, for example a transistor, thyristor or triac, being positioned between the intermediate connection point (1) between the coils (2) and (3) and the connection to the neutral N. At the opposite output of the coil (3), a threshold component (7) of the varistor or avalanche diode type is also connected to the neutral N. Other equivalent components, such as those cited above, may also be used if applicable. [0021] The operation is as follows: when the control component (6) becomes on, in normal operating mode, the threshold component (7) is not activated and only the NI turns of the portion (2) of the coil are traveled by a current. The magnetic force generated by the magnetic field caused by the appearance of an abnormal current in the coil (2), for example in case of short circuit, if applicable makes it possible to move the mobile core (4) and activate the lock. This activation is typically done by bimetallic strip in case of overvoltage, and by the actuator according to the invention in case of short circuit. [0022] In case of shock caused by transient overvoltages arising from lightning type phenomena, the transient voltage is much greater than that normally managed, and the threshold component (7), for example a varistor, allows passage of the current. The portion (3) of the coil, i.e., the N2 residual turns, are in that case also traveled by current. They nevertheless induce a magnetic force opposite that induced by the turns NI, and the resulting force does not necessarily cause the mobile core (4) to move, allowing activation of the lock, in the case where the line is not subject to abnormal intrinsic conditions.