EP2270829A1 - Controlling via a device for magnetic compensation of repulsion forces and contactor comprising such a device - Google Patents

Abstract

The device i.e. magnetic compensator (30), has a magnetic piece (32) functionally coupled to a contact bridge (18) of a movable contact (16). A measuring unit (40) measures a magnitude representative of current flowing between the movable contact and a fixed contact (14). A processing unit (42) processes the magnitude representative of the current for comparison to a threshold. A control unit (44) controls supply units of a coil (22) according to the result of the processing unit to increase the current supplied to the coil when the current flowing between the contacts exceeds the threshold. An independent claim is also included for an electrical apparatus including a supply unit provided with an interrupter for disconnecting one of windings.

Description

TECHNICAL AREA

The invention relates to the field of protection of contactors, including the establishment of devices for compensating the electrodynamic repulsion forces that tend to cause the inadvertent opening of the contacts generating their wear or welding. The invention relates to the optimization of such compensation devices so that the size and power consumption of the contactors are minimal while allowing them to properly perform their function in case of overloads due to short circuits.

STATE OF THE ART

In a contactor, to ensure the passage of current, an equilibrium is established between a spring mechanism ensuring a pressure between the contacts and the repulsive force generated at the contacts by the passage of the current. A contactor is normally provided to withstand effective currents of the order of several times, for example twelve times, its rated current according to the controlled load; beyond that, the repulsive forces predominate and can overcome the action of the pressure spring, so that the contacts will separate to close as soon as the current decreases. But shocks between contacts create a risk of welding, or at least excessive wear. A contactor is therefore conventionally associated with a cut-off or limitation device which avoids the passage of an excessive current in the event of a short-circuit or a significant overload, so that the contactor does not in principle have the time to undergo a pity.

However, if the overload corresponds to smaller effective currents (for example of the order of fifteen times the nominal current), the limiter device does not act, or not immediately. In fact, there is a zone of overload current in which the threshold of repulsion of the contacts is exceeded without limitation of the current. To compensate for the effect of the electrodynamic repulsion forces during the time interval between the apposition of the overload and the opening of the circuit without unduly increasing the size of the pressure springs, magnetic compensators have been proposed, for example in the Documents FR 2,517,463 , US 3,887,888 or EP 0 974 997 . A compensation device, also called magnetic U or "iron hand" comprises two magnetic parts forming between them a variable air gap and surrounding the movable contact, so as to form an electromagnet.

The magnetic compensator can be fixedly positioned relative to the contactor housing, in which case it can interfere with the reopening of the contacts and degrade the performance of the contactor during the break; preferably, one of the two U-shaped parts is connected to the support mechanism of the movable contacts. The magnetic compensator is dimensioned to not contribute significantly to the contact pressure in nominal current operation; when an overload develops significant repulsive forces, the compensator effectively strengthens the contact pressure, thus maintaining their closed position.

However, the magnetic U acts directly on the moving part of the electromagnet and, in the case of significant compensation forces, it can pull out this mobile part, in particular for an electromagnet powered by alternating current. To counteract this effect, an increase in the contactor maintenance current would be necessary, but at the expense of its size and its power consumption.

SUMMARY OF THE INVENTION

Among other advantages, the invention aims to overcome the disadvantages of existing magnetic compensators by optimizing their operation. In particular, the invention relates to a control of the holding current (current in the closed position) of the electromagnet, so as to keep a minimum value in normal operation and to increase it only when the contact force must be complemented by the magnetic U. Because of this dissociation, the effort generated by the repulsion does not lead to a pullout of the actuator, and the power consumption remains minimal in normal operation, without oversizing of the actuator.

In one of its aspects, the invention relates to a contactor provided with a magnetic compensation device and enslaved. The contactor preferably comprises at least one movable bridge of two contacts, and an electromagnetic actuator formed of a coil and a movable part integral with a contact carrier device coupled to the contact bridge to drive it. The compensation device, which is also an object of the invention, comprises two magnetic parts movable relative to each other, preferably a U-shaped part and a substantially flat part closing the recess of the U, but retaining between them a non-zero air gap. Between the two magnetic parts is a support conductor of the movable contact of the contactor so as to form an electromagnet; the support is operatively coupled to one of the magnetic parts so that a decrease in the air gap exerts a force towards the closure of the contacts.

The actuator coil of the contactor is provided with controllable supply means. According to one option, the coil may comprise a plurality of windings, and the power supply means comprise switch means, such as transistors, for disconnecting one of the windings, so as to modify the field created by the coil and therefore the force generated by the electromagnet in the magnetic parts according to the control of the switch means. According to another embodiment, the coil of the magnetic compensator comprises electronic power supply means, and a control of said means makes it possible to modify the current flowing in the coil, for example via the frequency of a modulated signal, in particular in modulation of voltage.

The power supply means of the coil allow its servocontrol, and thus the servocontrol of the force of the actuator as a function of the action developed by the compensator; they are associated with means for measuring a magnitude representative of the current flowing in the two magnetic parts of the compensator, that is to say between the contacts of the contactor, and means for comparing this magnitude representative at a threshold of way to control the feeding means. The measuring means can be of different natures, and for example allow a direct measurement of the current flowing between the poles, or the measurement of a parameter dependent on the current. In particular, the measuring means comprise means for measuring the magnetic flux within the magnetic parts of the compensator.

• au moins une paire de contacts mobiles l'un par rapport à l'autre ;
• un actionneur électromagnétique des contacts comprenant une bobine formant un électroaimant avec un support conducteur d'un contact mobile ;
• un dispositif de compensation magnétique de la répulsion de contacts comprenant une première pièce magnétique couplée fonctionnellement au support de contact mobile et une deuxième pièce magnétique définissant entre elles un entrefer variable non nul et un passage dans lequel est positionné ledit support de contact mobile de façon à former un électroaimant ;

caractérisé en ce que l'appareil comprend en outre : des moyens d'alimentation de la bobine de l'actionneur susceptibles d'être commandés ; des moyens de mesure d'une grandeur représentative du courant circulant entre les contacts ; des moyens de traitement de la grandeur représentative du courant circulant entre les contacts pour la comparer à un seuil ; et des moyens pour commander les moyens d'alimentation de la bobine en fonction du résultat des moyens de traitement de façon au augmenter le courant alimentant dans la bobine lorsque le courant circulant entre les contacts dépasse le seuil.More generally, the invention relates to an electrical apparatus comprising:

• at least one pair of movable contacts relative to each other;
• an electromagnetic contact actuator comprising a coil forming an electromagnet with a conductive support of a movable contact;
• a contact repeater magnetic compensation device comprising a first magnetic part operatively coupled to the movable contact support and a second magnetic part defining between them a non-zero variable gap and a passage in which said movable contact support is positioned so as to form an electromagnet;

characterized in that the apparatus further comprises: actuator coil feed means operable; means for measuring a magnitude representative of the current flowing between the contacts; means for processing the magnitude representative of the current flowing between the contacts to compare it with a threshold; and means for controlling the supply means of the coil according to the result of the processing means so as to increase the current supplied to the coil when the current flowing between the contacts exceeds the threshold.

BRIEF DESCRIPTION OF THE FIGURES

• La figure 1 représente le mécanisme d'un contacteur muni d'un dispositif de compensation qui peut être associé à un asservissement selon l'invention.
• La figure 2 montre les efforts exercés au cours du temps dans un contacteur avec compensateur magnétique selon l'art antérieur en présence d'un court-circuit.
• La figure 3 illustre l'utilisation d'un compensateur selon un mode de réalisation préféré de l'invention.
• Les figures 4A et 4B montrent le schéma d'asservissement d'une bobine selon un mode de réalisation d'un contacteur selon l'invention.
• La figure 5 représente un asservissement pour un autre mode de réalisation d'un contacteur selon l'invention.

Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention, given by way of illustration and in no way limiting, represented in the appended figures.

• The figure 1 represents the mechanism of a contactor provided with a compensation device which can be associated with a servocontrol according to the invention.
• The figure 2 shows the forces exerted over time in a contactor with magnetic compensator according to the prior art in the presence of a short circuit.
• The figure 3 illustrates the use of a compensator according to a preferred embodiment of the invention.
• The Figures 4A and 4B show the control scheme of a coil according to an embodiment of a contactor according to the invention.
• The figure 5 represents a servocontrol for another embodiment of a contactor according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The figure 1 schematically represents the opening and closing mechanism of a unipolar contactor 10. Two conductors 12 each carry a fixed contact 14 which cooperates with a movable contact 16 between an open position and a closed position; the two movable contacts 16 are interconnected via a bridge 18, and are actuated by an electromagnetic device 20 comprising a coil 22 associated with a contact holder device 24 integral with the support 18 of the movable contacts 16. A pole spring 26, housed inside the contact holder 24 generates a force between the contacts 14, 16 to keep them closed; it determines the contact pressure F _P.

The contact carrier 24 also supports a magnetic compensator 30 comprising a first magnetic piece 32 integral, by coupling or simple support, the contact bridge 18, and a second magnetic part 34 U, the two parts being arranged to form an orifice through which the contact bridge 18 is located. The magnetic compensator 30 thus forms an electromagnet 18, 32, 34 when the contacts 14, 16 are closed; its components are arranged and dimensioned so that a non-zero gap e remains between the two magnetic parts 32, 34 in the closed position of the contacts 14, 16, regardless of their degree of wear.

When a current I flows in the conductors 12, a repulsive force F _R is generated at the contacts 14, 16, soliciting opening; this force F _R is all the more strong that the conductors 12 are J and therefore that the current flows in opposite directions in the two branches at the contact 14, 16. Moreover, a magnetic flux Φ is created within the compensator 30, in the magnetic circuit formed by the two magnetic pieces 32, 34; the flow passes through the air gap e and consequently generates a compensating force F _C between the bridge 18 and the second U-shaped part 34 which is added to the force F _P of the spring 26.

As illustrated in figure 2 it is thus noted that in a first "normal" operating phase, in particular at nominal current, the repulsion force of the contacts F _R is minimal, like the force F _C generated by the iron hand 30: the force F _P of pole spring 26 ensures the closing of the contacts 14, 16. The higher the current I increases, while the pressure force F _P remains constant, the more the repulsion force F _R increases, as the force F _C of the iron hand 30 which reaches an asymptote F _max corresponding to the saturation of the magnetic material forming the compensator 30.

The electromagnet 20 exerts a force F _E on the contacts 14, 16. Conventionally, this effort F _E is constant, depending on the current flowing in the coil 22 to keep the actuator 20 closed, called holding current. In view of the configuration of the compensator 30, the electromagnet 20 undergoes a stress F resulting from the various previous forces, and in particular corresponding to the difference between the repulsion force F _R and the pressure force F _P + F _C of the iron hand 30 and pole springs 26; the force F undergone by the actuator 20 is bell-shaped. However, the magnetic U 30 acts directly on the movable portion 18, 24 of the actuator 20 and, in case of great effort, the imposed stress F can cause its tearing exceeding the effort F _E that can support the actuator 20 ( figure 2 ). In fact, the current within the coil 22 is usually kept to a minimum to reduce consumption while ensuring the closure of the contacts 14, 16. To avoid tearing, one of the solutions would be to increase the force F _E of the actuator 20, increasing the current, or oversize the iron hand 30.

According to the invention, it is proposed to modify the force F _{E to} which the actuator 20 resists only when this is necessary. In particular, it is proposed to use a so-called electronic coil 22, and to control its power supply as a function of the current I circulating in the conductors 12: if the current I exceeds the nominal current of a certain threshold, the supply of the coil 22 is increased so that the force F _E of the actuator 20 exceeds the resulting stress F. It is thus possible to avoid tearing, and not to over-size the iron hand 30.

In particular, the threshold I ₀ chosen may correspond to half of the maximum peak current held by the contactor 10, which makes it possible to anticipate the increase of the current in the coil 22 of the actuator 20: for example, if the The contactor 10 is adapted for rated currents of 400 A, i.e. the pole springs 26 are adapted so that the power contacts 14, 16 do not open for peak values of 8000A at all times. milliseconds although the current I is considered faulty from 15 × 400 = 6000 A, as soon as the current I reaches I ₀ = 4000 A, a signal indicates that the holding current of the coil 22 must be increased. This threshold value I ₀ is appropriate because a short-circuit current I of 100 kA reaches the trigger value I ₀ approximately after 100 μs while the springs 26 keep the contactor closed about 200 μs and that, as illustrated in figure 2 , the maximum force F experienced by the actuator 20 is not yet reached. Other options are possible.

In order to control the coil 22, means are used to detect that the current I exceeds the threshold I ₀ , or that a quantity directly dependent on the current exceeds a threshold. According to one embodiment, the measurement is directly carried out by current sensors present in the contactor 10: in fact, certain contactors 10, in particular of high range, can use current measurements for the electronic magneto-thermal protection. According to another embodiment, the threshold detected relates to the force exerted by the current I on the components of the contactor 10, and in particular on the second magnetic part 34, provided for this purpose with a suitable sensor; for example, a strain gauge is inserted between the magnetic compensator 30 and the electromagnet 20, and a processing electronics allows, from this measurement, to determine the triggering threshold of the current control in the coil 22.

According to a preferred embodiment, for greater precision and sensitivity, the magnitude representative of the current is determined directly on the magnetic compensator 30. In particular, as illustrated in figure 3 for another embodiment of a contactor 10 'provided with an iron hand 30, an exploratory winding 40 of the flow Φ is put in place around the second U-shaped part 34. The current I passing in the current line 12, 18 creates a flow Φ in the compensator 30; this is measured by the winding 40 which transmits a representative value to the processing means 42, for example comparison means by an array of values. In particular, the induced voltage is of the form U = 2n × π × f × Φ, with n number of turns of the winding 40 and f frequency of the current I. For a current of 4000 A of frequency f = 50 Hz, the flux will be 1.25 · e ^-04 Wb, which corresponds to an induced voltage of 1.98 V if the exploratory coil 40 comprises n = 50 turns. The processing means 42 can thus associate a threshold of 2 V with the induced voltage to trigger the servocontrol of the coil 22.

The processing means 42 associated with the measuring means 40 make it possible to rapidly detect the exceeding of a threshold I ₀ by the feed current I, in particular by exceeding a characteristic quantity (U, effort ...). Means 44 then receive the signal corresponding to the overshoot, and transmit this information to the supply of the coil 22 to enslave it. As the compensator 30 is closed during the modification of the supply of the coil 22, there is no latency between this modification and the increase of the force F _E exerted by the actuator 20; Moreover, the control means 44 are adapted to react quickly, so that the force F _E of the actuator 20 is greater than the force F it undergoes. In the previous preferred embodiment, the peak force F experienced by the actuator 20 appears at about 0.35 ms: according to the invention, it is preferred that the change in the speed of the coil 22 takes place before, and preferably in the 200 μs following the exceeding of the threshold I ₀ (or its equivalent on the quantity U, Φ, ... measured).

According to a first variant illustrated in Figure 4A , the actuating coil 22 is in fact a system with at least two windings 22A, 22B put in series, the first holding winding 22A having a much higher resistance to the second winding 22B of call; for example, the winding 22A comprises 2400 turns for a resistance of 100 Ω, and the winding 22B comprises 200 turns for a resistance of 1.1 Ω. In normal operation, the holding winding 22A is predominant, and provides the current in the coil 22. In the presence of an overcurrent, the servo means 44 send a signal on the interruption means 46 so as to disconnect the holding winding 22A of the assembly: the Call Winding 22B takes over and generates a superior power supply. For the system to be reactive, it is advantageous for the interruption means 46 to be of the transistor type: as soon as the servocontrol means 44 receive processing means 42 the signal indicating an overload, the transistor 46 is called upon to opening for a fast increase, in less than 100 μs for a voltage front U ₂₂ ( Figure 4B ).

In another embodiment, the coil 22 is electronically powered, via a pulse modulated type signal, or PWM (for "Pulse Wave Modulation "). In particular, the supply of the coil 22 is carried out directly from a control device 48 ( figure 3 ) creating pulses of predetermined width T for the control voltage. As illustrated in figure 5 in normal mode, the pulse signal has a first frequency f ₁ , for example 1% of the fixed frequency f, making it possible to obtain a holding current current I ₁ in the coil 22, the said average current I ₁ corresponding to the average of the current which decreases between two pulses. As soon as the servo-control means 44 receive processing means 42 the signal indicating an overload, they transmit to the command control device 48 an order of increase of the pulse frequency so that the average current I ₂ obtained at the second pulse frequency f ₂ is increased sufficiently to counteract the force F undergone. It turns out that a doubling of the frequency, in particular f ₂ = 2% of the fixed frequency, is sufficient for the desired effect; this type of modification in the supply of the coil 22 is also very fast, and in particular the actuator 20 reacts within 0.1 ms.

The servocontrol of the coil 22 is preferably continued by a return to the minimum holding current as soon as the current I returns to a nominal value, that is to say that the current in the coil 22 is increased during the phases of transient current, or fault before tripping of line protection devices.

Although the invention has been described with reference to a contact bridge contactor 18, it is not limited thereto: other elements may be concerned by the invention, in particular, inverters, relays or other devices. Similar. Preferably, the invention is used in a large contactor 10, in which the current sensor is integrated, the compensation device 30 and the servocontrol can then be put in place in an existing contactor. Moreover, other systems for controlling the current of the coil 22 may be provided, as well as other means for measuring a magnitude representative of the exceeding of a threshold I ₀ by the feed current I. it is also possible to tolerate a partial opening of the actuator 20 and thus a slightly slower action in the process "measurement of the magnitude / determination of the exceeding of the threshold and triggering of the servocontrol / servocontrol / actual action on the actuator 20 ": indeed, between the beginning of opening of the actuator 20 and the opening of the contacts 14, 16 a latency time corresponding to the crushing of the pole springs 26 (distance of the order of 4 mm in the previous case).

Claims (9)

Magnetic compensation device (30) for the repulsion of contacts (14, 16) of an electrical apparatus (10) provided with an electromagnetic actuator (20) of the contacts (14, 16) comprising a coil (22) having the means power supply (46, 48) are controllable, said device (30) comprising a first magnetic part (32) operably coupled to a movable contact conductive support (18) and a second magnetic part ( 34) defining between them a non-zero variable gap and a passage in which said movable contact support (18) is positioned to form an electromagnet;
characterized by means (40) for measuring a magnitude representative of the current (I) flowing between the contacts (14, 16), means (42) for processing the magnitude representative of the current (I) flowing between the contacts ( 14, 16) for comparing it with a threshold (I ₀ ), means (44) for controlling the supply means (46, 48) of the coil (22) according to the result of the processing means (42) of to increase the current supplied to the coil (22) when the current (I) flowing between the contacts (14, 16) exceeds the threshold (I ₀ ). Magnetic compensation device according to Claim 1, in which the means for measuring a magnitude representative of the current comprise means (40) for measuring the flow (Φ) induced by the current (I) in the magnetic parts (32, 34). . Magnetic compensation device according to one of claims 1 or 2 wherein the second piece (34) is in the form of a U, the first piece (32) is in the form of a plate. Electrical apparatus (10) comprising at least one pair of contacts (14, 16) movable relative to each other, an electromagnetic actuator (20) of the contacts (14, 16) comprising a coil (22) having the means (44, 46) are controllable, and a magnetic compensation device (30) according to one of claims 1 to 3 coupled to a conductive support (18) of a contact mobile (14) of the contactor (10) and the supply means (46, 48) of the coil (22). An electrical apparatus according to claim 4 wherein the coil (22) comprises a plurality of windings (22A, 22B) in series, and the coil supply means (22) includes switch means (46) for disconnecting at minus one (22A) of the windings. An electrical apparatus according to claim 5 wherein the switch means comprises a transistor (46) and the processing means comprises transmitting an opening signal of the transistor (46). An electrical apparatus according to claim 4 wherein the coil supply means (22) comprises a control device (48) for modulating the supply voltage of the coil (22). An electrical apparatus according to claim 7 wherein the processing means (44) comprises means for changing the modulation frequency of the supply voltage of the coil (22). Electrical device according to one of claims 4 to 8, comprising a movable contact bridge (18) supporting two movable contacts (16), two fixed contacts (14), a contact-carrier device (24) associated with the movable bridge (18) and secured to the movable portion of the electromagnetic actuator (20), wherein the second piece (34) of the magnetic compensation device (30) is associated with the contact carrier device (24) and the first piece (32) is in support on the contact bridge (18).

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