FR2834121A1 - Excess current circuit breaker having outer inductive coil and inner moving contact moving parallel spiral winding following Lorenz force action when current value exceeded. - Google Patents

Abstract

The circuit breaker has an inductive coil (5) and moving contact (3) opening at a set current level. The moving contact moves in a plane parallel to the spiral widening under the action of a Lorenz force.

Description

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 The invention relates to a current limiting circuit breaker comprising an induction coil and a movable contact arranged to open when the current passing through the circuit breaker is above a certain threshold.

 Such a circuit breaker is known from French Patent No. 2719152, in which the movable contact is integral with a metal ring mounted on the induction coil. In this known circuit breaker, the metal ring covers the induction coil while being articulated relative to the latter so as to be able to open or close in the manner of a cover on the coil. This ring is held pressed against the coil by a return spring. The magnetic field produced by the induction coil gives rise to induced currents - or eddy currents - in the ring which generate electromagnetic forces opposing the force exerted by the spring and tending to move the ring away from the coil. . When the current passing through this circuit breaker is greater than a certain threshold, these electromagnetic forces are greater than the return force of the spring, which produces a rotation of the ring. The movable contact which is integral with the ring is thus opened in the event of an overcurrent in the coil to limit the current in the circuit breaker.

In this known circuit breaker, the opening of the movable contact gives rise to an electric arc which is then transferred to a helical expansion chamber. This helical expansion chamber is designed to split the arc into several arcs in series with each other so as to increase the total arc voltage to form an electromotive force capable of reducing the intensity of the current flowing through the circuit breaker.

 In this known circuit breaker, it is necessary that the ring has a large volume so that the induced currents are sufficient to trigger its opening. This large mass represents a high inertia which penalizes the speed of movement of the ring and therefore the reaction time of the circuit breaker in the event of overcurrent. More generally, choosing a size of the ring to have a sufficiently short opening time is delicate and does not always make it possible to satisfy the operating conditions.

 The object of the invention is to remedy this drawback by proposing a current limiting circuit breaker having a finer sensitivity in the event of the occurrence of a fault current.

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 To this end, the subject of the invention is a current limiting circuit breaker comprising an induction coil and a movable contact arranged to open when the current passing through the circuit breaker is above a certain threshold, characterized in that the movable contact is arranged near one end of said induction coil, and in that it is movable in a plane parallel to the winding plane of the turns at said end of said coil to open under the action of so-called Lorentz forces.

 With this construction, the moving contact is immersed in the magnetic field generated by the coil. The electromagnetic forces tending to open the movable contact are large and independent of its dimensioning, which significantly improves the opening time of the circuit breaker. In addition, the sensitivity of the circuit breaker can be adjusted by modifying the number of turns constituting the induction coil.

 The induction coil may surround a central electrode, this central electrode also being surrounded by a helical interrupting chamber spaced from the induction coil along the central electrode, the movable contact being mounted between the induction coil and the helical expansion chamber . With this arrangement, the induction coil generates a magnetic field both to open the movable contact and to split the electric arc in the expansion chamber, which reduces the manufacturing cost of the circuit breaker.

 The movable contact can be rotatably mounted on a base linked in movement to an actuator of the circuit breaker by being retained by a spring forming an articulated elbow with the movable contact. With this arrangement, the opening of the current limiting circuit breaker can also be triggered by an operator or by a control device through the actuating member.

 The invention will now be described in more detail, and with reference to the accompanying drawings which illustrate an embodiment by way of non-limiting example.

Figure 1 is a first view along a first sectional plane of the circuit breaker according to the invention;
Figure 2 is a view along a second sectional plane showing the movable contact of the circuit breaker according to the invention in the closed position.

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 Figure 3 is a view along the second section plane in which the movable contact is in the open position under the action of the current.

 Figure 4 is a view along the second cutting plane in which the movable contact is in the open position and ready to be closed after actuation of a mechanical control.

 The current limiting circuit breaker shown in Figure 1 according to a first section plane comprises a frame 1 on which is mounted a central electrode 2 having substantially the shape of a bar. This electrode extends along an axis AX included in the cutting plane of FIG. 1 and is electrically connected to an electrical supply network. A movable contact 3 also connected to the power supply network is able to move to close the circuit breaker 1 when it is in contact with the central electrode and to open the circuit breaker 1 when it is no longer in contact with this central electrode 2. The central electrode is surrounded by a helical arc expansion chamber 4 and by an induction coil 5 spaced along the axis AX, and coaxial with this axis. More particularly, the movable contact 3 is electrically connected to the network via the inductor coil, so that this inductor coil is traversed by all the current passing through the circuit breaker. Upon opening of the movable contact, an electric arc appearing between the movable contact and the central electrode is moved along the central electrode to position itself in the arc expansion chamber. More particularly, the electric arc is part of a current loop which tends to widen, which forces the arc to move along the central electrode to position itself in the expansion chamber. In this expansion chamber, the magnetic field produced by the induction coil 5 rotates this arc around the central electrode 2 to split it into a plurality of arcs in series with each other so as to increase the voltage of bow. More particularly, the helical expansion chamber 4 comprises a plurality of metal plates 4 ′ which are substantially equidistant from each other and arranged in a helical ramp. Under the effect of the magnetic field produced by the coil, the electric arc splits into a plurality of arcs in series between the successive plates to form a helical arc whose total voltage which is the sum of the voltages of each arc is high . As stated in patent document No. 2719152, this

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 Arc voltage forms an electromotive force, which reduces the intensity of the current flowing through the circuit breaker.

 According to the invention, the movable contact 3 is disposed near an end 5 ′ of the induction coil 5 which is here one face of the coil, it is movable in a plane parallel to the winding plane of the turns at this end 5 'to open under the action of the so-called Lorentz forces. This movable contact is held in the closed position by a spring 6. When the current passing through the circuit breaker exceeds a certain threshold, the magnetic field created by the induction coil 5 produces electromagnetic forces in the movable contact 3 which tend to open in s 'opposing the restoring force exerted by the spring 6. As visible in Figure 2 which shows the circuit breaker according to a second cutting plane substantially perpendicular to the first cutting plane of Figure 1, the movable contact is able to move in a plane parallel to the end of the inductor coil so as to be substantially perpendicular to the magnetic field produced by the coil throughout its displacement.

Thus, the mobile contact is moved by the Lorentz forces which are a function of the square of the intensity passing through it. A short opening time can thus be obtained by the use of a movable contact having a low mass and a low inertia. The sensitivity of the circuit breaker may be modified by adjusting the number of turns forming the induction coil 5 or by modifying the stiffness of the spring 6. More particularly, the spring 6 may be calibrated to exert on the movable contact a return force corresponding substantially equal to Lorentz forces produced by the current value corresponding to the opening threshold desired for the circuit breaker.

 In a preferred embodiment of the circuit breaker, the movable contact is mounted between the arc expansion chamber 4 and the induction coil 5. The coil thus generates a magnetic field both to open the movable contact in the event of overcurrent and to split the electric arc in the arc expansion chamber 4, which reduces the manufacturing cost of the circuit breaker according to the invention.

 This movable contact may have any suitable shape insofar as it is able to move in a plane substantially parallel to the induction coil 5 to open, so as to take advantage of the magnetic field that it generates. In a preferred embodiment, the movable contact is rotatably mounted on an axis A 1 which is substantially parallel to the electrode

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 central 2. When an overcurrent crosses the circuit breaker, the magnetic field generated by the coil increases, which produces electromagnetic forces opposing the return spring 6 to cause the rotation of the movable contact around the axis A 1. In firstly, an electric arc appears between the central electrode 2 and one end of the movable contact. In this example, the movable contact encounters at the end of the opening stroke a stop 7 secured to the chassis which interrupts its stroke in an open position shown in FIG. 3. Advantageously, this stop 7 may be an arc horn on which the arc is transferred, in particular to reduce wear on the end of the movable contact. The arc is then transferred to the expansion chamber to be fractionated there and to produce an electromotive force intended to reduce the intensity of the current.

 In a preferred embodiment, the spring 6 is mounted so as to form with the movable contact 3 an articulated elbow still known as a toggle joint, having a neutral point located substantially halfway between the open position and the closed position. In this embodiment, the movable contact 3 has substantially the shape of a lever and the axis of rotation A 1 is disposed between the ends of this lever. The spring is mounted around a telescopic bar which it tends to lengthen, this bar having one end rotatably mounted on the axis A2. The telescopic bar and the lever are connected to each other by a pivot link to form the articulated elbow. The neutral point of this articulated elbow corresponds substantially to a position for which the telescopic bar and the lever are in alignment with one another. In this way, when the movable contact 3 opens under the effect of the electromotive forces due to an overcurrent, it passes the neutral point of the articulated elbow before its end meets the arc horn 7, which immobilizes it resting on the bow horn in a stable open position.

With this articulated elbow, the circuit breaker opens and then remains stabilized in the open position shown in Figure 3 after the threshold is exceeded by the current flowing through the circuit breaker.

 In another preferred embodiment of the circuit breaker according to the invention, the movable contact is mounted on a base 8 which can rotate relative to an axis A2 also parallel to the central electrode 2 on which the axis of rotation A 1 is fixed of the movable contact 3. More particularly, the base 8 is linked in movement to an actuating member 9 which is capable of making it

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 rotate relative to axis A2. Thus a rotation of the movable base which carries the movable contact via the axis A 1 also causes an opening of the circuit breaker. The opening of the circuit breaker through the member 9 causes the base 8 to rotate in the same direction of rotation as for the opening of the movable contact 3, namely the indirect direction in FIG. 2. With this movable base 8 the circuit breaker which opens in the event of overcurrent can also be opened by an operator or by a control device associated with the circuit breaker.

 Advantageously, as in the example of FIGS. 2 to 4, the articulated elbow and the spring 6 are mounted on the rotary base 8. The movable contact is rotatably mounted on the base 8 having its end located in the extension of this base. The base 8 is rotatably mounted on the axis A2 which is parallel to the central electrode 2, so as to allow a plane rotation of the base in a plane substantially perpendicular to the central electrode 2.

 In the event of an overcurrent, the movable contact 3 turns in the indirect direction and passes the neutral point of the articulated elbow to open and come to rest against the arc horn 7. This rotation of the movable contact occurs without rotation of the base. 8 and leads the circuit breaker to an open position shown in FIG. 3. After this opening of the movable contact, a rotation in the indirect direction of the base 8 causes the articulated elbow to close: the movable contact which has its end resting on the arc horn 7 rotates in the direct direction under the effect of the rotation in the indirect direction of the base 8 and the articulated elbow returns to neutral. The articulated elbow is then in a new position visible in FIG. 4. During this movement of the base 8, the articulation of the elbow meets a stud 7 ′ also mounted on the base 8 on which it stops. More particularly, this pad 7 ′ stops the movement of the movable contact 3 before it meets the central electrode 2. In this implementation, the movable base makes it possible to reset the circuit breaker when its movable contact 3 is opened further at an overcurrent so that the circuit breaker is again ready for closing. After this resetting, an operation of the movable base 8 in the direct direction makes it possible to close the movable contact 3 on the central electrode to close the circuit breaker again.

 More particularly, the circuit breaker according to the invention could be coupled to a control system causing rotation of the mobile base 8.

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 In this case, an overcurrent in the circuit breaker initially causes a rapid opening of the movable contact 3 under the effect of Lorentz forces, followed in a second step by a rotation of the movable base 8 triggered by the command to reset the circuit breaker in order to position it ready for a new closing.

Claims (7)

1 / Current limiting circuit breaker comprising an induction coil (5) and a movable contact (3) arranged to open when the current passing through the circuit breaker is above a certain threshold, characterized in that the movable contact (3) is arranged near one end (5 ') of said induction coil (5), and in that it is movable in a plane parallel to the winding plane of the turns at said end (5') of said coil (5) to open under the action of the so-called Lorentz forces.  2 / A circuit breaker according to claim 1, comprising a helical expansion chamber (4) coaxial with said induction coil (5) and disposed at said end (5 ') of said induction coil (5), and in which said movable contact is mounted between said induction coil and said helical expansion chamber (4).  3 / A circuit breaker according to claim 1 or 2, comprising a central electrode (2) which extends coaxially inside said induction coil (5) and in which said movable contact (3) is movable around an axis ( A1) substantially parallel to said central electrode (2).  4 / A circuit breaker according to claim 3, comprising a base (8) on which is fixed the axis of rotation (A 1) of the movable contact (3), said base being able to pivot around another axis (A2) fixed and substantially parallel to said central electrode (2).  5 / A circuit breaker according to claim 3 or 4, comprising a spring (6) forming with said movable contact an articulated elbow retaining said movable contact (3) in a stable open or closed position, said articulated elbow having a dead center located between said open position and said closed position, said spring being calibrated to trigger an opening of said movable contact (3) when the current passing through the circuit breaker exceeds said threshold. <Desc / Clms Page number 9>  6 / Circuit breaker according to one of claims 1 to 5, comprising a stop (7) on which said movable contact (2) is held in support when it is in the open position.  7 / Circuit breaker according to one of claims 6, wherein said stop is an arcing horn (7) intended to transfer an electric arc appearing at the end of said movable contact during its movement.