EP0537090B1 - Electric circuit breaker with insertion of extra-turns in the magnetic trip mechanism winding - Google Patents

Description

The invention relates to a low voltage electrical circuit breaker having a pair of contacts, one of which is movable, a contact pressure spring urging the movable contact in the closed position, a mechanism for controlling the opening and closing of the circuit breaker. actuated by a lever, and an electromagnetic trip device comprising a coil electrically connected in series with the contacts and a movable armature actuated when the current flowing through the coil exceeds a predetermined threshold and arranged to on the one hand trigger said mechanism and thus cause the opening of the circuit breaker, and on the other hand to act by percussion on the crew of the movable contact and move the latter quickly in the open position.

A known electric circuit breaker of the kind mentioned (French patent 2,605,454) makes use of the force generated by the electromagnetic trip device during a short-circuit current to accelerate the opening of the contacts. A rapid opening of the contacts is essential for cutting the current and the use of a striker actuated by the electromagnetic trip device whose impact force on the movable contact adds or replaces the opening force of the mechanism spring. opening, allows a much higher contact separation speed to be obtained. It is possible to increase this percussion force by using an electromagnetic trigger coil having a high number of turns. This coil is continuously traversed by the current and an increase in the number of turns is accompanied by an increase in heating which quickly becomes prohibitive. In particular in large-caliber devices, the number of turns of the coil is limited and the action of the striker is consequently itself limited.

The present invention aims to allow the realization of a circuit breaker with accelerated opening of the contacts and increased breaking capacity.

The circuit breaker according to the invention is characterized in that said coil is subdivided into first and second parts connected in series, by a connection point connected to one of said contacts, so that the current passing through the contacts closed traverses only the first part of the coil, that the number of turns of this first part is low enough to avoid excessive heating when it is traversed by the nominal current or that said first part has no turns, and that the second part of the coil is connected to an electrode arranged in the arc displacement zone, drawn during the separation of the contacts, so as to pick up the arc and to switch the current in the first and in the second part of the coil to increase the displacement force of the movable armature and / or the impact force of the movable contact.

In normal operation, the nominal current flowing through the circuit breaker travels through the first part of the coil, the number of turns of which is determined in the usual way to generate an actuating force of the tripping mechanism when the current exceeds a given threshold. As soon as the contacts are separated and the arc drawn between the separate contacts is switched, on the electrode, the second part of the coil is switched on by adding a sufficiently small number of additional turns of the coil to allow switching. The current flows through the first and the second part of the coil by exerting an increased force of displacement of the movable armature which can inter alia be used to increase the force of percussion of the movable contact. The heating of the coil is of course increased but the duration of excitation of the two parts of the coil is extremely short since it disappears as soon as the current is cut by the circuit breaker.

The circuit breaker contacts are arranged to be subjected to a electrodynamic repulsion force capable of causing the separation of the contacts against the force exerted by the contact pressure spring, when the current exceeds a given threshold generally greater than the tripping threshold. The contacts can thus separate quickly and anticipate the opening action transmitted by the opening mechanism. The insertion of additional turns, in this case the insertion of the second part of the coil takes place only after the switching of the arc on the electrode, and this switching is advantageously accelerated by shaping the electrode by relative to the path of movement of the movable contact to quickly capture the arc. For this purpose, the electrode extends near the end of the contact arm, substantially parallel to the initial path of the latter, when the contacts are separated, so that the spacing between the end of the arm contact and the electrode quickly becomes smaller than the spacing of the separate contacts, causing the arc to switch on the electrode. The two parts of the coil are preferably arranged coaxially and they can be constituted by a single coil having an intermediate tap constituting the connection point between the two parts of the coil. This connection point is electrically connected to one of the contacts, preferably to the fixed contact, while the electrode is connected to the end of the second part, opposite to said connection point. The end of the first part of the coil, opposite the connection point, is connected to one of the end terminals of the circuit breaker. The movable armature is advantageously a sliding core inside the coil which, on the one hand acts on the triggering mechanism, and on the other hand cooperates with the movable assembly or directly with the movable contact arm, by percussion to accelerate the movement of the movable contact during a short circuit. The insertion of turns according to the invention can of course be used in a circuit breaker without a striker and in which the increase in the magnetic field generated by the coil is used for other purposes, for example at rapidity actuation of the triggering mechanism or a magnetic blow of the arc. The electrodynamic repulsion of the contacts advantageously results from a loop path of the current flowing through these contacts, and the separation of the contacts under the effect of these repulsion forces occurs preferably before the action of the tripping mechanism.

• La figure 1 est une vue schématique en élévation, la face avant étant supposée enlevée d'un disjoncteur selon l'invention, représenté en position de fermeture;
• La figure 2 est une vue analogue à celle de la figure 1, montrant le disjoncteur en cours d'ouverture.

Other advantages and characteristics will emerge more clearly from the description which follows, of an embodiment of the invention, given by way of example, and represented in the appended drawings in which:

• Figure 1 is a schematic elevational view, the front face being assumed removed from a circuit breaker according to the invention, shown in the closed position;
• Figure 2 is a view similar to that of Figure 1, showing the circuit breaker being opened.

The invention is described below as being applied to a miniature circuit breaker with molded case, but it is clear that it is applicable to other types of circuit breakers.

In the figures, a molded insulating case (10) of standard profile contains, a pair of contacts, one of which (11) is movable and the other (12) of which is fixed, a breaking chamber with deionization plates (13 ), an electromagnetic trip device (14), a bimetallic strip (15) and an actuation mechanism (31) of the movable contact. The actuation mechanism (31) which is not shown in detail, may be of the type described in the aforementioned French patent 2,605,454, arranged to be controlled manually by a lever (32) or automatically by the bimetallic strip (15) or the electromagnetic release (14). The movable contact (11) is carried by a contact arm (16) pivotally mounted on a fixed axis (17) and a tension spring (18) attacks the contact arm (16) to urge the movable contact (11) in support of the fixed contact (12).

The electromagnetic trip device comprises a coil in two parts (19,20) electrically connected in series by a connection point (21). In the example shown, the two parts (19,20) are constituted by the same coil having an intermediate tap constituted by the connection point (21), but it is clear that these two parts could be separate or be arranged a different way, including overlapping. Inside the coil (19,20), is slidably mounted a movable frame constituted by a sliding core (22) the end of which carries a striker (23) striking the movable contact arm (16) during 'an excitation of the coil (19,20) to move this movable contact to the open position. The circuit breaker has two terminals diagrammatically represented by input and output areas (24,25), the area (24) being connected to the base of the bimetallic strip (15) whose opposite end is connected by a braid (26 ) to the arm of the movable contact (16). The fixed contact (12) is electrically connected to the connection point (21) of the two parts (19,20) of the coil, the opposite end of the first part (19) of the coil being connected to the opposite pad (25 ). At a given instant, the current enters through the range (24), travels through the bimetallic strip (15), the braid (26), the closed contacts (11,12), the first part of the coil (19) to exit through the opposite range (25). Such an arrangement is well known to specialists and there is no need to describe it in more detail.

According to the present invention, the end (26), opposite the connection point (21), of the second part (20) of the coil is electrically connected to an electrode (27) which extends near the contacts (11 , 12) with a first part (28) substantially parallel to the fixed contact (12), a second part (29) disposed at a short distance from the end of the contact arm (16) and extending parallel to the displacement path from this end of the movable contact arm (16) and extending by a third part (30) curved in the direction of the breaking chamber (13).

It is easy to see that the distance between the movable contact arm (16) and the second part (29) of the electrode (27) remains constant and small during the initial phase of opening the contacts (11,12) and that this spacing quickly becomes less than the separation distance of the contacts (11,12) by causing a switching of the arc, drawn during the separation of the contacts (11,12), on the electrode (27). As soon as this switching of the arc, shown in FIG. 2, the current flows through the range (24), the bimetallic strip (15), the braid (26), the movable contact (11), the electrode (27), the second part (20) and the first part (19) of the coil to exit through the opposite area (25), as shown by arrows in FIG. 2. The switching of the arc on the electrode (27) Thus causes the insertion of the second part (20) of the coil and an increase in the number of turns of the latter, increasing the intensity of the magnetic field and therefore the force of displacement of the sliding core (22). The contacts (11,12) are arranged to impose a loop path of the current which generates electrodynamic repulsive forces tending to move the movable contact (11) in the opening direction against the force of the tension spring ( 18). The mechanism 31 is arranged to allow such separation of the contacts (11,12).

The circuit breaker according to the invention operates as follows:

In the closed position of the circuit breaker, shown in FIG. 1, the current passing through the closed contacts (11,12) flows only through the first part (19) of the coil of the electromagnetic trip device (14). The heating produced by the nominal current passing through the first part (19) of the coil is low, the number of turns of this first part being nevertheless sufficient to cause tripping of the circuit breaker during a short circuit, as described thereafter. The circuit breaker can be opened manually by actuation of the handle (32) which controls the mechanism (31).

During an overload, the deflection of the bimetallic strip (15) acts by a path not shown on the mechanism (31) to cause the opening by displacement of the movable contact arm (16). The nominal current or the overload current are insufficient to generate an electrodynamic repulsion of the contacts (11, 12), or to excite the electromagnetic trip device (14).

During a short-circuit current of an intensity greater than a predetermined threshold, the short-circuit current flowing through the first part (19) of the coil is sufficient to actuate the movable core (22) which transmits to the mechanism ( 31) a trigger order. During its movement, the movable core (22) also strikes the contact arm (16) to move or accelerate the movement of this contact arm (16) towards the open position of the circuit breaker. The short-circuit current flowing through the contacts (11,12) generates an electrodynamic repulsion force of these contacts which moves the contact arm (16) and causes the contacts (11,12) to separate. The arc drawn between the separate contacts (11,12) quickly switches to the electrode (27) by switching on the second part (20) of the coil of the electromagnetic trip device (14). The insertion of additional turns increases the magnetic field generated by the current passing through the coil and the displacement force of the movable core (22). The increased impact force causes the movable contact to move rapidly, thereby cutting off the current. It is clear that the separation of the contacts (11,12) by electrodynamic repulsion is faster than the operation of the mechanism (31) during a short circuit, and that the insertion of the second part (20) of the coil by switching the arc on the electrode (27) occurs before the movement of the movable contact by the mechanism (31). The action of the mechanism (31) confirms or completes the opening of the contacts (11,12) caused initially by the electrodynamic forces of repulsion and the percussion of the mobile core (22) on the contact arm (16). The speed of breaking the current limits the time of excitation of the parts (19,20) of the coil and therefore the heating thereof. This speed is particularly advantageous in circuit breakers ensuring cut selectivity.

It should be noted that the increase in the intensity of the magnetic field, due to the insertion of additional turns, can be used for other purposes than the displacement of the striker core (22), in particular to exert a magnetic blowing on the arc, and that it would not go beyond the scope of the invention using a first part (19) of a coil having no turn, the displacement of the movable core (22) being in this case generated during the excitation of the second part (20) of the coil.

The invention is of course in no way limited to the mode of implementation more particularly described, but includes all the variants which do not depart from the scope of the invention as claimed.

Claims (7)

1. A low voltage electrical circuit breaker having a pair of contacts (11, 12), one (11) of which is movable, a contact pressure spring (18) biasing the movable contact (11) to the closed position, an operating mechanism (31) for opening and closing of the circuit breaker actuated by a handle (32), and an electromagnetic trip device (14) comprising a coil (19, 20) electrically connected in series with the contacts (11, 12) and a mobile armature (22) actuated when the current flowing in the coil (19, 20) exceeds a preset threshold and arranged on the one hand to trip said mechanism (31) and thus bring about opening of the circuit breaker, and on the other hand to act by striking on the movable contact assembly (11) and to move the latter at high speed to the open position, characterized in that said coil (19, 20) is subdivided into a first part (19) and a second part (20) connected in series by a connection point (21) connected to one of said contacts (11, 12), so that the current flowing via the closed contacts (11, 12) flows through the first part (19) of the coil only, that the number of windings of this first part (19) is sufficiently small to prevent an excessive heat rise when the rated current is flowing through it, or that said first part (19) does not have any windings, and that the second part (20) of the coil is connected to an electrode (27) located in the displacement zone of the arc, drawn when separation of the contacts (11, 12) takes place, so as to pick up the arc and switch the current to the first (19) and second (20) part of the coil to increase the displacement force of the mobile armature (22) and/or the striking force of the movable contact (11).
2. The circuit breaker according to claim 1, characterized in that the number of windings of said first part (19) of the coil is sufficient to cause tripping of the mechanism (31) when the circuit exceeds said preset threshold.
3. The circuit breaker according to claim 1 or 2, characterized in that said connection point (21) of the coil is connected to the stationary contact (12), that the end of the second part (20) of the coil opposite the connection point (21) is connected to said electrode (27) and that the end of the first part (19) of the coil opposite said connection point (21) is connected to a terminal (25) of the circuit breaker, in such a way that switching of the arc onto the electrode generates flow of the current in the two parts of the coil.
4. The circuit breaker according to claim 1, 2 or 3, wherein the movable contact (11) is disposed at the end of a contact arm (16), characterized in that said electrode (27) extends in proximity to said end of the arm (16), appreciably parallel to the initial trajectory of movement of this end when opening takes place to achieve high-speed switching of the arc onto the electrode (27) and connection of the first (19) and second (20) part of the coil into the circuit.
5. The circuit breaker according to claim 1, 2, 3 or 4, characterized in that said mobile armature comprises a core (22) sliding inside said coil and that said core is securedly united to a striker (23) which strikes the movable contacts (11).
6. The circuit breaker according to claim 1, 2, 3, 4 or 5, characterized in that said contacts (11, 12) define a loop trajectory of the current generating electrodynamic repulsion forces which displace the movable contact (11) in the separation direction against the contact pressure spring (18) when the current flowing in the contacts exceeds a given threshold.
7. The circuit breaker according to claim 6, characterized in that separation of the contacts (11, 12) takes place before tripping of the contact opening mechanism (31).

Images