CURRENT-LIMITER ELECTRICAL CIRCUIT BREAKER, WITH CONTACT OPENING BY ELECTRODYNAMIC REPULSION

Abstract: In a current-limiter electrical circuit breaker with contact opening by electrodynamic repulsion, comprising at least a couple of contacts inserted between a power supply terminal and a load terminal, the contact-holder arms of which form two branches substantially parallel and closely approached to each other, through which cur­ rents of opposite sign flow, a control mechanism kinema­ tically linked to one of the two contact-holder arms through a compound toggle lever formed by two sectors and a spring suitable to pass from one side to the other side, and vice-versa, of a dead-point position, a block­ ing device for the locking of the control mechanism in its active position, and thermomagnetic devices suitable to act on a release device for the disengaging of said blocking device; the hinge connecting the two sectors of the compound toggle lever to each other is constituted by a limitedly sliding slot-pin coupling, and the second one of the two contact-holder arms is linked to said release device through a kinematic chain.

Description: The object of the present invention is a current-limiter electrical circuit breaker with contact opening by electrodynamic repulsion. Several types of circuit breakers of such a kind are known. From a general viewpoint, in such a circuit breaker at least a couple of contacts are always provided, inserted between the power supply terminal and the load terminal, said contacts being held by related support arms which form branches substantially parallel and suitably closely approached to each other, through which currents of opposite sign flow, so that - in case of strong current overloads due to short circuit - repulsive electrodynamic forces are generated, which tend to istantaneously open the contacts. On one of the two coupled contact-holder arms, a control mechanism can act to the purpose of displacing the related contact, either by manual or by remote control, from a contacts open position to a contacts closed position, and vice-versa. Along the current path comprising said closely approached parallel branches, suitable devices are moreover inserted in series, which are sensible to low- and medium-intensity currents, said devices being generally of thermal and/or of magnetic type, suitable to act, in case of abnormal current overloads, on a release device to cause the control mechanism to be disengaged, to the purpose of automatically moving the contact-holder arm connected to it to a position of final opening. This automatic release of the control mechanism is, however, less rapid than the contacts opening caused by the repulsive electrodynamic forces. Electrical circuit breakers of this kind are known, in which the contact - belonging to the couple of coupled contacts - which can be forced to move to the opening direction by the repulsive electrodynamic forces against the action of a spring, is the contact on which the control mechanism does not act. In particular, this spring can be so positioned as to cause it to cross, during the opening movement of the related contact caused by the electrodynamic repulsion, a dead point, so that, at the end of said movement, it keeps the related contact in its open position. At the beginning of the opening stroke of this contact, caused by the electrodynamic repulsion, the other contact, viz., the one on which the control mechanism is active, is still locked, and hence it cannot move. Only with the progressing of the opening movement of the first contact under the action exerted by said repulsive electrodynamic forces, and in particular when the related spring is crossing its dead point, a suitable mechanical kinematic chain causes the action of release of the control mechanism controlling the other contact to take place, so that eventually also the other contact is automatically brought to its final open position. This is obtained however also by means of the thermal and/or magnetic release devices. An electricl circuit breaker of this type is known, e.g., from DE-A- 17 88 148. According to another proposal of the prior art, one contact belonging to the couple of coupled contacts is stationary, and the other one is movable and is linked to the control mechanism provided with a blocking device which keeps locked the two contacts in their closed position, the release of this control mechanism locking device being possible by means of thermomagnetic release devices sensible to currents of low or medium intensity. This other contact can be moved against elastic means, in the direction of opening of the coupled contacts, also by the repulsive electrodynamic forces, in case of heavy overloads due to short circuit. An electrical circuit breaker of this type is known, for example, from DE-A- 24 43 771 and from the document DE-A- 33 36 207. In order to obtain, in a circuit breaker of this latter type, the final opening of the contacts within more restricted times, without being obliged to wait for the intervention of the thermomagnetic release devices causing the release of control mechanism, it has already been also proposed to provide a direct connection interposed between the mobile contact-holder arm and the control mechanism release device, to directly cause the disengaging due to a shift of the mobile contact-holder arm by electrodynamic repulsion. It must be anyway stressed that in all the electrical circuit breakers proposed to date, wherein the opening of the contacts can be caused by repulsive electrodynamic forces, it is always only one of the two coupled contacts which is moved under the direct action of said forces, whilst the second contact is brought to its final open position - due to the disengaging of the control mechanism - in a second time only, or it is even a stationary contact, and is not moved to any opening position at all. It results therefrom that the mutual spacing apart of the two contacts, at the beginning of the opening movement of one of them, under the action of the electrodynamic repulsion, can assume relatively limited values and, consequently, the extinction of the arc formed between the two contacts at the time of their mutual spacing apart is of limited efficaciousness. The purpose of the present invention is hence to provide a current-limiter electrical circuit breaker with contact opening by electrodynamic repulsion which allows, in case of very high current overloads due to short circuit, a greater and still quicker opening of the two coupled contacts, and hence a more efficacious and quick extinction of the arc occurring between the two contacts at the opening time, to be obtained. To the purpose of achieving this, according to the invention, a current-limiter electrical circuit breaker is proposed with contact opening by electrodynamic repulsion, comprising at least a couple of contacts inserted between a power supply terminal and a load terminal, the contact-holder arms of which form two branches substantially parallel and closely approached to each other, through which currents of opposite sign flow, a control mechanism kinematically linked to one of the two contact-holder arms through a compound toggle lever formed by two sectors and a spring suitable to pass from one side to the other side, and vice-versa, of a dead-point position, a blocking device for the locking of the control mechanism in its active position, and thermomagnetic devices suitable to act on a release device for the disengaging of said blocking device, characterized in that the hinge connecting the two sectors of the compound toggle lever to each other is constituted by a limitedly sliding slot-pin coupling, and that the second one of the two contact-holder arms is linked to said release device through a kinematic chain. By this arrangement, it has been possible to render movable both the contacts of the circuit breaker directly under the action of the repulsive electrodynamic forces, so that, in case of very high current overloads due to short circuit, under the action of said repulsive electrodynamic forces, both the contacts get mutually spaced apart, with a consequent greater and quicker opening of the contacts, and hence a more efficacious extinction of the arc. In fact, whilst the second contact-holder arm on which the control mechanism does not act can istantaneously move towards the opening direction in order to cause, after a certain opening stroke, the disengaging of the blocking device of the control mechanism of the other contact-holding arm, the latter is also allowed to move into opening direction under the action of high repulsive electrodynamic forces, even if the control mechanism is still blocked, and hence before the intervention of the other release device, and this thanks to the fact that the two sectors of the compound toggle lever are not hinged to each other in a fixed way, but through a sliding coupling constituted by a pin with possible roller solid with a sector and slidingly inserted into a slot provided in the second sector. The invention is disclosed hereunder in greater detail with reference to the attached drawings, which illustrate a possible form of practical embodiment thereof. In the drawings: Fig. 1 shows a schematic side view of a pole of a circuit breaker according to the invention, with the contacts being closed; Fig. 2 shows a schematic side view from the control side, always in position of circuit breaker closed; Figs. 3-4, 5-6 show views respectively analogous to those of Figs. 1 and 2, in various sequential steps of contacts opening by elctrodynamic repulsion; and Figs. 7-8 show views analogous to those of Figs. 1 and 2 in position of open circuit breaker. The circuit breaker pole shown comprises a couple of contacts 10, 11, respectively held by contact-holder arms 12, 13. The contact-holder arm 12 is rotatable around a pin 14, whilst the contact-holder 13 is fastened onto a rotary shaft 15. The contact-holder arm 12 is connected through a flexible conductor 16 to a first terminal 18 and the contact-holder arm 13 is connected through a flexible conductor 17 to a terminal 19 with known thermomagnetic release devices, schematically indicated in 20, 21, being interposed. The current path, with the contacts 10 and 11 being closed, comprises two branches parallel and near to each other, constituted by the contact-holder arms 12 and 13, through which branches currents of opposite sign flow, and which current path the thermomagnetic release devices 20 and 21 are furthermore inserted in series. The contacts 10, 11 are inserted, in a known way, in an arc-quenching system, indicated in a schematic way only. Of the couple of contacts 10, 11, the contact on which the control mechanism for the controlled opening and closing of the circuit breaker acts, is contact 11, held by arm 13. In fact, as it can be seen at Fig. 2, the shaft 15, with which the contact-holder arm 13 is solid, bears also a sector 23 which constitutes one of the two sectors of a compound toggle lever. The other sector is constituted by an element 24 hinged in 25 to a lever 26 mounted in a rotary way around a stationary pin 27. The sector 24 has a suitable profile and rests with an edge surface thereof 24a on pin 27. The sector 24 is provided at a free end thereof with a pin 28 with roller 29, which roller is slidingly guided inside a slot 30 provided in sector 23. The coupling between slot 30 and pin 28 with roller 29 forms a sliding hinge for mutual connection of sectors 23 and 24. A control lever 31 is rotatably mounted around a stationary fulcrum 32 and, between a pin 33 solid with the lever 31 and the pin 28 solid with the sector 24, a spring 34 is active. The lever 26 is kept in the position as illustrated in Fig. 2 by a blocking device constituted by a two-armed lever 35 rotatably mounted around a pin 36 and bearing at the end of one of its arms a hook 37 suitable to engage a slot 38 provided in lever 26. On the other arm of lever 35, the thermomagnetic release devices 20, 21 can act through interposed mechanical means, of which a rod 39 is schematically shown. On the same other arm of lever 35 also a small lever 40, rotary around a pin 41, can act. The small lever 40 is a part of a kinematic chain constituted by a lever 42 solid with a shaft 43, which lever 42 bears an adjustment grub-screw 44 suitable to act on small lever 40. The shaft 43 holds, solid with itself, also a second lever 45 which is in contact with a projection 46 of contact-holder arm 12 (Fig. 1). Thus, the disengaging of locking hook 37 from the slot 38 of lever 26 can be caused not only by the thermomagnetic release devices 20, 21 through rod 39, but also directly by the contact-holder arm 12 when the same moves away from its position of contacts closed, under the action exerted by the electrodynamic repulsion forces. The position of circuit breaker closed is that shown in Figs. 1 and 2. When, in this condition, a short circuit occurs with a current overload of, e.g., about 30 times the rated current value of the circuit breaker, the repulsive electrodynamic forces which are generated in the two parallel branches closely approached to each other, cause a movement in the opening direction of the contact-holder arm 12 around pin 14 and against a thrust spring 22, as illustrated in Fig. 3, and through the kinematic chain formed by elements 45, 43, 42, 44, 40 the lever 35 is rotated in the direction which causes hook 37 to get disengaged from slot 38 of lever 26. In that way, after a certain opening stroke of arm 12, the control mechanism is disengaged, and spring 34 brings automatically the contact-holder arm 13 into its position of final opening, shown in Figs. 7 and 8, whilst the contact-holder 12 returns eventually to its original position under the action of spring 22. When, on the contrary, due to a short circuit, a higher current overload, for example of the order of about 80 times the rated current value of the circuit breaker, occurs, the consequent repulsive electromagnetic forces between the two contact-holder arms 12, 13 become high enough to cause not only the contact-holder arm 12 to move, as described above, but also the contact-holder arm 13 to move, as shown in Figs. 5 and 6. The opening movement of the contact-holder arm 13 is made possible, notwithstanding the fact that the control mechanism is initially still locked, by the fact that the hinge of the compound toggle lever is not fixed, but sliding, the two sectors 23 and 24 of this compound lever being linked to each other through the sliding coupling of roller 29 - held by the sector 24 - in the slot 30 provided in sector 23. In other words, without the lever 26 being released from hook 37, the sector 23 of the compound toggle lever solid with the contact-holder arm 13 can rotate around the axis of shaft 15, causing also the sector 24 to rotate around pin 25, thanks to the sliding of roller 29 inside slot 30. In this way, both the contact-holder arms 12, 13 are directly caused to rotate by the repulsive electrodynamic forces, with a consequent istantaneous and greater opening or mutual spacing apart of contacts 10, 11, and thus with a more effective extinction of the arc generated between the two contacts. Of course, the release of the control mechanism to the purpose of bringing the contact-holder arm 13 into its final stable opening position, is caused also in this case in the way as described above, viz., through the kinematic chain beginning from the contact-holder arm 12. The arrows shown in Figs. from 3 to 6 indicate the directions of movement of the related elements during their respective displacements. It is clear how by means of the circuit breaker according to the invention, in a structurally very simple way considerable advantages are gained, in particular when the circuit breaker is subject to very high current overloads due to short circuit.

Claims: Current-limiter electrical circuit breaker with contact opening by electrodynamic repulsion, comprising at least a couple of contacts (10,11) inserted between a power supply terminal and a load terminal, the contact-holder arms (12,13) of which form two branches substantially parallel and closely approached to each other, through which currents of opposite sign flow, a control mechanism kinematically linked to one (13) of the two contact-holder arms (12,13) through a compound toggle lever formed by two sectors (23,24) and a spring (34) suitable to pass from one side to the other side, and vice-versa, of a dead-point position, a blocking device for the locking of the control mechanism in its active position, and thermomagnetic devices (20,21) suitable to act on a release device for the disengaging of said blocking device, characterized in that the hinge connecting the two sectors (23,24) of the compound toggle lever to each other is constituted by a limitedly sliding slot-pin coupling (30,28), and that the second one (12) of the two contact-holder arms (12,13) is linked to said release device through a kinematic chain. Electrical circuit breaker according to claim 1, where in said pin (28) supports a roller (29) which is slidingly engaged inside said slot (30).

Inventors: MOSTOSI, ANGELO
Applicants: ABB SACE S.P.A.
Application year: 1986
Main classification: H01H77
IPC codes: H01H3, H01H71, H01H77