EP0168888A2

EP0168888A2 - Ultrarapid-release current-limiter electrical switch

Info

Publication number: EP0168888A2
Application number: EP85201125A
Authority: EP
Inventors: Angelo Mostosi
Original assignee: SACE SpA
Current assignee: ABB SACE SpA
Priority date: 1984-07-18
Filing date: 1985-07-09
Publication date: 1986-01-22
Also published as: EP0168888A3; IT8422616V0

Abstract

In an ultrarapid-release current-limiter electrical switch comprising at least a support with a stationary contact, at least a movable contact borne by an arm rotatably mounted in a movable unit and submitted to the action by a spring reacting against the movable unit, and a control mechanism with a control lever, an oscillatable lever kept stopped by a release device, a toggle lever system between said movable unit and said oscillatable lever and an extension spring acting between said control lever and the hinge of said toggle lever system, said support of the stationary contact and said movable contact bearing arm defining, under contact closure conditions, two portions parallel and close to each other in the current path, wherein currents of opposite sign flow, which are suitable to produce, in case of strong current intensities due to short-circuits, repulsive electrodynamic forces; between said movable contact bearing arm and said release device for the oscillatable lever of the control mechanism mechanical means are interposed suitable to cause, on a displacement of said arm by eletrodynamic repulsion, directly the release of said oscillatable lever.

Description

The object of the present invention is a ultrarapid-release current-limiter switch.
In a switch of this type, the instantaneous opening of the contacts is automatically caused, in case of heavy current overloads due to short-circuits, by the repulsive electrodynamic forces produced by the flow of strong currents of opposite sign inside two portions parallel and suitably close to each other of the current path connecting the movable and stationary contacts of the switch at the power supply and load terminals, said parallel portions being normally constituted by the same supports of the movable contacts and of the stationary contacts. To that purpose, it is known to assemble the movable contacts supporting arms rotatably and in an elastically yielding fashion in a movable unit which can be moved, by means of a control mechanism, due to a direct manual intervention or to a remote intervention, from an open-contact position to a closed-contact position and vice-versa. Inside said current path comprising said parallel portions close to each other, devices are moreover inserted in series which are sensible to the low- and medium-intensity currents and are generally of thermic and/or magnetic type, suitable to act, in case of abnormally high current overloads, on a control mechanism release device, to automatically cause the displacement of said movable unit to the open-contact position. This automatic release is usually less rapid than the contact opening caused by said repulsive electrodynamic forces.
A current-limiter electrical switch as above briefly set forth is known, e.g., from the German Patent N° 2443771 and from the German Patent Application publ. N° 33 36 207. The opening of the contacts by means of the intervention of the release device occurs, in these known switches, as mentioned above, with a certain delay which may result too long for certain practical application requirements. This is due to the fact that the release device is controlled, through suitable mechanisms, by said thermomagnetic devices, so that it has not been possible to date to shorten the intervention times of the release device under certain limits.
Purpose of the present invention is to provide a current-limiter electrical switch of the type with contact l opening by rodynamic repulsion in case of heavy current overloads, wherein the release, i.e., the ultimate and long-lasting opening contact, is obtained within still shorter times.
This purpose is achieved according to the invention in that a direct link is provided interplaced between the movable contact bearing arm and the final release device of the control mechanism suitable to cause the release directly upon a shift of the movable contact bearing arm by electrodynamic repulsion.
Thanks to this direct action on the release device by the movable contact bearing arm, it has been possible it to considerably shorten the total circuit-opening time, and namely up to one third of the time to date required by the known switches of this type.
Said direct link interplaced between the movable contact bearing arm and the final release device may be simply constituted by a thrust rod assembled in the movable unit supporting the movable contact bearing unit and onto which this latter acts when it is displaced by the repulsive electrodynamic forces in contrast to the action of elastic means, said rod acting in its turn either directly or through a lever on the final element of the release device of the control mechanism of the movable unit.
An embodiment of the switch according to the invention shall be described in more detail hereinunder with reference to the attached drawings, wherein Figs. 1 and 2 are schematic views of a pole of the switch respectively with the contacts closed and with the contacts shown in the first step of the opening movement caused by electrodynamic repulsion.
As it is seen in the drawing, the schematically illustrated switch pole comprises generally a first terminal 10, e.g., connected to the power supply, and a second terminal 11, e.g., connected to a load. To the terminal 10 a conductor 12 is connected which ends with U-bent portion 13 bearing a stationary contact 14.
Around a pivot 15 a movable unit 16 is rotatably assembled wherein an arm 18 bearing a movable contact 19 is supported in a rotatable way around a spindle 17.
To the second terminal 11 a conductor 21 is connected which is in its turn electrically connected to the arm 18 through thermomagnetic release devices known, schematically indicated in 22 and 23. The current path, on stationary contact 14 and movable contact 19 closed, comprises hence two portions parallel and close to each other, constituted by the bent portion 13 of the conductor 12 and by the arm 18 bearing the movable contact 19, along which portions currents of opposite sign flow. Moreover, in said current path the thermo- magnetic release devices 22 and 23 are inserted in series.
In order to bring the movable unit 16 into the position of closure and into the position of opening of the contacts 14 and 19, as desired, a known control mechanism is provided, which is hence only schematically shwon in the drawing.
This mechanism comprises a control lever 24 pivoted in 25 and linked, through a a toggle lever, to the movable unit 16. The toggle lever is formed by two links 26 and 27 hinged to each other in 28. The free end of the link 26 is hinged in 29 to the movable unit 16, whilst the free end of the link 27 is hinged in 30 to a lever 31 hinged in 32. Between the hinge 28 connecting the two links 26 and 27 and a point 33 of the control lever 24 an extension spring 34 acts. The lever 31 with its point 35 is suitable to abut against a stop 36 constituted by a step of a rotary shaft 37 bearing an arm 38 solid with it. The shaft 37 with its step-shaped stop 36 and with the arm 18 form a release device for the lever 31, which device can be driven by the thermomagnetic release devices 22, 23, through interposed mechanical means, of which a rod 39 is schematically shown suitable to act on the arm 38 to cause the shaft 37 to rotate and thus disengage the stop 36 from the point 35 of the lever 31. In this case, the force of the spring 34 via the lever 31 fulcrumed on the rotation pivot 32 brings the toggle lever system 26 and 27 back into the open-contact position.
The structure of the switch as it has been herein described is substantially that of the known art and the operating way is also known, including that of the thermomagnetic release devices and of the release devices of the con trol mechanism.
Unfortunately, as it has been set forth, the intervention of the release device as obtained in this way requires a certain time, which for particular practical needs may be excessive. This time may be acceptable when the opening of the contacts of the switch is caused by the intervention of the thermic release device and/or of the mag netic release device, i.e. due to currents higher than the calibration currents of the switch, but not high enough as to produce such repulsive electrodynamic forces as to cause the separation of the movable contact bearing arm from the stationary contact, indipendently from a shift \ o( the movable unit on to which the movable contact bearing arm is mounted.
On the contrary, when the instantaneous opening of the contacts is caused, under conditions of very strong current intensities due to a short-circuit, by the repulsive electrodynamic forces, the intervention time of the release device to the purpose of bringing also the mobile unit into the opening position may result too long for determined needs, if the control of said release device takes place through the normal thermomagnetic release devices.
At this point the present invention intervenes, which envisages the control of the release device directly by the movable contact bearing arm due to a shift of the same caused by said repulsive electrodynamic forces.
In fact, the present invention provides to this purpose a thrust rod 40 slidingly assembled inside the movable unit 16 and associated with the arm 18 bearing the movable contact 19. This rod 40 is moreover provided with a concentric spring 41 acting between a shoulder on the movable unit 16 and a small disk 42 solid with the rod 40, in contact with a lever 43 hinged in 44 to the movable unit 16, which lever 43, to the purpose of exerting the necessary pressure on the contacts is pressed in its turn against an idle roller 45 mounted on the rear edge of the arm 18 bearing the movable contact 19. The free end of the thrust rod 40 is extended outwards from the movable unit 16 and is suitable to act on the arm of a bell crank 46, pivoted in 47, the other arm of which cooperates with a second arm 48 solid with the shaft 37 of the release device.
When, with the contacts being closed (see fig. 1), the arm 18 bearing the movable contact 19 is in its normal operating position under the action of the spring 41, the thrust rod 40 does not exert any actions on the bell crank 46 and the lever 31 is stopped by the step 36 of the shaft 37. The control mechanism is capable of holding the movable unit 16 in its position in which the switch contacts are closed.
When, on the contrary, due to a very strong current intensity due to a short circuit, the arm 18 bearing the movable contact 19 is displaced in contrast with the force of the spring 41 by the repulsive electrodynamic forces (see fig. 2), said arm acts, through the roller 45 and the lever 43, on the thrust rod 40 so as to cause it to protrude outwards from the movable unit 16 to a greater extent, whereby its free end exerts a thrust on the bell crank 46, causing it to rotate clockwise, so as to act on the arm 48 and to cause the shaft 37 to rotate counterclockwise, thus clearing the stop step 36 of the point of the lever 31. In such a way, the release occurs of the control device and by the action of the spring 34 and with the contribution of the repulsive electrodynamic forces the movable unit 16 is brought to the opening position of switch contacts.
Practical tests have shown that, thanks to this direct control of the release device by the movable contact bearing arm, the total circuit-opening time can be reduced down to about one third of the time needed when the release is controlled by the traditional thermomagnetic release devices of the known art.

Claims

1. Ultrarapid-release current-limiter electrical switch comprising at least a support with a stationary contact, at least a movable contact borne by an arm rotatably mount ed in a movable unit and submitted to the action by a spring reacting against the movable unit, and a control mechanism with a control lever, an oscillatable lever kept stopped by a release device, a toggle lever system between said movable unit and said oscillatable lever and an extension spring acting between said control lever and the hinge of said toggle layer system, said support of the sta tionary contact and said movable contact bearing arm defining, under contact closure conditions, two portions par allel and close to each other in the current path, wherein currents of opposite sign flow, which are suitable to produce, in case of strong current intensities due to short-circuits, repulsive electrodynamic forces, characterized in that between said movable contact beaming arm and said release device for the oscillatable lever of the control mechanism mechanical means are interposed suitable to cause, on a displacement of said arm by electrodynamic repulsion, directly the release of said oscillatable lever.

2. Switch according to claim 1, characterized in that said mechanical means comprise a thrust rod slidingly mounted in the movable unit ad in contact with said movable contact bearing arm, the free end of said rod extend ind outwards from the movable unit being suitable to act on the release device.

3. Switch according to claim 2, characterized in that said thrust rod is hold in contact with the movable contact bearing arm through a lever fulcrumed in the movable unit, which lever acts against an idle roller mounted on the rear edge of said movable contact bearing arm.

4. Switch according to claim 2, characterized in that the free end of said thrust rod is suitable to act on the release device through a bell crank cooperating with an arm being part of the release device.