EP0118333A1 - Switch device with insulating barrier introduced between the contacts when they open and with arc cutting means between the barrier and an insulating wall - Google Patents

Abstract

A switch device is provided comprising means for controlling the separation of the contacts and for inserting an electrically insulating screen between the contacts during opening thereof, said screen cooperating with an electrically insulating surface formed by one of the walls of a substantially closed arc chamber, for shearing the arc between the contacts, the control of the movement of the screen being obtained by propulsion means essentially separate from those causing the separation of the contacts, while the whole is arranged so that substantially complete shearing of the arc is obtained before it has had time to stabilize itself, substantially total sealing being obtained between the screen and said surface when they are in abutment.

Description

The invention relates to the extinction of the electric arc which arises when a circuit is opened by a switch device, operating on direct or alternating current.

It relates more particularly to low and medium voltage breaking devices (ranging for example from 110 V to 5 KV) in which the discharge occurs in the air and more especially, those in which an electrically insulating screen is interposed between the contacts in order to favor the rapid extinction of the arc and to avoid its re-ignition.

These devices include: limiters, where the separation of the contacts is for example obtained by means of electrodynamic repulsion forces which are exerted in conductive portions of contact support when the current which crosses them exceeds a predetermined threshold, other types circuit breakers, where contact separation is achieved by releasing accumulated mechanical energy or by magnetic energy developed by the short circuit, and even some contactors.

In the prior art, the cutting technique mainly used, in the aforementioned field, an arc elongation effect.

Now the arc voltage which is made to grow as much as possible to cause extinction depends, not only on its length, but on the electric field, which is proportional to the intensity of the current and inversely proportional, of a part to the conductivity, on the other hand to the section of the arc. This latter factor has so far not been used systematically - with appropriate measures which allow it to be controlled, with the aim of increasing the arc voltage.

The Applicant has discovered that a much faster extinction of the arc is obtained, if, all other things being equal, there is practically complete shearing of the latter between the screen and an electrically insulating wall with which it cooperates. , on the express condition that the screen moves at a sufficient speed to continuously destabilize the arc from its birth and until the effective moment of shearing, and that the breaking chamber is arranged so as to offer no path of flight for the arc, outside the path along which the destabilization takes place. When these conditions are met, the arc voltage grows almost as fast as in a fuse.

According to patent DT No. 84 9138, filed on July 8, 1949, two pivoting flaps fold back towards a central wall with which they come into contact so as to interpose an obstacle on the paths of the arc between two pairs of respective contacts. However, after separation, the arrangement is such that the flaps take their folded position in a time equal to the contact opening time, which is also relatively long, because this opening is controlled by mechanical means. The arc can therefore stabilize and it is neither indicated nor probable, that its extinction is caused by the subsequent interposition of the screen, rather than by the passage of current through zero. This device seems in fact intended to prevent a rearming of the arc; before the arc goes out, it is in contact with the screen for a relatively long time long, from which it follows that a significant risk of metallization of the screen by the arc exists. In addition, strangulation is not completely ensured and escape routes are not avoided; finally, the entire structure is neither reliable nor likely to allow efficient and long-term operation.

According to the published patent application DT 1010618, filed on January 21, 1952, the screen, subjected to a translation perpendicular to the direction of spacing of the contacts, does not come between the contact pads until after they have been separated from each other by the cooperation, with their support blades, of bosses with which it is provided. The means for opening the contacts merges here with the means for propelling the screen and the latter must completely overcome the pressure for maintaining the contacts in the closed state. It necessarily follows that the interposition on the path of the arc of the screen thus braked in its translation occurs after a relatively long time, so that the arc will have had time to stabilize. A blowing coil is also arranged in the vicinity of the contact pads to drive the arc thus formed towards a slot into which the edge of the screen penetrates.

The constriction of the arc only intervenes after it has undergone a significant elongation and the whole device is housed in a very resistant sealed chamber, so that it creates an overpressure: these two factors (elongation and overpressure) contribute to increasing the arc voltage; with regard to strangulation, it is neither indicated nor probable that it is complete and that it constitutes a significant factor contributing to extinction.

According to the invention, the substantially complete shearing of the arc before it has had time to stabilize is obtained by controlling a sufficiently rapid movement of the screen by means of a member separate from the control member of separating the contacts and arranging the cooperating surfaces of the terminal edge of the screen and the wall insulating so that a substantially complete seal is obtained between them when the screen has come into abutment position against said wall.

According to a preferred embodiment, the linear speed of movement of the screen is greater than 2m / s.

According to another aspect of the invention, the screen is guided in its movement by a groove arranged to provide a lateral seal.

Other features, as well as the advantages of the invention, will become apparent in the light of the description below.

• la figure 1 est un schéma de principe, vu en coupe longitudinale par le plan médian I-I de la figure 2, d'un dispositif interrupteur faisant application de l'invention, en position de fermeture des contacts.
• la figure 2 est une coupe selon II-II de la figure 1 ;
• la figure 3 est une vue partielle, à échelle plus grande, représentant les contacts ouverts ;
• la figure 4 est une coupe par IV-IV de la figure 3 ;
• la figure 5 représente schématiquement et partiellement un mode d'exécution dans lequel l'écran est prolongé par une lame médiane dans laquelle est noyée une pastille conductrice ;
• la figure 6 est une vue en perspective, partiellement éclatée, d'un dispositif interrupteur à un seul contact mobile, avec un écran en marche d'escalier.
• la figure 7 est une vue en perspective, partiellement éclatée, d'un dispositif interrupteur dans lequel le contact non pivotant est noyé dans l'écran ;
• la figure 8 est une coupe longitudinale de ce dispositif interrupteur ;
• la figure 9 est une coupe suivant IX-IX de la figure 8 ;
• les figures 10 et 11 représentent une variante de la figure 8 ;
• les figures 12 et 14 représentent schématiquement et partiellement un dispositif interrupteur comportant deux écrans à engagement mutuel ;
• la figure 13 est une coupe transversale de l'extrémité de l'écran 6a, selon XIII-XIII de la figure 12 et d'une coupe partielle du boîtier ;
• les figures 15 et 16 illustrent un mode d'exécution dans lequel l'écran a la forme d'un peigne ;
• les figures 17 et 18 représentent un dispositif interrupteur dans lequel l'écran subit une translation circulaire, vu, à la figure 17, en coupe selon XVII-XVII de la figure 18 ;
• les figures 19 à 21 représentent un dispositif à deux écrans en forme de demi-disques pivotants ; et
• la figure 22 représente une variante où l'écran a la forme d'une couronne cylindrique.

In the attached drawing:

• Figure 1 is a block diagram, seen in longitudinal section through the median plane II of Figure 2, of a switching device applying the invention, in the closed position of the contacts.
• Figure 2 is a section on II-II of Figure 1;
• Figure 3 is a partial view, on a larger scale, showing the open contacts;
• Figure 4 is a section through IV-IV of Figure 3;
• FIG. 5 schematically and partially represents an embodiment in which the screen is extended by a central strip in which a conductive patch is embedded;
• Figure 6 is a perspective view, partially exploded, of a switch device with a single movable contact, with a screen running stairs.
• Figure 7 is a partially exploded perspective view of a switch device in which the non-pivoting contact is embedded in the screen;
• Figure 8 is a longitudinal section of this switch device;
• Figure 9 is a section along IX-IX of Figure 8;
• Figures 10 and 11 show a variant of Figure 8;
• Figures 12 and 14 schematically and partially show a switch device comprising two screens with mutual engagement;
• Figure 13 is a cross section of the end of the screen 6a, according to XIII-XIII of Figure 12 and a partial section of the housing;
• Figures 15 and 16 illustrate an embodiment in which the screen has the shape of a comb;
• Figures 17 and 18 show a switch device in which the screen undergoes a circular translation, seen in Figure 17, in section along XVII-XVII of Figure 18;
• Figures 19 to 21 show a device with two screens in the form of pivoting half-discs; and
• Figure 22 shows a variant where the screen has the shape of a cylindrical crown.

In Figures 1 to 4, there is shown a switch device comprising, housed in a housing 1, two contact supports 2 and 3 provided with contact pads 201 and 301 and able to pivot around two points 202-202 '. The latter is connected to a conductor 303 which leads to a connection terminal 304. A coil 4 is supplied from a connection terminal 204.

We have symbolized in 5 means that for convenience, we will call hereinafter "contact opening control lock" 2-201 and 3-301. For a circuit breaker device, these means will respond for example to a predetermined current overcurrent, corresponding to a short circuit and may be of different known types: thermal response members such as bimetallic strips, electromagnetic response members such as coils or electrodynamic response (repulsive forces exerted between the conductive supports of the contacts).

A screen 6 of electrically insulating material and, advantageously, a good conductor of heat, is disposed between the contact supports 2-3 and parallel to them when they are at rest. The front edge 601 of this screen is located a short distance dl behind the point of contact. This screen is propelled forward by means which have been symbolized here by the coil 4 and a system of levers 401-402 connected to a plunger core 403 with which it is provided. These means are, in the illustrated example, electromagnetic and actuated by the effect of the short-circuit current. However, they could be of various types: for example, armed spring triggered at the desired moment, or others.

It should however be emphasized that these propellant means must be capable of communicating on the screen a considerable translation speed, at least equal to 2 m / s and which will often, in practice, be of the order of 10 to 20 m / s , as will be explained below. This necessarily implies that the movement of the screen is not significantly slowed down by the contacts and that the screen is therefore not used to ensure opening by a mechanical action that it would exert on them to overcome their pressure to maintain the closed state; the movement of the screen must also not be dependent on the complete opening of the contacts, since it must be interposed between them as soon as the arc has started to strike, to ensure its destabilization. This is why it is necessary for the lock and the propellant means to be essentially separate. It is however possible that the screen, whose movement is very rapid, comes to strike against the contact pads before they have had time to separate and exerts on the contacts an unlocking action of their propellants : the main thing is that this action only concerns tripping, the movement of the contacts then being independent of that of the screen.

In FIG. 2, where certain members have been omitted for simplicity, it can be seen that the lateral edges of the screen are guided in grooves 602-602a formed in the wall of the case in a plane perpendicular to the parallelepiped housing 101 which contains the contacts , the propellant and the lock. Once the screen has penetrated into the slot 603 formed in the front wall 102 which delimits this housing and extends the housing of the screen, it is clear that thanks to the presence of the oblique insulating partitions 2020 and 3030, the internal volume of the housing is divided into two chambers between which the air can only pass through the lateral clearance which exists between the screen and the grooves, the edge 601 coming into full abutment at the bottom of the slot 603. It is important that this lateral clearance or very weak, for example less than 1/5 of the thickness and of the grooves. For example, the play will be less than 2/10 mm.

The slot 603 communicates with the outside. By degassing means, such as baffles 604 and channels 605 forming expansion chambers 606.

The distance d ₂ between the point of contact of the pellets and the bottom of the slot is relatively small, so that the path of the arc which forms between the pellets is not considerably extended when the screen pushes it towards the slot. The essential phenomenon is that the arc is completely sheared without ever having had time to stabilize and experience shows that this results in a growth of the arc voltage as brutal as that which occurs in a fuse, therefore an extremely rapid extinction and a considerable reduction (by a factor given as an indication of the order of 2 to 3) of the energy of the arc compared to what happens in the absence of this phenomenon of abrupt reduction of the section S of the arc to a practically zero value.

• El = R_aI, I étant le courant et Ra la résistance d'arc, elle-même égale à ℓ/σS, α étant la conductivité de l'arc.

We know that the arc voltage is equal to the product of the electric field E by the arc length i, hence:

• El = R _a I, I being the current and Ra the arc resistance, itself equal to ℓ / σS, α being the conductivity of the arc.

We deduce: E = I / aS, from which it follows that it is possible to increase E, therefore the arc voltage, by reducing the section S. According to the invention, S is practically reduced to zero, so that E becomes very important, hence the extremely rapid rise of the arc voltage.

This result is only obtained if the shear is practically complete, hence the need to make the front edge of the screen abut against an insulating surface with which the mechanical contact will be as good as possible: between the complete shear and the simple arc rolling, the difference is absolutely critical.

It is essential that the arc does not have time to stabilize between the contacts, because it would more or less quickly cause their deterioration; experience has shown that this result is obtained if the speed of movement of the screen exceeds 2 m / s and is preferably of the order of 10 m / s. It will be noted that a too high speed (for example, greater than 20 m / s) would cause a derivative of too high power, with the generation of shock waves liable to explode the housing. It is obvious that speed limits depend on multiple factors: intensity of presumed current, volume of the arc chamber, etc .; but, in each application, it will be possible to control the speed and determine its optimum value, provided that the propellants of the screen are, as explained above, essentially distinct from the lock.

The front edge of the screen must have reached the appropriate speed when it touches the arc: this is why the distance d _l mentioned above must have an appropriate value.

Another essential condition for producing the critical phenomenon of very rapid extinction of the arc by complete shear is that no escape route is offered to it; hence the importance of the sealing arrangements and low lateral clearance mentioned above.

It will be noted that, in the structure described above, the screen completely isolates the contact supports from one another, thus eliminating any risk of welding: this function of the screen is previously known.

Given the speed of extinction, the screen cannot be metallized by the arc and, consequently, the performance of the device will not be degraded by repetitive cuts. Such a device can thus be used even in contactors.

The degassing means are obviously intended to prevent an excessive increase in the pressure inside the arc chamber.

The device described can be the subject of very diverse applications and present a very wide variety of embodiments.

The receiving slot of the front edge of the screen may be eliminated in certain cases, the screen then abutting against a flat surface or otherwise shaped to ensure adequate mechanical contact, with sealing between the screen edge and said surface. Note, however, that the use of a slot, associated with degassing means, prevents the rebound of the screen which arrives at high speed on the wall.

The screen can receive different profiles and, for example, include, at its front edge, a blade of thinner thickness which extends it and comes into the slot. Said blade can be located in the longitudinal plane of symmetry of the screen, as shown in FIG. 5, where there has been shown such a median blade, 607 on the lateral faces of which the contact pads 201 and 301 are in support in the closed state of the switch: the contact is then ensured by a conductive pad 608 incorporated in the blade 607. The cut is made when this pad has moved relative to the pads 201 and 301. At the end of the cutting movement, it is then not necessary for the front edge 6071 of the blade to come up against the bottom of the slot 603: these are the shoulders 6072 and 6073, formed between the thick part of the screen and the blade, which will abut on the insulating surface 102 on both sides of the entry of the slot and it is at these abutment points that the shearing of the arc will occur.

The device of Figure 5 also includes the same members, not shown, as that of Figures 1 to 4 and the contact supports 2 and 3 are pivotable.

In Figure 22 there is shown a screen 6 in the form of a cylindrical crown guided by an insulating cylindrical column 6081 in which is embedded a fixed contact 3 which leads to a surface conductive pad 6080 in the form of a ring. The front end of this column is integral with the wall 102 of the housing surrounded by a groove 1023 into which penetrates the front edge of the screen 6 when the latter is propelled by means not shown, at the time of pivoting of a movable contact 2 which deviates from the range 6080. The screen 6 thus completely separates the two contacts from one another and the arc is throttled inside the groove 1023. The latter communicates with degassing channels 605 on each side of the column 6081.

In Figure 6, there is shown an embodiment of the device of Figure 5, in which a single pivoting contact 2 is provided.

The blade 607a extends the base of the thick body of the screen and thus forms a stair step which enters the slot 603 and abuts (by the surface 6072a) against the wall 102 as indicated above. The conductive pad 608a embedded in the blade is then connected to an electrical connection 609 embedded in the screen, to constitute the fixed contact. This figure allows you to understand the shape of the housing, with the guide grooves of the screen. The degassing channels are designated by 610. The contact 2 pivots upwards while the pellet 608a undergoes a translation and is received in the slot 611.

In the variant of FIGS. 7 to 9, where a fixed contact 3 is also embedded in the screen 6, the latter is not extended by a thinner blade and it enters, with the contact pad 301, into a housing 612 of the housing. The lower half of the screen 6, located below the contact 2, then stops against a shoulder 6120 formed inside this housing, while the patch 301 comes into a narrower extension 6121 of this housing . The movable contact 2, for its part, pivots under the action of the lock, not shown, opposite the edge of a partition 1020 which delimits on one side the housing 612 and, on the other, a chamber of arc expansion 1021.

There is shown in dotted lines, in FIG. 9, the position of the fixed contact pad 301 at the moment when the arc arises: it can be seen that it is then sheared by an oblique shear, in the vicinity of the lower edge of the partition 1020 and between the lower surface of this partition and the upper surface very close to the screen (the clearance between these two surfaces is for example less than 2/10 mm).

In this variant, since the arc arises on both sides of the partition 1020, means for evacuating the ionized air 1022-6122 are provided on both sides.

This is also also the case in the embodiment of FIG. 6, in which the arc is sheared, on the one hand between the front face 102 of the partition 1020 and the shoulder 6072a, on the other hand between the lower face of the partition 1020 and the upper face of the step 607a.

Figures 10 and 11 schematically illustrate an embodiment of the device of Figures 7 to 9, where the terminal part of the screen has a portion of smaller thickness 613 connected to the main body by an inclined ramp 614. This arrangement improves the shearing of the arc, the main body of the screen and the ramp then ensuring its stopping and the shoulder 6120 of FIG. 9 is unnecessary here.

In all of the above embodiments, a single screen, movable in translation parallel to the contact supports in their rest position and cooperating with an insulating surface shears the arc by shearing perpendicular to its natural path, or more or less oblique to said path, but, in any case, not tangential. This same type of shearing can be obtained with completely different structures of the screen and the insulating surface and different movements of a translation. For example, there is shown in Figures 12 to 14, a device comprising two screens 6a and 6b movable in translation relative to the housing 1 and whose opposite end portions have a complementary shape, so that the front edge of the thin screen 6b will come, at the end of the open position of the pivoting contacts 2-3, engage to the bottom of the narrow open housing 600a of the screen 6a. In this final position where the arc is completely extinguished, the contacts 2 and 3 are separated and arranged on either side of the end of the two terminal portions, nested one inside the other, of the two screens, so well that the housing is divided into two sealed chambers with respect to one another (the screens sliding, for this purpose, in appropriate grooves in the housing).

In an intermediate position, shown in Figure 14, the arc begins to be sheared between the edges of the opening of the housing 600a and the front edge of the screen 6b. By way of example, a means of propelling the screens has been shown, comprising two pivoting levers 601a and 601b, normally returned to the separated position by respective springs 602a and 602b and which approach each other under the action of two magnetic cores 603a, 603b controlled by a coil 625, until they come into contact with each other.

In all of the foregoing devices, at least one of the contacts is pivotable or moves away elastically to let the screen pass.

FIGS. 15 and 16 show a comb screen structure intended to be interposed between fixed contacts such as 20-21 and contacts such as 30-31 movable by translation perpendicular to the screen. This structure makes it possible to produce devices with multiple contact couples (mobile contact bridge 3). Each tooth of the comb that forms the screen is guided by its lateral edges in grooves such as 622-623 formed in partitions arranged in the housing 1. The bottom of the intervals 624 between fingers stops the screen by abutting against narrow parts 100 of these partitions. These partitions, located upstream of the contacts relative to the displacement of the screen, prevent the arc from developing between the contacts located on the same side of the screen.

The portion of insulating surface against which the ends 614-615 of the fingers abut to ensure the shearing of the arc is not shown in the drawing.

Instead of providing for a displacement of the screen by rectilinear translation, it is still possible to envisage a screen in circular translation, as shown in FIGS. 17 and 18. An axis 616 whose ends rotate in two walls of the housing 1 supports a stirrup 617 whose legs 6170-6171 carry a screen 6 in the form of a portion of cylindrical crown capable of moving in a groove 620 the bottom of which communicates with the outside via vents such as 621. The propulsion of the assembly is ensured by a spring hairspring 619 pre-armed and triggered by means symbolically shown at 40. The movable contact 22 is pivotally mounted about an axis 220 parallel to the axis 616 and which also pivots in two _walls of the housing. The end of the contact 22 enters the groove when the screen is in the rest position to come, in the closed position shown, in contact with the fixed contact 3.

When the contacts open, controlled by a lock (not shown), the pivoting of the contact 22 (clockwise in FIG. 7) separates its end from the contact 3, and, moreover, the spring is triggered and the screen performs a circular translation in the same direction as the contact 22, so as to abut the bottom bottom of the guide housing 620; the final shear of the arc therefore occurs between this bottom bottom and the bottom edge of the screen.

In Figures 19 to 21, there is shown a device composed of two screens 6c and 6d which is interposed between two contacts 2 and 3, which, when the complete device is opened, (not shown) move apart. one of the other perpendicular to the screens. Each screen has two integral parts, each a little smaller than a semicircle, namely an external part and a base. The latter has a pivot axis, such as 6000a, fixed to the housing, not shown, of the device.

A ring 40, itself mounted in the housing so as to be able to turn on itself when it is actuated by a non-illustrated propellant means, comprises two diametrically opposed pins 401 and 402 which are respectively engaged in notches 403 and 404 contained in the respective external parts of the two screens. The rotation of the ring therefore has the effect of rotating each of the two screens around an eccentric fixed axis. As shown in Figures 19 and 20, in which the screens have been shown in their position at the end of opening of the contacts, the bases of the two screens are located in the plane of the ring and are applied one against the other by their straight edge, while the outer part of each screen partially covers the base of the other , so that the arc path, open in the position of Figure 21, is completely interrupted by shearing between the cooperating surfaces of the two screens.

It goes without saying that various other embodiments can be imagined by those skilled in the art, without departing from the spirit of the invention.

Claims (7)

1. Electric switch comprising, in a chamber of an insulating housing, two movable electrical contacts with respect to each other between a closed position and an open position, a movable insulating screen of which -two parallel edges are guided in two grooves of the housing so as to be able to move under the effect of propulsion means between a starting position for which the contacts are closed and a finishing position for which a front edge of the screen, after having passed between two contacts previously separated by means of opening separate from the propulsion means and having encountered the arc established between these contacts, enters a slot in the housing by dividing the chamber into two half-chambers isolated from one another and each connected to the atmosphere,
characterized in that the front edge (601) of the thin screen (6) performs, before passing between the contacts (201, 301), a preliminary stroke (d _l ) which allows it, on the one hand, to reach a speed between 2 m / s and 20 m / s at this point and, on the other hand, quickly reach the slit, placed at a sufficiently short distance, so that the arc is completely sheared there before be stabilized and before having undergone a significant elongation. 2. Switch according to claim 1, characterized in that the slot (603) is connected directly to the atmosphere by a degassing channel (604, respectively 605, respectively 606). 3. Switch according to claim 1 or 2, characterized in that the screen (6) is extended forward by a blade of thinner thickness (607 or 607a) forming with it at least one shoulder (6072, 6073 or 6072a) which abuts against said wall (102). 4. Switch according to claim 3, characterized by a conductive pad (608) housed in said blade and ensuring the electrical connection between the contacts (201-301) in the closed position. 5. Switch according to one of claims 1 to 4, characterized by a screen in the form of a comb, each finger (614-615) being interposed between two movable contacts relative to each other by translation perpendicular to the 'screen. 6. Switch according to claim 1 or 2, characterized by a screen (6) in the form of a portion of cylindrical crown in circular translation in a housing of the same shape (620). 7. Switch according to claim 1 or 2, characterized in that the screen (6) has the shape of a cylindrical sleeve guided along a fixed column (6081) which is integral with the housing (102) and whose surface carries the fixed contact (3), the front edge of this sleeve penetrating into a circular groove (1023) of this housing.

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