EP0517618A1 - Load-break device for electric circuit - Google Patents

Abstract

This break device, such as a circuit breaker switch, is of the so-called "arcless break" or "clean break" type. It includes a fixed contact (2), a moving contact (4), which latter is associated with opening/closing control means, and an auxiliary resistive circuit arranged so as to interpose, between the fixed contact (2) and the moving contact (4), when the latter is moved in the direction for opening, an electrical resistance of increasing value. The auxiliary resistive circuit comprises at least one positive temperature coefficient resistor (11, 12) which is temporarily inserted into the circuit during the opening motion of the moving contact (4), but is held outside this circuit when the device is in the closed position. <IMAGE>

Description

The present invention relates to a load cut-off device for an electrical circuit, this device possibly being in particular a switch-circuit breaker, but the field of the invention also includes contactors, switches, circuit breakers, relays and other similar devices. More particularly, this invention relates to a cut-off device under load called "cut-off without arc" or "clean cut-off", that is to say an apparatus provided with provisions which eliminate the risk of arcing between its contacts, when the relevant electrical circuit is cut under high current.

French patent 8507804/2581790, in the name of the Applicant, describes a switch-circuit breaker with clean cut, of a particular structure. This switch-circuit breaker is of the type comprising a fixed contact, a movable contact, latching and tripping control members, means for hooking the movable contact carrier and the control member in the latched position, and means for actuating, in the direction of detachment, the means for hooking the mobile contact holder and the control member and neutralizing it, the mobile contact and the control member being subjected to the action of spring means tending to keep them in the tripped position. According to the invention which is the subject of this patent, an auxiliary resistive circuit is provided arranged between the fixed and movable contacts, so as to interpose between them, when the movable contact is moved in the opening direction, an electrical resistance of value growing. The insertion of this resistance makes it possible to reach, just before the total opening of the contacts, a current intensity sufficiently low to attenuate the risk of arcing; conversely, when the switch closes, the auxiliary resistance circuit introduces a resistance of decreasing value, also advantageous. This auxiliary resistive circuit is associated with the fixed contact, and it is arranged on the path of the mobile contact, or of an auxiliary contact associated with the mobile contact, to serve as a sliding track. Thus, the auxiliary resistive circuit is presented as a graphite or charged ceramic or doped polymer track, along which the movable contact or the auxiliary contact slides, the variable useful length (between the fixed contact and the movable or auxiliary contact ) of this track defining the value of the resistance inserted. Of course, in the cut-off position, therefore at the end of the opening stroke, the movable contact or the auxiliary contact has entirely left this track.

In the embodiment mentioned above, the value of the resistance inserted during opening or closing varies according to purely "mechanical" criteria, depending on the movement of the movable contact in the direction of opening or closing , and it is practically not influenced by physical factors such as the intensity of the current or the temperature.

Furthermore, it has already been envisaged, in load cut-off devices, the use of current limiting elements whose resistance increases with the increase in their temperature, therefore in the intensity of the current flowing through them. However, the limiting elements are not part of an auxiliary resistive circuit of increasing value "mechanically" during the displacement of a movable contact. In addition, these elements are permanently maintained in the circuit normally traversed by the electric current; thus they are permanently requested by an electric current and a voltage, which can lead to their deterioration and limits the possibilities of operation of the circuit, in voltage and in current. In this regard, reference may be made to British patent 1214682 and its equivalent US 3529210, or to US patent 4583146.

The present invention aims to improve the kind of embodiment mentioned in the first place, so as to further improve the conditions under which the intensity of the current is lowered during the opening of the switch-circuit breaker or other similar breaking device, without altering the structure and functioning of the circuit under normal conditions.

To this end, the subject of the invention is essentially a cut-off device under load for an electrical circuit, of the type known as "cut-off without arc" or "clean cut-off", comprising a fixed contact, a movable contact with which means are associated. for opening / closing control, and an auxiliary resistive circuit arranged so as to interpose between the fixed contact and the movable contact, when the latter is moved in the opening direction, an electrical resistance of increasing value, the device being characterized in that the auxiliary resistive circuit comprises at least one resistance with a positive temperature coefficient capable of being temporarily inserted into the circuit traversed by the electric current during the opening movement of the movable contact, the resistance or resistors with coefficient of positive temperature being maintained outside the circuit traversed by this electric current, when the breaking device is in the closed position.

Thus, the invention is based on the principle of insertion between the contact fixed and the movable contact, during the opening movement of the latter, of at least one resistance with a positive temperature coefficient, also known by the abbreviated designation "PTC", which is an electrical resistance whose ohmic value is a strongly increasing function of temperature. Thus, the passage of a current of high intensity in this resistance causes its immediate heating and consequently a sudden increase of its ohmic value, from where an acceleration of the lowering of this intensity, the current being very quickly reduced to a residual current of a few amperes, and the effect being all the more noticeable the higher the initial current. On the other hand, in steady state, the resistance or resistors with a positive temperature coefficient are kept outside the circuit and are not stressed by any electric current and voltage, which preserves them and offers extended possibilities of circuit operation, in voltage and running.

According to a preferred embodiment of the invention, the auxiliary resistive circuit comprises at least two resistors with a positive temperature coefficient, arranged so as to be inserted successively between the fixed contact and the movable contact when the latter is moved in the direction of the opening. Advantageously, the resistors with a positive temperature coefficient are of increasing values, considered in their order of insertion between the fixed contact and the movable contact during the opening movement. Thus, the first resistance with positive temperature coefficient inserted intervenes to lower the strongest currents and limit them to a residual current, while the second resistance with positive temperature coefficient, in series with the first (which did not intervene ) once inserted, intervenes to lower the medium or low currents and also limit them to a residual current. Two or more resistors with a positive temperature coefficient can, according to this principle, be successively inserted in series in the circuit between the fixed contact and the movable contact.

The auxiliary resistive circuit can also comprise at least one ordinary electrical resistance, which during the opening movement of the movable contact is inserted in series with the resistance or resistors with positive temperature coefficient. According to a first possibility, the ordinary electrical resistance (s) are arranged so as to be inserted between the fixed contact and the movable contact, during the opening movement, after the resistance (s) with positive temperature coefficient, therefore at the end opening; in this case, the ordinary resistance has no particular function during opening, but it intervenes on closing to protect the resistance or resistors with a positive temperature coefficient, by limiting the intensity of the current to an admissible value. . According to another possibility, the ordinary electrical resistance (s) are arranged so as to be inserted between the fixed contact and the movable contact, during the opening movement, before the resistance (s) with positive temperature coefficient, therefore at the start of opening, which makes it possible to lower the intensity of the current to an admissible value by the resistance or resistances with positive temperature coefficient.

According to another arrangement aimed at protecting the resistance or resistors with a positive temperature coefficient, the auxiliary resistance circuit also comprises at least one varistor, mounted in parallel with respect to at least one resistance with positive temperature coefficient.

For the practical realization of the auxiliary resistive circuit, the load breaking device according to the invention advantageously comprises an insulating support which carries the fixed contact and several fixed conductive pads, all placed on the path of the movable contact, the resistors with a positive temperature coefficient and the ordinary resistance (s), if any, being inserted between the fixed contact and the first fixed stud and / or between the pairs of successive fixed studs, the movable contact being able to cooperate simultaneously with two successive studs during its opening or closing movement.

• Figure 1 est une vue de face simplifiée d'un appareil de coupure conforme à la présente invention, en position de fermeture du circuit électrique ;
• Figure 2 est une vue similaire à la figure 1, mais montrant l'appareil en cours d'ouverture ;
• Figure 3 est une vue en coupe de cet appareil de coupure, suivant III-III de figure 2 ;
• Figure 4 est une vue de face simplifiée du même appareil, en position d'ouverture du circuit ;
• Figure 5 est une vue similaire à la précédente, montrant l'appareil en cours de fermeture ;
• Figure 6 est un schéma électrique correspondant à l'appareil des figures 1 à 5 ;
• Figures 7 et 8 sont des schémas électriques illustrant deux variantes de cet appareil ;
• Figure 9 est une vue partielle d'une autre variante.

In any case, the invention will be better understood with the aid of the description which follows, with reference to the appended schematic drawing representing, by way of nonlimiting examples, some embodiments of this load cut-off device for circuit electric:

• Figure 1 is a simplified front view of a switching device according to the present invention, in the closed position of the electrical circuit;
• Figure 2 is a view similar to Figure 1, but showing the apparatus being opened;
• Figure 3 is a sectional view of this switching device, along III-III of Figure 2;
• Figure 4 is a simplified front view of the same device, in the open position of the circuit;
• Figure 5 is a view similar to the previous one, showing the apparatus in closing price;
• Figure 6 is an electrical diagram corresponding to the apparatus of Figures 1 to 5;
• Figures 7 and 8 are electrical diagrams illustrating two variants of this device;
• Figure 9 is a partial view of another variant.

Figures 1 to 5 are partial and simplified views of a load cut-off device, such as a circuit breaker, these figures essentially showing the parts concerned by the present invention, while the control members and the housing do not are not shown.

The device comprises an insulating support 1 in the form of a circular sector, which carries a fixed contact 2. The support 1 is crossed by an axis 3, on which is mounted a pivoting movable contact 4, able to cooperate in a particular angular position with the fixed contact 2. As shown in FIG. 3, the mobile contact 4 here has a stirrup configuration, with two opposite branches located on either side of the support 1.

On the insulating support 1 are also arranged several fixed conductive pads 5,6 and 7, all placed on the trajectory in an arc of a circle described by the end of the pivoting movable contact 4. The fixed contact 2 is also possible in the manner of a plastic cone. A helical spring 8, mounted around the pivot axis 3, ensures the pressure of the two branches of the movable contact 4 on the fixed contact 2 and on the pads 5, 6 and 7.

An electrical input conductor 9 is connected to the movable contact 4, while an electrical output conductor 10 is connected to the fixed contact 2.

Between this fixed contact 2 and the first fixed stud 5 is inserted a first electrical resistance with a positive temperature coefficient 11. Between the first fixed stud 5 and the second fixed stud 6 is inserted a second electrical resistance with positive temperature coefficient 12, of higher ohmic value. An ordinary electrical resistance 13 is inserted between the second fixed stud 6 and the third fixed stud 7.

Figure 1 shows the cut-off device in the closed position or "engaged" position. The movable contact 4 is pressed against the fixed contact 2. The electric current thus flows directly, through the contacts 2 and 4, from the input conductor 9 to the output conductor 10, without passing through the resistors with a positive temperature coefficient 11 and 12 and the resistor 13 which are then kept outside the circuit traversed by this current.

During the opening movement, the movable contact 4 pivots passing successively from the fixed contact 2 to the first fixed pad 5, from the first pad 5 to the second pad 6, and from the second pad 6 to the third pad 7, before reaching the beyond this last pad 7.

At the start of opening, when the movable contact 4 is passed over the first fixed stud 5, the first resistor with a positive temperature coefficient 11 is temporarily inserted in the circuit traversed by the electric current between the input conductor 9 and the output conductor 10. If the current is initially of high intensity, the resistance with positive temperature coefficient 11 heats up quickly, and its ohmic value increases suddenly, which contributes to considerably limit the intensity of this current. On the other hand, the first resistor with a positive temperature coefficient 11 does not see its value suddenly increased, if it is traversed by a current of relatively low intensity.

The opening movement continuing, the movable contact 4 then passes from the first fixed stud 5 to the second fixed stud 6, as illustrated in FIGS. 2 and 3. The second resistance with a positive temperature coefficient 12 is thus inserted into the circuit, in series with the first resistance with positive temperature coefficient 11.

If previously the first resistance with a positive temperature coefficient 11 has intervened, to attenuate a current of high initial intensity, the second resistance with a positive temperature coefficient 12 does not intervene. On the other hand, this second resistance with positive temperature coefficient 12 sees its ohmic value increase suddenly, if the first resistance with positive temperature coefficient 11 has not intervened previously, therefore for a current of medium or low initial intensity; the intervention of the second resistor with a positive temperature coefficient 12 leads to lowering the intensity of this current to an even lower value.

The opening movement continuing to take place, the movable contact 4 passes over the third fixed stud 7, then it continues its travel beyond this last stud 7 and finally reaches the open position or "triggered" position, shown in Figure 4, in which the flow of current between the input conductor 9 and the output conductor 10 is completely prevented. It should be noted that during this opening movement, the resistor 13 is temporarily inserted in the circuit but then has no particular function.

It will also be noted that the movable contact 4 is wide enough to be able to be in momentary support on two successive pads, the next pad therefore being reached before this contact leaves the previous pad so that during the opening movement the values resistors 11, 12 and 13 can only be added. The operation of the device also requires that between each of the pairs of successive studs the voltage difference remains limited, and is for example below a maximum value of 20 volts.

When closing, the movable contact 4 describes a reverse movement from the previous one, and it first reaches the third fixed stud 7, as shown in FIG. 5. In this position, the resistor 13 inserted in the circuit protects the second resistance with positive temperature coefficient 12, by limiting the intensity of the current to a value admissible by the latter.

Preferably, at the instant when the movable contact 4 reaches the fixed stud 7, suitable means measure the intensity of the current thus limited, and control the continuation of the movement of the movable contact 4 towards the fixed contact 2 if the measured current is weak, or the return of the movable contact to the open position if the current measured is too strong. The two resistors with a positive temperature coefficient 11 and 12 therefore practically do not intervene during the closing movement described by the movable contact 4.

FIG. 6 gives the electrical diagram corresponding to the embodiment described above, using the same numerical references.

FIG. 7 illustrates, in the form of an electrical diagram, a first variant which comprises, between the fixed contact 4 and the first two fixed pads 5 and 6, a combination of resistors with positive temperature coefficients 11a, 11b, 12a, 12b in series , and varistors (resistors varying as a function of the electrical voltage) 14a, 14b, 15a, 15b in series; these provide voltage protection for resistors with a positive temperature coefficient, with respect to which they are connected in parallel. A resistor 13 is always inserted between the last two fixed studs 6 and 7. This variant allows the use of the cut-off device at a voltage greater than the admissible voltage by a single resistor with a positive temperature coefficient.

FIG. 8 shows another variant, in which a first ordinary resistor 16 is inserted between the fixed contact 2 and the first fixed stud 5, a second ordinary resistor 17 is inserted between the first stud fixed 5 and the second fixed stud 6, and a resistance with a positive temperature coefficient 18 is inserted between the second fixed stud 6 and the third and last fixed stud 7. This arrangement makes it possible, first of all during cutting, to lower the intensity of the current, by the resistor 16 then by the resistor 17 added to the previous one, so as to bring this intensity to an admissible value by the resistor with positive temperature coefficient 18. In this case also, it is important that 'between the consecutive pads the voltage is kept below a maximum value, for example 20 volts, during the opening process.

FIGS. 1 to 5 show resistors in the form of components separated from the fixed contact 2 and from the fixed pads 5, 6 and 7, and connected to the latter by conductors such as that indicated in 19; FIG. 9 illustrates a different embodiment, in which the resistors with a positive temperature coefficient 11 and 12, and the resistor 13, are in the form of strips inserted directly between the fixed contact 2 and the pads 5, 6 and 7 The operating principle is not modified by this configuration and it always requires that, in its movement, the movable contact 4 reach the next pad before having completely left the previous pad.

The resistors with a positive temperature coefficient, used here, can be in particular made of polymer or ceramic.

• en augmentant le nombre des plots intermédiaires et des résistances à coefficient de température positif, insérées successivement dans le circuit au cours du mouvement d'ouverture, ces résistances étant de valeurs ohmiques croissantes ;
• en prévoyant des associations de résistances à coefficient de température positif de mêmes caractéristiques, branchées en parallèle, pour augmenter la valeur maximale de l'intensité du courant pouvant être coupé ;
• en modifiant la disposition des plots fixes et le mouvement du contact mobile, comme le suggère d'ailleurs la figure 9, ce mouvement pouvant être un glissement et/ou un roulement ;
• en prévoyant un trajet différent du contact mobile, pour le mouvement de fermeture, de manière à ne pas insérer les résistances à coefficient de température positif lors du rétablissement du courant ;
• en appliquant l'invention à des appareils de coupure en charge autres que des interrupteurs-disjoncteurs, tels que des contacteurs, des interrupteurs, des disjoncteurs, des relais et autres appareillages similaires.

It goes without saying that the invention is not limited to the sole embodiments of this load cut-off device for an electrical circuit which have been described above, by way of examples; on the contrary, it embraces all of the variant embodiments and applications respecting the same principle. Thus, in particular, that one would not depart from the scope of the invention:

• by increasing the number of intermediate pads and resistors with a positive temperature coefficient, successively inserted into the circuit during the opening movement, these resistors being of increasing ohmic values;
• by providing associations of resistors with a positive temperature coefficient of the same characteristics, connected in parallel, to increase the maximum value of the intensity of the current which can be cut;
• by modifying the arrangement of the fixed pads and the movement of the movable contact, as moreover suggests in FIG. 9, this movement possibly being a sliding and / or a rolling;
• by planning a different route from the mobile contact, for the closing movement, so as not to insert resistors with a positive temperature coefficient when power is restored;
• by applying the invention to load breaking devices other than switch-circuit breakers, such as contactors, switches, circuit breakers, relays and other similar equipment.

Claims (10)

Cut-off device under load for an electrical circuit, of the so-called "arcless cut-off" or "clean cut-off" type, comprising a fixed contact (2), a movable contact (4) with which opening control means / closing, and an auxiliary resistive circuit arranged so as to interpose between the fixed contact (2) and the movable contact (4), when the latter is moved in the opening direction, an electrical resistance of increasing value, characterized in that that the auxiliary resistive circuit comprises at least one resistor with a positive temperature coefficient (11,12; 11a, 11b, 12a, 12b; 18) capable of being temporarily inserted in the circuit traversed by the electric current during the opening movement of the movable contact (4), the resistance or resistors with a positive temperature coefficient (11,12; 11a, 11b, 12a12b; 18) being kept out of the circuit traversed by this electric current when the breaking device is in the closed position e. Cut-off device under load for an electrical circuit, according to claim 1, characterized in that the auxiliary resistive circuit comprises at least two resistors with a positive temperature coefficient (11,12; 11a, 11b, 12a, 12b), arranged so as to be inserted successively between the fixed contact (2) and the movable contact (4) when the latter is moved in the opening direction. Cut-off device under load for an electrical circuit, according to claim 2, characterized in that the resistors with a positive temperature coefficient (11,12; 11a, 11b, 12a, 12b) are of increasing values, considered in their order of insertion. between the fixed contact (2) and the movable contact (4) during the opening movement. Cut-off device under load for an electrical circuit, according to any one of Claims 1 to 3, characterized in that the auxiliary resistive circuit also comprises at least one ordinary electrical resistance (13; 16,17), which during the movement of opening of the movable contact (4) is inserted in series with the resistor or resistors with a positive temperature coefficient (11,12; 11a, 11b, 12a, 12b; 18). Cut-off device under load for an electrical circuit, according to claim 4, characterized in that the ordinary electrical resistance (s) (13) are arranged so as to be inserted between the fixed contact (2) and the movable contact (4), at during the opening movement, after the resistance or resistors with a positive temperature coefficient (11,12; 11a, 11b, 12a, 12b). Cut-off device under load for an electrical circuit, according to claim 4, characterized in that the ordinary electrical resistance (s) (16,17) are arranged so as to be inserted between the fixed contact (2) and the movable contact (4) , during the opening movement, before the positive temperature coefficient resistance (s) (18). Cut-off device under load for an electrical circuit, according to any one of Claims 1 to 6, characterized in that the auxiliary resistive circuit also comprises at least one varistor (14a, 14b, 15a, 15b), mounted in parallel with respect to at least one resistance with positive temperature coefficient (11a, 11b, 12a, 12b). Cut-off device under load for an electrical circuit, according to any one of Claims 1 to 7, characterized in that the auxiliary resistive circuit comprises associations of resistors with positive temperature coefficient of the same characteristics, connected in parallel. Cut-off device under load for an electrical circuit, according to any one of Claims 1 to 8, characterized in that it comprises an insulating support (1) which carries the fixed contact (2) and several fixed conductive pads (5,6 , 7), all placed on the path of the movable contact (4), the resistance or resistors with a positive temperature coefficient (11,12; 11a, 11b, 12a, 12b,; 18) and the possible ordinary resistance (s) (13 ; 16,17) being inserted between the fixed contact (2) and the first fixed stud (5) and / or between the pairs of successive fixed studs (5,6,7), the movable contact (2) being able to cooperate simultaneously with two successive studs during its opening or closing movement. Cut-off device under load for an electrical circuit, according to claim 9, characterized in that it also comprises means which, when closing, at the instant when the movable contact (4) reaches the last fixed stud (7), measure the intensity of the current and control the continuation of the movement of the movable contact (4) towards the fixed contact (2) if the measured current is low, or the return of the movable contact (4) in the open position if the measured current is too strong.

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