Abstract:
The invention relates to a device for neutralizing an electric switching unit. One or several power poles, each of which is provided with movable contacts separable form fixed contacts are actuatable between opened and closed positions by an actuator for switching-on an electric charge. A mechanical actuating device interacts with the movable contacts. It is used for actuating a device for neutralizing the electric switching unit by switching-off the control electric circuit thereof when the wear degree of pellets is greater than a predetermined threshold. The control circuit is switched-off, for example, by cutting a wire thereof. An electric switching unit is provided with the device.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a neutralization device for an electrical switching unit, such as a contactor, a starter or a contactor breaker, equipped with one or more power poles. The neutralization device is activated when the degree of erosion of the contacts for a pole is greater than a predetermined threshold. The invention also relates to an electrical switching unit including such a neutralization device. 
     An electrical switching unit such as a contactor has, at each power pole, movable contacts that are separable from stationary contacts, moved using a solenoid to switch an electrical load to be controlled. The pads mounted on the contacts erode more or less with each switching according to the current or voltage load. After a high number of operations, this erosion may lead to failure of the electrical switching unit, the consequences of which may be significant, especially in terms of safety. To prevent such consequences, one solution consists in systematically replacing either the contact pads or the electrical switching unit after a certain number of operations. In order to avoid replacement that is premature or too late, electrical switching units have been equipped with systems indicating to the user the real degree of erosion of the contact pads. In this way, the user is alerted at the desired moment of the end of the lifetime of the electrical unit, which allows failures of the electrical unit and the damages that these failures might cause to be prevented. 
     2. Related Art 
     In the patent applications WO 2004/057633, WO 2004/057635 or U.S. Pat. No. 6,225,807 electrical switching units are equipped with devices indicating to a user the degree of erosion of the contact pads of the unit. For example, in the patent application WO 2004/057635 the remaining lifetime of the contactor is determined from the variation in the contact force exerted by the spring in the course of time to hold the movable contacts against the stationary contacts when the contacts are closed. In U.S. Pat. No. 6,225,807 the remaining lifetime of contact pads is determined by calculating a modification of the contact pressure during an operation of opening the contacts. 
     The systems described in these documents only allow an indication to be given to the user and do not protect against the possible dangers if the unit continues to be used when the contact pads have reached a high degree of erosion. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is therefore to propose a device allowing certain avoidance of all risks or damage caused by the electrical switching unit when its contact pads have reached too high a degree of erosion. 
     This aim is attained by a device for neutralizing an electrical switching unit which comprises one or more power poles, each equipped with movable contacts that are separable from stationary contacts and moved by an electrically controlled actuator between an open position and a closed position to switch an electrical load, said device being characterized in that it comprises mechanical means of movement cooperating with the movable contacts and able to move the means of neutralizing the electrical switching unit, said neutralization means cutting off an electrical circuit that controls the actuator when the degree of erosion of the contact pads is greater than a predetermined threshold. 
     According to a first embodiment, the cutting-off of the circuit that controls the actuator is effected by severing a control circuit wire. The severing of the wire therefore causes the cutting-off of the electrical supply to the actuator and therefore takes the electrical switching unit out of operation. 
     According to a first configuration of this first embodiment, the neutralization means comprise an abruptly transforming bistable elastic membrane. This membrane is set up so as to retract abruptly under the action of the means of movement when the erosion of the contacts becomes too high. Advantageously, the neutralization means comprise at least one cutting blade attached to the elastic membrane. When the membrane abruptly retracts, this cutting blade is therefore propelled sufficiently hard to sever the control circuit wire. To improve the efficiency of the device, the control circuit wire may be brought against a stationary second cutting blade. 
     According to a second configuration of this first embodiment, the neutralization means comprise an instrument for receiving the control circuit wire and stretching it according to the erosion of the contact pads until it is severed when the degree of erosion of the contact pads is greater than the predetermined threshold. 
     According to a second embodiment, the cutting-off of the control circuit is effected by opening the control circuit. According to a distinctive feature of this second embodiment, the neutralization means comprise an abruptly transforming bistable elastic membrane. The elastic membrane carries, for example, an instrument able to open the control circuit. The elastic membrane plays the same role as in the first configuration of the first embodiment, but it no longer carries a cutting blade but a simple instrument allowing, for example, a flexible blade to be pushed to open the control circuit of the actuator. 
     According to the invention, the mechanical means of movement mentioned above comprise, for example, a movable piston, moved in translation, according to the erosion of the contact pads, by the movable contacts when the contacts are in the closed position. 
     Advantageously, the piston is fitted on a guiding device. The guiding device comprises, for example, flexible strips pressing against the piston and able to keep it in its position. The flexible strips thus form notches marking the successive positions of the piston according to the erosion of the contact pads. 
     According to the invention, the electrically controlled actuator used in the electrical unit is, for example, a solenoid comprising a control coil. In this case, the severed wire might be, for example, the wire of the control coil or a wire of the supply circuit for this coil. 
     The aim of the invention is also attained by an electrical switching unit comprising one or more power poles, each equipped with movable contacts that are separable from stationary contacts and moved by an electrically controlled actuator between an open position and a closed position to switch an electrical load, the device being characterized in that it comprises a neutralization device as described above. 
     According to a distinctive feature of this electrical switching unit, the movable contacts are mounted on a bridge that is movable in translation and able to move a piston in translation according to the erosion of the contact pads when the contacts are in the closed position. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
       Other features and advantages will become apparent in the following detailed description with reference to an embodiment, given by way of example, and shown by the appended drawings in which: 
         FIGS. 1A and 1B  show, in a simplified manner, the device according to a first embodiment of the invention, when the pads are new and when they have reached a high degree of erosion respectively; 
         FIGS. 2A and 2B  show two possible configurations of the piston used in the device according to the first embodiment; 
         FIGS. 3A and 3B  show a first configuration of the neutralization device according to a second embodiment of the invention, when the contact pads are new and when they have reached a high degree of erosion respectively; 
         FIGS. 4A and 4B  show another configuration of the neutralization device according to the second embodiment of the invention, when the contact pads are new and when they have reached a high degree of erosion respectively; and 
         FIGS. 5A and 5B  show two guiding devices for the piston capable of being used in the device according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In a known way, an electrical switching unit such as an electromechanical contactor, contactor breaker or starter comprises one or more power poles, for example three power poles. 
     An electrical switching unit comprises upstream current lines (source lines) which establish electrical continuity between the electric supply network and the power poles, and downstream current lines (load lines) which establish electrical continuity between poles of the electrical switching unit and an electrical load, generally an electrical motor that it is desired to control and/or protect by means of the electrical switching unit. The upstream current lines are connected to or disconnected from the downstream current lines by pole contacts. The poles may be single break or double break. On the appended figures the pole is double break and comprises movable contact pads  20  arranged on a movable bridge  2  and stationary contact pads  30  arranged on stationary contacts  3 . The movable bridge  2  is moved along a principal axis (A) by an electrically controlled actuator. An electrically controlled actuator may, for example, be:
         of an electromagnetic type, such as a control solenoid for example. The control solenoid typically comprises a stationary yoke, a movable armature, a return spring and a control coil. The movement closing the movable armature is generated by passing an excitation current through the control coil;   of a piezoelectric type;   of a magnetostrictive type. When subjected to a magnetic field, a magnetostrictive material undergoes an induced mechanical deformation.       

     In the rest of the description, we will use the term “electrical actuator” to designate an electrically controlled actuator. 
     The invention consists in neutralizing an electrical switching unit when the degree of erosion of the contact pads  20 ,  30  of at least one pole becomes greater than a predetermined threshold, that is, when their erosion becomes too great. Several solutions allow this result to be reached. 
     In these solutions the movable bridge  2  of each of the power poles cooperates with the mechanical means of movement when the contacts are closed. According to the erosion of the contact pads  20 ,  30  of the pole, the movable bridge  2  thus presses against the first end of a piston  1 . The position of the piston  1  therefore reflects the state of erosion of the contact pads  20 ,  30 . 
     The piston  1  is guided in translation along the principal axis (A) by a guiding device comprising, for example, flexible strips  40  ( FIG. 5A ) pressing against the external surface of the piston  1  and keeping piston  1  in the position reflecting the state of erosion of the contacts, even when the contacts are open. 
     Flexible strips  41  in the form of teeth ( FIG. 5B ) may cooperate with corresponding flexible strips  42  standing up against the external surface of the piston  1 , the cooperation between the strips  41 ,  42  creating notches successively marking different positions of the piston  1  during its translation and keeping the piston  1  in its position when the contacts are open. 
     In the embodiments described below a “control circuit wire”, or a wire of the circuit controlling the electrical actuator, is understood to be a wire connecting the electrical actuator with its current source, a wire of the electrical actuator itself, such as a wire of the control coil when the actuator is a solenoid, or a power wire of the control circuit for the electrical actuator. 
     In the embodiments described below, the electrical actuator is, for example, a conventional solenoid comprising a control coil supplied by a current source via the electrical control circuit (designated subsequently “control circuit”). 
     According to a first embodiment of the invention ( FIGS. 1A to 2B ), the neutralization of the electrical switching unit is produced in a first configuration by cutting a wire  5  of the control circuit or in a second configuration by cutting a wire supplying an alarm circuit. 
     In the first configuration, a part of the control circuit wire  5  is stretched in a direction perpendicular to the principal axis (A). The piston  1  comprises a slot  10  into which the control circuit wire  5  is inserted ( FIG. 2A ) or an opening  11  through which the control circuit wire  5  passes ( FIG. 2B ). In order to concentrate the force of piston  1  in an area of the control circuit wire  5 , the piston  1  is able to be translated across a support  12  placed below the control circuit wire  5 . 
     According to the erosion of the contact pads  20 ,  30 , the piston  1  therefore presses against the control circuit wire  5  ( FIG. 1B ). When the degree of erosion of the contact pads  20 ,  30  is high and greater than a predetermined threshold, the tension in the wire  5  is too high and it breaks. With the control circuit of the electrical actuator then being cut off, the electrical switching unit is therefore neutralized. 
     In the second configuration, instead of completely neutralizing the electrical switching unit, the user may simply be alerted of the state of erosion of the contact pads  20 ,  30  of the unit. In this configuration, the cutting of the control circuit wire  5  is therefore replaced by that of a wire supplying an alarm circuit. So long as the wire is not severed, the alarm is inactive. When the wire is severed by being cut by the piston  1 , as described in the first configuration, the user receives a piece of information, for example visually (an indicator light goes out), indicating that the contact pads  20 ,  30  are worn out and that the electrical switching unit should be replaced. 
     According to a second embodiment, the second end of the piston  1  comes to press against the neutralization means, comprising, for example, an abruptly transforming bistable elastic membrane  6  that can move between a high position and a low position. When the contacts are closed, the piston  1  is therefore carried between the movable bridge  2  and the elastic membrane  6  in the high position. 
     The flexible strips  40 ,  41 ,  42  of the guiding device oppose the return constraint exerted by the elastic membrane  6 , in order to keep the piston  1  in its position corresponding to the real erosion of the contact pads  20 ,  30 , even when the contacts are open. 
     The retraction of the elastic membrane  6  occurs in the direction of translation of the piston  1 . When the piston  1  reaches a position corresponding to a degree of erosion of the contact pads  20 ,  30  greater than a predetermined threshold, the membrane  6  reaches a critical position and abruptly retracts, generating a strong and irreversible mechanical movement. 
     In a first configuration of this second embodiment ( FIGS. 3A and 3B ), a part of the control circuit wire  5  is stretched in a direction perpendicular to the principal axis (A) and is positioned within range of the elastic membrane  6 . 
     The elastic membrane  6  carries, for example, a cutting blade  60  drawn along in translation according to the erosion of the contact pads  20 ,  30 . When the contact pads  20 ,  30  are new, the membrane  6  is in the high position ( FIG. 3A ). When the degree of erosion of the contact pads  20 ,  30  is greater than a predetermined threshold, the elastic membrane  6 , pushed by the piston  1 , reaches its critical position and retracts, rapidly drawing the cutting blade  60  in translation until this slices through the control circuit wire  5  ( FIG. 3B ). In order to guarantee the cutting of the control circuit wire  5 , a stationary second blade  61 , playing the role of scissors, may be positioned below the control circuit wire  5 , slightly offset in relation to the first blade  60 . 
     In a second configuration of the second embodiment (not shown), instead of neutralizing the electrical switching unit, the user may be alerted of the state of erosion of the contact pads  20 ,  30  of the unit. In this configuration, the cutting of the control circuit wire  5  is replaced by that of a wire supplying an alarm circuit. So long as the wire is not severed, the alarm is inactive. When the wire is severed by being cut by the cutting blade  60 , the user receives a piece of information, for example visually (an indicator light goes out), indicating that the contact pads  20 ,  30  are worn out and that the electrical switching unit should be replaced. 
     In a third configuration of the second embodiment ( FIGS. 4A and 4B ) the abruptly transforming bistable elastic membrane  6  has a pin  62  designed to open the control circuit  50  of the electrical actuator. The control circuit  50  of the electrical actuator is, for example, closed by means of a flexible blade  51 . When the contacts are closed and the contact pads  20 ,  30  are new, the piston  1  is in the high position, as is the elastic membrane  6  ( FIG. 4A ). When the contact pads  20 ,  30  are eroded and have reached a high degree of erosion, greater than a predetermined threshold, the elastic membrane  6 , having reached its critical position, retracts. The pin  62  carried by the membrane  6  then presses against the flexible blade  51  to move it away and so to open the control circuit  50  of the electrical actuator ( FIG. 4B ). 
     In a final configuration, instead of neutralizing the unit by opening the control circuit, as in the second configuration of this second embodiment, the user is simply alerted of the state of erosion of the contact pads  20 ,  30  of the unit. In this final configuration, the opening of the control circuit  50  by the pin  62  is replaced solely by opening an alarm circuit realized using this same pin  62 . When the alarm circuit is open, the user receives a piece of information, for example visually (an indicator light goes out), indicating that the contact pads  20 ,  30  are worn out and that the electrical switching unit should be replaced. According to a variant embodiment, the opening of the alarm circuit may be replaced completely by the closing of an alarm circuit. In this case, the pin  62  presses against the flexible blade  51  not to move it away, but to bring it closer to the circuit until the alarm circuit is completely closed. 
     It is understood that other variations and improvements in detail may be imagined, and even the use of equivalent means envisioned, without departing from the scope of the invention.