Abstract:
A gas current blow-out switch has an electrically conducting compression cylinder, a stationary hollow power contact pin supported in the cylinder and a piston surrounding the pin and slidably received in the cylinder for compressing an arc-extinguishing gas therein. A nozzle is affixed to the cylinder for bounding one end thereof. A movable hollow power contact pin is supported coaxially with the stationary contact pin to assume open and closed positions. The switch has an  electrically conducting stationary tube axially aligned with and spaced from the compression cylinder; a contact bridge slidably supported by and being in continuous electric contact with the stationary tube and the movable contact pin. The contact bridge has a closed position in which it electrically contacts the compression cylinder and an open position in which it is separated therefrom. An insulator cylinder which surrounds the compression cylinder and is slidable thereon, is coupled to the contact bridge for shifting the latter into its open position upon motion of the insulator cylinder in one direction. A carriage is shiftably arranged on a support and an externally actuated drive member is secured to the carriage and is displaceable between two limits with respect to the carriage. The drive member displaces the carriage after the drive member reaches either one of the limits. The drive member is arranged to displace the piston and the carriage is arranged to displace the insulator tube.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a heavy-duty electric switch of the gas current blow-out type which includes a stationary compression cylinder provided, at one end, with a stationary nozzle made of an electrically insulating material. In the cylinder there is coaxially arranged a stationary hollow contact pin. The switch further comprises an annular piston which can be driven into the compression cylinder for compressing the gas therein and which is mechanically coupled with a movable hollow contact pin cooperating with the stationarily supported hollow contact pin. During opening of the switch, the movable hollow contact pin is displaced in the same direction as the piston. 
     Switches of the above-outlined types are known and are disclosed, for example, in German Laid-Open Application (Offenlegungsschrift) No. 2,316,009. In contradistinction to other gas current blow-out switches which in most cases have a driven nozzle, the above-named Offenlegungsschrift discloses a stationarily arranged nozzle. The driven member, in turn, is a compression piston for compressing the gaseous extinguishing medium, in most cases SF 6  which, during opening of the switch, moves in a cylinder in the direction of the nozzle. When a predetermined pre-compression has been reached, contact separation takes place. The movable contact which is mechanically coupled to the piston and is moved by the same mechanism, is displaced in the same direction as the piston and is separated from the stationary contact supported in the cylinder. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an improved mechanical coupling between a drive mechanism, a compression piston and a movable contact in a high-voltage, heavy-duty switch which operates with high breaking capacity for high rated currents for providing a satisfactory pre-compression and a subsequent rapid separation of the contacts. 
     It is a further object of the invention to provide, for an electric switch of the above-outlined type, a drive linkage which transmits the force of a grounded, preferably hydraulic, drive mechanism to the piston and the movable contact. 
     It is still another object of the invention to further improve the breaking capacity of switches of the type outlined above, by the provision of a synchronous, current-responsive triggering mechanism. 
     These objects and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the gas current blow-out switch has a stationary, electrically conducting compression cylinder, a stationary hollow power contact pin supported in and coaxially with the compression cylinder and an annular piston surrounding the stationary power contact pin and slidably received at one end of the cylinder for compressing an arc-extinguishing gas in the cylinder. A nozzle is stationarily affixed to the cylinder for bounding the cylinder at the other end thereof. A movable hollow power contact pin is supported coaxially with the stationary contact pin; the movable contact pin has a closed position in which it engages the stationary contact pin and an open position in which it is separated from the stationary contact pin and in which compressed gas from the cylinder flows between the separated contacts. The switch further has an electrically conducting stationary tube arranged in axial alignment with and spaced from the compression cylinder; a contact bridge slidably supported by and being in continuous electric contact with the stationary tube and the movable contact pin. The contact bridge has a closed position in which it electrically contacts the compression cylinder and an open position in which it is separated from the compression cylinder. The tube and the contact bridge constitute a movable rated current contact and the compression cylinder constitutes a stationary rated current contact. There is further provided an insulator cylinder surrounding the compression cylinder and being slidable thereon; the insulator cylinder is coupled to the contact bridge for shifting the latter into its open position upon motion of the insulator cylinder in one direction. A spring is connected to the contact bridge and the movable contact pin to urge the latter towards its open position upon displacement of the contact bridge towards its open position. A carriage is shiftably arranged on a support and a drive member -- operated by an externally actuated mechanism -- is secured to the carriage and is displaceable between two limits with respect to the carriage. The drive member is arranged for displacing the carriage after the drive member reached either one of the limits. The drive member is connected to the piston for effecting displacement of the piston by the drive member. The carriage is connected to the insulator tube for effecting displacement of the insulator tube by the carriage. 
     By virtue of the above-outlined arrangement there is achieved a rated current separation which is delayed with respect to the motion of the piston. Further, by means of a spring-effected non-rigid coupling between the rated current contact and the power contact and by virtue of the short-period locking of the power contact with subsequent synchronous triggering, the circuit breaking capacity is significantly increased. 
     Expediently, a drive linkage is provided for moving the piston and the movable contacts. The drive linkage comprises a pull rod which lies in the pole column and which is guided in a support, a first push rod which is articulated to the upper end of the pull rod and a second push rod which is articulated to the lower end of the first push rod. 
     Further, for the current-dependent locking of the movable contact pin there is provided a synchronous triggering device which operates only when a predetermined value of the short-circuited current is exceeded. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal schematic sectional view of one pole of a two-pole heavy duty switch according to a preferred embodiment of the invention, shown in a closed position. 
     FIG. 2 is a schematic enlarged detail of FIG. 1. 
     FIG. 3 is a schematic sectional view taken along line A--A of FIG. 2. 
     FIG. 4 is a diagram illustrating the current change during circuit breaking. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to FIG. 1, there is illustrated only the right-hand pole of a two-pole switch arranged on an insulator column. The left-hand pole corresponds to the mirror-image of the right-hand pole. Further, for a better visibility of the components essential for understanding the invention, the gas-tight outer housing of the switch pole and the pole column are not shown. The housing and the pole column are filled with an extinguishing gas at a pressure of approximately 3 atmospheres. 
     The pole includes external current terminals 40 and 41 which are electrically connected with a hollow stationary contact pin 10 and with a hollow movable contact pin 11, respectively. The contact pin 10 is secured within an electrically conducting compression cylinder 1. The compression cylinder 1, the stationary contact 10 and the movable contact 11 are arranged coaxially with respect to one another. 
     One end of the cylinder 1 is closed off by an annular piston 6 which surrounds the stationary contact pin 10 and is slidable with respect thereto and with respect to the cylinder 1. The other end of the compression cylinder 1 is closed by a nozzle 5 which has a central opening slidably and sealingly receiving the movable contact pin 11. 
     An electrically conducting stationary tube 2 is supported coaxially with and spaced from the compression cylinder 1. An electrically conducting contact bridge 3 is slidably received at 33 in the stationary tube 2 and is in continuous electric contact with the movable contact pin 11. The contact bridge 3 has an advanced, or closed position (shown in FIG. 1) in which its contact terminus 32 is in engagement with the cylinder 1 and a withdrawn, or open position in which it is spaced from the cylinder 1. An insulator tube 4 is slidably received on the compression cylinder 1. The contact bridge 3 is displaced by the insulator tube 4 by virtue of a mechanism described below. 
     The electric connection between the terminal 41 and the movable contact pin 11 is effected by means of a coil 19 and an annular slide contact 20 which is arranged in the inside of the hollow contact pin 11. Further, the current terminals 40 and 41 are, for conducting the rate current, connected with one another through the wall of the cylinder 1, the rated current contact 32, the contact bridge 3, the slide contact 33 and the tube 2. 
     For performing the circuit breaking operation, a pull rod 7 made of insulating material and positioned in the pole column (not shown) and guided in a support 37, is moved downwardly by means of a drive mechanism (also not shown). To the upper terminus of the pull rod 7 there is articulated a first push rod 8 which, at its other end, is secured to a drive pin 34. The push rod 8 need not be made of insulating material. The drive pin 34 is supported in a slot of a carriage 9 which is displaceable on a support 36. The drive pin 34 is coupled with the piston 6 by means of a second push rod 38. 
     Upon downward motion of the pull rod 7, the piston 6 is, by means of the push rods 8 and 38, displaced towards the right as viewed in FIG. 1. As a result, the gas enclosed in the annular space between the cylinder 1 and the stationary contact pin 10 is compressed. A premature escape of the gas is prevented by the movable contact 11 sealingly engaging the stationary nozzle 5. 
     The linkage system 7, 8 and 38 designed according to the invention is advantageous in that the pulling force generated in the pull rod 7 and necessary for the circuit breaking operation, does not increase despite the significantly increased pressure exerted on the piston 6 at the end of its displacement. For this reason, a compression of the gas up to a very small residual volume is possible. Since the push rod 8 forms, at the end of the compressing motion of the piston 6, an angle of approximately 90° with the pull rod 7, the linkage system is adapted to take up the further increasing counterpressure caused by an arc drawn between the opened contacts 10 and 11 and exerted on the piston 6. 
     After the pin 34 abuts the right-hand terminus (limit position) of the slot in the carriage 9, at which time there is already achieved a certain pre-compression of the gas in the cylinder 1, the carriage 9 is moved by and with the pin 34. The thrust generated upon the start of carriage motion is taken up by a damping device, not shown. The motion of the carriage 9 is transmitted to the contact bridge 3 by means of the insulating cylinder 4 affixed to the carriage 9. The rated current separation occurs as the contact 32 separates from the cylinder 1. Only after completing the interruption of the rated current is the movable contact 11 displaced towards the right by means of a radial projection 39 arranged on the contact bridge 3 and a biased disc spring stack 12 engaging the radial projection 39 and an annulus 18 affixed to the outer face of the movable contact 11. By this time the gas prevailing in the cylinder 1 is compressed to a very small residual volume. The arc drawn between the contacts 10 and 11 is put out by a powerful gas blast as the compressed extinguishing gas escapes through the separated hollow contacts 10 and 11. 
     The circuit making operation is carried out in a reverse manner. For this purpose, the pull rod 7 is moved upwardly. In the illustrated embodiment of the drive, the pull rod 7 has to be so designed that it is also able to transmit pushing forces which, however, are significantly smaller than the pulling forces generated during circuit breaking. The pull rod 7 can be completely relieved of pressure forces if, for example, between the stationary support 37 and the upper terminus of the pull rod 7 there is inserted a compression spring (not shown). 
     As a result of the rearward motion of the piston 6 (that is, towards the left, as viewed in FIG. 1), the cylinder 1 is again charged with gas. Such charging can be assisted by check valves (not shown) arranged in the piston 6 or the nozzle 5. 
     The closing (leftward) motion of the rated current contact 32 and the power contact 11 occurs subsequent to the partial filling of the cylinder 1, after the pin 34 has abutted against the left-hand terminus (limit position) of the slot in the carriage 9. The contact bridge 3 is moved back into its closed, circuit making position by the insulating cylinder 4 affixed to the carriage 9 and the contact bridge 3. The movable contact pin 11 is shifted back into its circuit making position by the radial projection 39 in cooperation with a ring 13 attached to the pin 11. An engagement of the contact pins 10 and 11 occurs before the closing of the rated current contact 32. 
     In order to further increase the circuit breaking capacity of the switch designed according to the invention, a synchronous triggering device generally indicated at 35 is provided for the current-dependent blocking of the movable contact 11. The device 35 is illustrated on an enlarged scale in FIGS. 2 and 3. 
     The purpose of the synchronous triggering device is to ensure that in case of circuit breaking operations for interrupting a high-intensity current (for example, in excess of 40 kA) caused by a short circuit, the separation of the contacts 10 and 11 occurs at an accurately defined part of the current half-wave, that is, at a moment shortly after the current maximum. In this manner, the switch is capable of interrupting the current at the next subsequent zero point of the current intensity. 
     In the description which follows, the structure and the mode of operation of the synchronous triggering device will be explained in conjunction with FIGS. 1-4. 
     As a predetermined value of the short-circuited current is exceeded, a solenoid armature 15 affixed to one end of a locking pin 17 is attracted by a solenoid annulus 14 (attached to the tube 2) against the force of a spring 16. As a result, the lower end of the pin 17, the path of travel of which is substantially normal to that of the contact pin 11, projects into a recess or groove of the ring 18 affixed to the contact pin 11 and thus the pin 11 is immobilized. 
     By means of the shoft-circuited current flowing through the tube 2, a further locking pin 25, which is provided at one end with a plate 27, is pushed upwardly by electrodynamic forces against the force of a spring 26, with a frequency of 100 Hz, assuming a 50 cycle current. It will be understood that the plate and the spring, if necessary, should be adjusted to provide for a 120 Hz vibration in case of a 60 cycle current. To ensure that a repelling effect is generated, the tube 2 is provided with a slot 23 as shown in FIG. 3. As may be observed, the plate 27 is in an at least partial overlap with the slot 23. 
     The pin 25 has, at its lower terminus, a lug 24 which in its lower position, projects into a recess or groove 22 of a short-circuiting ring 21. The spring 26 is so designed that approximately between the moments t 2  and t 3  (FIG. 4) the pin 25 is in its upper position and between moments t 3  and t 4  it is in its lower position. The curve F represents the repelling force exerted on the plate 27. This force is proportionate to the square of the short-circuited current I. 
     There is further provided a camming pin 28 which has a skewed free end that is adapted to project into an opening 30 provided on the locking pin 17. The other, right-hand terminus of the camming pin 28 is connected with the short-circuiting ring 21. The latter is adapted to be repelled by the electrodynamic force of the short-circuited current which flows in the adjacent coil 19 after the separation of the rated current contact 32. The short-circuiting ring 21 is repelled against the force of a spring 29. It is seen that the path of travel of the camming pin 28 is substantially normal to that of the locking pin 17, while the path of travel of the locking pin 25 is substantially normal to that of the camming pin 28. 
     The course of the circuit breaking operation for a short-circuited current in excess of 40 kA will now be described in connection with FIG. 4. 
     At moment t 1  the flow of the short-circuited current starts. The locking pin 17 is pulled downward and thus blocks the contact pin 11. Simultaneously, the locking pin 25 begins to vibrate with a frequency of 100 Hz (assuming a 50 cycle current). The magnetic system 14, 15, together with the locking pin 17 is, however, so designed that the pin 17 does not vibrate but, due to its inertia, dwells in its lower position. 
     Let it be assumed that approximately at moment t 5  the switch receives the command signal to start the circuit-breaking operation. The separation of the rated current contact 32 may occur at the assumed moment t 6 , several half-waves after the beginning of the short-circuited current flow. Immediately after the separation on the rated current path, the short-circuited current diverts itself onto the still-locked contact pins 10 and 11. The current thus will drop to zero in the principal current path 1,3,2. The insulator cylinder 4 moves further forward (that is, towards the right as viewed in FIG. 1) and compresses the spring 12. The current now flowing through the coil 19 exerts a repelling force on the short-circuiting ring 21 which, however, is still locked by the pin 25. The lug 24, which is hooked into the recess or groove 22, prevents an upward motion of the pin 25. 
     At moment t 8 , shortly before the short-circuited current passes through the zero value, the spring 29 forces the camming pin 28 towards the right against the decreasing repelling force generated by the current flowing through the coil 19. As a result, the pin 25 is released (unlatched) and is moved upwardly by the spring 26. Since the current is zero in the principal current path, the pin 25 remains in its upward position. 
     Assuming that the interruption of the rated current occurs at moment t 7  (rather than at moment t 6  as previously assumed), the pin 26 is, in the course of its vibration, in its upper position and remains there. The repelling force generated by the current flowing through the coil 19 has not yet reached the magnitude which is sufficient to move the camming pin 28 towards the left against the force of the spring 29. 
     Whether the rated current is interrupted at moment t 6  or t 7 , the released pin 28 moves, approximately at moment t 9 , by virtue of the force generated by the current flowing in the coil 19, against the force of the spring 29 towards the left. The skewed terminal face of the pin 28 which constitutes a cam face and which projects into the opening 30 of the pin 17 drives the pin 17 in the upward direction against the force of the spring 16 as well as against the force exerted by the pin 11 due to the attracting force of the magnet ring 14. As a result, the contact pin 11 is released by the locking pin 17 at moment t 9  and is accelerated towards the right by the armed spring 12. The pin 17 is, by means of another camming pin 42 which projects with its skewed terminal face into the opening 31 of the pin 17, moved upwardly for safety reasons in the open end position of the contact bridge 3 independently from the pin 28. The path of travel of the camming pin 42 is substantially normal to that of the locking pin 17. 
     The separation of the contacts 10 and 11 occurs at moment t 10 . A damping mechanism (not shown) is provided for braking the motion of the contact pin 11 which is of lightweight structure. 
     During the period t 10  -t 11  an electric arc burns between the pins 10 and 11 which is exposed to a powerful gas blast as the highly compressed gas escapes from the cylinder 1 through the separated, hollow contacts 10 and 11. As a result, the arc is extinguished as the short-circuited current passes through its subsequent zero value at moment t 11 . 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.