Abstract:
The invention relates to a compressed gas switch with two contact pieces, a contact element by-passing the contact pieces when in the on position, and two isolating distances connected to each other in series. The second contact piece opposing the first isolating distance is arranged axially by an annular piston to be displaceable forming a switching chamber. The switching chamber is separated from the heating chamber by a bulkhead partition having a current-dependent valve, and the second isolating distance is produced after opening of a blowing hole located between the second contact piece and the contact element.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a compressed gas power switch, in particular for extinguishing an arc of a high short-circuit current, which has a first switching piece and a second switching piece, installed on a common axis with a space between them, and an axially displaceable contact piece, which bridges the space when in the on state and moves away from the first switching piece during switch-off, and is at least partially surrounded by a heating chamber, a second isolating distance being connected in series to a first isolating distance formed between the first switching piece and the contact piece during switch-off. 
     BACKGROUND INFORMATION 
     A compressed gas switch is described in principle, for example, in German Patent No. 40 10 007 regarding the contact arrangement and the operation of the axially displaceable contact piece. A heating chamber arranged coaxially with the contact arrangement is described in German Patent No. 41 03 119. Regardless of the particular design of these compressed gas switches, they have the disadvantage that the hot gas makes it difficult to establish the isolating distance during switch-off, so that the time at which the isolating distance is re-established cannot be determined with sufficient accuracy. In addition, controlled switching at zero current is almost impossible, since the inherent delay of the compressed gas power switch is included in the switching sequence (each compressed gas power switch has a different inherent delay determined by the respective manufacturing tolerances, age, environmental conditions, and different masses). European Patent No. 0 334 181 and European Patent No. 0 400 523 describe that a second isolating distance may be connected in series to the first isolating distance of a compressed gas power switch, but this involves a disproportionately large, and therefore high-cost, drive, since the extinguishing gas may only enter the inside containing the secondary contact of the second isolating distance from the outside. This, however, means not only that gas must be made available from the outside, but also that the compressed gas power switch requires a large space. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a compressed gas power switch which allows reliable switching with low drive power and adequate re-establishment of the isolating distance to be achieved regardless of its particular inherent delay or the hot gas in the heating chamber, yet without an increase in the volume occupied by the compressed gas power switch. 
     This object is achieved according to the present invention by the fact that the second switching piece is axially displaceable and is connected to a piston that may be driven in a switching chamber in respect to the contact piece by the hot gas flowing from the heating chamber into the switching chamber so that the second switching piece moves away from the contact piece. 
     This provides drive support, since the second switching piece is moved by the extinguishing gas pressure. In addition, the operation of the second switching piece depends on the extinguishing gas and therefore on the current, so that the opening of the second isolating distance is controlled by the characteristics of each individual switching sequence. 
     According to one advantageous embodiment of the present present invention, the heating chamber is separated from the switching chamber by a bulkhead, which has a valve controllable through the current to be switched and the pressure difference between the heating chamber and the switching chamber. The valve allows the opening time of the second isolating distance to be controlled with an even greater accuracy. 
     The present invention may also be advantageously configured so that the second switching piece is axially displaceable on the inner periphery of a tubular main current path connected to the compression piston of a compression device forming a sliding contact, the second isolating distance being formed between the second switching piece and the axially displaceable contact piece after a blow hole has been opened by the current-dependent valve via the hot gas driving the piston designed as an annular piston. 
     Regardless of how the heating chamber is designed, the annular piston in the switching chamber may be connected to the compression piston of the compression device via a compression spring, so that after the completion of a switch-off sequence, it is ensured that the compression spring brings the annular piston and the switching piece connected to it back to their original position. 
     In order to provide a sufficiently large heating chamber for receiving the hot gases, in particular when switching high short-circuit currents, in another embodiment of the invention the switching chamber downstream from the heating chamber is delimited by a partition running coaxially with the switch axis, which is rigidly connected to both the bulkhead and the compression piston of the compression device, so that an additional heating chamber, connected to the heating chamber upstream from the bulkhead, is formed on the outer periphery of the partition. 
     According to another feature of the present invention, the valve has one or two ferromagnetic bodies, which in the high-current phase hold the blow hole in the bulkhead closed against the force of compression springs, but open it when the current has reached a certain lower value. The forces of the current of the current path of the compressed gas power switch, i.e., the forces between the two ferromagnetic bodies in a magnetic field (a concentric magnetic field formed around the compressed gas power switch current path due to the short-circuit current to be switched off) may be used. 
     In order to make use of the forces of the current, a ferromagnetic body in the form of a cover plate over the blow hole may be slidably arranged to form a valve. The cover plate is supported by the compression springs against the current path formed by the switching piece and the axially movable contact piece and its movement is limited by a stop. To guide the ferromagnetic cover plate taking into account a slight friction resistance, it is mounted on tracks or in grooves, preferably made of polytetrafluoroethylene (PTFE). 
     The current-dependent valve may also be conveniently made of two cover plates made of ferromagnetic material, which oppose one another at the end face of the bulkhead facing the switching chamber at the height of the blow hole and support one another through compression springs. 
     Both embodiments of the current-dependent valve are also well suited for arrangement on the annular piston at the height of the blow hole; however, in this case it must be ensured that, at least in the area of the current-dependent valve, the annular piston not be made of magnetic material. 
     Using the forces arising between two ferromagnetic bodies in a magnetic field, in a preferred embodiment of the invention, the current-dependent valve may also be made of a frame made of ferromagnetic material, arranged concentrically with the blow hole within the bulkhead and for which a cover plate made of ferromagnetic material is provided on the side facing the heating chamber upstream from the blow hole. This cover plate is preferably guided by four rods attached to the bulkhead and supported against the bulkhead by compression springs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a section of a compressed gas power switch according to the present invention in the on position. 
     FIG. 2 shows a section of a compressed gas power switch according to the present invention after the first isolating distance is formed in the area of its contact arrangement. 
     FIG. 3 shows a section of a compressed gas power switch according to the present invention in the off position. 
     FIG. 4 shows a section of a compressed gas power switch with a first isolating distance and having a design different than FIGS. 1 through 3 in the area of its contact arrangement. 
     FIG. 5 shows a section of a compressed gas power switch with a second isolating distance and having a design different than FIGS. 1 through 3 in the area of its contact arrangement. 
     FIG. 6 shows a cross sectional view of a first embodiment of the current-dependent valve of the compressed gas power switches shown in FIGS. 1 through 5. 
     FIG. 7 shows a cross sectional view of a second embodiment of a current-dependent valve of the compressed gas power switches shown in FIGS. 1 through 5. 
     FIG. 8 shows a third embodiment of the current-dependent valve of the compressed gas power switches shown in FIGS.  1  through  5 . 
    
    
     DETAILED DESCRIPTION 
     As FIGS. 1 through 3 show, the compressed gas power switch has basically two pin-shaped switching pieces  1 ,  2  mounted on a common axis, which may also have a tubular design; an axially movable contact piece  3 , which coaxially surrounds and, in the on state, bridges the switching pieces; a first heating chamber  4  concentric with contact piece  3 ; main current path  5  with stationary rated current contact  6 ; movable rated current contact  7 ; and compression device  8  with compression piston  9 . 
     While FIG. 1 shows the compressed gas power switch in the on position, in FIG. 2 the contact arrangement assumes a position in which, after the previous opening of main current path  5 , the first isolating distance  11  is formed after the subsequent separation of sliding contact  10  of contact piece  3  from switching piece  1 . FIG. 3 shows the compressed gas power switch in the off position. 
     Based on this principle of the design of the compressed gas power switch, contact piece  3  is now fixedly connected to the area of main current path  5  carrying movable rated current contact  7 , and thus to axially displaceable compression piston  9  through a bulkhead  13 , made of insulating material and having a blow hole  12 . The space behind bulkhead  13  is subdivided by a partition  15 , coaxial with switch axis  14 , into a heating chamber  16  and a switching chamber  17 . While heating chamber  16  is connected to first heating chamber  4  through an opening  18  in bulkhead  13  thus forming an additional heating volume, partition  15  is fixedly connected with both bulkhead  13  and compression piston  9 , and accommodates, in an axially displaceable manner, an annular piston  21 , fixedly connected to second switching piece  2  and subdividing switching chamber  17  into two partial chambers  19 ,  20 . Annular piston  21  is under the effect of a compression spring  22  arranged in partial chamber  20 . As further shown by FIGS. 1 through 3, compression piston  9  is connected to switching piece  2  via a sliding contact  23 , and the second isolating distance  24  is formed after the blow hole  12  has been opened by a current-dependent valve after the first isolating distance  11  has been opened by switching piece  2  and by sliding contact  26  of the axially displaceable contact piece  3 . 
     If a switch-off operation is to be performed on the basis of this embodiment of the compressed gas power switch, the main current path is opened first. If the distance between rated current contacts  6 ,  7  is sufficient, first isolating distance  11  opens and arc  27  is formed. The arc  27  heats the gas in heating chamber  4  delimited by isolating material nozzle  28  with its flow duct, so that the pressure of the gas increases and, since blow hole  12  is initially closed by the current-dependent valve, it is built up further. As the switch-off current approaches zero, the force acting on current-dependent valve  25  decreases and blow hole  12  is opened toward partial chamber  19  of switching chamber  17 . Therefore, the gas flows from heating chamber  4 , and thus also from additional heating chamber  16  into partial chamber  19 , acts upon annular piston  21  actuating this piston, and thus second switching piece  2 , opening second isolating distance  24  between switching piece  2  and contact piece  3 . Since the current resulting from arc  27  of the first isolating distance  11 , is near zero crossing at this point, the extinguishing capability of second isolating distance  24  is not very high. Additional extinguishing gas may be supplied from compression device  8  via opening  30  in compression piston  9 . 
     Thus the invention provides controlled switching at zero current independently of the inherent delay of the compressed gas power switch, using low drive power. This results not only in reliable reestablishment of the isolating distance, but also the effects aimed at by the invention are achieved without an increase in the size of the compressed gas power switch. 
     These effects of the compressed gas power switch are also achieved according to the embodiment of FIGS. 4 and 5. While FIG. 4 shows the switch position assumed during a switch-off sequence, in which first isolating distance  11  is already effective, FIG. 5 shows the compressed gas power switch in the switch position in which second isolating distance  24  is already open. This compressed gas power switch differs from that of FIGS. 1 through 3 basically by the fact that the current-dependent valve is directly attached to annular piston  21 , which is fixedly connected to switching piece  2  at the height of blow hole  12  in bulkhead  13 , and annular piston  21  (and therefore also switching piece  2 ) is accommodated in an axially displaceable manner by the area of main current path  5  carrying rated current contact  7 . 
     Current-dependent valve  25  according to FIGS. 1 through 5 may be either a current-dependent valve  31  using the forces of the current or a valve  32 ,  33 . 
     In current-dependent valve  31  using the forces of the current according to FIG. 6, a cover plate  34 , made of ferromagnetic material, is displaceably arranged over blow hole  12  and is supported by compression springs  35  against current path  36  formed by switching pieces  1 ,  2  and contact piece  3 . The movement of the cover plate  34  is limited by a stop  37 . 
     Current-dependent valve  32  shown by FIG. 7 makes use of the forces generated between two ferromagnetic bodies in a magnetic field. Thus, two cover plates  38 ,  39 , made of ferromagnetic material, oppose one another at the height of blow hole  12  and are also supported by one another via compression springs  40 . Both current-dependent valve  33  and the one of FIG. 6 are particularly well suited when the current-dependent valve is to be arranged on annular piston  21 . 
     Current-dependent valve  33  of FIG. 8 also makes use of the forces generated between two ferromagnetic bodies in a magnetic field. In this current-dependent valve  33 , a frame  41  made of ferromagnetic material is provided concentrically with the blow hole  12  within bulkhead  13 . Furthermore, upstream from blow hole  12 , a cover plate  42  made of ferromagnetic material, guided by rods  43  attached to frame  41  and supported by compression springs  44  against bulkhead  13 , is arranged on the side facing away from heating chamber  4  of the compressed gas power switch. The movement of cover plate  42  made of ferromagnetic material is limited by stop  46  with elastic body  45  between them, as shown by FIGS. 1 through 3. 
     Regardless of the design of current-dependent valves  31 ,  32 ,  33 , they operate so that they keep blow hole  12  closed due to their cover plates  34 ,  38 ,  39 ,  42 , made of ferromagnetic material, being attracted in the main current phase. However, if the switch-off current drops to a certain value, the force of compression spring  35 ,  40 ,  44  exceeds the forces of the current, or the forces generated between two ferromagnetic bodies in a magnetic field, so blow hole  12  is opened. In the embodiment of current-dependent valve  33  according to FIG. 8, opening of blow hole  12  is also supported by the pressure of the gas from heating chamber  4 .