Metal encapsulated, pressurized gas insulated high voltage switching apparatus
This is a continuation of application Ser. No. 49,323 filed June 18, 1979, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to metal encapsulated, pressurized gas insulated high voltage switching apparatus in general and more particularly to disconnect switches, of the type having two field electrodes which define, in the &#34;off&#34; position, a switching gap between two potentials, and having a movable switching rod which crosses the switching gap in the &#34;on&#34; position and together with which the field electrode which surrounds the rod coaxially can be moved into an intermediate position which favors the electric field between the two field electrodes during the closing process. 
     From DE-OS No. 27 11 166, a metal encapsulated, pressurized gas insulated grounding switch for metal encapsulated high voltage switching installations is known, the switching rod of which is coaxially surrounded by a field electrode. During the closing process, this field electrode is moved in the same direction as the switching rod and transferred to a position closer to the mating stationary contact. Thereby, the breakdown spacing is reduced in this known high voltage switch. The effect of the field electrode is to delay the firing instant of the arc. The movement of the field electrode is accomplished by friction at the switching rod; it accordingly depends on factors determining the friction contact such as, for instance, heating, wear and manufacturing tolerances. Due to the free movement of the field electrode between two fixed stops chosen for the motion, the electrode is carried along even at the beginning of the switching off process when the grounding switch is opened. 
     In high voltage switch gear such as disconnect switches, which switch at velocities of about 4 cm/sec, the movable switching rod is, as a rule, actuated by a motor drive. The switching on time is then between 5 and 10 sec, depending on the size of the switching gap which depends on the rated voltage. If disconnect switches of this type are switched on, a pre-breakdown with a subsequent low current arc always occurs if the disconnect switch is switched under voltage. The duration of the preliminary arc can then be several seconds, depending on the circumstances. 
     In the known designs of disconnect switches which are suitable for voltages up to 245 kV, this breakdown gap is so small, especially in sulfur hexafluoride which is used as the quenching and insulating medium in metal encapsulated installations, that the arc is not expected to wander off while it is burning. 
     In disconnect switches for voltages higher than 245  kV, the pre-breakdown length of the arc is larger because of the longer switching gap so that the danger exists that the arc, while it burns, will travel away from its point of origin and settles at the grounded encapsulation of the installation. 
     When disconnect switches are opened, arcs that can similarly wander off can occur during the opening operation, for instance, due to unavoidable charges on the connected transmission lines, especially cables. If the arc wanders away from its point of origin and settles at the grounded encapsulation of the installation, the danger exists that parts of the installation will be destroyed due to the then existing short to ground. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to describe metal encapsulated pressurized gas insulated high voltage switching apparatus, especially disconnect switches of the type mentioned at the outset, in which wandering off of the arc during the closing and opening process is prevented. 
     According to the present invention, this is accomplished by a lever linkage which is provided with steering rods for the switching rod and the field electrode and which controls the motion cycles of the switching rod and the field electrode during the closing and opening process. 
     Through the application of the present invention, it is ensured that the field electrode moves, during the closing process, as well as during the opening process, unequivocally and independently of heating, wear and manufacturing tolerances. In addition, a favorable electric field between the field electrodes is also obtained by the forced control of the field electrode during the switching processes. The arc, which is drawn with relatively little length, burns between two electrodes, the spacing of which, relative to the diameter of the encapsulator, can be designed so that the field between the electrodes exerts a strong influence on the arc, while the influence of the field influenced by the encapsulation is similarly kept small. 
     In one preferred embodiment according to the present invention, the steering rods are linked to cranks which are connected to each other with great angular stiffness and are fastened in a torsion proof manner on a common rotatable shaft. In this embodiment, the steering rods can be coupled directly to the switching rod or to the field electrode. This results in a motion in opposite directions between the field electrode and the switching rod which sets in at the beginning of the switching operations but is unimportant for the operation of the high voltage disconnect switch. If the switching rod is to be prevented from traversing the space between the two field electrodes, during the opening process as well as during the closing process, until the movable field electrode has reached a given intermediate position, it is advantageous to couple the steering rod for the switching rod to the switching rod via a connecting rod and to guide the joint between the steering rod and the connecting rod in a stationary, curved guide rail. 
     Two examples of a metal encapsulated pressurized gas insulated high voltage switching apparatus according to the present invention, designed as a disconnect switch, will be described with the aid of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows, diagrammatically, in a cross sectional view, a high voltage disconnect switch for metal encapsulated pressurized gas insulated high voltage switching installations. 
     FIG. 2 is a side elevation corresponding to FIG. 1. 
     FIG. 3 shows a somewhat different embodiment of a high voltage disconnect switch according to the present invention. 
     FIG. 4 is a diagrammatic side elevation corresponding to FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The high voltage disconnect switch shown in FIG. 1 is intended for metal encapsulated, pressurized gas insulated high voltage switching installations with nominal voltages of preferably above 245 kV. It has a tubular outer encapsulation 1 which consists of metal and as a rule is at ground potential. In its interior 2, the encapsulation 1 contains a gaseous insulating medium, particularly sulfur hexafluoride at a pressure of, for instance, 5 bar. In the interior 2, the contact system of the high voltage disconnect switch and the essential parts of the drive are arranged. The high voltage disconnect switch has a fixed contact 3 which cooperates with a movable switching rod 4. The fixed contact 3 is surrounded by a field electrode 5. 
     The switching rod 4 runs inside a support tube 6. It is surrounded by a field electrode 7. The switching rod 4 is connected to a steering rod 8 which is connected to a crank 10 via a joint 9. The crank is mounted, secure against torsion, on a drive shaft 11, on which a further crank 12 is fastened in a torsion proof manner. 
     To the crank 12 is connected, via a joint 13, a second steering rod 14 which actuates a rod 15. The rod 15 drives the electrode 7, as can be seen from FIG. 2. 
     When the contact system of the high voltage disconnect switch is transferred from the &#34;off&#34; position shown by the solid lines into the &#34;on&#34; position shown by the dashed lines, the crank 10 and the crank 12 are rotated 180° by the shaft 11. This brings the switching rod 4 into engagement with the fixed contact 3 and at the same time moves the field electrode 7. As long as the field electrode 7 is being transferred into the position near the electrode 5, the switching rod 4 is held back. In this manner, the electric field between the electrodes 5 and 7 is not yet stressed by the tip of the switching rod 4. The influence of the field which results from the outer metal encapsulation remains relatively small in this closer position of the electrodes if the switching rod subsequently traverses the space between the electrodes 5 and 7. An arc that might occur cannot be influenced by the field of the grounded encapsulation 1. A corresponding effect is obtained during the opening motion. 
     A guiding rod 16, which is arranged inside the support tube 6 parallel to the axis for guiding the switching rod 4, is shown in FIG. 2. Otherwise, like parts in FIG. 2 are provided with the same reference symbols. FIG. 2, in addition, shows a drive insulator 17 for the shaft 11. 
     In the embodiment shown in FIGS. 3 and 4, like parts are shown with the same reference symbols as in FIGS. 1 and 2. The difference between this embodiment and the previous one is that the joint 9 runs in a stationary curved guide 18, so that a controlled motion of the switching rod 4 during the closing and opening process using a different kind of control is obtained. This embodiment with the stationary, curved guide rail 18 requires, besides the crank 10 and the steering rod 8, a connecting rod 8a for moving the switching rod 4.