Low-fluid volume outdoor power circuit breaker
United States Patent [1 1 Widmer LOW-FLUID VOLUME OUTDOOR POWER CIRCUIT BREAKER [75] Inventor: Hans Widmer. Zurich. Switzerland [73] Assignee: BBC Brown Boveri &amp; Company Limited. Baden. Switzerland [22] Filed: Dec. 8. I971 [21] Appl. No.: 206,052  
 [52] US. Cl. 200/150 R; 200/150 B [51] Int. Cl. &#34;01h 33/68 [58] Field of Search ZOO/I50 R. I50 B. 150 D [56] References Cited UNITED STATES PATENTS 3.l 18.997 1/1964 Bergstrom 200/l50 R FOREIGN PATENTS OR APPLICATIONS l.203.659 8/]959 France 200/150 R l,l6l.340 l/l964 Germany 200/150 R Primary Examiner-Robert S. Macon Attorney. Agent, or Firm-Pierce. Scheffler &amp; Parker [451 Apr. 29, 1975 [57] ABSTRACT A low-fluid volume outdoor power circuit breaker includes an outer porcelain insulator structure within which are housed a quenching chamber tube that encloses a quenching chamber having associated therewith the stationary and movable contact structure of the breaker. In order to protect the circuit breaker structure against the destructive forces of great pressure waves generated within the circuit breaker by steep current surges having a high peak value and which result from the switching of capacitors. a pressure-absorbing barrier is provided. This barrier. which may be in the form ofa helically wound gas filled tube of insulating material or a sheath of expanded insulating material. is located intermediate the outer porcelain insulator structure and the quenching chamber tube. being applied to the outer surface of the latter. The pressure absorbing barrier may also be surrounded by a porous dielectric fabric sheath as a safety measure to prevent any portions of the barrier from being broken away by the pressure waves.  
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 Ci uI&#39;BR A ER&#34; outdoor power circuit breaker makes increased idemands andzimposes higher stresses onthe. circuit elements in special circuits, for,.exarnple for theswitching ofcapacitors... h v I I Capacitors are frequently connected in series with the lines, or to earth, in order to improve the power factor in long high-voltage transmission lines. Shortcircuiting or switching-on of such capacitors results in extremely steep current surges with a high peak value and a high make&#34; frequency. This, in turn, results in powerful pressure waves which propagate very rapidly and in surges from the prestriking of the make arc. Insulating materials of the kind used at the present time and employed in circuit elements are unable to withstand such pressure waves and are accordingly destroyed thereby. The external insulator of such a circuit element is constructed of porcelain and is particularly exposed to risks due to such pressure waves, this also applying to parts of the quenching chamber which are adjacent to the pressure source.  
  Using known arrangements of outdoor switching elements it is not however easily possible for a circuit breaker, designed for conventional and normal switching of mains and systems as regards voltage, current and rating, to be employed for switching capacitors without risk to the switching elements.  
  The primary object of the present invention is to provide a switch arrangement which is free of the disadvantages and defects of known systems.  
  According to the present invention this problem is solved in that a pressure-absorbing barrier is provided in the switching element for absorbing high order pressure waves generated by high order switching currents produced when capacitors are switched.  
 In particular, the advantage of the invention is due to the fact that insulating parts disposed close to the pressure wave can be adapted to extreme stresses while the provision of a barrier for absorbing the pressure wave peaks protects the insulator. Accordingly, the circuit breaker will be capable of performing capacitor switch-.  
 ing without calling for expensive means, for example the provision of inductors, designed for the full shortcircuit current, in order to attenuate the steep current peaks.  
  It is particularly advantageous that a damping tube of insulating material is disposed in the switching element to function as the pressure-absorbing barrier, both ends of the said tube being closed and being filled with air or a dielectric gas.  
  The damping tube, filled with air at atmospheric pressure, or with a dielectric gas, and being preferably constructed of a gas-tight elastic material or a plastics composition, is coiled onto the quenching chamber tube and secured thereon with a suitable adhesive material. The individual turns of the gaseous filled damp ing coil may also be adhesively joined to each other.  
  According to a further embodiment of the invention the pressure-absorbing barrier consists of a sheath of expaii&#39; de dinsulatiiig mate rial which is disposed in the switching &#34;element.  
  quenching chamber and th dute&#39;i porcelain insulating member. According to aifurther embodiment of the invention, the pressure-absorbing barrier is surrounded by a porous, dielectric fabric sheath to prevent any part of the dampinggtube turns or&#39; &#39;th e&#39;exp&#39;anded material from becoming detached bythe pressure waves.  
  Two different embodiments according to the invention are illustrated respectively in the accompanying drawings in which: i ,7  
  FIGS. 1 and 2 are partial longitudinal median sections through a low-fluid volume power circuit breaker shown in simplified form.  
  According to FIG. 1, the numeral 1 refers to ari outer porcelain insulator of an outdoor power circuit breaker having disposed therein a quenching chamber tube 2, adapted to accommodate the quenching chamber 3, movable contacts 4 and stationary contacts 5, and a contact pin 6 which extends through the quenching chamber 3. A damping tube 7, surrounded by a porous dielectric fabric sheath 8, shown in broken lines, is coiled around the exterior of the quenching chamber tube 2.  
  A further example of a damping arrangement is illustrated in FIG. 2 wherein the damping member is constituted by a cylindrical tube made from an insulating, pressure-absorbing expanded material 9 located on the outer side of the quenching chamber enclosing insulator tube 2. The tube 9 can thus be made from foam rubber, Styropor or a similar material. Except for this difference, the circuit breaker construction is the same as 7 that illustrated in FIG. 1 and corresponding components have been assigned the same reference numerals.  
  All structural features, for example, the terminals, the circuit breaker drive mechanism and the quenching fluid control system, not directly necessary for understanding the invention, have been omitted from FIG. I.  
  The mode of operation of the arrangement according to the invention is as follows:  
  When the contact pin 6 is closed, pre-striking takes place before the movable contacts 4 are touched. The resultant arc closes the oscillating capacitor circuit and a current oscillation having a steep rise characteristic, high initial peak value and high frequency is produced. A small quantity of oil is evaporated so that a corresponding pressure wave is produced which rapidly penetrates through the oil and the insulation of the switching element and advances in the direction of the outer porcelain insulator 1. However, the said pressure wave is absorbed by the pressure-absorbing barrier according to the invention and is therefore prevented from reaching the outer insulator 1.  
  The power rating of the switching elements is improved with simple means in the system according to the invention and conventional, low-fluid volume circuit breakers may be employed as capacitor circuit breakers.  
 I claim:  
  1. A low-fluid volume outdoor power circuit breaker comprising a set of switching contacts, a cylindrical insulator tube forming a closed quenching chamber of the fluid medium type in which said set of switching contacts are located, an outer cylindrical porcelain insulator surrounding and spaced radially from said.insu lator tube,and a cylindrical pressure absorbing barrier surrounding and in contact with-the outer surface of said insulator tube, the pressure waves generated in said fluid quenching .mediu m upon operation of said contacts in switching high order currents produced when switching capacitors being directed against and primarily takenup by said insulator tube whereas the peaks of said pressure waves are damped by absorption within said pressure absorbing barrier thereby to prevent said pressure peaks from reaching the wall of said outer porcelaininsulator.  
  2. A low-fluid volume outdoor power circuit breaker according to claim 1 wherein said pressure absorbing barrier is constituted by a helical damping tube of insusheath.  
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