Friday, April 1, 2011

Single Pressure Puffer Type SF6 Circuit Breaker

5. Description of different Circuit Breaker
5.4  Sulphur Hexafluoride (SF6) Circuit Breaker and SF6 Insulated Metalclad switchgear
5.4.4 Single Pressure Puffer Type SF6 Circuit Breaker
       This type of circuit breakers employs the principle of puffer action, illustrated above. Figure 24(a) illustrates the fully closed position of the cylinder.

(a )

( b )
Figure 24   Puffer action principle

  • The moving cylinder is coupled with the movable conductor against the fixed piston, and there is a relative movement between the moving cylinder and the fixed piston.
  • The gas is compressed in the cavity.
  • This trapped gas is released through the nozzle, during arc extinction process.
  • During the travel, of the moving contact and the movable cylinder, the gas puffs over the arc and reduces the arc diameter by axial convection and radial dissipation.
  • At current zero, the arc diameter becomes too small and the arc gets extinguished
  • The puffing action continues for some time, even after the arc extinction, and the contact space is filled with cool, fresh gas.
       Figure 25 illustrates the configuration of a 245 KV/420 KV single-pressure SF6 circuit breaker. The two interrupters are mounted on the hollow support insulators. The operation mechanism, installed at the base of the insulators, is linked with the movable contact in the interrupter, by means of insulating operating rod and a link mechanism.

Figure 25   One pole of 245 KV puffer type SF6 circuit breaker

       The circuit breaker is filled with SF6 gas at a pressure of about 5  kgf/cm2  . During the opening operation, the operating rod is pulled downwards by the operating mechanism. the link mechanism converts the vertical motion into horizontal motion. The contact and the movable cylinder, in the interrupter, are moved against the fixed position.
       Break-time up to 3 cycles can be achieved by puffer principle described above. For achieving 2 cycle break-time, differential position is used, in which the puffer cylinder and piston move in opposite directions, thus reducing total stroke and time of travel.

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