Page 146 - Practical Power System and Protective Relays Commissioning

Gas Insulated System Substations Chapter | 14 145

FIGURE 14.3 Gas insulated system disconnect switch.

breaking capacity, and a self-blast type that is used for medium breaking
capacity.

14.3.1 Puffer Circuit Breakers
In this type of CB, there are two parts: a moving contact and a fixed contact.
Both have a nozzle shape. Also involved is a blast cylinder. During the open-
ing process, the moving contact moves and the volume of the blast cylinder
is reduced. This increase the SF 6 gas pressure in the blast cylinder,which is
released in the Wright moment to blow the arc and extinguish it as shown in
Fig. 14.4.
This type of CB is used in 400 and 500 kV GIS systems.

14.3.2 Self-Blast Circuit Breakers
In this type of CB, the SF 6 gas in the breaking chamber is injected by means
of a piston mechanically coupled to the mobile contact. The piston com-
presses the gas at a high pressure to blow the arc at the zero crossing of the
current waveform. See Fig. 14.5.
Compared to the puffer type, the energy required in a self-blast to blow
the arc is reduced by 80%, but it is used only in a medium breaking capacity
in 132 kV GIS systems.