Dismantling the circuit-breaker
Overhaul Instructions
10
1HSB435409-201 enrev1
4.2 Gas
Work on the circuit-breaker’s insulators or other live components as well as
transport and dismantling of complete circuit-breaker poles from the frame, may not
be done until the gas has been evacuated to a pressure of max 0.125 MPa (abs).
Gas shall be emptied fully to atmospheric pressure, when a normal pressurised
space, e.g. a breaking unit, shall be opened.
WARNING
When nitrogen gas is used for cleaning inside the circuit-breaker, the gas
may be emptied into the atmosphere via a dust and absorption filter. The
emptying operation must be done outdoors and at ground level.
WARNING
Unused SF
6
gas is non-toxic, odourless and colourless. It is heavier than
air and can therefore easily collect in low-lying places, e.g. cable trenches,
tanks, etc., if released in large volumes.
When large quantities of SF
6
gas collect in such places, a risk of
asphyxiation may occur due to lack of oxygen.
4.2.1 Emptying the gas:
The SF
6
gas is evacuated and the circuit-breaker should be vacuum pumped using
the gas handling equipment. This cleans and compresses the gas so that it can be
reused or destructed.
After vacuum pumping, the circuit-breaker is filled with dry nitrogen gas until
atmospheric pressure is reached and is then vacuum pumped again. In this way any
free-floating dust inside the circuit-breaker will be extracted.
Finally the circuit-breaker is filled again with dry nitrogen gas until atmospheric
pressure is reached. The circuit-breaker is now ready to be dismantled.
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