Circuit breaker

How arc can be quench in SF6?

What is the electrical & thermal properties of SF7?

asked 7/5/2012

1 Answer

On opening of contacts, the gas is moved through the arc chamber. The electrons in the arc generated between the contacts are captured by the SF6. Loss of the electrons extinquishes the arc.

SF6 Properties

 - chemically inert, non-flammable, non-toix, non-corrosive, colourless, orderless, arc-quencing
 - high insulation properties
 - auto regenerates after breakdown

 - dielectric strength 2.5 to 3 times that of air 
 - permittivity 1.0021 at 20 °C 
 - tan delta less them 2.0 x10-7

From Wikipedia

 - thermal conductivity at STP (101.3 kPa and 0 °C) = 12.058 mW/(m.K)
 - heat capacity at constant pressure (Cp) (101.3 kPa and 21 °C) = 0.097 kJ/(mol.K)
 - critical temperature: 45.5 °C 
 - critical pressure: 37.59 bar (3.759 MPa)

From Solvay Chemicals

 - melting point (2.26 bar) –50.8 °C
 - gas density (20 °C, 1 bar) 6.07 g /l
 - liquid density (0 °C, 12.65 bar) 1.56 kg / l
 - solid density (–100 °C) [12] 2.77 kg / l
 - critical temperature 45.58 °C
 - critical pressure 37.59 bar
 - critical density 0.74 kg / l 

answered 7/6/2012 Steven McFadyen 240
Steven McFadyen

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