4.6.1.4 Gaseous Contamination
The gaseous contamination in the SF6 gas may result from three different
sources. The fi rst source of contamination is from the factory where it may
have been introduced into the gas. The second source of contamination is in
fi lling or operation of the gas-insulated equipment due to improper handling
and procedures. The third source is due to arc decomposition products. The
gaseous contamination may be checked by performing mass spectroscopy
or gas chromatography in the laboratory. The laboratory will usually provide
the metal sample cylinders for gas sampling with sampling instructions.
Also, a fi eld test for excessive oxygen content may be performed with any
simple instrument designed for this purpose.
4.6.1.5 Arc Products
The SF6 gas is referred to as a self-healing gas. This is because the gas absorbs
the free electrons generated by the arc which causes the gas to ionize. These
ions recombine to reform the SF6 gas. Not all of the ions and free atoms
recombine properly and some permanent breakdown products can form.
Therefore, all arced SF6 gas should be regarded as containing toxic byproducts.
The byproducts are usually lower fl uorides of sulfur.
After a major fault, the gas will usually exhibit the smell of rotten eggs.
If this odor is present, the following precautions should be taken before
working on the equipment.
1. Remove the gas from the equipment, keep personnel clear of
discharge.
2. Open doors, purge the enclosure, and provide forced ventilation.
3. Remove the arc products (solids) as much as possible before entering
the equipment. Appropriate protective clothing and other equipment
should be worn when entering the equipment.
4. The arc products should be deposited in plastic containers and
placed in sealable containers to be deposed of in a safe manner.
4.6.1.4 Gaseous Contamination
The gaseous contamination in the SF6 gas may result from three different
sources. The fi rst source of contamination is from the factory where it may
have been introduced into the gas. The second source of contamination is in
fi lling or operation of the gas-insulated equipment due to improper handling
and procedures. The third source is due to arc decomposition products. The
gaseous contamination may be checked by performing mass spectroscopy
or gas chromatography in the laboratory. The laboratory will usually provide
the metal sample cylinders for gas sampling with sampling instructions.
Also, a fi eld test for excessive oxygen content may be performed with any
simple instrument designed for this purpose.
4.6.1.5 Arc Products
The SF6 gas is referred to as a self-healing gas. This is because the gas absorbs
the free electrons generated by the arc which causes the gas to ionize. These
ions recombine to reform the SF6 gas. Not all of the ions and free atoms
recombine properly and some permanent breakdown products can form.
Therefore, all arced SF6 gas should be regarded as containing toxic byproducts.
The byproducts are usually lower fl uorides of sulfur.
After a major fault, the gas will usually exhibit the smell of rotten eggs.
If this odor is present, the following precautions should be taken before
working on the equipment.
1. Remove the gas from the equipment, keep personnel clear of
discharge.
2. Open doors, purge the enclosure, and provide forced ventilation.
3. Remove the arc products (solids) as much as possible before entering
the equipment. Appropriate protective clothing and other equipment
should be worn when entering the equipment.
4. The arc products should be deposited in plastic containers and
placed in sealable containers to be deposed of in a safe manner.
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