TABLE 4.8
Types of Faults and Key Gases
Operating Condition Interpretations
1. Nitrogen plus 5% or less oxygen Normal operation
2. Nitrogen, carbon monoxide, and carbon
dioxide
Transformer winding insulation overheated;
key gas is carbon monoxide
3. Nitrogen, ethylene, and methane—some
hydrogen and ethane
Transformer oil is overheated; minor fault
causing oil breakdown. Key gas is ethylene
4. Nitrogen, hydrogen, small quantities of
ethane and ethylene
Corona discharge in oil; key gas is hydrogen
5. Same as #4 with carbon dioxide and
carbon monoxide
Corona involving paper insulation; key gas is
hydrogen
6. Nitrogen, high hydrogen and acetylene;
minor quantities of methane and ethylene
High-energy arcing; key gas is acetylene
7. Same as #6 with carbon dioxide and
carbon monoxide
High-energy arcing involves paper insulation
of winding; key gas is acetylene
210 Electrical Power Equipment Maintenance and Testing
4.4 Insulating Liquid Sampling Procedures
The validity of the test results is dependent upon the sampler being certain
that the oil sample is truly representative of the oil in the equipment. Glass
bottles are recommended as containers for samples because they can be easily
inspected for cleanliness. The glass bottles may be either cork or glass stoppered
or fi tted with screwcaps having cork or aluminum liners (inserts).
Corks should be of good quality. Do not use rubber stoppers. Clean, new,
rectangular-shaped, 1 quart (qt) cans with screwcaps have been found to be
satisfactory containers for shipping samples. Samples should be taken from
the equipment in accordance with ASTM D 923, Standard Test Method for
Sampling Electrical Insulating Liquids.
Containers should be rinsed in lead-free gasoline (which is fl ammable and
should be used out-of-doors only) or chlorothene (a nonfl ammable solvent),
dried, and washed in strong soapsuds. Then they should be thoroughly
rinsed with water, dried in an oven at about 105°C for several hours, and
removed from the oven. As the bottles cool, they should be sealed by dipping