equipment, which is available from several companies, who provide this
service. Power factor tests on oil and transformer liquids are commonly
made with ASTM D-924 test cell.
Good new oil has a power factor of 0.05% or less at 20°C. Higher power
factors indicate deterioration and/or contamination with moisture, carbon or
other conducting matter, varnish, glyptal, sodium soaps asphalt compounds,
or deterioration products. Carbon or asphalt in oil can cause discoloration.
Carbon in oil will not necessarily increase the power factor of the oil unless
moisture is also present. It is suggested that the following serve as guides for
grading oil by power factor tests.
Oil having a power factor of less than 0.5% at 20°C is usually considered
satisfactory for service.
Oil having a power factor between 0.5% and 2% at 20°C should be considered
as being in doubtful condition and at least some type of
investigation should be made.
Oil having a power factor of over 2% at 20°C should be investigated and
should be reconditioned or replaced.
The preceding guides may be elaborated on by saying that good new oil
has a power factor of approximately 0.05% or less at 20°C and that the power
factor can gradually increase in service to a value as high as 0.5% at 20°C
without, in most cases, indicating deterioration. When the power factor
exceeds 0.5%, an investigation is indicated. The question of what decision to
make regarding disposition of the oil depends on what is causing the high
power factor. Dielectric strength tests should be made to determine the presence
of moisture. The necessity for further tests will depend to a large extent
on the magnitude of the power factors, the importance of the apparatus in