1) Clear sampling bottles or plastic bottles are not used for Transformer insulation oil sampling, Why?
An amber glass bottle is the preferred container. Clear glass bottles may be used but they shall be protected from direct light until ready to be tested. Plastic containers which are not reacted by the transformer oil (to be tested) may be used, but these shall not be used more than once. For sealing, screw caps with polyolefin or polytetrafluoroethylene are preferred.
2) What is the standard method for sampling insulation oil?
When sampling, Containers should be almost filled with samples, leaving about 3% of the container volume as free air space.
Precautions shall be taken to avoid contamination of the sample. Do not talk while taking samples. It is not recommended to collect samples during windy, rainy, dusty, high humid, or very cold conditions.
Refer: IEC 60475
3) Is it ok, to collect the hot oil sample immediately after oil processing?
Yes. It is possible to collect for testing. But it is recommendable to collect the oil sample after it is cool down to ambient temperature.
However, at the time of test, the temperature of the insulation oil and ambient temperature shall not differ by more than 5°C
4) Where to collect the oil sample for BDV test, transformer top or bottom?
Transformer tank bottom.
Unless otherwise required, the sample is taken where the liquid is likely to be most contaminated, usually at the lowest point of the transformer tank.
The same location should be used each time a sample is collected to ensure it represents the historic trend.
5) What details shall be provided along with the Transformer Oil sample collection container?
Date of sampling, Project /Station Name, Area/ Unit No., Equipment Description, Equipment Make, Year of Make, Equipment Tag No/Serial No., Equipment rating (voltage), Oil Type, Oil Temperature, Reason for the test, Collection point, collected by (name).
6) What is the method of cleaning the sampling bottles after the test?
Containers shall be rinsed with acetone, traces of which shall be removed by blowing with warm air. After cleaning, containers shall be immediately capped and kept sealed until used.
7) What is the IEC standard for the Insulation oil Breakdown Voltage (BDV) Test?
IEC 60156
8) What are the acceptable criteria for the BDV test result?
Acceptance criteria are different for new (unused) and used oils.
But for the acceptable limits, it is recommendable to follow project/utility specifications, if specified, or refer manufacturer's O&M manuals.
one can refer to IEC 60296 (for unused) and IEC 60422 (in-service).
