Transformer Oil Testing – Methods and Acceptable Values

Transformer oil (insulating oil) is critical for cooling and insulation. Over time, oil degrades due to heat, oxidation, and moisture. Regular testing ensures transformer reliability and prevents failures.

Why Transformer Oil Testing is Important?

• Maintains insulation strength
• Prevents overheating and arcing
• Detects early signs of faults
• Extends transformer life

Main Transformer Oil Tests

1. Dielectric Breakdown Voltage (BDV): Measures oil’s insulation capacity.
   Acceptable: > 60 kV (new oil), > 40 kV (in service)
2. Moisture Content: High moisture reduces dielectric strength.
   Limit: < 20 ppm
3. Acidity Test (Neutralization Value): Measures oil aging.
   Limit: < 0.03 mg KOH/g (new oil)
4. Dissolved Gas Analysis (DGA): Identifies fault gases like H2, CO, CH4.
5. Furan Analysis: Detects paper insulation degradation.

Acceptable Test Values

Parameter	Good Oil	Action Level
BDV	>60 kV	<40 kv="" td="">
Moisture	<20 ppm="" td="">	>40 ppm
Acidity	<0 .03="" td="">	>0.3

FAQs

1. How often should transformer oil be tested?

At least once a year, or more frequently for critical transformers.

2. What is the first sign of bad transformer oil?

Low BDV and high moisture content.

3. Can transformer oil be recycled?

Yes, through filtration and regeneration processes.