16 Sept 2025
Expert Oil Diagnostic Services
Introduction
Oxidation stability is a critical property of insulating oils, directly influencing their performance, longevity, and reliability in electrical equipment. Two internationally recognized methods for assessing this property are: R
PVOT (Rotating Pressure Vessel Oxidation Test) – ASTM D2272 (for turbine oils) and ASTM D2112 (for mineral insulating oils)
Oxidation Stability Test – IEC 61125 (for insulating liquids)
RPVOT (ASTM D2272/D2112)
This method evaluates the induction period, the time before rapid oxidation begins by subjecting the oil to high temperature and oxygen pressure in the presence of a copper catalyst. The test ends when a pressure drop of 175 kPa (25 psi) is observed, indicating significant oxygen consumption due to oxidation.
Advantages
Simple and direct measurement of oxidation resistance
Useful for trending oil condition over time
Applicable to both fresh and in-service oils
Limitations
Long test durations for modern oils (up to 3000 min)
May not clearly indicate induction point for advanced formulations
Susceptible to seal leakage and pressure drif
Oxidation Stability (IEC 61125)
This method simulates long-term oxidative stress by bubbling air through the oil at elevated temperatures in the presence of a copper catalyst. After a fixed duration, the oil is analyze for degradation indicators such as acidity, sludge, and dielectric dissipation factor (DDF).
Advantages
Comprehensive assessment of oil degradation
Simulates real-world aging conditions
Suitable for quality control and acceptance testing
Limitations
Time-consuming and resource-intensive
Requires post-test chemical analysis
Less direct than RPVOT in measuring oxidation resistance
Comparative Summary
Feature | RPVOT (ASTM D2272/D2112) | Oxidation Stability (IEC 61125) |
Measurement Focus | Good but degrades over time | Chemical degradation post-aging |
Duration | Variable (200-3000 min) | Fixed (48-500 hours) |
Temperature | 150°C | 120°C |
Catalyst | Copper coil | Copper wire |
Oxidizing Agent | Pure oxygen | Zero air |
Key Parameters | Pressure drop | DDF, acidity, sludge |
Type of Oil | Inhibited Oil | Uninhibited Oil and Inhibited Oil |
Suitability | Trending and condition monitoring | Batch quality control |
[image]
For more info on our insulating oil analysis services, please do not hesitate to contact our team members:
Shaily Hatun Mohamad Saleh (shaily.saleh@tnb.com.my)
Muhammad Hadi Ahmad Fauzi (hadi.fauzi@tnb.com.my)
Roshaniza Ismail (roshaniza.ismail@tnb.com.my)
Nur Syahida Akryl Azam (nursyahida.azam@tnb.com.my)