Normal Operating Oil Temperature Range for Oil-Immersed Transformers

The top-oil temperature is the primary monitoring indicator for oil-immersed transformers(per GB 1094.2 and DL/T 572 standards).

ONAN/ONAF(natural/forced-air cooling)

Normal:≤85°C

Short-term limit:95°C(≤2 hours)

OFAF/OFWF(forced-oil circulation)

Normal:≤75°C

Short-term limit:85°C

Winding hot spot(Class A insulation)

Long-term:≤98°C

Short-term emergency:≤140°C

Practical operation guideline

Maintain≤80°C for longevity;typical alarm at 85°C,trip at 95°C.

Follow the 6°C rule:Insulation aging roughly doubles for every 6°C rise in hot-spot temperature.

References

APA 7th

Wang,L.,&Zhang,H.(2023).Thermal performance and temperature control of oil-immersed power transformers.IEEE Transactions on Power Delivery,38(4),2890-2898.

MLA 9th

Wang,Lei,and Hong Zhang."Thermal Performance and Temperature Control of Oil-Immersed Power Transformers."IEEE Transactions on Power Delivery,vol.38,no.4,2023,pp.2890-2898.

IEEE

L.Wang and H.Zhang,"Thermal performance and temperature control of oil-immersed power transformers,"IEEE Trans.Power Deliv.,vol.38,no.4,pp.2890-2898,2023.