Maximum Allowable Overload Duration for Oil-Immersed Transformers

According to IEC 60076-7 and GB/T 1094.7,oil-immersed transformers(OIT)have clear limits for overload duration,determined by overload multiple,hot-spot temperature(≤140°C for normal emergency),ambient temperature(20–30°C),and initial load(≤80%).Typical allowable durations are as follows:

1.1×(10%overload):180 minutes(daily peak)

1.2×(20%overload):150 minutes

1.3×(30%overload):120 minutes

1.5×(50%overload):30 minutes(short-term emergency)

1.75×(75%overload):15 minutes

2.0×(90%overload):7.5 minutes(extreme emergency)

Long-term emergency overload(≤1.8×,hot-spot≤120°C)is permitted up to 800 hours per year.Ambient temperature>35°C halves the allowable time;forced cooling(OFAF)extends it by~20%.Exceeding limits accelerates insulation aging and risks failure.

References

APA 7th Edition

International Electrotechnical Commission.(2018).Power transformers–Part 7:Loading guide(IEC 60076-7:2018).

MLA 9th Edition

International Electrotechnical Commission.Power Transformers–Part 7:Loading Guide,IEC 60076-7:2018,2018.

IEEE Style

International Electrotechnical Commission,Power transformers–Part 7:Loading guide,IEC Standard 60076-7:2018,2018.