Temperature Rise — Transformer Glossary

The increase in winding and oil temperature above ambient when the transformer operates at rated load. A key specification for transformer longevity.

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Temperature Rise

The increase in winding and oil temperature above ambient when the transformer operates at rated load. A key specification for transformer longevity.

IEC 60076 specifies: top oil temperature rise ≤ 60K, average winding rise ≤ 65K (for Class A insulation at 40°C ambient). IEEE C57 specifies: top oil ≤ 65°C, average winding ≤ 65°C above ambient. For every 6–8°C above rated hot-spot temperature, insulation life is halved (Arrhenius rule). Tropical regions (55°C ambient) require derating or enhanced cooling to maintain insulation life.

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transformersCast Resin Dry Type TransformersIndoor-rated dry-type transformers for clean and sensitive environments.

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ONAF (Oil Natural Air Forced)Cooling method where oil circulates by natural convection but fans force air over the radiators, increasing cooling capacity by 25–40%.

Insulation ClassClassification of insulation materials based on their maximum continuous operating temperature. Determines the transformer's thermal endurance.