Insulation Class — Transformer Glossary

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

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Insulation Class

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

Class A (105°C): oil-impregnated paper — standard for oil-filled transformers. Class B (130°C): used in some dry-type designs. Class F (155°C): standard for cast resin dry-type transformers. Class H (180°C): high-temperature dry-type applications. Higher insulation class allows higher operating temperatures but doesn't change the fundamental 6–8°C halving rule for thermal ageing.

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Where this term matters in the ETS portfolio.

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

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

Partial Discharge (PD)Localised electrical discharge that does not fully bridge the insulation between conductors. A precursor to insulation failure.