Overview
IEC TR 60076-26:2020 is an IEC Technical Report that assembles and categorizes the functional requirements of insulating liquids for use in power transformers (including reactors and HVDC transformers). Rather than providing detailed test procedures, the report acts as a structured reference or roadmap for the transformer industry, listing which liquid properties matter for design and service, and indicating the current status of validation methods for each parameter.
Key topics
The report organizes functional requirements into six practical categories and provides a relevance index (design vs service) and validation status for each parameter:
- General (physical / chemical)
- Fundamental liquid properties relevant to transformer design and handling.
- Dielectric / Insulation
- Parameters linked to the liquid’s dielectric performance and electrical safety.
- Thermal / Cooling
- Requirements for heat transfer and coolant performance under operating conditions.
- Ageing and Stability
- Indicators of in-service degradation and long‑term stability of insulating liquids.
- Liquid–solid system
- Interactions between liquid and solid insulation materials important for system performance.
- Material compatibility
- Compatibility of liquids with seals, coatings, paper, plastics and other materials found in transformers.
For each parameter the report shows:
- a relevance index (Important / High / Critical) for design and service,
- the status of test-method validation (IEC/ISO method exists, needs updating, or is absent),
- and concise comments about applicability and gaps.
The report notes some functional tests currently exist as ASTM or IEEE procedures and flags areas needing harmonized IEC/ISO methods.
Applications
IEC TR 60076-26:2020 is a practical reference for:
- Transformer designers and manufacturers - to check which liquid properties affect performance and lifetime.
- Insulating-liquid suppliers - to understand industry expectations and validation gaps.
- Test labs and standards committees (IEC, CIGRE, IEEE) - to prioritize development or update of validation methods.
- Utilities, asset managers and maintenance engineers - for informed selection, monitoring and diagnostics of insulating liquids during service.
Use cases include specification development, procurement, R&D of new liquids, comparative assessment, and planning of type or routine testing.
Related standards
This Technical Report complements existing liquid specification standards and test practices. Relevant documents mentioned in the report include:
- IEC 60296, IEC 62770, IEC 61099 (liquid specification standards)
- Various ASTM and IEEE test methods (noted where IEC/ISO methods are missing)
IEC TR 60076-26:2020 is intended to be maintained and updated as new validation methods and industry data become available, helping to align liquid functional requirements with evolving transformer technologies.