Overview
IEC TR 61858-3:2020 provides guidance for the identification and thermal evaluation of electrical insulating materials (EIMs) and auxiliary materials when modifying an established electrical insulation system (EIS). It helps engineers and test labs select feasible evaluation procedures and understand the impact of material changes on thermal classification, life expectancy and system compatibility.
Key objectives of this technical report include:
- Clarifying roles of major (EIMs) and minor (auxiliary) materials within an EIS
- Advising selection of suitable test procedures for validating substitutions or modifications
- Supporting consistent thermal evaluation to maintain or verify EIS thermal classification
Key Topics
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Material identification and ‘generic identical’ proof: The report outlines techniques to demonstrate generic identity, including molecular spectroscopy (FTIR preferred, NIR, Raman, UV/Vis), thermal analysis (TG, DSC, DMA, DTA) and determination of activation energy for degradation. These methods support decisions on when a material can be treated as equivalent.
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Evaluation procedures: IEC TR 61858-3:2020 defines five procedures for assessing changes:
- Procedure G: Proof of generic identical materials using spectroscopy and thermal analysis
- Procedure A: Changes without test (e.g., geometric/thickness adjustments where no material change occurs)
- Procedure B: Chemical compatibility (sealed tube conditioning to assess decomposition effects; standard sealed conditioning is 336 h ± 2 h at thermal class + 25 K)
- Procedure C: Standard single-point thermal aging (concurrent testing of reference and candidate EIS with target test life ~1 000–2 000 h)
- Procedure D: Full thermal aging per IEC 61857 series
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EIS assessment principles: Before substitution, evaluate the function of the component in insulation coordination, the consequences of failure, and compatibility with other system components. Auxiliary materials must not compromise reinforced, basic or supplementary insulation.
Applications
This report is directly applicable to manufacturers, R&D teams, and test labs involved in winding insulation, motor and transformer manufacturing, and insulation-system qualification. Typical uses:
- Assessing supplier material changes and equivalence claims
- Planning compatibility tests for varnishes, impregnation resins, bondable wires and additives
- Determining whether single-point or full thermal aging is required for a reliable thermal-life evaluation
Related Standards
- IEC 61857 (all parts) - Procedures for thermal evaluation of EIS
- IEC 61858-1 / IEC 61858-2 - Parts addressing wire-wound and form-wound EISs
- IEC 60505 - General principles for evaluation and qualification of EIS
By following IEC TR 61858-3:2020, stakeholders can apply consistent, practical methods for material identification, compatibility testing and thermal-life evaluation to maintain safe and reliable electrical insulation systems.