Overview
IEC 61857-31:2017 defines thermal evaluation procedures for electrical insulation systems (EIS) intended for applications with a designed life of 5 000 hours or less. It adapts the general EIS evaluation approach of IEC 60505 and the IEC 61857 series to provide streamlined, application-focused screening and classification methods for short-life products (for example, many automotive and other transient-service components).
Key topics and technical requirements
- Scope and purpose: Establishes EIS thermal endurance (TE) ratings for systems with designed life ≤ 5 000 h, using modified procedures based on IEC 60505.
- Three test procedures:
- Procedure A - One-temperature ageing for designed life ≤ 1 500 h. Ageing temperature = 10 K above maximum design temperature. Average life (AL) of the specimen set must be ≥ 1 500 h. Typical ageing cycle described (168 h cycle recommended to accumulate hours efficiently).
- Procedure B - One-temperature ageing extended to accumulate up to 5 000 h (builds on Procedure A).
- Procedure C - Two-temperature ageing using two specimen sets: lower temperature 20–30 K above expected thermal class, higher temperature 30–35 K above expected thermal class; results from both sets are used to project TE to the required time coordinate.
- Data analysis and TE assignment:
- For Procedures A/B, if no failures occur before the target time, no projection is required; otherwise calculate average life per IEC 61857-1.
- For Procedure C, use both temperature data sets to project life; if only the higher-temperature set completes, the result is conservative.
- TE is reported as EIS TE x/y (x = thermal class in °C, y = time in hours), e.g., EIS TE 180 °C/1 200 h.
- Reporting: Test reports must reference this document and include EIS description, ageing temperatures and durations, conditioning and diagnostic tests, results and analysis.
Practical applications and users
- Targeted at short-life or limited-duration applications such as automotive components, power electronics, sensors, connectors, and consumer devices where designed life ≤ 5 000 h.
- Primary users:
- Materials and insulating-system engineers
- Test laboratories and qualification teams
- OEMs, component manufacturers and R&D groups
- Quality and reliability engineers assessing thermal endurance and thermal class
Related standards
- IEC 60505 - Evaluation and qualification of electrical insulation systems
- IEC 61857-1 - General requirements for thermal evaluation (low-voltage)
- IEC TR 61857-2 - Selection of appropriate test method
- IEC 61857-21 / IEC 61857-22 - Specific model requirements (wire-wound, encapsulated-coil)
Keywords: IEC 61857-31, electrical insulation systems, thermal evaluation, thermal endurance, EIS evaluation, designed life 5000 h, one-temperature ageing, two-temperature ageing, IEC 60505.
Open preview (PDF)Electrical insulation systems - Procedures for thermal evaluation - Part 31: Applications with a designed life of 5 000 h or less
