IEC 61857-31:2017

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.