Overview
IEC TS 60815-4:2016 is the Technical Specification that provides a first‑approach method for the selection and dimensioning of high‑voltage insulators for d.c. systems in polluted environments. It defines how to determine the required d.c. Unified Specific Creepage Distance (USCD) for insulators exposed to pollution, and gives guidelines to judge probable insulator behaviour for different pollution conditions. The document applies to glass and porcelain insulators, and composite and hybrid insulators (with HTM or non‑HTM housings). It is intended for preliminary design and requires comparison with operating experience or additional tests by agreement to avoid over‑ or under‑design.
Key topics and technical requirements
- Determination of d.c. site pollution severity: procedures for using prior d.c. experience or converting a.c./unenergized measurements to d.c. reference severity.
- Reference USCD (RUSCD): how to derive a reference Unified Specific Creepage Distance for the site and transfer it to candidate insulators.
- Correction factors and parameters:
- Pollution accumulation correction (K)
- NSDD (Non‑Standard Deposit Density) and CUR (Chemical composition / uniformity) corrections for Type A pollution
- Corrections for diameter (effect on pollution accumulation and flashover) and altitude
- Correction for the number of similar insulators in parallel
- Profile and geometry checks: shed overhang, spacing, minimum distance between sheds, creepage vs clearance, shed angles and creepage factors for candidate profiles.
- Materials and HTM: treatment of hydrophobicity transfer materials (HTM) and their improved pollution performance, with caveats on hydrophobicity loss.
- Design verification: emphasis on using operating experience and laboratory testing (by agreement) to confirm design assumptions.
- Scope exclusions: insulators with coatings are excluded in this edition until coatings are better defined.
Practical applications and users
IEC TS 60815-4:2016 is aimed at professionals involved in HVDC infrastructure who need practical, pollution‑aware insulator selection guidance:
- Utilities and transmission system planners designing HVDC overhead lines, converter stations and substations
- Insulator manufacturers and R&D teams developing glass, porcelain, composite and hybrid insulators
- Design engineers, specification writers and procurement teams preparing technical requirements
- Test laboratories and consultants performing site severity assessments or verification testing
The specification is especially useful for preliminary design to determine required creepage distances and to set test/agreement conditions for final verification.
Related standards
- IEC 60815 series (other parts covering a.c. and site classification)
- CIGRE HV d.c. Pollution Application Guidelines (reference for statistical design and field experience)
Keywords: IEC TS 60815-4:2016, d.c. insulators, pollution, Unified Specific Creepage Distance, USCD, HTM, high‑voltage insulators, HVDC design, insulator selection.