Iec 60815-2 Pdf Link -

IEC 60815-2 provides a modern, scientifically refined methodology for dimensioning ceramic and glass insulators in polluted AC environments. Its introduction of SPS classes with ESDD ranges, shape factors, and voltage corrections makes it far more accurate than the 1986 version. For any utility or engineer designing outdoor HV AC lines or substations in polluted areas, compliance with this standard is essential to prevent flashovers and ensure long-term reliability.

From Table 2 (Level d → 31–43 mm/kV). Choose 38 mm/kV as a conservative interim value. iec 60815-2 pdf

This is the fundamental design metric provided by the standard. It defines the minimum leakage path (creepage distance) required per kilovolt of system voltage ( IEC 60815-2 provides a modern