If you don't need the full standard text, consider these free resources:
Standards for longevity in harsh environments. 3. Insulation Requirements iec 618691 pdf
Outlines requirements for ambient temperature, altitude, vibration, and corrosion resistance. Mechanical and Safety: Includes standards for internal arc fault protection If you don't need the full standard text,
The standard establishes standard baselines for environmental operation. If equipment operates outside these parameters, special designs must be negotiated between the manufacturer and the purchaser. iec 618691 pdf
Standard values for insulation levels, frequencies, and thermal currents.
The to obtain the official IEC 61869 PDF is through authorized standards resellers. The standard is copyrighted and must be purchased.