You can purchase the IEC 60099-5 standard from the IEC website or other authorized distributors. The standard is available in PDF format, which can be easily downloaded and accessed.
Because traveling voltage waves reflect when they hit an inductive impedance (like a transformer winding), the physical distance between the arrester and the transformer increases the voltage at the transformer. IEC 60099-5 gives precise formulas to calculate this "lead-length effect." Searching for the "IEC 60099-5 PDF": What You Need to Know iec 600995 pdf
The IEC 60099-5:2018 edition introduced significant changes to align with the energy and charge classification system first set in IEC 60099-4:2014. The PDF outlines formulas and methods to determine: You can purchase the IEC 60099-5 standard from