What’s going on? – 1.2/50 voltage surge generator basics

Traditionally 1.2/50 voltage impulse generators have been used for insulation testing. The voltage waveform is defined by the IEC TC42 standard IEC 60060-1:2010, High-voltage test techniques – Part 1: General definitions and test requirements. The 1.2/50 is termed as the standard lightning impulse voltage having a front time of 1.2 µs ±30%, a time to half value of 50 µs ±20% and a peak value tolerance of ±3 %. When testing oscillations or an overshoot may occur around the waveform peak and IEC 60060-1 defines how these are treated and allows a maximum overshoot value of ±15 %.

The effective output impedance of the 1.2/50 impulse generator cannot be higher than 500 Ω, as defined by the IEC TC 109 standard IEC 60664-1:2007, Insulation coordination for equipment within low-voltage systems – Part 1: Principles, requirements and tests. For functional insulation and basic insulation, IEC 60664-1 defines preferred impulse withstand voltage values of 0.33 kV, 0.50 kV, 0.80 kV, 1.5 kV, 2.5 kV, 4.0 kV, 6.0 kV, 8.0 kV and 12 kV.

This document studies specific ITU-T and the IEC 1.2/50 impulse generators.