IEC 61000-4-18: 2019 focuses on the immunity requirements and test methods for electrical and electronic equipment, under operational conditions, with regard to: a) repetitive slow damped oscillatory waves occurring mainly in power, control and signal cables installed in high voltage and medium voltage (HV/MV) substations; b) repetitive fast damped oscillatory waves occurring mainly in power, control and signal cables installed in gas insulated substations (GIS) and in some cases also air insulated substations (AIS) or in any installation due to high-altitude electromagnetic pulse (HEMP) phenomena. The object of this document is to establish a common and reproducible reference for evaluating the immunity of electrical and electronic equipment when subjected to damped oscillatory waves on supply, signal, control and earth ports. The test method documented in this part of IEC 61000 describes a consistent method to assess the immunity of an equipment or system against a defined phenomenon. NOTE As described in IEC Guide 107, this is a basic EMC publication for use by product committees of the IEC. As also stated in Guide 107, the IEC product committees are responsible for determining whether this immunity test standard is applied or not, and if applied, they are responsible for determining the appropriate test levels and performance criteria. The document defines: test voltage and current waveforms; ranges of test levels; test equipment; calibration and verification procedures of test equipment; test setups; test procedure. This second edition cancels and replaces the first edition published in 2006 and its Amendment 1:2010. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: a) addition of a mathematical modelling of damped oscillatory wave waveform; b) new Annex B on measurement uncertainty;