IEC 61400-21-1:2019 includes:· definition and specification of the quantities to be determined for characterizing the electrical characteristics of a grid-connected wind turbine;· measurement procedures for quantifying the electrical characteristics;· procedures for assessing compliance with electrical connection requirements, including estimation of the power quality expected from the wind turbine type when deployed at a specific site.The measurement procedures are valid for single wind turbines with a three-phase grid connection. The measurement procedures are valid for any size of wind turbine, though this part of IEC 61400 only requires wind turbine types intended for connection to an electricity supply network to be tested and characterized as specified in this part of IEC 61400.This first edition cancels and replaces the second edition of 61400-21 published in 2008. This edition includes the following new items with respect to 61400-21:a) frequency control measurement;b) updated reactive power control and capability measurement, including voltage and cos φ control;c) inertia control response measurement;d) overvoltage ride through test procedure;e) updated undervoltage ride through test procedure based on Wind Turbine capability;f) new methods for the harmonic assessment.