Citing a rapid evolution in the technology, the IEC (International Electrotechnical Commission) has published the second edition of its standard for measuring the power quality of wind turbines.

Developed
by IEC Technical Committee 88 (Wind turbines), IEC 61400-21 sets out
the tests that can be used to compare wind turbines of different
types/makes, as well as different electricity grid requirements. (The
latter are complex, says IEC, as they typically consider the capability
of a wind farm rather than that of a single wind turbine.)



Some 20
years ago, the common wind turbine was rated at about 50kW. Today,
multi-MW wind turbines are concentrated on big wind farms. Modern wind
farms may control the reactive power or voltage just like any other
power plant, and may also control active power or frequency as long as
wind conditions permit. Hence, connecting modern wind power plants to
the grid presents very similar challenges to those of connecting any
other power plant.



Different
wind turbine types have different power quality characteristics. IEC
61400-21 provides a uniform methodology for ensuring consistency and
accuracy in the presentation, testing and assessment of power quality
characteristics of grid-connected wind turbines. The power quality
characteristics described in the standard include: wind turbine
specifications; voltage quality (emissions of flicker and harmonics);
voltage drop response; power control (control of active and reactive
power); grid protection; and reconnection time.