IEC 61400 is the international standard series for wind turbines: design requirements and load cases, offshore and floating foundations, power performance, power quality, lightning protection and SCADA communications. It underpins type certification through the IECRE system.
IEC 61400-1 The core part. Defines wind turbine classes (reference wind speed Vref, turbulence categories A/B/C), the set of Design Load Cases (DLC) covering normal, extreme and fault situations, and the verification of extreme and fatigue loads over a 20-25 year life.
IEC 61400-2 Simplified design and safety requirements for small machines (rotor area below 200 m²).
IEC 61400-3-1 / -3-2 Additional requirements for offshore turbines — wave, current and ice loads, support structures (-3-1 fixed) and floating substructures (-3-2).
IEC 61400-4 / -5 / -6 Component-level design standards for the most critical and most failure-prone parts of the machine.
IEC 61400-12 How to measure the power curve and annual energy production (AEP) — the basis for performance guarantees.
IEC 61400-21 / -27 Measurement of power quality characteristics (-21) and validated electrical simulation models used in grid integration studies (-27).
IEC 61400-25 A uniform SCADA information model and communication mappings for monitoring and controlling multi-vendor wind farms — closely aligned with IEC 61850.
(DLC) A wind turbine is a structural, electrical, control and grid-connection problem at once, so IEC 61400 is not one document but a series — each part owning a slice of the machine and its lifecycle. In day-to-day work you cite the part, not “IEC 61400” in general: -1 for loads, -3 offshore, -12 for power performance, -25 for SCADA.
The series is the technical backbone of type certification: an independent body checks that a turbine design and a specific project meet the relevant parts before it is built and connected.
IEC 61400-1 sorts sites by wind turbine class — reference wind speed (I/II/III) and turbulence category (A/B/C). The class fixes the design envelope: a class-III low-wind machine has a larger rotor and lighter structure than a class-I machine built for storms.
Design is then proven against a list of Design Load Cases — normal production, gusts, grid faults, parked-in-storm, emergency stop — for both extreme loads (the worst single event) and fatigue loads (billions of cycles over 20-25 years). Fatigue usually governs the blades, main shaft and tower base.
IEC 61400-3-1 (fixed) and -3-2 (floating) add the marine environment — wave, current and ice loads, corrosion, and the coupled dynamics of a floating substructure. Offshore drives larger machines (14-15 MW), HVDC export for distant farms, and weather-constrained access that makes condition monitoring essential.
A wind farm is hundreds of machines under one supervision system. IEC 61400-25 defines a vendor-neutral information model and communication mappings, reusing the abstract services of IEC 61850 so multi-vendor farms behave consistently. IEC 61400-21 measures power quality and -27 provides validated electrical simulation models for the grid-integration studies that grid codes require — the studies that, after the 2016 South Australia blackout, became non-negotiable.
The IECRE system gives a recognised, cross-market route to certify a turbine type and a project against the IEC 61400 series — reducing duplicate assessments between countries and underpinning the financing of large wind projects.