The gearbox on a wind turbine is essential for uprating the low speed of the main shaft attached to the rotor hub from low to top gear. It does so by converting slowly rotating, high torque (turning force) power from the wind turbine rotor and shaft to high speed, low torque power. This is then transferred to a high-speed shaft connected to an electrical generator.
The new IEC standard now requires wind turbine gearboxes to be reliable and have a design lifetime similar to that of the wind turbine. For wind turbine classes I to III (high to low wind), this must be "at least 20 years" according to IEC 61400-1, Wind turbines – Part 1: Design requirements. IEC 61400-4: Wind turbines – Part 4: Design requirements for wind turbine gearboxes, is an essential addition to the IEC 61400 series of International Standards for wind turbines. It has been prepared by IEC TC 88 in co-operation with ISO TC 60: Gears.
Essentially the standard is a technical revision of ISO 81400-4, which it cancels and replaces. Its content has been extensively expanded and includes the following significant technical changes:
extension of the scope to wind turbines above 2 MW rated power
considerations for converging differing approaches to reliability in gear, bearing and wind turbine standards
new clause on wind turbine loads specific to drivetrains
new clause on testing and validation of new gearbox designs
updated bearing selection tables for different locations in a wind turbine gearbox
expanded design considerations on the use of bearings based on avoiding standard failures
new clause on considerations and requirements in the design and analysis of gearboxes structural elements
updated considerations and requirements for lubricants and lubrication systems
IEC 61400-4 also identifies overall and specific test criteria and plans for all elements that need testing and also lists the gearbox and drivetrain design changes that require further testing. Detailed criteria for workshop prototype, field, production and robustness tests are given as well as indications of what lubrication systems to use. Where mechanical systems are concerned, proper operation, service and maintenance are central to reliability and durability and to ensuring that the gearbox remains operational for its full expected lifetime.
To ensure this is the case, IEC 61400-4 gives detailed guidelines in terms of service, maintenance and inspection, commissioning and run-in, transport, handling and storage, installation, repair, condition monitoring and lubrication requirements – including oil type, oil test and analysis
Extensive documentation including terms, definitions and conventions, symbols and dozens of figures is available and ensures this International Standard provides all of the information needed by manufacturers and suppliers of gearboxes and all associated elements along the entire length of the production line. It is also invaluable to the wind turbine industry in general, since gearboxes form a central element of any wind turbine installation.
IEC 61400-4 is a landmark International Standard and the first that applies to gearboxes used in wind turbines above 2 MW rated power, which are currently being deployed throughout the world. Wind turbine manufacturers, who regularly reference several IEC 61400 International Standards as guarantees of their products’ certification, will undoubtedly be adding a mention of IEC 61400-4 to their sales documentation.
“Ultimately in the wind energy business all wind turbines end up being certified; it's a market imperative” said TC 88 Chairman Sandy Butterfield “All wind turbine designers who know that their product is going to be shipped internationally will design to IEC standards because they can't possibly design to the range of national standards that are out there.”
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