ISO/DIS 20816-21

This document provides information about the measurement and evaluation of the mechanical vibration of wind turbines and their components. The working principle of wind turbines covered by this document is described in annex B. On account of the great influence which the place of installation and type of mechanical drive train can have on the vibration magnitude of all wind turbine components, it is necessary to divide the wind turbines into two groups: group 1: horizontal axis wind turbine installations with generators coupled to the rotor via a gearbox; group 2: horizontal axis wind turbine installations with generators coupled to the rotor without a gearbox (direct drive). This part of ISO 20816 applies to group 1 and group 2 wind turbines. It applies to horizontal axis wind turbines with rated generator outputs exceeding 200 kW and the following design and operation characteristics: a) installation onshore or off the coast (offshore); b) installation on supporting systems (tower and foundation) made of steel and concrete; c) horizontal-axis rotor with several rotor blades; d) rotor bearing separate from or integrated into the gearbox or into the generator; e) generator direct coupled (gearless) or driven via gearbox; f) generators of the synchronous or asynchronous type; g) generators with only a fixed pole number or which are pole-changeable for speed adjustment; h) permanent magnet or electrical excited induction generator with inner or outer rotor; i) power output control by rotor blade angle control (pitch adjustment – individual or collective); j) nacelle with active yaw system to align to wind direction. This document recommends zones for evaluating the vibration at continuous load operation. However, in most cases these evaluation zone boundaries might not be suitable for the early detection of faults. Annex A presents evaluation zone boundaries based on vibration data from thousands of wind turbines with rated generator output up to 5 MW. They can be helpful in facilitating discussion between users and manufacturers. The evaluation criteria contained in this standard mainly serve to ensure a reliable, safe long-term operation of the wind turbine and its components. It is intended to standardize measurements, to assist in their evaluation and to make possible a comparative evaluation of the vibration measured in wind turbines and their components. In addition, recommendations are given for the determination of limit values for operation. Although the type and implementation of broad-band vibration monitoring for wind turbines is addressed, this document does not apply to diagnostics or fault detection by condition monitoring of wind turbines. The evaluation of the balance quality of the slowly turning wind turbine rotor, which requires special measurements and analysis, is not covered by this document. This document does not apply to the evaluation of torsional vibration in the drive train. Although coupled lateral and torsional vibration of tower and drive train can affect the amplitudes of the defined vibration characteristics, diagnosis of this kind of vibration source is not feasible by the described measurement methods described in this document. For general design verification purposes and for specific fault diagnosis, special measurements are required which are beyond the scope of this document. This part of ISO 20816 also does not apply to acceptance measurements on gearboxes and generators in the manufacturer's test facility. This document does not apply to measurements of shaft displacement, due to the small number of turbines equipped with such measurements.