Standards and Practices - Structural Integrity of Offshore Wind Turbines - page 37

INTERNATIONAL ELECTROTECHNICAL COMMISSION

Background on Land-Based Wind Turbines:
Historical Perspective

During the early 1990s, the wind energy industry—through IEC—began
to establish international standards for land-based wind turbines. There
were at least two motivations for establishing international standards:

• The existing European design standards (e.g., in Denmark, Germany,

and the Netherlands) were insufficient in that they did not result in
reliable performance over the 20-year design life of the turbines. Many
wind turbines experienced breakdowns in major components, such as
gearboxes and blades, after less than 10 years of operation, leading to
excessive downtimes.

• The industry wanted to make sure that all wind turbines complied with

the same standard so that price competition could take place on a uni-
form basis (excluding substandard wind turbine designs).

The United States saw the IEC standards activities of the 1990s as a way
to provide a fair and unified approach to the emerging world wind energy
market and has participated in the development of the IEC standards since
their inception. Technical Committee 88 (TC 88) was established to
develop and manage a suite of applicable standards for wind turbines.

Description of Relevant Standards

The primary standard for wind turbine structural design requirements
is IEC 61400-1 Ed. 3 (IEC 2005). This standard defines design classes,
external (environmental) conditions for each design class, DLCs, fault con-
ditions that must be included in the design, procedures for assessing static
and dynamic loads, electrical requirements, and methods for assessing the
site-specific suitability of the turbine. Perhaps the most important part of
the standard is a detailed definition of the turbulent wind environment.
Because understanding the minute characteristics of wind is so important
in assessing unsteady aerodynamic load distributions along the rotating
blades, it is crucial that this part of the external conditions be defined in a
manner consistent with the analytical theory used for rotor load estimation.