Page 235 - Wind Energy Handbook

5

Design Loads for Horizontal-Axis

Wind Turbines

5.1 National and International Standards

5.1.1 Historical development

The preparation of national and international standards containing rules for the
design of wind turbines began in the 1980s. The first publication was a set of
regulations for certification drawn up by Germanischer Lloyd in 1986. These initial
rules were subsequently considerably refined as the state of knowledge grew,
leading to the publication by Germanischer Lloyd of the Regulation for the Certifica-
tion of Wind Energy Conversion Systems in 1993. This was further amended by
supplements issued in 1994 and 1998. Meanwhile national standards were pub-
lished in The Netherlands (NEN 6096, Dutch Standard, 1988) and Denmark (DS
472, Danish Standard, 1992).
The International Electrotechnical Commission (IEC) began work on the first
international standard in 1988, leading to the publication of IEC 1400-1 Wind turbine
generator systems – Part 1 Safety Requirements in 1994 (Second Edition IEC, 1997). A
revised edition containing some significant changes appeared in 1999, bearing the
new number IEC 61400-1. The following sections describe the scope of the IEC
61400-1, Germanischer Lloyd and Danish requirements in outline.

5.1.2 IEC 61400-1

IEC 61400-1 Wind turbine generator systems – Part 1 Safety Requirements identifies four
different classes of wind turbines to suit differing site wind conditions, with
increasing class designation number corresponding to reducing wind speed. The
wind speed parameters for each class are given in Table 5.1.
The reference wind is defined as the 10 min mean wind speed at hub-height with
a 50 year return period. To allow for sites where conditions do not conform to any
of these classes, a fifth class is provided for in which the basic wind parameters are
to be specified by the manufacturer. The normal value of air density is specified as
3
1:225 kg=m .
A crucial parameter for wind turbine design is the turbulence intensity, which is