Page 102 - Fluid Power Engineering

80 Chapter Six

Class A Class B
Average flow inclination −3to +3 −15 to +15
angle in degrees
Wind speed range (m/s) 4to16 4to16
Turbulence intensity 0.03 to 0.12+0.48/V 0.03 to 0.12+0.96/V
Turbulence structure Nonisotropic Isotropic
◦
Air temperature, C 0to40 −10 to 40
Air density, kg/m 3 0.9 to 1.35 0.9 to 1.35

Source: From International Electrotechnical Commission (IEC). Wind Turbines –
Part 12-1: Power Performance Measurements of Electricity Producing Wind
Turbines. 2005. IEC 61400-12-1. With permission from IEC.

TABLE 6-1 Description of Class A and B Influence Parameter Ranges, per IEC
61400-12-1

a wind tunnel when the correct wind speed is 10 m/s. At this wind
speed, a Class 0.5 anemometer has a maximum deviation of ± 0.5%;
a Class 1 anemometer has a maximum deviation of ± 1%.
The second part of the anemometer classification is the influence
of terrain. The inflow angle or the flow inclination angle has a sig-
nificant impact on accuracy. Classes A and B are used to describe the
terrain (see Table 6-1). Class S (S for special) is associated with influ-
ence parameters that are not in the ranges specified for Class A or B.
The classification of most commonly used anemometers is shown in
Table 6-2.
Class 2 or better sensors are used for power curve measurements
of wind turbines, permanent met-towers, and temporary met-towers
that are used to prove wind resources at a site. Class 1.5 or better

Anemometer Class A Class B
Thiess First Class Advanced 0.9 3.0
Risoe Windsensor P2546A 1.4 5.1
Thiess First Class 1.8 3.8
Vector A100LK 1.8 4.5
NRG #40 2.4 8.3

Source: From Young, M., Met Towers & Sensors–Science & Equipment Considerations,
DNV Global Energy Concepts, AWEA Resource and Project Energy Assessment
Workshop, Minneapolis, MN, 2009.
TABLE 6-2 Deviation of the Most Commonly Used Anemometers