Generator and Electrical System - Small Wind Turbines: Analysis, Design, and Application - page 249

poorly conducting anti-vibration mounts. National standards on lightning protec-
tion in general specify the minimum size, typically 35 mm 2 in cross-section.
Power cables and connected equipment should have surge protection such as
clamping components, e.g. suitable varistors, transient absorption zener diodes etc.
If a turbine is to be installed in an area of high lightning risk, the nosecone and
nacelle cover should be metal to protect the generator. The path to ground will
then be through the turbine's yaw assembly. The yaw bearing may suffer damage
from the lightning current in the form of pitted bearing balls, rollers and races. The
bearing may also weld itself in a fixed position.
Generally the tower, regardless of type, provides a sufficient path to ground.
Whether earthing is needed at the tower base depends on the foundations and soil
type. If, for example, the bolts holding the tower baseplate are electrically con-
nected to the rest of the reinforcing cage, then a concrete foundation can provide
sufficient earthing depending on the soil type.
11.8.1 Further Reading
Many references on controllers, rectifiers, inverters and grid connection, as well as
a number of important IEEE standards, can be found on the IEE Xplore web site. If
your University subscribes to this site you will have free access to all the IEEE-
based references cited in this text. Start at: http://ieeexplore.ieee.org/
11.8.2 Exercises
1. The Ginlong 500-A PMG has a maximum efficiency of 73%. For the design
example from Chap. 7 , how much heat has to be transferred away from the
generator at rated conditions?
2. From Figs. 6.2 and 6.5 , estimate the rpm at which the generator of the 500 W
turbine is switched on.
3. It is now possible to buy micro-inverters intended for standard photovoltaic
panels and rated at about 200 W (see for example http://www.enphaseenergy.
com/products/ ). How would you use three micro-inverters for a 600 W wind
turbine?
4. If you were designing a 10 kW wind turbine using a PMG, what sensors would
you consider installing on the turbine?
References
1. Gieras JF, Wing M (2002) Permanent magnet motor technology. Dekker, New York
2. Proca AB, Keyhani A, EL-Antably A, Lu W, Dai M (2003) Analytical model for permanent
magnet motors with surface mounted magnets. IEEE Trans Energy Convers 18:386-391