sin αst

GENERATOR AND ELECTRICAL SYSTEM
be connected to. The result of the rectification is denoted ripple current and shown on
figure 7.5.
Figure 7.5: The result of 3-phased AC converted into DC ripple current [34]
As stated in the requirement list, ID 2, the system voltage must be 48 V DC. This means that
the rippled output voltage from the rectifier must be at least 48 V before any voltage is
transmitted to the batteries. The angular velocity of the generator, at which the voltage of
48 V is reached, is the cut-in speed, i.e. 250 rpm as described in section 7.1.
Input breaker
An input breaker, or circuit breaker, is an automatic switch, which protects the system
from damage caused by overload. If a fault condition is detected the input breaker imme-
diately discontinues the electric flow. When the breaker is activated the wind turbine is be
free spinning, as there is no resistance from the generator. The previously described shut-
down switch should therefore be activated once the input breaker is activated in order to
brake the wind turbine.
Battery Bank
It is recommended to use deep-cycle lead-acid batteries, which, contrary to normal lead-
acid automotive batteries, may be fully discharged without damage. The size of the battery
bank and the manner in which the individual batteries are connected depends on the spe-
cific needs and will therefore vary from site to site.
Earthing system
IEC 61400-2 requires that the wind turbine design includes a local earthing system,
which ensures that tower (including guy wires) are appropriately earthed to reduce
damage from lightning [5, p. 111].
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