Electrical - Wind Energy: Renewable Energy and the Environment - page 143

Voltage
V pre-fault
ΔV dip
V fault
Time (cycles)
I rated
I pre-fault
I post-fault
Time (cycles)
Duration of
the fault
FIGURE 7.14 Illustration of voltage and current connection to wind farm after fault on utility line.
disconnected from the wind farm, as the loss of a single generator in a wind power plant may be less
than 1% of the total generation. For the 1 year, only 1% of all the faults caused high power genera-
tion losses ( P gen 0.8 P rated ). In this type of discussion, many use wind plant rather than wind farm,
because it really is a wind-powered electric generation plant.
7.4 ELECTRONICS
Electronics are used extensively in the control of the wind systems, and in general, the controllers
contain one or more computer processing units (CPUs) and programmable logic controllers (PLCs),
which can be hardwired, for wind turbine control and operation. Control systems run the gamut
from simple controls for battery storage to supervisory control and data acquisition (SCADA) for
entire wind farms. Electronics for power conversion and control are a major part of any wind turbine
system, and solid-state inverters allow variable-frequency output to be connected to the utility grid.
Induction generators on constant-rpm units may require a soft start to reduce mechanical stress and
to reduce the interaction between the utility grid and the wind turbine during connection.
7.4.1 C ONTROLLERS
The controller monitors the condition of the wind turbine, may collect statistics on its operation, and
controls switches for different operations and functions. The controller contains one or a number of
computer processing units.
The most simple is the controller to sense the voltage level of batteries, for both full charge and
discharge, which may have light indicators to display that information. As the battery bank voltage
approaches the regulation voltage, the wind turbine is furled manually, or the controller could switch
power to a regular load or a dump load. If there is no load available, the wind turbine may be brought
to a slow rpm. The controller could have an electrical braking mode, which is used for parking the
turbine before climbing or lowering the tower to work on the turbine. Equalization of the batteries,
which is the process to bring the batteries up to a high rate of charge, needs to be performed once a
month. Then the water level should be checked and distilled water added as needed.