Wind turbine cooling technologies - Wind Power Generation and Wind Turbine Design - page 616

2.2 Generator
The generator rotor is connected to the high-speed shaft of the gearbox. It
drives the generator to rotate at a high speed and to cut the magnetic lines of
force, by which electric energy is obtained. During the operation of a wind
turbine, the generator will produce a huge amount of heat mainly in its wind-
ings and various internal wastes of iron core, primarily comprised of iron loss,
copper loss, excitation loss and mechanical loss [7]. Besides, the temperature
rise of the generator also has a correlation with power, operational condition,
and duration of runs [8]. Moreover, there is a tendency of the unit-capacity
enlargement of wind turbine which can be implemented by magnifying wind-
ing factor or magnetic fi eld intensity. Since adding electromagnetic load is
unsatisfactory with the restriction of magnetic saturation, at present, a popu-
lar method for enlarging the unit capacity is to increase inductance coil load.
However, by applying this method, copper loss of bar will rise, which results in
high coil temperature, acceleration of insulation aging and, eventually, damage
of the machine. Because of this, a proper cooling method should be applied to
control the internal temperature of various components of the generator within
a permissible range. Hence, it can be concluded that the enlargement of the
unit capacity of wind turbine mainly depends on the improvement of the cooling
technology [9, 10].
2.3 Control system
As the wind speed and direction are changing all the time in the operation of
wind turbine, auxiliary apparatus should be installed to adjust the operating sta-
tus promptly to ensure the secure and stable operation of the wind turbine. The
common system auxiliary apparatuses include: anemoscope, wind vane, yawing
system, mechanical brake and thermometer. The anemoscope and the wind vane
are used to detect immediate wind status; and the thermal sensor is responsible
for monitoring the temperature changes in the generator and gearbox. When the
operating status changes, the anemoscope, the wind vane and the thermal sensor
will feed back the detected signal to the control system in the nacelle, then the
input signal is diagnosed and processed by the control system and fi nally output
to the yawing system and the mechanical brake, which changes the operating
status of the wind turbine. Meanwhile, the control system has functions of dis-
playing and recording parameters such as instantaneous mean wind speed, mean
wind direction and mean power and other operating parameters. In addition,
frequency converter is equipped in the control system, which aims at converting
the unstable frequency of wind turbine signal to suffi ce to the demands of paral-
lel operation. Therefore, the control system is also called control converter. In
the operation, as a core component for the failure-free operation of wind turbine,
the control system will produce a large amount of heat, which needs to be taken
away timely.