Wind turbine cooling technologies - Wind Power Generation and Wind Turbine Design - page 617

3 Current wind turbine cooling systems
As has been mentioned above, in the operation of wind turbine, the gearbox,
generator and control system will produce a large amount of heat [11]. In order
to ensure the secure and stable operation of wind turbine, effective cooling mea-
sure has to be implemented to these components. Since the early wind turbines
had lower power capacity and correspondingly lower heat production, the natural
air cooling method was suffi cient to meet the cooling requirement. As the power
capacity increases, merely natural air cooling can no longer meet the requirement.
The current wind turbines adopt forced air cooling and liquid cooling prevalently,
among which, the wind generating set with power below 750 kW usually takes
forced air cooling as a main cooling method. As to large- and medium-scale wind
generating set with power beyond 750 kW, a liquid recirculation cooling method
can be implemented to satisfy the cooling requirement [11].
3.1 Forced air cooling system
The forced air cooling system comes up where a znatural air cooling system cannot
meet the cooling demands. When the air temperature in the wind turbine exceeds a
certain prescribed value, to achieve the cooling objective, the control system will
open the fl ap valve connecting internal and external environment of the nacelle
and, meanwhile, fans installed in the wind turbine are switched on, which produce
forced air blast to the components inside the nacelle. As the performance of air
cooling ventilation system has a decisive infl uence on the cooling effect and operating
performance of the wind turbine, the ventilation system should be well designed [9].
Thus, the design of the ventilation system is vital to an air cooling system project.
In the implementation of a forced air cooling system, different combinations are
chosen according to the amount of system heat production and heat dissipation of
various components. For a wind turbine with a power below 300 kW, since the
heat dissipation of the generator and control the converter is relatively low, their
heat is removed mainly by the cooling fans installed on the high-speed shaft, and
the gearbox is cooled using a method of splash lubrication due to the rotation of
the gear, where the heat of formation (or producing heat) is delivered through the
gearbox and additional fi ns to the nacelle, and fi nally taken away by the fans. The
cooling performance is mainly subject to the ventilating condition in nacelle [5].
By comparison, a wind turbine with power capacity beyond 300 kW possesses a
comparatively larger heat production and, therefore, it is not suffi cient for the
gearbox to control the temperature rise only by the cooling fan installed on the
high-speed shaft and the radiated rib on the box. The method of lubricating oil
circulation can realize effective cooling. The basic operating procedure is described
as follows: the gearbox is confi gured with an oil circulation supply system, driven
by a pump and an external heat exchanger. The oil temperature can be adjusted
under the permissible maximum value by regulating the oil delivery rate and the
wind speed fl owing through the heat exchanger according to the temperature rise