The design of a wind turbine gearbox is challenging due to the loading and environmental conditions in which the gearbox must operate.
Torque from the rotor generates power, but the turbine rotor also applies large moments and forces to the wind-turbine drivetrain. It is important to ensure that the drivetrain effectively isolates the gearbox, or to ensure that the gearbox is designed to support these loads.
Wind-turbine drivetrains undergo severe transient loading during start-ups, shut-downs, emergency stops, and during grid connections. Load cases that result in torque reversals may be particularly damaging to bearings, as rollers may be skidding during the sudden relocation of the loaded zone. Seals and lubrication systems must work reliably over a wide temperature variation to prevent the ingress of dirt and moisture, and perform effectively at all rotational speeds in the gearbox.
In traditional gearbox-operated wind turbines, the blades spin a shaft that is connected through a gearbox to the generator. The gearbox converts the turning speed of the blades—15 to 20 rotations per minute for a 1 MW turbine—into about 1,800 rotations per minute that the generator needs to generate electricity.
The multiple wheels and bearings in a gearbox suffer tremendous stress because of wind turbulence and any defect in a single component can bring the turbine to a halt. This makes the gearbox the highest-maintenance part of a turbine. Gearboxes in offshore turbines, which face faster wind speeds, are even more vulnerable than those in onshore turbines.
With growing focus on improving project returns, there has been an additional focus on increasing the power produced from wind turbines by improving the capacity factor i.e. ensuring wind turbines are operational and available. Given the importance efficient and highly reliable gearboxes in improving the capacity factor, major strides have been made in the gearbox technology.
The availability of wind turbines 10 years ago was about 80 to 85 percent. Today many of the wind turbines are running at close to 98 percent availability, matching their counterparts running on conventional fuels including nuclear, gas and coal.
Most of the global players today are focussed on improving gearbox reliability along with finding innovative solutions for minimizing the downtime when a gearbox does have a mechanical failure. For this the design and manufacturing processes are being brought closer together.
Uptower maintenance is something that will further help significantly reduce the downtimes of turbines. With turbine technology getting more sophisticated each year, use of sophisticated tools and softwares are helping testing and manufacturing processes. 3D modeling technology, which allows companies to use computer simulations to see how products will respond before manufacturing and testing the product in the field.
With Indian wind industry preparing for new growth phase of the onshore wind sector and prepare to tap the vast offshore wind energy potential, matching global technology standards is now a must for Indian wind turbine manufacturers.