Sophisticated transmissions incorporating planetary drives and frequency converter control are used in drive systems for wind generators ranging in size from small systems for village power supply in India through to 5 MW leviathans.

These ruggedly reliable and compact drive systems - incorporating technology already proved in Australasian industrial applications ranging from mining to manufacturing and materials handling - provide as high as possible an energy yield and as low as possible risk potential for the system at the same time.

With their help, the generator's gondola (and thus the wind turbine) is constantly matched to the wind direction on the one hand, while on the other the rotor blades are brought into an ideal position.

Operation at an optimal speed is decisive for the efficiency of the energy producing drive train extending from the rotor to the generator. If it turns too slowly, insufficient energy will be produced; if it turns too quickly, there are dangers to the complete wind turbine.

Two main final control elements ensure that the speed is kept as optimal as possible:

• The first control element governs the positioning of the gondola, which has to keep the rotor directly in the wind. The wind must always hit the rotor at right angles in order to ensure optimal exploitation of the power.
• The second final control element, which is responsible for the optimal speed, relates to the position of the individual rotor blades. Aerodynamics are strongly influenced by the inclination of the blades against the wind. Incorrect inclination can result in rotor standstill in strong winds. The rotors must remain head-on to the wind

Given the huge dimensions and masses to be moved with 5 MW turbines it is obvious what amounts of force are necessary in order to perform the tasks described above.

However, system designers have to consider not only the movement torque, but also the holding torque, both of which are decisive for the design of the azimuth drive.

Several geared motors with brakes are used in order to always maintain the gondola at right angles to the wind and keep it there (no small task when you consider its weight of more than 100 tons and a rotor span of up to two football pitches).

The sensor technology employed reports wind direction changes to a control unit, which then puts several geared motors in motion in a matched way via the frequency converters, so as to track the gondola.

The tracking is usually triggered by a wind direction deviation of seven degrees. The requirements for precision and exactly matched drive behaviour are decisive in the choice of the drive system.

Drives of a few thousand Newton meters are sufficient for this task for small systems. Constructors readily find suitable geared motors from 1,000 Nm rated torque in the Bonfiglioli product range.

Azimuth drives
The bigger challenges arise with the bigger drives. Azimuth drives designed for 1.1 million Nm peak torque were recently put into operation for Repower 5 MW generators.

Eight single drives with specially designed planetary gear motors coupled with 5.5 kW motors from the Bonfiglioli 700 series are used. They each yield 70,000 Nm rated torque and 140,000 Nm peak torque for a gear reduction of i = 1.281. With their individual weights of 1.200 kg, they contribute a total of about 10 tons to the weight of the gondola, but they are the first choice because of their power-to-weight ratio.

Pitch drives
The pitch drives, which are responsible for the efficiency of the complete system, maintain optimal rotation speed via the positioning of the individual rotor blades. If the speeds are too high, there is a risk of the system being damaged by the wind pressure.

Critical factors in the design include thickness and precision of the drives. These qualities are vital because the adjustment ranges are surprisingly small. The gear reduction ratios are in the range of 1:600 to 1:2000. The pitch controller reacts to the smallest changes in speed in the threshold range and effects a coordinated adjustment of the rotor blades via the three pitch drives in order not to exceed the maximum rotation speed.

As well as the requirements already mentioned (due to the position in the rotor hub), the pitch drive must also be particularly small, light and easily installed.

In addition, these drives are fitted with special seals in order to perform their service in any weather conditions uncomplainingly year in year out.

Drive electronics prerequisites
Building on decades of experience with geared motors in wind energy system construction, Bonfiglioli now also provides the control and linking of the azimuth and pitch drives with its own frequency converters from the Bonfiglioli Vectron product range.

The high end Active converter series meets all the criteria for this application. Specifically, it has a very economic internally developed system bus which also minimises the complexity for assembly and cabling. The compensation runs completely synchronously via the bus connection and thus always places and holds the system in the ideal position.

Furthermore, the equipment itself also provides high flexibility for assembly and cooling and also offers advantages through its high IP 65 protection class.

Thus, in conjunction with the planetary gear motor range, system constructors are offered a construction kit of integrated and competitive solutions meeting the most important requirements for wind energy systems.

Smaller and medium systems
Planetaries also best meet the design requirements of constructors of smaller and medium size systems, which include compact size and low weight.

As one of the largest industrial gearbox manufacturers in Europe, producing two million products a year, Bonfiglioli it has extensive experience to offer in the construction of high-torque planetary gears.

Planetary gears up to 500,000 Nm are supplied in the company's standard series, which keeps the technology cost-competitive. Lower costs are further guaranteed by highly efficient production, which now has extended into Mobilhydraulik types (planetary gears with hydraulic motors).

Vectron experience
For other capacities, the experience of the Bonfiglioli Vectron subsidiary in Krefeld, Germany, comes into play - not only with the most up- to-date converter technology, but also with expertise in mains regenerative feedback.

Bonfiglioli application engineers In Krefeld can draw on a wealth of experience of supplying energy into grids from applications outside drives technology, especially from photovoltaics.

This means smaller and medium-sized plants can be fitted out with a complete system drawing on Bonfiglioli's international experience.
Reliability is a key advantage of this experience. Surprises must not occur either in the mechanics or in the electronics of systems for their required 20 years service life. The planetary gear motors in the Bonfiglioli Trasmital product line have already proved themselves over time and in a wide variety of applications worldwide and in Australasia.

Bonfiglioli is now one of the largest suppliers for azimuth drives and pitch drives in Europe, which is itself a leader in wind power technology.

Bonfiglioli invests more than $A85 million a year on its product ranges and facilities, designing drives from the ground up to be a leader in their class.

The company has invested extensively in Australia and New Zealand to extend its range and capabilities across the spectrum here.

As demand expands in Australasia for clean energy alternatives, we are positioning ourselves to deliver the benefits access to truly global experience in this market.