Planetary gearboxes are the energy saving choice

All across Europe, Brevini's planetary gearbox range is being used in horizontal axis wind turbines, by far the most widely used, due to their flexibility of design

In the run-up to the introduction of the Climate Change Levy the focus among engineers works managers - and accountants even - has been firmly on the role of AC drive systems and energy efficiency motors as the means of reducing energy costs.

This focus is entirely justified by the undeniable contribution to energy saving that inverter/motor combinations can make in most applications.

However, it does not take into account the instances where energy saving drives and high efficiency motors are routinely fitted as part of a larger power transmission chain, and where the torque requirement of the system is such that a reduction gearbox is required.

In these types of applications the choice of gearbox - or rather the wrong choice - can easily wipe out the extra efficiencies provided by the drive/motor combination.

A quick example illustrates this.

High efficiency motors on their own provide an approximately 3% improvement in operating efficiency, but with efficiency losses for most gearboxes (excepting planetary types) of anywhere between 5% (Helical and Spur) and 30% (Worm) per stage, the positive saving can quickly become a negative.

This is not the case with planetary gearboxes, which minimise efficiency losses to just 1% per stage.

The relative size of the losses for Helical, Spur and Worm gearboxes means that it is impractical for engineers to specify any of these units in applications where the energy efficiency of a power train is paramount.

When considering applications that fit into this category, alternative methods of energy generation immediately come to mind.

The generation of electricity by wind and water power is growing steadily as fears about the effects of global warming increase.

Even governments are waking up to the possibilities: the UK has recently announced a major tranche of funding to aid the establishment of offshore wind farms.

The levels of efficiency demanded from gearboxes in wind and water generation mean that only one type is really suitable for use in these type of applications: the epicyclic planetary.

As evidence of this, all across Europe Brevini's planetary range is being used in horizontal axis wind turbines, by far the most widely used, due to their flexibility of design.

The horizontal wind turbines comprise a rotor, which captures the force of the wind, and an energy conversion system, which uses a gearbox in combination with a generator to transform the mechanical power into electricity.

In order to get the maximum energy out of the wind, and since the direction of the wind changes constantly, the rotor has to be forced into a position that is perpendicular to it.

This position is calculated by a microcomputer, based on data regarding the direction of the wind and the present position of the turbine.

The results are then used to operate a motorised slewing planetary gearbox from Brevini's RPR range.

In addition to ensuring the correct tower position, another major factor in the efficiency of the turbine is the correct orientation of the turbine blades.

This is also ensured by the microcomputer in conjunction with a two or three stage planetary gearbox from Brevini's Standard series range.

Brevini's planetary gearboxes have become a standard for wind-turbines due to a number of factors.

Firstly, the planetary drive can be up to 98% efficient and, critically, is able to provide extremely low speeds without any loss of efficiency.

Secondly, planetary gear trains are able to deliver high reduction ratios in small packages, and to transmit several times the torque of similarly sized, conventional gear units.

Thirdly, they are remarkably compact and lightweight, and require little installation space.

Finally, high levels of reliability are a feature of the planetary design, thanks to the distribution of stress among several load-bearing components.

The same basic efficiency which makes Brevini planetary gearboxes the first choice for wind turbines has also resulted in the their application on another form of clean generation: this time using water power.

In a truly unique application a two-stage gearbox from Brevini's standard range is providing efficiencies approaching 96% on the largest hydraulic wheel for generating electrical power ever built.

The Boga-Wasserkraftanlagen GmbH company of Bochum have supplied the Turas hydraulic wheel (or turbine) to provide power to Kasendorft, a small city near Karlsbach, in Germany.

The project stands because of its originality and unique design and the ability to combine technological innovation in a so-called "rural" environment.

The patented, high-efficiency turbine has a diameter of 4 meters and an absorption capacity of 300 l/s.

Manufactured from aluminium alloy, to be resistant to sea water, it the largest ever built with its own integrated transmission system.

A central part of this system is a high efficiency two-stage planetary gearbox made by Brevini.

This minimises the power losses between the main output of the wheel and the electric generator which interfaces to the Brevini gearbox by a highly efficient belt drive system.

The success of this project can be judged from the numerous awards it has received since its was commissioned.

Principal among these is the much coveted "Bayrischer Staatspreis", which recognises the role the project plays in developing the use of renewable or alternative types of energy.

The Kasendorft turbine project is at present unique.

However, like the wind turbine, it sets a precedent for energy generation systems using natural resources.

The key to the success of these new generation mediums is to maximise the efficiency of their transmission systems.

What is becoming evident from current applications is that the planetary gearbox, with its inherent design advantages of size, weight and power, is the unit to achieve this objective.

It is fair to assume therefore that, as alternative energy assumes a greater role in our everyday lives, the role of the planetary gearbox will grow accordingly and assume even greater importance.

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