Hydropower made simple

A privately owned watermill in Germany has been adapted by its owner to produce electricity using its two paddle wheels to drive a generator. One year on, and its simple chain-and-sprocket setup is still looking good.

Harnessing the power of water is one of the greenest ways of producing electricity. And the more efficient, simple and reliable the power transmission package between the motive force and the generator, the better.

A privately owned water mill on the river Ems in northern Germany has been adapted by its owner to produce hydropower electricity using its two paddle wheels to drive a generator. The driving energy of the paddle wheels is transferred to the generator via a chain-and-sprocket arrangement.

The design is highly efficient, easy to install, robust in short-term overload conditions, and easy to maintain.

The solution was adopted because a force of just 500N was required to start producing electricity - much less than the alternative gear drive considered. It also offered the advantage of being able to span the large shaft centre distances involved while the simple chain-and-sprocket configuration delivers maximum power (74kW) from the water wheel shafts to the drive chains.

The chain types selected for the two-stage drive mechanism are Rexnord's triple-stranded 48 B-3 and 28 B-3. These chain sizes, together with centre distances and number of sprocket teeth, were specified to ensure maximum power transmission plus optimised service life.

Also considered were the clearances between the inner and outer links to ensure effective lubrication penetration to prevent possible fretting corrosion and cold welding, and consequently is as equally important as wear elongation and fatigue strength.

Rexnord's triple-stranded chains were selected in order to distribute drive loads. This chain type also offers high tensile strength characteristics, products of the company's use of high-quality materials and high case-hardening of the chain components.

Considered in conjunction with the chain's properties were the sprocket dimensions as well as tooth size and number. The former was with regard to wear properties, and the latter to minimise the risk of vibration arising from the effect of polygonal action.

Different transmission ratios are employed on the two drive stages to reduce the impact of centrifugal forces, and thereby minimise lubrication requirements. Ultimately, power is delivered to the generator via a spur gear when input speed reaches 90rpm.

After more than a year in use, the Rexnord roller chains are exhibiting no signs of significant wear. And, unlike the neighbours, the German owner is hoping for frequent heavy rain.

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