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Reliable snow over Östersund Biathlon stadium with VLT® AQUA Low Harmonic Drive

26 July 2010

Östersund has a long history as a centre of outdoor activities with its modern cross-country ski stadium. Östersund hosted several World Championships in various sports such as biathlon, speed skating and ski orienteering along with Swedish National Championships in cross country skiing and snow-cross.

Although Östersund is located in the middle of Sweden, snow does not come with a guarantee. To allow the many outdoor activities to take place, multiple snow guns ensure that sufficient snow is always present at the stadium and pistes around Östersund during the winter season.

The snow canon solution
The many snow canons spray pressured water out through a set of nozzles. The thin water particles formed in the air are then pushed forward by an air fan. The water fog becomes snow if the temperature is close to freezing point. Each snow canon has its own water pressure actuator but the water is supplied by one large centrally installed pump which feeds the snow canons whenever they are connected to the piping system.

Harmonics
Due to the long distances from the power supply to the loads and because of the multiple small motors consuming power, the supply is weak and harmonic distortion becomes an obvious problem. The Östersund local authority has consequently imposed a maximum current THiD (total harmonic current distortion) of 5%.

This limitation is set to keep the voltage pollution low, maintain cable and transformer loading at a minimum but most important, to ensure a reliable power supply and so snow for future snow events around Östersund.

The VLT® AQUA Low Harmonic Drive
As part of a more extensive renovation to bring Östersund stadium up to date for the Biathlon World Cup this winter, Areco Snowsystem AB, one of the largest manufacturer of snow guns in the world, purchased a new VLT® AQUA Low Harmonic Drive for a new feed pump that will be part of the new fully automated snow system. The drive has to maintain a constant flow of water through the hundreds of meters of pipes. The pump and drive system are installed in a movable hut near the stadium allowing the installation to be moved quickly and easily during tournaments.

Test results
In this application the drive, a 200kW Low Harmonic Drive, was tested with and without the active filter to see the impact of the harmonic currents on the grid. The background voltage distortion of the grid was 1,3% during the testing period.

The test results show the significant reduction of line-side current harmonics from a THiD of 41% without the active filter down to 3.1% with the active filter. This proves all the aforementioned benefits required by Östersund authorities, of lower losses in the cables and transformer, lower voltage distortions, thus ensuring the reliability of the power system.

Why Danfoss Low Harmonic Drive
Besides the obvious lower harmonic content and compliance with the local authority, the installed VLT® AQUA Low Harmonic Drive also reduces the RMS current thus increasing system efficiency. The transformer stress is dramatically reduced, due to the huge THiD drop, allowing the transformer to supply more loads and so allowing more snow guns to secure optimal conditions for future winter events.

For further information contact:

Danfoss Ltd
Capswood
Oxford Road
Denham
Buckinghamshire
UB9 4LH

Tel: 0870 241 7030
Fax: 0870 241 7035
Email: uk.controls.sales@danfoss.com
Web: www.danfoss.co.uk
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