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Active harmonic mitigation from Danfoss

18 June 2010

Excessive harmonic distortion of the mains supply has become an increasing problem in recent years with the rapid spread of power electronics such as variable speed drives, computers, and energy saving lights, all of which draw non-sinusoidal current. New active harmonic mitigation from Danfoss can now be successfully applied in many types of application.

The Danfoss VLT AAF005 active harmonic filter is typically installed near the supply transformer to simultaneously reduce the harmonic distortion from multiple loads in the installation. The filter automatically reduces the voltage distortion level to typically 5 or 8% THD and reduces reactive currents. These active filters are also suitable for retrofitting to existing installations.

Examples of successful applications include:
- HVAC systems in buildings with a large number of variable speed drives
- Pharmaceutical processing plants
- Clean room production facilities
- Hospitals with low harmonic voltage distortion limits
- Process plants with generator back-up
- Marine and offshore systems with multiple generators
- Power stations

The VLT Low Harmonic Drive is a variable speed drive with an integrated active harmonic filter that reduces the harmonic current distortion at the input of the drive to less than 5% THD.  Danfoss is the first company to offer a low harmonic drive that works on this principle. Low harmonic drives are typically used for installations with large individual drives and highly loaded transformers:

Examples of successful applications include:
- Water pumping stations
- Refrigeration compressors with variable speed drives
- Marine pumps
- Snow canons
- Test rigs


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