Harmonics Mitigation on VFD – Case Study

Harmonics mitigation of variable frequency drives

Harmonics Mitigation Increases Output with 30%

The water treatment process involves a large number of variable-speed pumps to process large amounts of fluids. By using Active Harmonic Filtering technology to optimize the electrical behaviour of their variable frequency drives, a major water processing plant in Sweden managed to increase the maximum output capacity of their systems by 30%.

Thanks to Active Harmonic Filtering we can now process 30% more fluids during periods of peak demand. We also save energy.
– Project Manager


The treatment plant is part of the sewage works in Gothenburg. It is one of the largest in all of Scandinavia and central to saving the environment from pollution. With heavy demands, the two basic requirements on this critical regional infrastructure are constant operation and sufficient treatment capacity. UPS power backup systems are crucial to ensure a secure and stable power supply.

Harmonics mitigation

To increase plant capacity, 17 new VFD-controlled pumps were installed at the processing plant. This increased harmonic distortion on the electrical system significantly and the resulting overcurrents caused the UPS fuses to melt. To avoid this, the pumps were run at reduced speed. This was however a temporary solution as it reduced treatment capacity below demand. Frequency converters are a well-known source of potentially damaging harmonics.

Harmonics Elimination – the Challenge

After consulting a premier Swedish consulting firm, the processing plant announced a public procurement process seeking the implementation of active harmonic elimination technology. The target was to retrieve full treatment capacity by eliminating the harmonics.

Solution – Active Filter Units

The result was the installation of two 600 kVA Active Harmonic Filter units to manage two transformers supplying 2160 kVA. There were a number of characteristics of the specific harmonic filter solution that led to the plant’s choice:

  • Flexible connection and system dimensioning
  • Reduced maintenance costs to other connected equipment
  • Disturbance free electrical environment
  • Reduced energy consumption through decreased transformer losses

Harmonics Eliminated – the Result

Eliminating the harmonics in the system resulted in an increased max output capacity of 30%.
In addition, the processing plant now manages to operate below the threshold value for harmonic distortion (SS 421 1811). The plant now enjoys further benefits with a reduced energy consumption and improved environmental performance.


  1. K.V.Subba Rao

    you havew mentioned here the Harmonic filters were employed in Transformers. how it will reduce harmonics generated by Variable frequency drives,

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s