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ADF increases GRYAAB water treatment plants output by 30%

The water treatment process features numerous variable-speed pumps to process large amounts of fluids. By optimizing the electrical behavior of pumps controlled by variable frequency drives (VFDs) with Comsys ADF Active Harmonic Filter technology, GRYAAB increased the maximum output capacity of these systems by 30%.


Thanks to ADF we can now process 30% more fluids during periods of peak demand. We also save energy.

– Roger Rosenqvist, Project Manager


GRYAAB is the sewage works of the Gothenburg region in Sweden and its treatment plant Ryaverket is among the largest in all of Scandinavia. Central to saving the environment from pollution, 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.

When 17 new VFD-controlled pumps were installed at Ryaverket to increase plant capacity, harmonic distortion on the electrical system rose significantly. The resulting overcurrents caused the UPS fuses to melt. This was avoided by running the pumps at reduced speed. This was however a temporary solution since this reduced treatment capacity below demand. Frequency converters are a well-known source of potentially damaging harmonics.

Key benefits – pump drives:

  • 30% increased plant output

  • Secured UPS performance provides for reliable production

  • Harmonic distortion below threshold values

  • Reduced energy consumption

The harmonic distortion with ADF operation to the left and without ADF to the right.

Challenge – eliminating the harmonics

After consulting Ångpanneföreningen (ÅF), a premier Swedish consulting firm, Ryaverket 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. Comsys won the procurement in competition with several renowned companies.

Solution – ADF active filter units

The result was the installation of two 600 kVA Comsys ADF Active Filter units to manage two transformers supplying 2160 kVA. There were a number of characteristics of the Comsys ADF solution that led to Ryaverket'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

Result – harmonics elimination

The harmonics elimination resulted in an increased max output capacity of 30%.

Furthermore, GRYAAB now manages to operate below the threshold value for harmonic distortion (SS 421 1811). The reduced energy consumption and improved environmental performance are welcomed additional benefits.