Category: Power Quality
Harmonics Mitigation on VFD – Case Study
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
Background
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.
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.
Harmonics Case Study
Harmonics Case Study:
Secure Food Production by Mitigating Harmonics
Highly automized processes often contain VFDs, which cause harmonics in the power supply. This can affect machinery and can cause downtime in production lines. This was the case at a major food processing plant in Dortmund, Germany.
Background
Before:
High harmonic current distortion
Large disturbance of production
The food processing plant is part of a federation of over 300 independent retail dealers and suppliers to approximately 540 grocery stores. The center is a 100.000 m² warehouse and distribution center with affiliated butcher. After the butcher was destroyed in a fire in 2009, it had been rebuilt and expanded in 2011 into an 18.000 m² large butcher shop. Since completion at the end of 2011, the new processing plant produces 250 tons of meat for the grocery stores and up to 25 tons of sausages every day. The new butcher shop contains state of the art logistics and meat processing systems.
Challenge
The VFDs connected to the new meat cutter created typical current harmonics of a six-pulse-converter (5th, 7th, 11th, 13th, etc). These harmonics resulted in commutation notches in the voltage, which influenced the whole production process. The harmonics caused blackouts and disturbances to the lighting. It also influenced the sausage stuffing and caused long production stops disturbing the process flow. Occasionally up to half of the employees had to be sent home for the day due to disturbances in the process.
After:
Low harmonic current distortion
No disturbance of production
Solution – Active Harmonic Filter with Harmonics Compensation
The food processing plant decided to use an Active Harmonic Filter to eliminate the problems in the power supply. The installed system consists of one filter with a capacity of 300 A harmonics compensation to provide the needed harmonic power for the meat cutter.
Result
After the installation and a short commissioning, all disturbing harmonics were cancelled and the commutation notches disappeared. All meat cutters could now, for the first time, be started at the same time, without any effect on lighting or the sausage stuffing process.
Active Harmonic Filters 