Unwanted harmonic disturbances which are introduced into an electrical power grid can cause problems both for the power companies and for the users of electricity. To discourage users from introducing harmonics into the grid, power companies can impose financial penalties on companies that are responsible for such disturbances.
Like many other utilities that work with water supply and wastewater treatment, Hamburg Wasser has been required by its local power company to take measures to minimize harmonic distortions that its equipment can cause. Dominik Seebold, project manager for electrical engineering at the company in Hamburg, Germany, describes the situation: "We have to consider our load on the electrical power grid and if our equipment is increasing harmonics, then we normally have to install additional filters to mitigate these distortions.”
Among the devices that can cause harmonics are variable speed drives, in addition to many other types of electronic equipment. To explore ways to minimize harmonics, but without using complex and costly external filters, Hamburg Wasser decided to test an ABB ULH drive which is designed for the water industry and does not create harmonics.
Testing side-by-side versus a conventional drive
A wall-mounted Ultra-Low Harmonic ACQ580-31 drive was installed in April 2019 at the Großhansdorf waterworks. This drive is designed specifically for pump applications in the water and wastewater industry. The ULH drive variant reduces Total Harmonic Distortion of current (THDi) by use of an active power supply unit and harmonic filter built-in, without any need for external filters or special equipment.
The ACQ580-31 was installed to control a feed pump delivering 450 m3 per hour of water, at a head of eight meters, from a water tank in the old section of the water plant to another tank in the new section. Another feed pump, controlled by an existing standard drive, is doing the exact same task on the same tanks and these two pumps alternate operating on a weekly basis, thus making them ideal for comparative testing.
Comparison confirms the excellent performance
The results have proven the benefits of the ULH ACQ580 drive. Harmonics are normally reported as a percentage THDi, which means the amount of sine waveform distortion compared to the purely sinusoidal wave. Testing data shows that when running close to the nominal operating point the ULH ACQ580 drive had a measured THDi of 2.73%, compared to the standard 6-pulse drive which had a much higher THDi of 45%. This means that the harmonics content with the ULH drive is 94% lower than with the standard drive.
Dominik Seebold is happy with the results and is planning to expand the use of the ULH ACQ580 drives to larger pumps: "We are interested in the operating behaviour of this drive. For us it is essential that it is reliable, and the ULH ACQ580 drive has been running smoothly since its commissioning. In the future we will be able to further stabilize the power network and thus avoid disturbances caused by harmonics. To test this, we will install the ULH drives on our more demanding large pumps."