The water supply of the Zweckverband Ammertal-Schönbuchgruppe (ASG), that is located southwest of Stuttgart, gets its water from several sources. ASG supplies drinking water to around 130,000 people in 14 municipalities with an annual water output of approximately 7.1 million cubic meters. 65 percent of its water comes from ASGs owned wells situated in the Ammer and Neckar valleys. 35 percent is extracted from Lake Constance. Water from ASGs wells flows to the Ammerbuch-Poltringen waterworks. The raw water tank needed upgrading after being in operation for over 60 years. It was replaced by a new building, which was commissioned in May 2023. The Stuttgart-based engineering company RBS Wave planned and supervised the new building project.
New and more flexible turbine pumps
With the new building in use, benefits included improved energy production for ASG. For optimal energy utilization, two existing turbine pumps were replaced with new ones that were installed in two water intakes. The new turbine pumps generate about 350,000 kilowatt hours of electricity per year using the incoming water. That amounts to an increase of 80,000 kilowatt hours compared to what was generated previously.
This new installation is also financially important for ASG considering rising energy prices. The water supplier uses almost all of the self-generated electricity to cover their own energy demand. The higher the cost is of purchased electricity, the quicker the investment pays itself back.
"The old turbine pumps had asynchronous motors with a fixed operating point of 60 liters per second and were therefore not very flexible," explains Jochen Rausch, who is responsible for electrical engineering planning and energy management at the special-purpose association. "The new units are more powerful with synchronous motors and variable speed drives that are more flexible with the feed rate of the upstream vessels. We can now run water volumes from 55 to 80 liters per second."
The benefit of using regenerative drives
Jochen Rauch continues explaining why they chose to use two ABB ACS880-11 regenerative drives to control the new 22 and 37 kilowatt turbine pumps. "Even if we use almost all of the electricity that we generate, we may have to feed electricity back into the public power grid as well. The drives in use must be able to do this." ABB had already worked with RBS Wave in the planning phase and advised them on the drives issue.
The ACS880-11 drive is equipped with an active front end inverter. This enables a full energy flow in both motoring and regenerative operations. The regenerative variable speed drives offer significant energy savings potential compared to other braking methods, such as mechanical braking and resistance braking, because the braking energy is fed back into the grid.
For Jochen Rausch, the ACS880-11 has the important advantage over a conventional drive that it also recovers energy. Thanks to the drives good mains harmonic behavior, they also help to mitigate harmonics. The drive units are equipped with an active feed unit and an integrated mains filter. This means they generate only very low levels of harmonics. Due to their compact size the wall-mounted drives save space.
Reliable integration of power network
Additional reason for choosing the ACS880 regenerative drive was that it was certified according to the VDE-AR-N 4105:2018:11 standard. The VDE application standard summarizes the essential aspects that must be taken into account when connecting and operating generation systems to the grid operator's low-voltage grid.
Power generation systems with a maximum output of less than 135 kilowatts must be designed in accordance with this VDE standard. It regulates among other things the shutdown conditions when feedback is no longer allowed and when the drives must be down regulated. "ABB is one of the only few manufacturers that offers such a certified solution," says Jochen Rausch.
Meeting all requirements
In the Ammerbuch-Poltringen waterworks, they have a R6 sized ACS880-11 drive in use. This size has been certified according to VDE-AR-N 4105:2018:11 to meet the requirements of the VDE standard. This means that the drive meets all the necessary requirements to ensure standard-compliant integration of generation systems into public low-voltage network.
By using the certified ACS880-11, ASG ensures that energy is fed into the public grid in accordance with applicable regulations and standards. The drive also meets the required protection and safety measures and ensure standard-compliant operation of the drinking water supply system.
About the VDE-AR-N 4105:2018:11 standard
The minimum technical requirements described in the application rule VDE-AR-N 4105:2018:11 are necessary to ensure that the safety and reliability of grid operation can be maintained in accordance with the requirements of the Energy Industry Act, even with a further increase in the proportion of distributed generation systems, and that the voltage quality limit values formulated in DIN EN 50160 can be maintained. The core of the current application rule is that the feed-in of decentrally generated regenerative power must be controlled for frequency and voltage stable grid quality.