Three submersible pumps are lowered into the basin to pump up the wastewater, which is then discharged into a nearby basin. Due to local conditions, a stand-alone grid is set up consisting of three generators, each of which provides the energy for one pump.

The control system was installed in an external control cabinet next to the wastewater tank. The fill level of the tank is recorded by two probes. The flow rates of the pumps are recorded by means of magnetic-inductive flow measurement. Depending on requirements, one, two or all three pumps can be operated simultaneously. Using a suitable circuit, the control circuit is fed by a currently running generator, taking into account the case that several generators are in operation.

A PLC, which is equipped with both a UPS and a mobile phone connection, controls the powerful frequency converters and sends signals to the generators to switch them on and off. The measured values and signals from the generators are also evaluated. For example, the user can receive a text message when a generator needs refueling.

When a sewage treatment plant is converted, a city’s wastewater has to be temporarily diverted.