Siemens Infrastructure & Cities and the municipal utility SWK STADTWERKE KREFELD AG (SWK) are working together to transform the existing power supply system in Wachtendonk on the Lower Rhine in Germany into a smart grid for research and testing purposes.

Siemens will supply the necessary components for the smart secondary substations, smart meters as well as measuring, monitoring and communications technology. SWK will combine these individual components into a smart system and test them in specially selected low-voltage networks. Other goals include developing and securing a data transmission system from the network to the SWK control center.

Through this project, Siemens and SWK will acquire detailed information about the behavior of a distribution network with a disproportionately high number of renewable energy sources. Another goal is to test the applicability of technical components in everyday use in order to obtain insights useful for the further development of the smart grid.

The 8,000-strong community of Wachtendonk in the Kleve district was selected as the smart grid model region because it has a very high proportion of distributed power generation plants that feed into the grid. About 80% of its electricity comes from renewable energy sources, for example, roof-mounted photovoltaic plants. In addition, the effects resulting from decentralized power feeds will become more evident in the rural power network. The voltage fluctuations occur due to the fluctuating feed of renewable energy sources, among other reasons, and currently the network operator generally is not systematically recording the fluctuations in the power distribution grid, especially in the low-voltage network. “Here we need sensors in the network to monitor grid quality and, if necessary, to take preventive action,” said Dr. Frank Burau, managing director of SWK NETZE GmbH.

As part of the project, smart meters will be installed in 100 homes and in numerous cable distribution boxes to perform the necessary measurement functions. For this purpose, Siemens has equipped its smart meters with an add-on function through which important data relating to the network status can be recorded and forwarded. The so-called power snapshot analysis allows “snapshots” to be taken of the otherwise “blind” low-voltage system in the form of synchronous network parameters. This enables the meters to do more than just record energy consumption, they also operate as low-voltage sensors that deliver data that will be used to analyze the power distribution grid in Wachtendonk in order to improve the stability and transparency of the grid.

As soon as a specific threshold is exceeded or undershot, the smart meters transmit the network data via power lines to the secondary substation and from there to SWK so that countermeasures respectively stabilization can be immediately initiated. Five smart secondary substations with controllable distribution transformers from Siemens are also used to stabilize the network. These controllable distribution transformers use real-time data from the low-voltage system measured by the smart meters as a control variable and then dynamically adapt the voltage conditions in the local network.

While cabling the entire system of medium- and low-voltage overhead line, which will be completed by 2014, SWK NETZE GmbH also laid empty conduits so that there are now 22 substations equipped with fiber-optic transmission equipment and connected to SWK's control center in Krefeld, and 52 of the 105 secondary substations have already been modernized and are ready to be equipped with smart grid components. This will make it possible to upgrade these substations to form the core of a smart secondary distribution network without a great investment of cost or effort.

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