The number of renewable energy systems has increased with the implementation of the feed-in tariff in Germany. Nowadays, more than 1.5 million photovoltaic systems are connected to the grid and over 85 % are installed at the low voltage level. The distribution system operators (DSO) have now to adapt their grid operation for high load as well as high feed-in times. An annual energy feed-in or demand value is not sufficient for planning and operating low voltage grids with volatile feed-in power characteristics exceeding the maximum power consumption by 5 to 10 times. Based on the historical development, there are normally no measurement devices in the low voltage grid, except the once yearly evaluated meters in the households and power drag-indicators in transformer stations. These power drag-indicators usually are also checked only once per year and do not solve the need for monitoring the grid state.
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