Abstract: A system, having a controller, with a 3-phase measurement sensor, wherein the 3-phase measurement sensor is connected at least for current measurement to a low-voltage feeder of a secondary unit substation, and wherein a distribution network with producers and/or consumers is connected to the low-voltage feeder. The controller and the 3-phase measurement sensor are arranged in the secondary unit substation. The controller has a data interface for detecting electrical measurement values of the connected 3-phase measurement sensor with associated timestamp. The controller has a communication interface for connection to a higher-level unit outside of the secondary unit substation. The controller has a first memory area in a local memory for storing the measurement values with associated timestamp.