Using AIS EM data to find the parameters of a distribution grid

This paper dwells upon identifying the parameters of a four-wire three-phase 0.4-kV distribution grid (DG) using current and voltage vector data as measured by the automation instrumentation system for electricity metering (AIS EM) at the beginning of the DG and at each of its end users. It analyzes an earlier proposed method for identifying the resistance values if inter-user DG segments, which is based on modeling the physical processes in the grid circuits and equivalent transformations of its equivalent circuits. The paper further shows that these proposed transformations are not equivalent. At the same time, the found resistance values do correspond to the phase resistances of the inter-user segments provided that the neutral wire of the DG has resistance values of zero; the found values are not equal to the actual resistances of the four-wire grid. The paper proposes a novel method to solve this problem; the method is based on measuring the current and voltage vectors online in two different DG operation modes. If the current mode of the grid does not change, the AIS EM control unit may command a single temporary disconnection of an end user to invoke a different mode. Research results might be of use for designing AIS EM subsystems tasked to diagnose and control the electrical parameters of the distribution grid mainline as well as to monitor commercial and process-related electricity losses in it online.