Method for determining an optimal placement of measurement units for estimating the state of a physical power distribution grid

A method for detecting and localizing faults in a medium voltage (MV) and low voltage (LV) distribution grid comprising a plurality of MV and LV nodes and a plurality of MV and LV branches, as well as several MV/LV transformers each arranged to connect one MV node with one LV node, the MV and LV distribution grid further being provided with a monitoring infrastructure comprising metering devices assigned to particular LV nodes of the distribution grid, each of one of said metering devices being arranged to measure a nodal voltage of the LV node to which it is assigned and a current flowing into or out of said LV node through an upstream branch incident on said LV node, each one of said particular LV nodes preferably being one of the nodes that a MV/LV transformer is arranged to connect with a MV node, the monitoring infrastructure further comprising a central processing unit and a communication means arranged for allowing communication between the metering devices and the central processing unit;

• wherein the method comprises the following steps:
• I. measuring, by the metering device at each one of said particular LV nodes, the voltage v(t) and the current i(t) with a sampling rate that is high enough for sampling said voltage and said current over a bandwidth with an upper limit of at least 1 kHz.
• II. calculating, by the metering device at each one of said particular LV nodes, using the voltages and the currents measured in step I, for each one of a succession of evaluation time windows, the mean value of the nodal negative-sequence voltage (Vneg), and further calculating a variation of the calculated mean value with respect to the previous evaluation time window,
• III. assessing, by the metering device at each one of said particular LV nodes, the following first criterion for each one of the evaluation time windows except the first one:
• “the variation of the mean value of the nodal negative-sequence voltage (Vneg-rltv) calculated in step II is larger than a first given threshold”, and, when the assessment comes out positive for a particular evaluation time window, sending, by the metering device, a fault notification comprising the calculated variation for the particular evaluation time window to the central processing unit;
• and
• IV. identifying, by the central processing unit using fault notifications received during a predefined time lag window from metering devices assigned to different LV nodes, the fault location with the help of grid topology information.