Measurement-based Estimation of Downstream Transmission Network

This paper addresses the problem of estimating an approximate downstream radial transmission network using exclusively voltage and current measurements obtained from an intermediate transmission bus. The objective is to separate the measured impedance into a downstream transmission network part and a constant power factor load, so that maximum power transfer conditions and voltage stability limits are correctly identified. It is shown that for a radial network with constant power factor load the locus of the measured impedance forms a straight line (uncompensated load), or an approximate straight line, when measurement noise, or distributed generation is considered. In the presence of constant capacitive compensation, the locus of the measured impedance becomes a circle. Indicative identification results are presented considering also the effect of random noise in the measured signals, as well as distributed generation, and tap-changer dynamics.