Characterising the power system at a load busbar by measurement

The paper presents the Theévenin equivalent network models for 3-phase 3- or 4-wire power systems and indicates how these models can be approximately determined by simple measurement. A simple measurement technique is defined as one requiring measurement of RMS quantities only. It is shown that the system impedance matrix is inherently non-reciprocal and that it is not possible to determine such non-reciprocity by simple measurement. Simple measurement methods for determining the phase and line impedances of the system at supply frequency and the terminal voltage sequence description are given. These methods require RMS voltage measurements alone; phase angle measurement is not required. The theory and measurement methods presented enable the voltage disturbance due to unbalanced loading at a load point in the system to be predicted a priori, and facilitate investigation of power system unbalance. The sequence network models for unbalanced load or fault conditions may also be determined.