Calculation of Transmission Line Parameters From Synchronized Measurements

Accurate knowledge of transmission system parameters, such as series impedance, optimizes distance relay settings and impedance-based fault location. A new method is developed to measure transmission line impedances and admittances from synchronized phasor measurements. Power system voltage and current phasors were recorded during commissioning tests of a 525 kV transmission system containing shunt and series compensation. Steady-state phase angles (delta) and magnitudes of line-side voltages and currents were measured relative to a satellite-based global time standard at two substations. Pairs of synchronized measurements were used to directly calculate real-time steadystate ABCD parameters. For comparison, two-port ABCD transmission system parameters were derived by classical methods and from an ElectroMagnetics Transients Program (EMTP) transmission system design model. To verify the accuracy of the measured parameters, a new method comparing field measured with calculated power flows was developed. Sending-end power flow was measured from accurate recordings and was compared with power flow calculated using the three estimates of ABCD parameters, sendingend voltages, and receiving-end voltages. Close agreement was found between field-measured power flows and calculations using the measured ABCD parameters.