Synchronizing Phasor Measurements Using Symmetrical Impedance Matching For Transmission Line Model Validation

Transmission line impedances are derived using modeling software based on the material and physical arrangement of the conductors. These computations often fail to capture all the real-world conditions that occur on transmission lines such as variations in the conductor sag and transmission tower height. In addition, the earth resistivity is usually unknown for the entire length of the line and there could be unknown parallel grounded conductors that could affect the zero-sequence impedance. Therefore, it’s important to measure the transmission line impedances with actual current and voltage readings to validate the calculated values. This paper presents a method called symmetrical impedance matching to synchronize phasor measurements from both ends of the transmission line during unbalanced conditions. This method is based on the fundamental property that the positive- and negative-sequence impedances of a transmission line are equal. The phasor measurements are synchronized by applying a phase shift to the receiving end, such that the calculated positive- and negative-sequence impedances are equal. Once the phasors are synchronized, the positive- and zero-sequence self impedances and positive- and zero-sequence shunt admittances can be calculated.