Estimation of power system Thevenin equivalent based on phasor measurements

This paper presents a novel algorithm based on phasor measurements for online estimation of power system Thevenin Equivalent (TE) from a generator terminal. Three consecutive phasor measurements of generator terminal voltage and current are used to estimate the system TE. In a real network, deviation of system frequency from its nominal value produces some phase drifts in consecutive phasors reported by Phasor Measurements Units (PMUs). To correct the phase drift and synchronize the reported phasors with the same reference, an improved triangulation method is developed. The improved method uses a virtual vector in its structure. This vector alleviates negative impacts of improper data resulting from noise or disturbances, which make the simple triangulation method useless. The algorithm is tested on standard NE-39 network and is implemented in Shahid Beheshti University's (SBU) protection laboratory to verify the results in practice. The obtained results show that the new method can efficiently estimate the Zth in online mode under steady-state and transient conditions.