Voltage stability of low frequency AC transmission systems

This paper investigates the voltage stability of a power system with low frequency AC (LFAC) transmission. Under low frequency conditions, transmission line reactance is reduced and thus the voltage drop along the transmission line is decreased. The LFAC system, therefore, is superior to the conventional 60-Hz system in terms of power transfer capability and, more importantly, voltage instability. In other words, the LFAC can drive a power system further away from instability mode in comparison to the conventional 60-Hz system. A power system voltage stability can be quantified and displayed with the eigenvalues of a Jacobian matrix and the self-sensitivity values by using the modal analysis method. In this paper, the theoretical stability of an LFAC system is discussed first and then validated using several transmission system case studies. The simulation and analysis results show that the LFAC system outperforms the conventional 60 Hz system in terms of voltage stability.