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The ongoing replacement of synchronous machine generators (SMs) with converter-interface generators (CIGs) is raising the voltage unbalance of power systems, affecting power quality and grid stability. This paper focuses on a key power quality index for power systems, i.e., the voltage unbalance factor. The purpose of this work is twofold. First, it presents the generalization of a three-phase power flow algorithm developed by University of Padova, named PFPD_3P, to assess the voltage unbalance factors of power systems supplied by CIGs. In particular, it is demonstrated that CIGs can be modelled as three-phase PV/PQ constraints embedding their positive-, negative- and zero-sequence admittances. Then, the concept of three-phase contingency analysis is introduced. Indeed, for static security evaluation, the classical single-phase contingency analysis may no longer be sufficient, as it lacks power quality computations, e.g., voltage/current unbalance factors. Numerical simulations evaluating the unbalance factors due to different generation mix scenarios and contingencies are tested on the Italian extra-high-voltage/high-voltage (EHV/HV) grid. The choice of this network relies on its representativeness, as CIGs are the majority of new installations in the Italian generation mix. [ABSTRACT FROM AUTHOR]

PV curves are generally obtained by considering lumped models of transmission lines. This approximated model can yield an inaccurate estimation of the maximum loading condition of the system. This letter shows that accuracy can be improved by considering line models with uniformly distributed parameters. Analytical evaluations of the PV curve and of the voltage collapse point of a two-bus system are obtained by applying the Ossanna's theorem. Then the impact of different line models on large-scale systems is evaluated through a continuation power flow analysis of a real-world model of the Sicilian transmission system including the Sicily-Malta 120 km cable connection. [ABSTRACT FROM AUTHOR]