A practical approach to voltage sag estimation in power networks

• Clear physical interpretation of voltage sags phenomena. • Intuitive estimation of voltage sags frequency at non-monitored buses. • The method only needs the system impedance matrix. • Validated in three networks with accurate results. • Robust against parameter uncertainties. Due to cost constrains, voltage sags performance of electric systems is often assessed by means of partial monitoring programs. When such approaches are implemented, two different concerns are addressed by the system operator: first, the optimal location for placing the available number of monitors must be identified and, second, the performance of voltage sag indices at non-monitored buses needs to be estimated from the values measured. This work addresses both aspects of the problem by proposing a very simple methodology grounded on the understanding of the electrical behaviour of power systems in the presence of faults, and requiring just knowledge of basic network data, specifically the system’s impedance matrix. The proposed methodology yields a useful tool for transmission and distribution utilities which can be implemented directly and intuitively, and without any mathematical difficulty in contrast to other existing approaches, in order to provide reliable results on the behaviour of voltage sags of the entire system through partial monitoring. Several cases studies are presented to illustrate and validate the proposed methodology applied to three different size and voltage level networks, i.e. the IEEE 24-busbar reliability test system, the IEEE 118-busbar data and a real transmission network with 357 buses. The criteria for finding the optimal number of monitors is also explored in this work for these networks. In addition, sensitivity of the method accuracy to network parameter uncertainties is also analysed.