Voltage Stability in Radial Distribution Networks

摘要

Voltage stability is a matter adressed mainly in transmission network. In distribution network the focus must consider a few variations with the traditional model, specially the well-known issues of unbalance and the R/X relation that causes the jacobian matrix bad condition. The length of the feeder is another matter among peculiarities of the system. This study case refers to a feeder of 23000 V and 120 km of trunk. During 2016-2017 summer some phenomena with typical voltage instability symptoms were observed: sostained low voltage periods, rise of reactive power, trip of protection relays and inability of voltage regulators to keep a suitable voltage level near the peak demand of the system. Voltage stability can be analyzed in steady state due to PV curves, which provide a considerable view about electrical system's behavior. Power system analysis Newton-Raphson's based is carried out to build PV curves increasing the demand slowly until the system reaches the saddle-node that matches witch the peak of the system. At this poit the jacobian matrix tends to a singularity. There are variations with the traditional model that search for a different strategy to find the saddle-node. This paper presents the Direct- Inverse Sweep as an alternative method to resolve those peculiarities.