A Simple Method to Assess Loadability of Radial Distribution Networks

This paper proposes a simple method to asses loadability in radial distribution systems. The relevant problem of voltage stability has been dealt with in past times with reference to higher voltage systems for generation and transmission. In more recent papers, the problem has been considered also at distribution level, since the new electrical energy market requirements and the increasing loadings are now more and more influencing these systems. The proposed method is based on a static approach and proceeds by first evaluating the stability indices and then the different loadability factors (related to real, reactive and apparent power). These calculations are carried out by identifying, starting from the network state in a defined loading condition, an equivalent in terms of the transfer of power from the source node to the different network nodes. Then the node showing the lowest stability index represents the weakest node in the system in terms of voltage stability; the real, reactive or apparent loading factor of the equivalent between the supply node and the weakest node represents the maximum loading increase (real, reactive or apparent) that the network can stand without voltage collapse. Finally, for the considered loading factors, the results on different test systems are reported and the comparison with heuristically attained loading factors prove that the obtained results show a small error, whose sign however preserves the system’s security.