Fast Algorithms for Detecting Circular VAR Flows in Large Power-Flow Models

Circular VAR flows are mainly caused by improper coordination of reactive power control devices such as transformers in the power system. Circular VAR flow results in wastage of reactive power resources, and could lead to higher line currents as well as unnecessary switching of reactive power controls. In large power system, locating the presence of circular VAR flows is a challenging task. By treating the reactive power-flow problem as a directed graph, two new algorithms are proposed in the paper for detection of circular VAR flows. The first algorithm extends the standard graph theory approach by finding all the strongly connected components of a graph. The second algorithm is based on certain simple yet powerful necessary conditions for circular VAR loops in power systems that are proposed in this paper. The two algorithms are shown to be extremely fast by detecting all circular VAR loops in two large-scale power-flow models.