Study on Voltage Stability of Distribution Networks

A new criterion of voltage stability for distribution network is deduced based on the existence of solution of power flow, i.e., the first class criterion. The profile of load is included in the proposed criterion. The weakness of the existing criterion based on load-voltage property, i.e., the second class criterion, is described. It is pointed that the first class criterion is the necessary condition of voltage stability but not the sufficient condition. To guarantee voltage stability, both the first and the second class criterion must be satisfied. The indexes of voltage stability margin and safe distance are defined. The proposed method is demonstrated by an example showing its feasibility. It is also shown that the proposed indexes can evaluate the voltage stability and the tolerance of disturbance.