Voltage stability indicator for identification of the weakest bus/area in power systems

Application of Newton optimal power flow (OPF) to identify the weakest bus/area, which is most likely to cause voltage collapse, is presented in this paper. The S-V curve (complex power to voltage) is examined via Newton OPF. Marginal costs (Lagrange multipliers) regarding power flow equations, VAr generations, voltages and taps, etc., to the system MW losses are obtained from Newton OPF. The weakest bus/area in the system is identified by an indicator achieved with these marginal costs via the Kuhn-Tucker theorem. This indicator helps users know which bus/area is most likely to cause voltage collapse. The IEEE 30-bus and a practical 251-bus systems are used to show the capability and feasibility of the proposed approach