Patent ID: 7816927

Claim:
A method of identifying a weakest monitored transmission line from a sending bus i to a receiving bus j within a power system having a plurality of transmission lines that is most likely to contribute to the power system collapse, comprising: a) acquiring either: (i) synchronized real-time measurements of voltage vectors and complex power flows at the sending bus i and receiving bus j for each of the monitored transmission lines from a phasor measurement unit (PMU) measuring system, said voltage vectors including real-time synchronized measurements of magnitudes (V i , and V j ) and angles (θ i and θ j ), and said complex power flows including real-time synchronized measurements of real power (P i and P ij ) and reactive power (Q i and Q ij ); or ii) estimates of voltage vectors and complex power flows at the sending bus i and receiving bus j of each of monitored transmission lines from a state estimator of an Energy Management System (EMS), said voltage vectors including estimated values of magnitudes (V i and V j ) and angles (θ i and θ j ) said complex power flows including estimated values of real power (P i and P ij ) and reactive power (Q i and Q ij ); b) using said acquired measurements or estimates to calculate a basic line voltage stability index (BLSI) value of each of the monitored transmission lines using the equation: B ⁢ ⁢ L ⁢ ⁢ S ⁢ ⁢ I = V i 2 2 ⁡ [ R ij ⁢ P ij + X ij ⁢ Q ij * + ( R ij 2 + X ij 2 ) ⁢ ( P ij 2 + ( Q ij * ) 2 ) ] ≥ 1 wherein R ij +jX ij is a line impedance associated with the monitored transmission line; P ij +jQ* ij is a line complex power flow with a charging reactive power excluded at the receiving bus j of the monitored transmission line; and V i is a voltage at the sending bus i of the transmission line; and c) selecting the monitored transmission line which has a lowest BLSI value for identification of system voltage stability and if the lowest BLSI value is close to 1.0, the system is about to lose voltage stability.