Patent ID: 7996116

Claim:
A method of monitoring voltage stability within an electrical power system, the method comprising the steps of: establishing a voltage stability margin Stability based on an operating characteristic of the power system including calculating: Margin Stability = Z L Z S - 1 where Z L is a load impedance connected to a bus of the power system and Z s is a source equivalent impedance of the power system, such that: Z L Z S = ( Z L ⁢ ⁢ 2 Z L ⁢ ⁢ 1 ) ⁢ M + 1 - ( MF + F 2 ) + [ ( MF + F 2 ) 2 - M 2 + 1 ] 0.5 where a) Z L1 and Z L2 are, respectively, initial and final values of the load impedance Z L , b) M = ⅆ S V 2 ⁢ ⅆ Y = ( Y S ) ⁢ ( ⅆ S ⅆ Y ) , S being a load apparent power, V being a power system voltage, and Y being the load admittance given by Y=1/Z L , and ⅆ S ⅆ Y = V 2 · 1 - ( Z S ⁢ Y ) 2 - 2 ⁢ ( Z S ⁢ Y ) ⁡ [ Y ⁢ ⅆ ( cos ⁢ ⁢ Δ ) ⅆ Y ] 1 + ( Z S ⁢ Y ) 2 + 2 ⁢ ( Z S ⁢ Y ) ⁢ cos ⁢ ⁢ Δ with Δ=φ s −φ L c) where φ s is the source equivalent impedance phase angle and φ L is the load phase angle, F=cos [0.5(Δ1+Δ2)], and d) F 2 = Y ⁢ ⅆ ( cos ⁢ ⁢ Δ ) ⅆ y Δ1 and Δ2 are respectively initial and final values of Δ indicating that the power system has become unstable when the voltage stability margin falls below a predetermined value; and initiating dynamic load shedding and/or restoration depending on the voltage stability margin.