Patent ID: 9291655
Filing Date: 2016-03-22
CPC Classification: G01R,H02J

Claim Text:
1. A method of monitoring voltage stability of a transmission corridor through which power flows between different parts of a power system, the method comprising the following performed by a voltage stability monitoring apparatus: monitoring an equivalent load impedance at an interface between the transmission corridor and a part of the power system designated as generating said power, the equivalent load impedance at said interface comprising a ratio of a voltage phasor at said interface to a current phasor at said interface; tracking a Thevenin equivalent voltage and impedance of said designated part by separately updating that voltage and impedance, wherein updating the Thevenin equivalent voltage comprises updating the imaginary part of the voltage to reflect the magnitude of any changes in said voltage phasor that are associated with large variations in the magnitude of the equivalent load impedance at said interface, said large variations including variations greater than a threshold-defined variation, wherein said updating the Thevenin equivalent voltage comprises, for each of a plurality of phasor measurement times, determining whether or not variation in the magnitude of the equivalent load impedance at said interface since a previous phasor measurement time is greater than the threshold-defined variation, and, if so, adjusting the imaginary part of the Thevenin equivalent voltage computed for the previous phasor measurement time by the magnitude of the change in said voltage phasor since that previous phasor measurement time, wherein said adjusting comprises computing the imaginary part of the Thevenin equivalent voltage E computing an index indicating said voltage stability as a function of the tracked Thevenin equivalent voltage and impedance.