Patent ID: 6690175
Filing Date: 2004-02-10
Classification: H02J,Y02E,Y04S

Abstract:
A method for assessing the stability of an electric power transmission network, where said network comprises a plurality of substations, buses and lines, and where the method comprises the steps of repeatedlya) measuring, at a given point of the power network and at a plurality of time instants, a plurality of measurement points, each consisting of a voltage phasor and a current phasor, b) determining at least one pair of measurements comprising a first measurement point (P1) and a second measurement point (P2), where the first measurement point (P1) comprises a first voltage phasor V1 and a first current phasor I1 and the second measurement point (P2) comprises a second voltage phasor V2 and a second current phasor I2, c) computing a ThÃ©venin impedance Zt as Zt=-â€ƒ&it;V2-V1I2-I1d) and computing, from the ThÃ©venin impedance Zt and from a present measurement point (P(k)), a present stability margin dS(k) that characterizes network stability, wherein the method comprises, for each of the at least one pair of measurements, e) computing a first boolean value that is true only if a minimal difference between the first and second measurement point (P1,P2) exists, f) computing, only if the first boolean value is true, from the first measurement point (P1) a first load impedance Za1=V1I1,g) computing, only if the first boolean value is true, from the second measurement point (P2) a second load impedance Za2=V2I2,h) computing, only if the first boolean value is true, a second boolean value that indicates whether a difference between the first and second load impedance Za1, Za2 exceeds a given impedance threshold, i) computing, from the first boolean value and, if the first boolean value is true, also from the second boolean value, a validity indicator (v) that is associated with the pair of measurements, and, for all of the at least one pair of measurements j) computing, from a plurality of ThÃ©venin impedances Zt, each of which is associated with a different pair of measurements, a composite ThÃ©venin impedance Zt, and k) computing, from all validity indicators (v) that are respectively associated with all of the at least one pair of measurements, a quality indicator (q) that is associated with the composite ThÃ©venin impedance value and with the present stability margin dS(k).