Voltage Instability Detection based on the Concept of Short Circuit Capacity

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Daniel Felix Ritchie School of Engineering and Computer Science, Electrical and Computer Engineering


Voltage stability, Short circuit capacity, Voltage stability index, Phasor measurement unit


This paper proposes an online detection method for power system voltage instability, which considers the internal impedances of generators and the voltage‐dependent and recovery characteristics of the electric loads. First, a novel voltage stability analysis method based on the concept of short circuit capacity (SCC) is established. Based on it, a SCC‐based voltage stability index (VSI) is defined as the ratio of the SCC supplied by the combined generation‐transmission system and the SCC required by load bus to maintain voltage stability. Then, for the calculation of SCC‐based VSI, a two‐step equivalent method of power system is presented to obtain the SCC supplied by the system side, in which the generator is modeled as a time‐varying internal voltage behind constant internal impedance. Meanwhile, a modification method of load power is proposed to deal with the voltage‐dependent characteristics and the restoration dynamics of system loads. As a result, the SCC required by loads can be precisely calculated. At last, the 5‐bus system and the New England 39‐bus system are used to validate the effectiveness of the proposed voltage instability detection method.

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