1529Abstract -This paper discusses the voltage stability analysis of large power systems using a modal analysis technique. ?he method computes, using a steady state system model, a specif ed number of the smallest eigenvalues and the associated eigenvectors of a reduced Jacobian matrix. The elgenvalues. each of which is associated with a mode of voltage/reacth power uariatlon. provide a relath memure of prodmity to voltage instability. The eigenvectors are used to describe the mode shape and to provide information about the network elements and generators which participate [n each mode. A simmultaneous iteration method, which is weU suUed to applications involving large power systems, is used for selective calculation of appropriate eigenvalues. Results obtained using a 3700 bus test system are presented illustrating the applimbruty of the approachAs power systems are operated under increasingly stressed conditions, the ability to maintain voltage stability becomes a growing concern. In planning and operating power systems. the analysis of voltage stability for a given system state involves the examination of two aspects: a) Proximi& : how close is the system to voltage instability 7 b) Mechanism : when voltage instability occurs. what are the key contributhg factors. what are the voltage-weak points, and what areas arc involved 7Proximity gives a measure of voltage security whereas mechanism provides information useful in determining system modiflcations or operating strategies which could be used to prevent voltage instability.Voltage stability is indeed a dynamic phenomenon and can be studied using extended transient/midterm stability simulations. However. such simulations do not readily provide sensitivity information or the degree of stability. They are also time consuming in terms of CPU and engineering required for analysis of results. Therefore. the application of dynamic simulations is limited to investigation of specific voltage collapse situations. including fast or transient voltage collapse. and for coordination of protection and controls.Voltage stability analysis often requires examination of a wide range of system conditions and a large number of contingency scenarios. For such applications, the approach based on 91 SM 420-0 PWRS by the IEEE Power System Engineering Committee of the IEEE Power Engineering Society for presentation at the IEEE/PES 1991 Summer Meeting, San Diego,

This paper discusses voltage stability analysis of power systems using static and dynamic techniques. Using a small test system, results of time domain simul0tion.s are presented to clarify the phenomenon of voltage instability and to better understand modelling requirements. The same system is then analyzed using a static approach in which modal analysis i s performed wing system conditions, or snapshots, which approximate different stages along the time domain trajectory. The results obtained using the dynamic and static methodr are compared and shown to be consistent.

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The objective of contingency screening and ranking function is to shortlist a specified number of critical contingencies from a large list of credible contingencies and rank them according to their severity. This paper summarizes the work conducted as part of the EPRIA3.C. Hydro on-line voltage stability project in developing a Contingency Screening and Ranking (CS&R) module. The two methods of Reactive Support Index (RSI) and Iterative Filtering are derived in this paper and tested on the large scale systems of B.C. Hydro and another Major Unnamed Utility. The results obtained indicate that RSI on its own or in combination with the Iterative Filtering method can be used for CS&R depending on the acceptable level of misranking. The RSI method is a very fast and powerful CS&R method and is suggested for systems where some misclassification of contingencies can be tolerated. On the other hand, for systems where an exact list of critical contingencies is intended, then the Iterative Filtering method can be used for screening complemented with another method like RSI for ranking. The latter technique is being integrated in the EPRU6.C. Hydro On-line Voltage Stability tool.

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