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.

No abstract

The Extreme Loading Condition (XLC) of a power system is defined by assuming a load increase (a m d i n g to a predefined pattern for both active and reactive powers) until a maximum is reached for anyone of the lods. The XUJ is significant for the assessment of voltage stability. Its calculation, as presented in the paper, is based on increasing the load admittances while first keeping the generator voltage phasors constant and then adjusting these phasors for satisfying operational requirements with respect to the generation powers. The secant method is used for the efficient and reliable determination of the maximal value of the loading parameter p, while for the voltage adjustment a fast convergent Newton module is employed. The XLC can be calculated for both normal operation and for contingencies. The new approach is fast and simple and can be used on larger systems. Its features have been illustrated on the 39 bus New England test system. The calculation identifies the weakest bus where remedial action may be needed for voltage support.

No abstract