Engineering foundations for the determination of security costs

Abstract

This paper characterizes system security by using distances to system operational limits (including voltage collapse limits, stability limits, line and transformer overloads, and generator limits). It. uses the Point of Collapse method based on the singularity of the power flow Jacobian to define an Operational Limit Boundary in load demand space. Distances to this boundary are then translated into probabilistic measures of likelihood of system failure: Probability of Normal Status, Expected Demand Not Served, Expected Unserved Energy and, ultimately, Expected Outage Cost. Sensitivities of these measures to load and generation changes (important for operational decisions and real-time pricing) are also described. A numerical example is presented. Computational issues are discussed. eywords: Sestability.curity, adequacy, outage costs, loadability, vo + tage collapse, I n t r o d u c t i o nThis paper establishes foundations for the determination of the expected costs resulting from system outages. Outages refer to the inability of the system to supply part or all of the system load, not to equipment outages. The paper uses primarily static system security (system adequacy) concepts to separate regions of normal operation from regions where outages occur."Outage costs" are not normally in the vocabulary of power engineers. Systems have traditionally been operated on the basis of "economic dispatch"' sabject to "security constraints." The constraints typically assume that secure operation is of the utmost importance, overriding cost considerations. However, as systems become more strained and as the responsibility for system operation becomes increasingly diversified, knowledge of the limits of secure operation becomes more important. The very idea of a system that is either "secure" or "insecure" comes into question. Systems have varying degrees of security. Absolute security can never be attained.All decisions about a system influence security to some 91 FE1 183-L PidRS A paper r e c o m e d e c ? and approved by t h e I E Z Porrer Systen Engineering Comnittee of t h e IEEZ Porrer Engineering S o c i e t y f o r p r e s e n t a t i o n a t t h e IE;E/PCS 1991 Winter I.leeting, Keir York, New York, r e b r u a r y 3-7, 1991 . !'anuscri?t s u b n i i t t e dSeptember 5, 1990; made a v a i l a u l e for p r i n t i n ;J a n u a r y 22, 1991.Dennis Ray Rodney Stevenson Eileen Cashman Member Non-member Non-member G r a d u a t e School of Business T h e University of Wisconsin -Madison degree. Security is a function of configuration and operating condition. Often, security is expressed as a function of a single variable (such as total load or transfer capability between two areas). More likely, it is expressed as a constraint on this variable. This can be done because security is highly nonlinear. When the system is secure, most actions have negligible impact on security. However, when security is in jeopardy, many actions can have a significant effect on security. Thus, while at times security can be ignored,...

Steady‐state security assessment method based on distance to security region boundaries

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Voltage Stability Limit of Electric Power Systems With Generator Reactive Power Constraints Considered

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