Probabilistic Modeling To Composite Power System Security

Stochastic and uncertain performance of power systems is thoroughly studied with a probabilistic simulation method in this paper. Based on modeling of element failure and dispatching measures, static, dynamic and integrated securities are analyzed, and hence operation states are quantitatively classified.In probabilistic static security assessment, sequential and non-sequential Monte-Carlo sampling techniques are applied considering time varying parameter and constraints. Random failures of generator, transformer, transmission line, protection system and topology of both power station and power network are constructed. After load fiow study in each sample, distance to static voltage stability boundary is calculated. When static voltage instability will occur, load curtailment with optimum location and amount is executed. When there is active power deficiency or line overloaded, linear programming method with multi dispatching strategies is applied to adjust generator output or shed load. When there is reactive power deficiency or bus voltage exceeding limit, reactive power dispatching and voltage correction program based on continual linear programming method are introduced to eliminate them. As the result, probabilistic static security indices based on system, load point and element levels are introduced.In probabilistic dynamic security assessment, probabilistic transient stability" is mainly discussed. Detailed models of transmission line, protection system and emergency control measures are added to step-by-step transient stability programs. Models of hybrid and probabilistic stability are constructed. The former combines enumeration and sample technique and is easy to implement, but only definite failure modes are simulated, which may be inaccuracy with bulk power system in which high order failures and protection failures are the main cause to instability. Probabilistic stability assessment based on Monte-Carlo sampling technique takes into account high order failure and correlation between failures. Static and dynamic securities are simplification based on different time frame and study purpose. They are inherently related however. A single contingency has influence on both static and dynamic security. Thus an integrated model is constructed to comprehensively evaluate power system security. As the result, probabilistic dynamic security and integrated assessment indices based on system, load point and element levels are introduced.Operation state of power systems are defined and classified to comprise security regulations and dispatcher's experience. Based on sequential simulation and integrated assessment to power system security, cause, property, duration, result are detailed analyzed to present a new and feasible state framework and it's quantitative calculation method. All the possible operation states are rationally incorporated into a practical state framework. Load curtailment is the major criterion to classify states, as well as severity of failure mode. Definition and classification of operation states present a new tool to evaluate security of power systems.