Transmission Security Comprehensive Assessment For Enhancing Situational Awareness

Situational Awareness (SA) plays the key role on improving self-healingcapability and robustness of power system. With frequent occurrence of large-scalecascading blackout and growth of wind power capacity, security assessment is facingunprecedented challenges as the most important analytical tool of SA. Thisdissertation studies on transmission security comprehensive assessment for enhancingsituational awareness based on security region methodology.Firstly, the dynamic security region which guarantees the transient stability ofpower system integrating double fed induction generator (DFIG) in power injectionspace is studied. Extensive transient stability simulation results show that, within theacceptable precision of engineering application, the boundary of dynamic securityregion with DFIG can be approximated by one or few hyper-planes, in engineeringpoint of view. This result highlights the superiority of security region which can betaken as the powerful tool of security monitoring, assessment and control forenhancing situational awareness.Secondly, an analytical method for calculating security transition probability isproposed and the efficiency of security transition probability is verified. Based onpractical parts of critical boundaries of security region represented by hyper-planes,complex integral in the process of calculating security transition probability can beconverted to a simple analytical calculation, which is then calculated by cumulantsbased expansion. The efficiency of the presented method is verified which makeintegrating uncertainties of injection power such as wind power and load available.Besides, it is proved that security transition probability is not only the key componentof elements of state transition probability matrix of Markov model in the followingprobabilistic steady-state and dynamic security assessment, but also an effectivesecurity index which help operators monitor system to take preventive control well.Thirdly, an effective method to formulate state transition probability matrix ofMarkov model is proposed. Based on component state transition rate matrix andsystem configuration array, system state transition rate can be calculated efficientlyand the rule of the distribution of non-zero elements is obtained. Then sparse storage of the state transition probability matrix can be formulated quickly which can befurther accelerated based on given order of system state and service set array ifcomponents only have two states. Test results show the efficiency of the methodwhich provide a valid analytical tool to apply Markov model to analyzing large-scalesystem such as power system.Finally, two-level system model is improved, based on which probabilisticsteady-state and dynamic security assessment is established through security regionand Markov model. Transitions between system configurations, renewable capacity ofsystem, uncertainties of wind power and load demand, steady-state and dynamicsecurity constraints, the effect of climate and natural disasters are incorporated in themodel. By solving a linear vector differential equation, time to insecurity and itsprobability distribution are obtained which give effective evaluation of future systemstate and provide time for taking actions. The model is implemented in complexsystem successfully for the first time by using several effective measures, whichpushed forward the process of practical application of the model. Numerical resultsdemonstrate that the model can provide more practical assessment of system security,evaluate effect of disturbance on security and conduct operators make decision andtake actions effectively. Thus the model can be used to enhance situational awarenessespecially the predicting level.