The Study Of The Assessment Of The Transient Stability Of Power System With The Protection Operation

With the continual increase of power system capacity, the analysis and assessment of the transient stability of power system is one of the key issues among the planning, operation and dispatching of power system. But the effect of protection operation upon transient stability was less paid attention in the previous analysis and assessment of transient stability. In fact, there are faults or abnormal operation states in the process of power system operation. Relay is the primary equipment which cut off the fault elements, deals with abnormal operation states to ensure the power system stable. Furthermore, voltage and current often undergo significant excursions during the transient period following the clearing of a large disturbance. This can result in unexpected switching events, which make the stable power system become instable, and then lead to more protection operation. It is very dangerous for the stability of the power system. Therefore, it is very important to consider the protection operation during the analysis and assessment of transient stability. Based on the above issue, this thesis does some research about the assessment of the transient stability of power system with the protection operation. And the content of this thesis is as following:At first, a new method for identifying critical cutset in power system is presented. At the peak of post-fault system potential energy, the most vulnerable line is found whose line potential energy is maximal. And the backup muster of vulnerable cutset is formed including the most vulnerable line. Then the vulnerable cutests (key lines) is found with synthetical index method. The test result shows the new method is effective and doesn't need the artificial backup muster of the vulnerable cutest, comparing with the other methods.On the basis of searching out critical cutset and the most vulnerable line, a new algorithm is presented to calculate the critical energy of transient stability assessment of the power system with protection operation. The critical energy is the system energy which just makes the post-fault trajectory be tangential to the protection surface of the key lines. That potential energy grad is projected onto protection surface is thought of to be the search direction at the new algorithm. The power flow equation is satisfied through using the control variable, namely generator angles and speeds, to solute the network bus voltage magnitudes and angles. The new algorithm owns good convergence because of not involving the large inverse computation. The examples show the convergence and veracity of the new algorithm are better than the two steps approach.