Microsoft Word - ICEE_69-Calculation of the Critical__ Energy of the Power ..

Whether a disturbance will trigger unexpected protection operation to exacerbate the normal operation state or even lead to the unstable state depends on the transient energy that the system gains during the fault period. The paper presents a new gradient projection approach to calculate the critical energy for transient stability assessment of the power system with the protection operation. The method takes the projection of the potential energy gradient on the key protection operation surface as search direction and iteratively searches for the critical energy at the surface; in order to let the optimal point be the feasible point, the generator angles are considered as control variables of power flow equation to solve network bus voltage and angle during the searching process. Examples show the convergence and precision of the new method proposed is much better than that of other methods, which demonstrates the validity and feasibility of the new method. Keyword--power system, transient stability, protection, critical energy, gradient projection