Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Electrical and Computer Engineering


Using the classical model of power system, Fouad and Vittal developed individual machine energy functions in order to identify the transient energy tending to separate a particular machine from the rest of the system('1);To improve the confidence in first swing transient stability assessment a more realistic model of the loads is used. In the proposed non-linear model, the loads are represented by any desired combination of constant impedance, constant current or constant-MVA models. The effect of the non-linear loads is reflected at the internal nodes of the generators as injected currents. The non-linear injected currents account for the sudden voltage changes immediately following the disturbance;Expressions for the individual machine energy functions, which represent the effects of the non-linear load models, are obtained. Using the criterion of stability suggested by Fouad and Vittal, first swing transient stability assessments are made for two multimachine test power networks. A number of cases, under a variety of load compositions, were tested. Analysis of the results obtained have demonstrated the effects of non-linear load representation on the energy absorbing capacity of the network, critical fault clearing time and the mode of instability. Comparisons have also been made between the critical fault clearing times obtained above and those;obtained using time solution such as Philadelphia Electric Co.'s transient stability program; ('1)Vittal, V. "Power System Transient Stability using the Critical Energy of Individual Machines." Ph.D. dissertation. Iowa State University, Ames, IA, 1982.



Digital Repository @ Iowa State University,

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Hamid Elahi



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98 pages