Fekadu, Shewarega (PhD)Melaku, Yigzaw2020-06-172023-11-282020-06-172023-11-282017-12http://etd.aau.edu.et/handle/12345678/21621Power system security is an important issue in power system operation and hence the operation of a power system requires regular security assessment. However, presently dynamic security assessments are not being performed on Ethiopian existing power network. Consequently, the power system operators do not have remedial action plans for various contingencies that may occur in the system. In this thesis work, the dynamic security of the Ethiopian existing power network is assessed using PSS/E software in off-line mode. The Ethiopian existing operational power network model has been extracted from the 2015 planning model and used for simulation studies. This model is validated by checking the models of each element one by one. In addition, the history of generators loading profile has been reviewed and their loading of April 11, 2017 at 19:45 o’clock resulting in the peak operational scenario is selected for the analysis. The dynamic simulations have been performed considering sever short circuit faults at the 400 kV and the 230 kV parts of the system and the outage of a generator at different power plants one by one. The voltage at 132 kV buses like Awassa, Dilla and Boculuguma doesn’t recover to 0.9 pu within 10 seconds for all cases considered in the analysis. In addition, the Sudanese system would be out of synchronism from the Ethiopian system for a short circuit fault on Akaki II-Kaliti I 230 kV line even if the fault is cleared as per the actual protection setting provided that the total tie-line flow is above 148MW. These results confirm that the Ethiopian operational power network was operating at insecure operating point for the operation scenario considered in the analysis. The frequency response plots for outage of a generator at different power plants depict that the frequency returns near to the normal value despite the outage. This indicates that the primary controllers of the generators which are in operation are working properly; and the remaining generators are jointly capable of covering the lost generation. Reactive power sources like capacitor banks need to be installed in the Southern Region of the system to improve the voltage profile. The generators need to be re-dispatched in such a way that the total tie-line flow is kept at 148MW and below to keep the Sudanese system in synchronous operation with the Ethiopian system for the operation scenario considered.en-USPower systemSecurity assessmentDynamic securitySecurity criteriaThesis