Dynamic Security Assessment on Ethiopian Existing Power Network
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Date
2017-12
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Addis Ababa University
Abstract
Power 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.
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Keywords
Power system, Security assessment, Dynamic security, Security criteria