δείτε την πρωτότυπη σελίδα τεκμηρίου στον ιστότοπο του αποθετηρίου του φορέα για περισσότερες πληροφορίες και για να δείτε όλα τα ψηφιακά αρχεία του τεκμηρίου*
Interactive long-term simulation for power system restoration planning
(EN)
Fountas, NA
(EN)
Hatziargyriou, ND
(EN)
Tasoulis, A
(EN)
Orfanogiannis, C
(EN)
Since blackouts seldom occur, the personnel in control centers and generating plants has little experience in handling such extreme disturbances. It is therefore necessary for an electric utility to set-up orderly restoration procedures for such events and to focus on training and education of engineers and dispatch operators. The increasing need for competent long-term dynamics (LTD) analytical tools to serve as supporting means to power system planners and dispatchers for the above purposes has been well recognized. To this end, a dynamic analysis program is specially adapted and used for the simulation of restoration procedures as followed by the Hellenic Public Power Corporation, PPC. The program offers two simulation modules. In the Full Integration (FI) module, short term dynamics are simulated and an implicit integration method is used. In the second Quasi-Stationary module only longer-term dynamics are simulated. The option exists to automatically switch from quasi-stationary mode to full transient simulation mode whenever there is a need for more detailed examination of the phenomena involved. For the long-term simulation required for Power System Restoration (PSR) studies, a quasi steady-state approach, that is the approximation of the system trajectory through successive transient equilibrium points has been used. Following a disturbance the transient dynamics are not simulated, but only the corresponding equilibrium point after the transients have died out is computed. A large scale model of 235 buses of the Hellenic power system corresponding to the actual summer peak of June 1994 has been developed in the Electric Energy Systems Laboratory of NTUA. Public Power Corporation utilizes a ""build-up"" restoration strategy: 1. assessment of power system status. 2. starting as soon as possible of all hydro stations -insure power supply of all thermal plant auxiliaries from hydro power stations. 3. sectionalization of the deenergized system into several island sub-systems 4. interconnection of generating stations within each island. 5. independent gradual load and generation build-up inside each subsystem. 6. resynchronization of islands. 7. completion of system rebuilt by picking-up the remaining unserved load and closing of ties with the interconnection systems. In the course of system reenergization some major concerns are: • Failure of thermal stations auxiliaries start-up due to low voltage supplied from small hydro stations. • Violation of island stability limits. • Poor coordination of the consumer load reconnection rate and of the island plants load pickup capability. • Excessive differences at the magnitude and the phase angle of bus voltages when closing loops. The Hellenic power system experienced a total blackout in 1989. In order to restore service, the station personnel followed the above restoration guidelines. Restoration of customer load was completed in 3 hours after fault occurrence. A set of cascading operating snapshots of the Hellenic power system during the restoration phase following the blackout has been replicated utilizing the program previously described. In Figure 1, frequency evolution in the three formed islands is given. (Figure Presented) Figure 1. Island frequencies trajectory (Figure Presented) Figure 2. Loop closure transient In different occasions the algorithm failed to converge to new equilibrium point. Such inadequacy is attributed to operating constraint violation; this conclusion has been verified in the FI module. Restoration process was often interrupted or delayed by excessive standing phase angles across a breaker which connects two adjacent lines. By switching to the FI module corresponding to a specific operating point it was found that it was infeasible to reach a new equilibrium point with this level of loading. By altering line loading and increasing the generation profile of the nearby stations, the energization was successfully implemented, Figure 2. Integrated LTD programs can provide an effective means by which the operator can be trained to deal with restoration situations in a secure, controllable and off-line simulation environment and they can be used for effective restoration planning.
(EN)
*Η εύρυθμη και αδιάλειπτη λειτουργία των διαδικτυακών διευθύνσεων των συλλογών (ψηφιακό αρχείο, καρτέλα τεκμηρίου στο αποθετήριο) είναι αποκλειστική ευθύνη των αντίστοιχων Φορέων περιεχομένου.
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