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4 Analysis, Findings and Results
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4.2 Dynamic System Simulations
The dynamic simulation models were individually set-up and validated for each synchronous area based on the load flow models. The UCTE dynamic model has been verified and developed over the last fifteen years and shows a good correspondence between real system measurements and simulation results. The IPS/UPS dynamic model was initially set up for the purpose of this study. This model was verified against recordings of actual disturbances by a Wide Area Measurement System installed in the IPS/UPS during the period 2005-2007.
Both models were merged in order to study the impact of a synchronous coupling on small signal and transient stability.
The results of the model analyses show that the synchronous coupling causes structural based oscillations. The Figure shows an example of the generated power oscillations in the synchronous coupled systems after a major disturbance in the North-Western part of the IPS/UPS. These oscillations create a new and poorly damped frequency mode of 0.07 Hz, and thus require special damping measures in the interconnected systems. The oscillations are of electromechanical origin, i.e. the rotors of the machines in the East part of the system oscillate against the rotors of the machines in the West. The final solution to adequate damping measures for the detected low frequency mode (e.g. voltage control or speed governor based) requires further development of the IPS/UPS dynamic model.
The main findings and results of the transient stability analyses are:
- 3-phase short circuits applied in the interface region, which were conceptually cleared, probably do not jeopardize the transient stability of the coupled systems.
- The analyses of more severe events revealed serious potential consequences for the synchronously coupled system of the IPS/UPS and the UCTE. These are in the first instance of a structural nature that needs both sophisticated countermeasures and further research in this respect.
Analyses were carried out following the disturbance in the UCTE on the 4th November, 2006 under conditions of a synchronously coupled IPS/UPS grid. This showed that the coupling of the IPS/UPS and the UCTE might not ensure reliable support between the systems in such emergency situations. Instead, it could worsen the situation due to severe stability risks. The simulation demonstrated the technical drawbacks of large synchronously interconnected systems when considering the survivability of the systems concerned in the event of major incidents.
Economical benefits that are mainly associated with the extension of power systems are to some extent countervailed by technical drawbacks. Priority has to be given to preventing, the unabated propagation of disturbances and their consequences throughout the interconnected system.
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