Sustainable development of large power plants' auxiliary supply

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Dr. Vokony István
Department of Electric Power Engineering

Due to expansion of converter-based renewable energy sources, permanent energy source of power system, and also quotient of natural (physical) and synthetic (controlled) inertia of power system continuously decrease. Therefore, significance of stability and capability of conventional power factories becomes enhanced and highly appreciated by TSOs and besides by Plant Operators also.

Master Thesis considers indirect improvement opportunities of large-scale power unit’s availability factor and power quality of auxiliary system’s electric supply. In case of safety critical energy conversion technology – such as at PWR nuclear and supercritical thermal power unit – 2 of 3 alternative supply routes have to be permanently provided during all basic design condition. So, after presenting generally current concept of modern power plant’s electrical technology, which is deducted from requirements of international and of national authorities (IEA, IEEE, IAEA and Hungarian Atomic Energy Agency), I build – in one case Simulink justified – equipment and eventually total auxiliary system model in DIgSILENT™ 15.1.2 software environment.

Following overviewing technical literature in terms of topology of switchyard, power station and instrumentation and control concept beyond auxiliary power supply systems, I elaborate Load-flow simulation of large-scale power unit’s normal, anticipated operation modes. As a first step I do obtain initial conditions of RMS (Root Mean Square) electromechanical transients induced by so-called ABT IED transfer (switch-over) methods and load rejection caused transients in order to be able to create proper result plots for RMS calculation results. In compliance with dynamic system modelling methods, I added derived mechanical pump load characteristics and electromagnetic parameters to asynchronous motoric consumers and generators (and not neglecting classic loads), since precise analysis of impact of overvoltage or voltage dip required that. Furthermore, I created simplified models of voltage-coordination functions (ABT and Undervoltage-protection) on relevant branches in order to improve transfer functions on the long run.

Dernier, I opt for possible solution concepts for issue of voltage deviation during transients and harmonic distortion. Finally, after evaluating state-of-the-art concepts, I analyse an economically acceptable solution by numeric simulation, including brief summarization of its Power Quality and Efficiency improving efficiency.


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