| Summary: | Nuclear and renewable energy systems will probably be used more and more
extensively in future due to high environmental demands regarding pollution and
exhaustion of the world's gas and coal reserves. Because most types of renewable
energy systems do not supply electric power at line frequency and voltage a converter
is used to connect these sources to the existing power system.
The Pebble Bed Modular Reactor (PBMR) is a nuclear power plant currently using a
50 Hz synchronous generator. A high-speed generator is now being investigated as an
alternative to the conventional 3000 rpm synchronous generator. This option is
considered, because the turbines in the thermo hydraulic system will run more
efficiently at high speed and can be smaller in diameter. It also implies a smaller
generator and possible reduction in the number of turbine shah.
By using a 150 Hz generator implies that the generated electrical power frequency is
also not that of the grid. This situation is similar to that of some renewable energy
systems like wind farms. Although the frequency of wind farm generated power is in
most cases lower than 50 Hz (nominal grid frequency in South Africa), the same
technique of converting the generated power to direct current (DC) can be used. Direct
current converters are also used to connect asynchronous networks, oil platforms,
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limiting flicker mitigation andl6- Hz railway systems to national grids.
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These applications are therefore used in this thesis as a starting point for discussing the
reason why a Medium Voltage Direct Current (MVDC) converter was chosen over a
High Voltage Direct Current w C )for the PBMR system. MVDC converters can be
used to start-up the PBMR without the Start-up Blower System and Static Frequency
converter. The converter can also control the active and reactive power flow and the
frequency control allows a standard PBMR design for 50 Hz and 60 Hz systems.
A high-speed induction generator was found to be a good combination for use in cooperation
with the converter. The construction of a 180 MW high-speed generator is
however currently not possible. MVDC and especially IGBT technology are new
technologies and are therefore expensive at this stage. === Thesis (M.Ing. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2005.
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