Interconnected grids are supposed to supply electric power at principally constant voltages. This has to be achieved using generation, distribution and transmission equipment that is not perfectly reliable with varying demand and variable reactive nonlinear loads. All generators must run at the same frequency and must be in phase with each other on the grid. A local governor regulates the driving torque of rotating generators, preserving constant speed while the load changes. Electrical energy is stored in the immediate short term by the rotational kinetic energy of the turbine -generators sets. Power balance across the entire grid has to be maintained because energy is consumed at the same time as it is generated. Droop speed control ensures that multiple parallel generators share load changes in proportion to their rating. As load increases, the frequency slows below the nominal frequency and local governors adjust their generators so that more electricity is generated. As load decreases grid frequency runs above the nominal frequency, and this is an indication for automated generation control (AGC) systems across the power grid that generators has to reduce their output. Small deviations from the nominal system frequency are very important in regulating individual generators and assessing the equilibrium of the grid as a whole. In addition, central control changes the parameters of the AGC systems over a minute timescale to adjust the regional grid power fl ow and operational frequency of the grid. For timekeeping purposes, to prevent line -operated clocks from gaining or losing significant time, the nominal frequency is allowed to vary to balance out transient deviations.
Effect of energy storage on transient regimes in the power system, Page 1 of 2
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