Optimal design of brushless AC exciter for large synchronous generators considering grid codes requirements
The performance of the excitation system plays a very important role in the voltage stability of the power grid. The brushless excitation system with a brushless alternating current exciter offers a lower failure rate and thus higher reliability in comparison with the static system with high-rated power electronics converters, brushes, and slip rings. However, its dynamic response is impaired due to the exciter lag in producing the required field current. In this study, the optimal design of an exciter for the large-scale power-plant synchronous generator based on the magnetic equivalent circuit method is pursued. The design goals are reducing the overall volume, minimising the magnitudes of the cogging torque and the field current ripples while satisfying the grid code requirements such as the ceiling values of available field voltage and current, rise time and settling time of the rectified output voltage under dynamic conditions. In addition, the other electrical, magnetic, thermal and mechanical constraints are included in the design algorithm. The proposed design method is used for obtaining the optimal specifications of an exciter for a 25 MW, 11 kV power-plant generator in order to attain superior characteristics than the existing one. The analytical results are validated using two-dimensional finite-element studies and experimental measurements.
