Enhanced Static Excitation System architecture for high-capacity Turbogenerators with improved current sharing and harmonic performance

(SES) employ parallel six-pulse thyristor bridges supplied through a common AC/DC bus, making them inherently prone to current imbalance and high harmonic distortion. Practical variations in bridge impedance and firing pulses lead to 10–20% current imbalance and high excitation current THD (~26.64%), resulting in thermal overstress, reduced field forcing capability, and diminished reliability.

To overcome these limitations, this paper proposes a 24-pulse static excitation system based on a multi-winding excitation transformer with independent, phase-shifted LV windings for each thyristor bridge. The proposed architecture eliminates the common AC bus, enables independent firing-angle control, and ensures robust current sharing under asymmetric operating conditions. The 24-pulse rectification scheme effectively suppresses dominant loworder harmonics, reducing HV-side current THD to 0.94% and minimizing DC ripple in the generator field current.

The paper presents a comprehensive comparison of the existing and proposed excitation system architectures using schematic representations and detailed software simulations, including current-sharing behavior and harmonic analysis under various operating conditions.