Turbine-generator blade and shaft torisonal torques due to line faults in six-phase transmission systems evolved from three-phase double-circuit line systems

Due to a restricted right-of-way and many factors, some of the local areas in Taiwan have become increasingly difficult to build new transmission lines. Since the majority of Taiwan power loads are located in the Norton, the demand of promoting transmission power could be of great urgency owing to the large amounts of power transferring from the South to the Norton. Aimed at overcoming this problem without changing the original conductors of the double-circuit transmission lines, the six-phase transmission scheme which could be one of the best schemes is presented and has several advantages such as transient stability enhancement, minimal corona, electric and magnetic fields, and radio interferences. As a result of the successful commercial operation of six-phase transmissions, the utility planner inevitably faces with the issue for the impact of turbine-generator torsional vibrations in the initial stage of the expansion into the six-phase network. From the simulation comparisons between the three-phase double-circuit and evolved six-phase system, the latter offers better stability characteristic without deteriorating torsional vibrations from the viewpoint of the same line voltages. For the case of the same transmission capability, it significantly reduces the torsional vibrations. These conclusions provide a constructive suggestion for the department of generation and transmission.