A new single-pole switching technique for suppressing turbine-generator torsional vibrations and enhancing power stability and continuity

The author presents a new single-pole switching technique for reducing torsional torques in turbine blades and shafts and enhancing power system stability and transmission continuity. During the dead time between single-pole tripping and line reclosing, the significant negative-sequence current flowing into the nearby turbine-generator may cause supersynchronous resonance effect on low pressure turbine blades and even results in fatigue damage. Thus, during this time, the proposed grounding capacitor set up at the neutral of the wye transformer is inserted not only to eliminate this negative current but also to recover the prefault power transmission in advance. The induced adverse effect on turbine blades can be precluded. Adaptive reclosing is then applied to reclose the tripped phase and the grounding capacitor is switched off. This effectively improves the power system stability again and prevents further torque amplifications. This scheme is suitable for a single-circuit transmission line and can improve system reliability.