Fast torsional vibration protection for large steam turbine generator

The transient torque amplification which may be resulted from series compensated capacitor could lead to fatigue cracks in the shaft of a large steam turbine generator within 0.5 seconds, the conventional torsional stress relay cannot work in time to protect in this extreme case. A fast protection method is proposed, which takes the over-component of power frequency variation of current or active power as the pick-up criterion, and the over-amplitude of fluctuation speed amplitude as the operation criterion. For the turbine-generator units of the Power Plant M in XM grid of China, twelve cases are selected for time domain simulation study. The simulative results show that the speed deviation amplitudes are obviously consistent with the torsional torque amplitudes and they are approximately proportional. Finally, the speed signals of the simulation cases are superimposed with on-sited measured speed noises, and then the protection algorithm and logic are verified. The study shows the fast protection doesn't operate when torsional vibration is slight, but trips fast when torsional vibration is severe, so that the fatigue value resulted from shaft torque amplification in the worst case will be decreased to less than 15 %. It should be noted that the effect of torsional vibration still exists after the generator is disconnected from the grid, and the protection setting threshold should have sufficient margin. © 2020, Electric Power Automation Equipment Press. All right reserved.