Safety Analysis On Torsional Vibration Of Large Steam Turbo-generator Shafts

Today, electric power industry is developing towards more large-scale unit capacity and more complicate grid, leading to increasingly prominent problems of the shafts torsional vibration,which is big threat to the security of the units and grid. This paper gives in detail the current research progress of safety analysis on torsional vibration of turbo-Generetor shafts at domestic and international, describs the problems of existing theories, and then does some further research about it and also puts forward corresponding solutions. The method of shafts modeling is discused, advantages and disadvantages of methods to calculate shaft inherent characteristics is compared and analysed, and the superiority of verified riccati-transfer-matrix method is verified, using the finite element method. The calculation principles of shafts response is analyzed, and the analytical algorithm of shafts response under two-phase short circuit is deduced. Thoroughly analysis is given to reverse fatigue S-N curve and its influence factors, such as torsional mean stress and high cycle fatigue. The corresponding analytical correction formula is obtained and its accuracy is verified by finite element method. This paper also presents an improved model of real-time rain-flow counting, which eliminates the defects of the original model which easily produces leakage point in the second stage. Combining the malfunction response characteristics, the threshold of the fatigue accumulating damage is analyzed specially and studied quantitatively under different load spectrum, which provides theory basis for torsional vibration monitoring and warning. The method of checking torsional intensity of axis is analyzed, the correlation of intensity checking and fatigue damage is discussed, and the changes of torsional fatigue limit is obtained under fatigue damage. The paper probes the safety strategy analysis of torsional vibration at home and abroad, gets fatigue life loss range of shafts withstanding an impact under all kinds of faults, and put forward the method of computing element's value at risk, which lay a foundation for torsional vibration safety analysis. The safety of shafts is analyzed by combining with low-pressure rotor wear fault of one power plant and two-phase short-circuit faults of the other power plant, which verifies the feasibility and accuracy of the corresponding theory. The study of this paper will have a positive significance on real-time life assessment and safety analysis of torsional vibration in power shafts.