Analysis On The Torsional Vibration Characteristics Of Large Steam-Turbine Unit Shaft

In china, the thermal steam turbine units are generally with unit capacity of600MW and the above as the development of the power industry. Because of the increase of the valley-to-peak and the elimination of the small thermal units, the large thermal power units have to take part in peak regulation which leads to more torsional vibration problems on shafts. This paper takes a domestic600MW supercritical unit shaft as an example, aims to calculate and analyze its torsional vibration characteristics using the lumped mass model established by the lumped parameter method. The contents and conclusions are as follows:(1) Simplify the shaft unit with the lumped mass method to obtain a discrete model and calculate the natural mode with the transfer matrix method. The first three orders of the stress distribution when resonance occurs are solved. The first resonance makes the maximum torsional stress appearing on the journal between1#and2#low pressure rotor, the second makes it on the journal between2#low pressure rotor and the generator rotor, while the third makes it between the high pressure rotor and1#low pressure rotor.(2) Conclude and study on the shaft structure of600MW steam turbine units made by the three major motor-makers in mainland. Draw the shaft structure diagram and introduce the operation characteristics of the steam turbine and the main way of peak regulation in our country.(3) Calculate the torsional vibration responses of the shafts with the method combined Riccati transfer matrix method with Newmark-β method. As a result, the maximum stress of the shaft appears on the coupling between the2#low pressure rotor and the generator rotor and the torsional fatigue expenditure is maximum when two-phase short circuit occurs at the exit of the generator which is known by local stress-strain method. (4) Calculate the torsional vibration responses of the shafts when the load rapidly changes. The time domain analysis and frequency domain analysis are carried out on the results. The torque oscillogram shows that the main frequency components include the first three order natural frequency of the shaft without the power frequency under quick load regulation.