Research On Shaft Vibration Feature Of Large Steam Turbine Unit Under Veriated Load

With the rapid development of economy in our country, peak-valley difference of the electricity load increases gradually. In recent years, power equipment has gone through the industrial structure adjustment of developing large units and suppressing small ones aiming at the requirement for energy conservation and environmental protection. A large number of600MW or more thermal power units have been put into operation and it brings new affects for the changes of the load of grid, In this context, the capacity of power units is increasing and a lot of units with large capacity are put into operation for adjusting peak according to the demand of grid load. The key question for thermal power units participating in the peaking with wide range of load is the adaptation for rapid change of grid load and the stability for operating under low load. The power units of our country are mostly designed for carrying the middle load. This kind of units exist major security risks because there are many extreme operating conditions in peaking process and it brings new questions such as shafting structure thermal stress, deformation, shafting vibration, stability and so on. It is the key technical issue to improve the operating safety of units with large capacity under the condition of rapid changing of wide range load.The operating safety and stability for the units of large capacity that participate in the peaking is highlight in our country as the difference between our country and western countries but this aspect is lack of further study. Aiming at the particularity of thermal power units of large capacity, the6Q0MW steam power units are studied. Shafting dynamics and stability, vibration performance in fault condition and fault feature extraction methods are studied with the support of science and technology project of national and enterprise for providing reference basis for operation and fault diagnosis of units. Research results have practical implications in technology and engineering for improving the safety and reliability of units in peaking operation.The main research contents and achievement are as follows:(1) Structure and operating characteristics of600MW power units. Combined the two detailed rules, the effects of AGC operating mode for the life, materials, and shafting vibration characteristics of steam turbine are analyzed. The technical status of vibration monitoring and protection system of large capacity units (TSI system and TDM system) is summarized. Aiming at a600MW subcritical thermal power unit, the effects of the load, main steam pressure and changes of main stream flow rate for shafting vibration under AGC operating mode is analyzed with practical data. From the trend reflected of the operating data, the rapid change of load for unit has an effect on bearing vibration of high-intermediate pressure. From the transient vibration data, the changes of load have small effect on vibration signal waveform and frequency spectrum and vibration operation of the shaft of high-intermediate pressure does not change.(2) Calculation and analysis of shafting vibration characteristics. Aiming at a600MW subcritical thermal power unit, the shafting bending vibration and torsional vibration properties, shafting torsional vibration properties under rapid changes of load and two phase short circuit fault of generator are simulated and compared by using the transfer matrix method and finite element method. The results show that dangerous shaft section of600MW shafting is located at joint part between each rotor. When the load increases rapidly, shafting torsional response possesses damped oscillation property, which indicates that the shaft is in a stable state when the load increases rapidly. In the response of two phase short circuit fault, the peak value is highlighted at the first and second order natural frequency. Power frequency and second harmonics is obvious. So the fault of two phase short circuit has big effect on the shafting safety.(3) Shafting vibration analysis of steam turbine transient process. Through practical cases, the abnormal vibration phenomenon that appears on large capacity thermal power units is analyzed. Abnormal vibration response characteristics are investigated and signal feature extraction methods are studied for shafting fault diagnosis. Vibration characteristics of slow hot deformation phenomenon of a600MW unit rotor in high-intermediate pressure are researched and the cause of the rotor thermal deformation is confirmed. A method by extracting the special frequency component based on Gabor transform time-frequency filtering for shafting stability analysis and fault judgment is proposed. Through the analysis of the vibration signal in the process of speed up or speed down and the unstable signal caused by gas exciting, the effectiveness of the method is proved.(4) The research of methods of monitoring and diagnosis for steam turbine rubbing fault. When the slight rubbing fault occurs, fault information is very weak in the relative shaft vibration response signal. Aiming at this characteristic, a new fault monitoring and diagnosis method is proposed that combined structure vibration monitoring and signal processing. The information of high-frequency impact vibration energy is used in this method and is suitable for abnormal vibration of the rubbing fault that contains transient impact. As relative shaft vibration monitoring is insensitive for impact vibration response caused by rubbing, a rubbing fault detection method by using wavelet singular value is proposed. The rubbing transient impact signal at specific scales is obtained by the multi-resolution analysis of wavelet. The amplitude envelope of transient impact signal is extracted. Then wavelet singular value detection method is used for detecting the saltation information caused by rubbing fault. It improves the effect of extracting features for weak rubbing fault obviously.(5) The analysis of blind source separation for steam turbine vibration source. The signal of large subcritical pressure steam turbine power units has the characteristics of non-stationary, nonlinear. Its background noise jamming is serious. The approach of propagation process and attenuation characteristic is complex. And the signal is the superposition of many fault-source signals in an intricate way. According to the characteristics above, independent component analysis is used for noise reduction and separation of fault-source signals. A fault feature extraction method for f non-stationary and nonlinear is proposed. The separation for fault source and extraction for fault information under complex operating conditions is researched and verified by using practical steam turbine rotor system vibration signal. And the accurate fault feature information is obtained from monitored signal.