Because the structure of the steam turbine itself is relatively complex, which makes the usual operation, maintenance and repair there are certain difficulties. Therefore, the safety, reliability and economy of steam turbine work have been paid much attention by people. The structural characteristics of the steam turbine determine that the start-up time of the steam turbine is longer. If a failure occurs during the start-up operation, the repair time is generally shorter, and the untimely maintenance or failure to complete the repair within a limited time will directly affect the economic power of the steam turbine. and service life. So Steam Turbine Repair What are the common failures? Please see the detailed introduction below!

1. Common fault types of steam turbines

Generally, in the working process of the steam turbine, most of the faults that occur will cause abnormal vibration of the unit. Through the observation of the oscillation phenomenon of the unit, the fault types of the steam turbine are summarized as follows:

(1) The four characteristics of the general forced oscillation of the unit: 1) The quality of the steam turbine is to reach a balance, and the characteristics of the fault are realized as the balance of the oscillation. 2) The stiffness of the steam turbine is reduced, and the fault is characterized by the large vibration of the joint surface, and the occurrence part is generally the floor bearing. 3) Resonance phenomenon, the fault features are: when the speed of the steam turbine is about to reach 1600r/min, the oscillation of the bearing seat will accelerate and rise. 4) The rotor of the steam turbine is not aligned, and the fault is characterized by a large sway.

(2) The abnormal forced movement of the crew. Compared with the general forcing oscillation, the phase and oscillation fluctuation of the abnormal forcing oscillation are very unstable, and the fault characteristics include: 1) The cylinder is not inflated smoothly. The characteristic of the fault is that the oscillation of the bearing seat gradually increases after the constant speed. The appearance of this phenomenon is closely related to the cylinder head difference and the expansion of the cylinder head. 2) The bolts of the coupling are loose. The fault characteristics of this problem are realized: the sloshing, oscillation and bearing load of the steam turbine are related. 3) The cracked rotor presents an unbalanced phenomenon, which leads to the frequent increase of the sway and amplitude of the cracked rotor itself. 4) The steam turbine rotor is heated and twisted. The primary reason for this phenomenon is that the temperature and oscillation of the rotor meet the normal requirements of the rotor. 5) Thermal tortuosity of the generator under the combined effect of excitation current and oscillation. 6) The center hole of the steam turbine enters the oil. This is because the rolling fluctuation of the rotor increases and the temperature rises, and the frequency of oscillation also increases, making the oil intake more and more. 7) The dynamic and static conflict between the bearing and the main shaft. After it is overhauled, it will show divergent oscillation, but this oscillation has nothing to do with the load carried by the steam turbine.

(3) Self-excited oscillation of steam turbine. Self-excited oscillation is the oscillation caused by the steam turbine itself during the motion process. The fault features are reflected in two aspects: 1) Under the high-load working condition of the steam turbine, the airflow of the high-pressure rotor is excited. 2) Because of the abnormal cylinder rise and the expansion of the cylinder head, the oil film oscillates.

2. Elimination of abnormal oscillations common in the work of steam turbine units

(1) Steam flow excitation. Steam flow excitation has two characteristics: 1) The appearance of low-frequency weights that are higher than many values. 2) The working parameters significantly affect the increase of oscillation. For example, the increase of the load is obvious and sudden, and the important reason for this phenomenon is that the uneven airflow impacts the blades, causing the steam turbine to vibrate. Especially for large-scale steam turbine units, because of the long final stage, it is likely to cause disorder of the flow passage at the end of the expansion. The existence of this problem is also an important reason for the steam-induced vibration of the steam turbine unit. In view of this special situation, there must be a corresponding method, which can readjust the high-pressure speed regulating valve under different load effects of the steam turbine, so as to achieve the purpose of eliminating steam flow excitation. To sum up, it is to first determine the characteristics and working conditions of the steam excitation, and then miraculously avoid the load scale of the steam excitation or reduce the change rate of the turbine load to prevent the steam excitation.

(2) The deformation of the rotor is one of the important reasons for the abnormal oscillation of the unit. The thermal deformation of the rotor is characterized by an increase in the one-fold amplitude, which is determined by the temperature and steam parameters of the rotor. This phenomenon often occurs after the unit starts at a constant speed in a cold state with load. During this process, the temperature of the rotor is constantly rising, and the internal stress of the raw material is released a lot, and the thermal deformation of the rotor is caused with the continuous increase of temperature, thus Increasing the one-fold frequency will accompany the phase change of the equipment. The tortuous deformation of the rotor is one of the important reasons for the abnormal oscillation of the unit. The treatment of the thermal deformation of the rotor is to check and replace the rotor in time to prevent the occurrence of oscillation force, thereby reducing the frequency of abnormal oscillation of the unit.

(3) Conflict oscillation of steam turbine. Through the analysis of the current situation of conflict oscillation, it can be seen that the thermal tortuosity and deformation of the rotor cause new unbalanced forces to occur, and the power frequency is still the main frequency of the oscillation signal, which will be affected by nonlinear factors and impact forces, forming a minority frequency division. , The appearance of high frequency weight and frequency doubling, and the phenomenon of "cut top" in the waveform also occurs from time to time. At the same time, when a conflict occurs, the phase and amplitude of the oscillation will fluctuate to a certain extent, and the fluctuation will last for a long time. When the conflict is more severe, the phase and amplitude of the oscillation stop shaking, and the amplitude continues to increase. Second, once the deceleration of the oscillation exceeds the critical value, it will be larger than the normal acceleration. After the unit is stopped, when the rotor is stopped, the sway of the large shaft is measured, and it will be found that the measured value increases significantly.

3. Abnormal rotation of steam turbine and occurrence of different causes

(1) The oscillation is abnormal. When the vibration of the steam turbine unit is abnormal and the conflicting sound of the equipment can be clearly heard, the vacuum should be forcibly damaged and the work of the unit should be stopped in time. When the load of the unit changes, and the unit makes suspicious noises accompanied by less violent oscillation, the unit load should be reduced in time until the oscillation stops. At the same time, look for the fault and analyze the cause of the oscillation. The possible causes of the failure are summarized as follows: the drop of lubricating oil pressure; the oil temperature at the bearing inlet is low or high; the expansion of the single surface of the steam turbine cylinder affected by the cold air flow; the oil temperature at the bearing outlet is high; The steam engine air temperature is too high; the temperature of the main steam has dropped to the point where the warm steam enters the steam turbine.

(2) The failure of the condenser in the steam turbine unit causes the vacuum degree to drop. When the vacuum level drops, the vacuum gauge will have a prominent indication. With the continuous rise of the exhaust gas temperature, the temperature of the condenser also rises. When dealing with this fault, the exhaust temperature and exhaust pressure should be checked first, and then the load should be adjusted reasonably until the vacuum degree returns to normal.