Vibration fault and treatment in turbine start-up process
Turbine vibration fault is often encountered in the production process of power industry, and it is also one of the difficult problems to solve. The reasons of vibration failure in turbine start-up process mainly include the following: the unbalance component is not completely eliminated in turbine manufacturing process; The weight of the mounting unit in the process of reaming and matching of the backrest wheel is unreasonable, resulting in a new unbalanced component. Shaft seal static and static impact grinding, etc.
This paper takes the No. 10 turbine unit of a power plant as an example. After the overhaul of the turbine unit, vibration failure occurred during start-up. Through the analysis of the vibration failure, it can be seen that the cause of the vibration failure was static and static friction at the shaft seal.
Vibration failure hazard in turbine start-up process
The turbine is equivalent to the heart of the human body in the production system. Once the turbine fails or has problems, it will have a direct impact on the safe operation of the entire production system. Therefore, the abnormal vibration during the start-up of the turbine cannot be underestimated. Vibration failure during turbine start-up will lead to the following hazards:
First, the turbine speed control system appears unstable swing, resulting in serious wear of the parts of the speed control system, increasing the delay rate, affecting the normal operation of the speed control system;
The rotating part is the core part of the steam turbine. Vibration failure will reduce the fatigue strength of the rotating part and directly affect the normal operation and service life of the rotating part.
Third, damage the sliding pin system, once the turbine unit has a large vibration, it will have a huge impact on the sliding pin, resulting in the turbine unit to produce uneven expansion phenomenon, forming a huge extrusion pressure, causing serious damage to the sliding pin system;
Fourth, destroy the steam seal, the diaphragm and the diaphragm between the way of sealing, once the turbine vibration failure, will destroy the steam seal, increase the leakage between the diaphragm, resulting in axial thrust of the rotor, affecting the normal operation of the turbine unit;
Fifth, the seal is not strict, and the vibration failure of the turbine unit caused by the seal is about 40% of the vibration failure rate, mainly because the vibration failure destroys the low-pressure end shaft seal, resulting in air entering the low-pressure cylinder, reducing the vacuum degree of the low-pressure cylinder, and steam entering the lubricating oil system, reducing the purity of the lubricating oil, affecting the lubrication effect and increasing wear. Shorten the service life of steam turbine units.
The process of vibration failure during turbine start-up
For example, turbine unit No. 10 of a power plant is N125-535/535 condensing, primary intermediate reheat, pressure and high temperature turbine. After the turbine unit was officially put into operation, after many years of operation, some faults occurred during the operation of the turbine, which directly affected the operation safety and efficiency of the turbine unit. The turbine unit was later overhauled, during which the turbine TSI system was installed. The vibration jump value of the rotating shaft is set to 260μm, and the jump logic is set to the "y" direction or "x" direction.
The No. 10 turbine unit of the power plant started operation after overhaul. Through the measured results, it can be seen that the axial vibration in the "y" direction at the No. 4 tile of the TSI system is 160μm, and the other axial vibration values are not more than 100μm, and there is also a small scratching sound at the No. 1 tile. With the acceleration of the speed, the tile vibration and shaft vibration of the No. 10 turbine unit are constantly increasing, through the detection, the tile vibration of the "⊥" direction of the tile at No. 2 has reached 12cmm, and the axis vibration of all the tiles in the "x" and "y" axis direction has exceeded the limit value. When the speed reaches 1500r/min, the machine is shut down, and when the speed is reduced to 1000r/min, there is a large scratching sound in the No. 1 bearing.
Vibration fault diagnosis
Based on the analysis of the vibration fault phenomena in the start-up process of steam turbine, it is preliminarily determined that the main causes of vibration fault include: static and static friction caused by improper adjustment of oil gap or shaft seal during overhaul; Because the cylinder hydrophobic is not smooth, resulting in water and shaft contact, resulting in shaft deformation; Because the temperature difference of each part is not well controlled before and during the process of punching, the temperature of the rotor exceeds the limit value and produces bending deformation; Because the rotor itself has quality problems, there is an imbalance problem in the process of operation.
During the steam turbine overhaul, No. 12 steam turbine was not changed. Therefore, due to the quality problems of the rotor itself, there is little possibility of vibration failure caused by unbalance in the process of operation. The staff consulted the operating records and found that the temperature difference of each department was not abnormal. Therefore, the possibility of vibration failure caused by bending deformation caused by the temperature of the rotor exceeding the limit value was also excluded because the temperature difference of each department was not well controlled before and during the punching process. The staff reviewed the low pressure cylinder, medium pressure cylinder and high pressure cylinder, indicating that there was no abnormality in the cylinder, and checked the deflection of the large shaft at the head. Before starting, the deflection of the large shaft was 4.5cmm, and after starting for half an hour, it became 5.0cmm, and there was scratching sound at the No. 1 tile during rotation. The vibration phenomenon with time delay occurs. It is preliminarily determined that the cause of vibration failure in turbine start-up process is static and dynamic grinding.
The "y" axial vibration at No. 3 tile appears a sudden jump, and the axial vibration value will return to the original state after each sudden jump. In the process of starting, the axial vibration and tile vibration at each tile are significantly reduced, and the decrease of tile vibration exceeds 50%, which indicates that the cause of turbine vibration failure is not the vibration failure caused by the falling off of rotating parts, nor the vibration failure caused by the mass imbalance of the rotor itself. By comparing the vibration conditions of two start-up processes, it can be confirmed that the cause of turbine start-up vibration failure is static and dynamic friction.
Vibration fault treatment measures
If vibration failure occurs during turbine start-up, it will seriously affect the safe operation of turbine. The treatment measures for vibration failure are as follows:
First, in order to prevent dynamic and static collision of shaft seals, the maintenance of shaft seals should be strengthened, and the shaft seal clearance should be adjusted during the maintenance process to prevent excessive clearance of shaft seals, otherwise it will lead to an increase in shaft seal air leakage and affect the economy of turbine unit operation. Installation, maintenance and commissioning should be carried out according to the actual condition of the turbine. Scientific setting of shaft seal clearance ensures not only the safety of turbine units, but also the economy;
Second, after the overhaul, if the turbine vibration failure occurs in the process of start-up, the static and static gap should be increased;
Third, after the overhaul of the turbine unit, the first critical speed should be rushed twice during the start-up process, which can effectively reduce the vibration processing time, if the turbine unit appears static and static friction, vibration protection should be thrown;
Fourth, in order to prevent vibration failure in the process of starting the steam turbine, sliding shaft seals should be used to replace the shaft seals at No. 2 and No. 3 tiles, so that the distance between the shaft seals can be adjusted in real time, which can effectively reduce the wear caused by the shaft seals on the main shaft and prevent more serious vibration failures.
Wuxi Houde Automation Instrument Co., Ltd. specializes in the production of large rotating machinery monitoring and protection equipment, through online monitoring, instant detection of anomalies and synchronous protection, can provide users with one-stop safety monitoring and protection solutions. If you have any technical consultation on rotating machinery vibration, speed, shaft vibration, welcome to our company to exchange and discuss! The services we will provide!
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