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Excessive axial displacement of the rotor and water hammer in the turbine: During operation of the unit, the reasons that lead to an increase in the axial displacement of the turbine rotor generally include an increase in load or steam flow rate； The flow-through section is damaged ； Severe scaling in the flow passage area ； Wear of thrust bearing pads ； Turbine water hammer ； The exhaust pressure of the turbine increases (for condensing turbines, this corresponds to a decrease in the vacuum level of the condenser) ； Rotor slippage in steam turbine generator sets ； Compressor surge in the steam turbine compression unit. Some of the more common situations and the corresponding measures to take are described as follows: Increase in load or steam flow rate: The operating conditions that cause an increase in shaft displacement vary among different units. 1. In units without extraction, when operating under overload conditions, the excessive increase in steam flow rate inevitably leads to an increase in the axial thrust on the turbine rotor. If this axial thrust exceeds the allowable limit, it is very likely to cause damage to the thrust bearings and result in excessive displacement of the rotor. To prevent such failures, when increasing the load further when the unit’s load is close to the rated power, it is necessary to monitor the temperature of the thrust bearings, the displacement of the rotor shaft, and the pressure in the wheel housing; if either of these values approaches the alarm threshold, the load should be reduced immediately. If the specific requirements of the installation necessitate the turbine to operate under overload, this can only be done for short periods of time, occasionally. If, due to changes in the operating conditions of the equipment, the turbine is unable to meet the new requirements, the correct and appropriate solution is to increase its output capacity through upgrades and modifications. 2. Steam turbine generator sets, low-frequency operation: For units connected to the grid, when the grid frequency decreases, the turbine automatically increases the opening of its control valves, which may lead to overloading. Therefore, it is necessary to monitor operation carefully when the grid frequency drops, and reduce the load if needed. 3. Decrease in steam inlet pressure and temperature, or increase in exhaust steam pressure: To maintain its original power output, the steam turbine generator set must increase the steam flow rate. Even if the unit is not overloaded, an excessive steam flow rate can lead to an increase in axial thrust ； When a turbine drives the compressor and a PI or PID regulator is used for the control system, the opening of the control valve increases automatically; as the steam flow rate rises, the axial thrust inevitably increases as well. Therefore, when the steam inlet parameters of the turbine decrease and the exhaust parameters increase, in addition to restoring the inlet and exhaust parameters to normal as soon as possible, it is necessary to limit the steam flow rate to the turbine if required. 4. In units with adjustable extraction steam, when loading is increased under conditions of \"0\" extraction steam or a low amount of extraction steam, even though both the steam inflow rate to the turbine and the unit’s power are far from reaching their rated values, the axial thrust may still exceed the allowable limit. Therefore, units with extraction steam must be operated strictly in accordance with the limitations specified by the extraction steam flow–power curve (operating chart). Wear of the internal steam seal: During the startup, operation, and shutdown of the turbine, various factors can cause a change in the relative position between the rotor and the stationary components, leading to friction against the steam seals. In particular, damage to the balance piston steam seal and the intermediate steam seal can result in an increase in axial thrust. Often, when the gas seal comes into contact, abnormal noises are generated inside the machine and vibration increases. In such cases, reduce the load first; if there is no significant improvement and the temperature of the thrust bearings exceeds the upper limit of the normal operating range, shut down the machine immediately for inspection and repair. Scaling in the flow passage: Scaling is the result of the deposition of salts and SiO2 in steam. Scaling in these areas reduces the cross-sectional area of the steam flow channels, increases the axial thrust, and thus leads to an increase in the rotor’s axial displacement. The amount of scaling increases over time as operation continues. The degree of scaling can be determined by analyzing the pressure in the wheel chamber; when necessary, the scaling can be removed through flushing (see 4-0600-). Incorrect installation of thrust pads: During installation or maintenance, when removing or installing the thrust bearings, care is not taken to pay attention to the orientation marks on the thrust pads, resulting in the correct and incorrect pads being installed in the wrong positions. The hazards arising from such mistakes become apparent during the unit’s trial operation; at a certain load level, the unit may suddenly stop operating due to excessive shaft displacement. The same situation occurs if the unit is restarted. When the machine is stopped for inspection of the bearings, it will be found that the thrust pads are damaged. Due to the incorrect installation of the tiles, the thrust tiles’ ability to withstand thrust is only about 1/3 of that when they are installed properly. As a result, even though the unit is not overloaded, the thrust bearings get damaged due to an \"overload\" condition; in this case, it are the fake positive thrust tiles that get damaged, while the real positive thrust tiles remain intact since they were installed on the secondary thrust side. When replacing the bearing tiles, it is important to ensure that there is a sufficient margin in terms of thickness for the spare tiles. The amount of additional processing required for these tiles should be determined based on the turbine’s certification document and the dimensions specified for rotor alignment during installation. All 8 tiles in a set must be processed simultaneously to maintain uniform thickness. Water impact: Water impact is one of the major accidents in steam turbines. During the operation of the unit, if the steam temperature drops suddenly, white steam will emerge from the shaft seal or water droplets will spray out ； Increase in thrust bearing temperature or increased shaft displacement ； Abnormal vibration indicates water hammer, and an immediate emergency shutdown is required. Water hammer in turbines is mostly caused by improper operation; in some cases, it results from the check valves in the extraction piping not closing properly, allowing water in the pipes to flow back into the turbine. If the boiler becomes full of water or if there is azeotropy between steam and water during operation, the steam entering the turbine will contain water. Due to the low flow velocity of these water droplets, they strike the back surface of the rotor blades, creating a braking effect that results in a significant reduction in the turbine’s output ； The water carried by the steam significantly increases the stress in the middle section of the blade, which can lead to its fracture ； The unit vibration is abnormal; simultaneously, steam containing water reduces the steam flow area, causing a sudden increase in thrust and threatening the safety of the thrust bearings. To avoid water hammer, it is essential to pay close attention to changes in steam temperature when connecting boilers, in order to prevent the steam temperature from dropping too low ； For turbines with different steam sources, special attention must be paid to drainage when switching the steam source. When operating a boiler, it is important to ensure that the steam pressure and temperature are within the specified ranges. When the turbine is started, if the steam inlet pipeline is not properly drained of water, and water accumulates in the steam pipeline causing water hammer, the pipelines and the turbine unit will experience intense vibrations accompanied by loud, dull noises; in such cases, the turbine must be stopped immediately.