“双碳”目标下火电机组故障及应对措施综述

Summary of faults and countermeasures for thermal power units under the "dual carbon" target

前 言Preface

为实现“碳达峰、碳中和”的战略目标，我国发电行业的结构正在发生深刻的变革：一方面，大规模的风力发电、太阳能发电快速增长，江河流域大型水力发电有序推进以及核能发电积极安全有序发展，清洁能源装机和发电量占比越来越大，将成为能源供应的主力军；另一方面，火电机组积极进行转型升级，加快推进实现节能降耗改造、供热改造和灵活性改造的“三改联动”。在当前形势下，火电机组在保证高效发电的同时，还要提供采暖供热和工业抽汽以及深度调峰、灵活性运行，以满足节能降耗和消纳风电、光伏等新能源的要求。

In order to achieve the strategic goal of "carbon peaking and carbon neutrality", the structure of China's power generation industry is undergoing profound changes. On the one hand, large-scale wind and solar power generation is rapidly growing, large-scale hydropower generation in river basins is advancing in an orderly manner, and nuclear power generation is actively and safely developing in an orderly manner. The proportion of clean energy installations and power generation is increasing, and it will become the main force of energy supply; On the other hand, thermal power units are actively undergoing transformation and upgrading, accelerating the implementation of the "three transformations linkage" of energy-saving and consumption reduction transformation, heating transformation, and flexibility transformation. In the current situation, while ensuring efficient power generation, thermal power units also need to provide heating, industrial steam extraction, deep peak shaving, and flexible operation to meet the requirements of energy conservation, consumption reduction, and absorption of new energy such as wind power and photovoltaic.

然而，随着火电机组节能降耗各项措施的实施，大流量供热和工业抽汽改造以及快速启停、深度调峰、灵活性运行，使得部分设备运行偏离了原设计工况。远距离输电采用交流串补、特高压直流输电等技术，使机组轴系承受更大的交变扭应力作用。这些都造成了电站主辅机设备安全可靠性下降，故障频次增多，故障严重程度增大。近些年来，发生了一些重大故障或事故，如大修后启机和运行中振动大、转子裂纹和断裂、汽轮机低压转子末几级叶片裂纹、断裂和腐蚀、汽轮机进汽阀门卡涩和振动、发电机转子热弯曲及绝缘失效等。这些故障对火电机组长周期安全、稳定运行带来极大地挑战，不仅使设备检修维护成本增加，还造成重大经济损失和恶劣的社会影响。因此，需要加强安全故障机理的研究，从设计制造、运行优化、在线监测和检修模式等方面提出防止故障或事故发生的措施，以保证当前形势下火电机组安全稳定运行。

However, with the implementation of various energy-saving and consumption reduction measures for thermal power units, the renovation of large flow heating and industrial steam extraction, as well as rapid start stop, deep peak shaving, and flexible operation, some equipment has deviated from the original design conditions. Long distance transmission adopts technologies such as AC series compensation and ultra-high voltage direct current transmission, allowing the unit shaft system to withstand greater alternating torsional stress. All of these have led to a decrease in the safety and reliability of the main and auxiliary equipment in the power station, an increase in the frequency of faults, and an increase in the severity of faults. In recent years, some major faults or accidents have occurred, such as high vibration during start-up and operation after major repairs, rotor cracks and fractures, cracks and corrosion in the last few stages of the low-pressure rotor blades of the steam turbine, jamming and vibration of the steam turbine inlet valve, thermal bending and insulation failure of the generator rotor, etc. These faults pose great challenges to the long-term safe and stable operation of thermal motors, not only increasing equipment maintenance costs, but also causing significant economic losses and adverse social impacts. Therefore, it is necessary to strengthen the research on the mechanism of safety faults, and propose measures to prevent faults or accidents from occurring in aspects such as design and manufacturing, operation optimization, online monitoring, and maintenance mode, in order to ensure the safe and stable operation of thermal power units under the current situation.

针对当前火电机组运行中出现的各种安全问题，一些学者进行了相关研究：文献[5]对大型汽轮机末级长叶片的冲蚀损伤机理进行了研究；文献[6]介绍了某330 MW机组切缸改造后，低压缸发生瞬时水冲击造成的振动保护动作事故；文献[7]结合实际运行情况，分析了机组深度调峰对汽轮机运行、汽轮机本体及其辅助设备寿命的影响，总结了普遍存在的问题；文献[8]通过调研分析了启停调峰及深度调峰对机组锅炉、汽轮机、环保及电气设备安全性的影响；文献[9-10]介绍了某300 MW机组高中压转子裂纹故障的诊断过程，指出深度调峰及灵活性运行诱发或加剧了该故障的产生；文献[11-12]研究了泵和风机变频改造后出现的弯曲和扭转振动问题，并提出了预防和处理建议；文献[13]分析了机组深度调峰时风机低负荷因流量过小、压力过大进入失速运行区，导致风机出现失速、喘振等情况，并给出风机改造和加装监测系统的预防技术措施。

In response to various safety issues that arise during the operation of thermal power units, some scholars have conducted relevant research: literature [5] has studied the erosion damage mechanism of the last stage long blades of large steam turbines; Reference [6] introduces the vibration protection action accident caused by instantaneous water impact on the low-pressure cylinder of a 330 MW unit after cylinder cutting renovation; Reference [7] analyzed the impact of deep peak shaving on the operation of steam turbines, as well as the lifespan of the turbine body and its auxiliary equipment, based on actual operating conditions, and summarized the common problems; Literature [8] conducted research and analysis on the impact of start stop peak shaving and deep peak shaving on the safety of unit boilers, steam turbines, environmental protection, and electrical equipment; Reference [9-10] introduces the diagnostic process of a crack fault in the high and medium pressure rotor of a 300 MW unit, and points out that deep peak shaving and flexible operation have induced or exacerbated the occurrence of this fault; References [11-12] studied the bending and torsional vibration problems that occurred after the frequency conversion transformation of pumps and fans, and proposed prevention and treatment suggestions; Reference [13] analyzed the low load of the fan during deep peak shaving of the unit, which entered the stall operation zone due to low flow rate and high pressure, resulting in stall and surge of the fan, and provided preventive technical measures for fan modification and installation of monitoring systems.

以上研究都是针对某一具体的安全问题进行分析，或没有全面阐述各种故障机理和防范措施。因此，本文将基于现场案例和经验，系统归纳总结当前形势下机组运行中主辅机设备存在的轴系振动、转子裂纹和转动部件脱落、汽轮机长叶片振动和腐蚀、进汽阀门卡涩和振动等典型故障的机理和特征，并给出相应的应对措施。

The above studies are all focused on analyzing a specific safety issue, or do not comprehensively elaborate on various fault mechanisms and preventive measures. Therefore, based on on-site cases and experience, this article will systematically summarize the mechanisms and characteristics of typical faults such as shaft vibration, rotor cracks and detachment of rotating components, vibration and corrosion of long blades of steam turbines, and jamming and vibration of inlet valves that exist in the operation of main and auxiliary equipment under the current situation, and provide corresponding response measures.

1 主辅机轴系振动Main and auxiliary machine shaft system vibration

1.1 故障机理和特征Fault mechanism and characteristics

1.1.1 主机Master

除采用超临界、超超临界及二次再热技术提高汽轮机热效率外，为防止漏汽量增大，进一步降低汽轮机热耗率，当前汽轮机安装时尽量减小汽封间隙，一般按下限或下限减0.1 mm实施。这就增大了启动和运行中发生动静碰摩的概率，摩擦振动往往造成振动超限，需花费一定时间在控制振动的前提下进行“磨和”处理，新建或检修后机组投运时发生动静碰摩已是常态化。此外，一些汽轮机高（中）压转子采用刷式汽封，由于其钴基合金材质很硬，具有“顽固”的耐磨性，造成许多机组启动“磨合”过程时间长，影响投运工期。如某650 MW机组汽轮机通流改造后（采用多道刷式汽封）启动19次，经历11天才定速3 000 r/min。

In addition to using supercritical, ultra supercritical, and secondary reheat technologies to improve the thermal efficiency of the steam turbine, in order to prevent increased steam leakage and further reduce the heat consumption rate of the steam turbine, the current installation of the steam turbine is to minimize the gap between the steam seals as much as possible, generally implemented by reducing the lower or lower limit by 0.1 mm. This increases the probability of dynamic and static rubbing during startup and operation. Friction vibration often causes vibration to exceed the limit, and it takes some time to "grind" under the premise of controlling vibration. It is normal for dynamic and static rubbing to occur when the unit is put into operation after new construction or maintenance. In addition, some high (medium) pressure rotors of steam turbines use brush type steam seals. Due to the hard cobalt based alloy material and its "stubborn" wear resistance, many units have a long "running in" process during startup, which affects the operation period. For example, after the modification of the flow passage of a 650 MW unit's steam turbine (using multiple brush seals), it started 19 times and experienced 11 days of constant speed of 3000 r/min.

大型汽轮机低压缸体积庞大，设计刚度较差。许多汽轮机低压缸采用座缸式轴承结构，低压缸轴承座与低压缸整体焊接。部分机组在低负荷或供热工况运行时，高真空会引起低压缸发生形变，造成低压轴承座动刚度下降，产生结构共振，瓦振超标。一些机组因低压缸形变量和轴承标高变化过大致使转子与汽封间隙消失，发生动静碰摩，引发低压转子振动爬升、超限。

The low-pressure cylinder of a large steam turbine has a large volume and poor design stiffness. Many steam turbine low-pressure cylinders adopt a seat cylinder bearing structure, and the low-pressure cylinder bearing seat is welded to the low-pressure cylinder as a whole. When some units operate under low load or heating conditions, high vacuum can cause deformation of the low-pressure cylinder, resulting in a decrease in the dynamic stiffness of the low-pressure bearing seat, structural resonance, and excessive bearing vibration. Some units experience significant changes in the shape of the low-pressure cylinder and the elevation of the bearings, resulting in the disappearance of the gap between the rotor and the steam seal, resulting in dynamic and static friction, causing the low-pressure rotor to vibrate and climb, exceeding the limit.

在机组快速启停或深度调峰过程中，由于汽轮机轴封供汽的汽源频繁切换，使得轴封处温度剧烈波动，容易引发转子或轴封片变形，导致动静间隙消失，产生动静碰摩、振动爬升。

During the rapid start/stop or deep peak shaving process of the unit, due to frequent switching of the steam source for the steam supply to the turbine shaft seal, the temperature at the shaft seal fluctuates sharply, which can easily cause deformation of the rotor or shaft seal, leading to the disappearance of dynamic and static clearances, resulting in dynamic and static friction and vibration climbing.

低压缸零出力汽轮机运行中发生甩负荷后负向轴向推力明显增大，可能引起推力瓦温超限，造成推力瓦块烧损。如某300 MW机组低压缸零出力供热运行时，因锅炉故障汽轮机甩负荷，停机过程推力瓦非工作面某处温度最高升至128 ℃，检查后发现推力瓦乌金面受损。

After load rejection occurs during the operation of the low-pressure cylinder zero output steam turbine, the negative axial thrust significantly increases, which may cause the thrust pad temperature to exceed the limit and cause the thrust pad to burn out. For example, during the zero output heating operation of a 300 MW unit's low-pressure cylinder, due to a boiler malfunction and turbine load rejection, the temperature at a non working surface of the thrust pad reached a maximum of 128 ℃ during the shutdown process. After inspection, it was found that the gold surface of the thrust pad was damaged.

为减小机组部分负荷下汽轮机热效率的下降程度，通常电厂对喷嘴调节汽轮机进行高压调节阀节能优化。但部分机组调节阀优化结果使得在有些运行工况，转子在汽缸中处于不利位置，造成高（中）压转子发生汽流激振或轴承失稳故障，引发振动激增，甚至振动保护动作，出现“非停”。

In order to reduce the decrease in thermal efficiency of steam turbines under partial load of the unit, power plants usually optimize the energy-saving of high-pressure regulating valves for nozzle regulating steam turbines. However, the optimization results of some unit control valves have resulted in the rotor being in an unfavorable position in the cylinder under certain operating conditions, causing steam flow excitation or bearing instability faults in the high (medium) pressure rotor, leading to a surge in vibration and even vibration protection actions, resulting in "non stop".

近年来，随着机组调峰幅度和调峰频次的增 加，加速了发电机转子线圈热胀冷缩效应，交变应力显著增加，加剧了线圈底下滑移层材料的老化和损坏，致使大型发电机转子线圈轴向膨胀受阻故障案例明显增多，造成大负荷工况发电机转子出现明显热弯曲和振动。同时，发电机转子绕组频繁膨胀收缩，产生的挤压变形也加大了其转子匝间绝缘的跑位、磨损，甚至引起绝缘失效，最终造成短路故障。如某1 000 MW机组发电机投运仅半年，由于频繁调峰运行，发电机振动随励磁电流增大现象越来越明显，热态下转子振动超过260 μm。后返制造厂解体检查发现部分垫条滑移层有明显磨损、发黑的情况，对应位置的线圈表面有滑移层残留。

In recent years, with the increase in the amplitude and frequency of unit peak shaving, the thermal expansion and contraction effect of the generator rotor coil has been accelerated, and the alternating stress has significantly increased, exacerbating the aging and damage of the sliding layer material under the coil. This has led to a significant increase in cases of axial expansion failure of large generator rotor coils, resulting in significant thermal bending and vibration of the generator rotor under high load conditions. At the same time, the frequent expansion and contraction of the generator rotor winding, resulting in compression deformation, also increases the displacement and wear of the rotor inter turn insulation, and even causes insulation failure, ultimately leading to short circuit faults. If the generator of a 1000 MW unit has only been put into operation for half a year, due to frequent peak shaving operation, the phenomenon of generator vibration increasing with the excitation current is becoming more and more obvious, and the rotor vibration exceeds 260 under hot state μ M. After returning to the manufacturing factory for disassembly and inspection, it was found that some of the sliding layers of the cushion strips had obvious wear and blackening, and there were residual sliding layers on the surface of the corresponding coils.

1.1.2 辅机Auxiliary equipment

风机、水泵等辅机设备实施高压变频改造、变频运行是当前采取重要节能措施之一。然而，一些大容量风机和水泵变频调速运行中出现振动、轴系裂纹故障或断裂事故。水泵组在变频工况运行时，可能在某一个或多个转速下，由于与支承部件固有频率重合而产生结构共振现象，造成振动超标，限制了机组出力。如某超超临界1 000 MW机组5B立式凝结水泵变频运行中，在40 Hz（1 189 r/min）时位于上部的电机水平振动高达713 μm。

The implementation of high-voltage frequency conversion transformation and frequency conversion operation for auxiliary equipment such as fans and water pumps is currently one of the important energy-saving measures taken. However, some large capacity fans and water pumps experience vibration, shaft system crack failure, or fracture accidents during variable frequency speed control operation. When the water pump unit operates under variable frequency conditions, structural resonance may occur due to the overlap with the natural frequency of the supporting components at one or more speeds, resulting in excessive vibration and limiting the output of the unit. For example, during the variable frequency operation of the 5B vertical condensate pump of a certain ultra supercritical 1000 MW unit, the horizontal vibration of the motor located at the upper part reaches 713 at 40 Hz (1189 r/min) μm.

如果变频器驱动的电动机输出的电磁转矩中含有与风机组或水泵组轴系某阶扭转固有频率相同的谐波分量，会致使产生轴系扭转共振，最终造成轴系裂纹或断裂。如某600 MW机组锅炉5A引风机变频改造后，试验过程中发生了电动机驱动端轴断裂事故。

If the electromagnetic torque output by the motor driven by the frequency converter contains harmonic components that are the same as the natural frequency of a certain order of torsional vibration of the wind turbine or water pump shaft system, it will cause torsional resonance of the shaft system, ultimately leading to shaft cracks or fractures. For example, after the frequency conversion transformation of the 5A induced draft fan of a 600 MW unit boiler, a motor drive end shaft fracture accident occurred during the testing process.

辅助设备频繁启停，也会对设备的可靠性、稳定性产生一定影响。锅炉风机在低负荷下运行，流量与系统阻力与风机特性不匹配，导致风机偏离设计工况进入失速区，破坏叶轮内部流场，产生额外气动负荷，造成风机失速和喘振，严重时可能诱发叶片高应力点处的疲劳、断裂问题。

Frequent startup and shutdown of auxiliary equipment can also have a certain impact on the reliability and stability of the equipment. The boiler fan operates at low load, and the flow rate and system resistance do not match the characteristics of the fan, causing the fan to deviate from the design conditions and enter the stall zone, damaging the internal flow field of the impeller, generating additional aerodynamic loads, causing the fan to stall and surge. In severe cases, it may induce fatigue and fracture problems at high stress points on the blades.

1.2 防范措施Preventive Measures

针对灵活性运行和大流量供热机组，应考虑变负荷工况转子和汽缸温度场分布不同引起热膨胀的变化，合理的调整汽轮机通流部分径向间隙，防止启机和运行中汽轮机长时间的动静碰摩。为防止低压缸零出力运行时汽轮机在甩负荷等工况因大的负方向轴向推力可能引发推力轴承瓦温超限、通流部分轴向碰摩，也需合理调整通流部分轴向间隙和推力轴承间隙。

For flexible operation and large flow heating units, it is necessary to consider the changes in thermal expansion caused by different temperature distribution of the rotor and cylinder under variable load conditions, and adjust the radial clearance of the flow passage of the steam turbine reasonably to prevent long-term dynamic and static friction of the steam turbine during start-up and operation. To prevent the turbine from exceeding the temperature limit of the thrust bearing pad and causing axial friction in the flow passage during load shedding and other operating conditions when the low-pressure cylinder is operating at zero output, it is also necessary to adjust the axial clearance of the flow passage and the thrust bearing clearance reasonably.

对于低压缸轴承结构振动和低压转子动静碰摩问题，可在低压缸增加辅助支撑或筋板，提高汽缸局部的刚度，同时在机组冲转及低负荷运行时控制凝汽器真空度。这样可减小低压缸变形，避免或缓解低压转子动静碰摩和轴承座结构振动。

For the vibration of the low-pressure cylinder bearing structure and the problem of static and dynamic friction of the low-pressure rotor, auxiliary support or rib plates can be added to the low-pressure cylinder to improve the local stiffness of the cylinder. At the same time, the vacuum degree of the condenser can be controlled during impulse starting and low load operation of the unit. This can reduce the deformation of the low-pressure cylinder, avoid or alleviate the dynamic and static friction of the low-pressure rotor and the vibration of the bearing seat structure.

对于为提高经济性实施了高压调节阀阀序优化、但部分负荷出现不稳定振动问题的机组，必要时需要牺牲一定的经济性，而采取对保持汽轮机振动状态良好的阀序和开度方式运行。

For units that have implemented high-pressure control valve sequence optimization to improve economic efficiency, but have unstable vibration problems under some loads, it is necessary to sacrifice certain economic efficiency and adopt valve sequence and opening mode operation to maintain good vibration status of the steam turbine.

对于立式泵组变频运行中某一转速下结构共振问题，现场一般采取减小激振力和调频隔振2种治理措施。除控制安装质量外，减小激振力常用措施就是精细动平衡试验。只要激振力足够小，也可以把振动控制在合格范围内。如果立式泵组2个方向刚度差异较大，使得其在工作转速范围内，存在2个共振峰值，那么在有限的现场加重平面上，有时很难同时把轴系2个固有频率下振动降至满意水平，只能避开某个转速区域运行。调频隔振就是改变结构固有频率，避开共振峰值，或增加系统阻尼，降低共振峰值。现场一般采取的方法是在泵组结构适当位置增加额外支撑进行加固。然而，对于已运行立式泵组的狭窄空间，有时寻找合适的支撑能够“生根”的位置较为困难，仅在泵体支座外焊接加强筋进行加固，效果可能有限。为保险起见，在实施具体的支撑加固方案前，最好先进行结构动力学计算分析，评估方案实施后的效果，确保方案能够明显增大结构刚度或改变固有频率。采用隔振垫等隔振阻尼器也是减缓结构振动的一种手段，选择合适的隔振垫能达到较好的隔振和减振效果。

For the structural resonance problem of vertical pump sets during variable frequency operation at a certain speed, two measures are generally taken on site: reducing excitation force and frequency modulation vibration isolation. In addition to controlling installation quality, a common measure to reduce excitation force is fine dynamic balance testing. As long as the excitation force is small enough, the vibration can also be controlled within a qualified range. If there is a significant difference in stiffness between the two directions of a vertical pump set, resulting in two resonance peaks within the operating speed range, it is sometimes difficult to reduce the vibration of the shaft system at both natural frequencies to a satisfactory level on a limited on-site weighting plane, and only to avoid operating in a certain speed range. Frequency modulation vibration isolation refers to changing the natural frequency of a structure, avoiding resonance peaks, or increasing system damping to reduce resonance peaks. The general method adopted on site is to add additional support at appropriate positions of the pump unit structure for reinforcement. However, for narrow spaces where vertical pump units have already been operated, it is sometimes difficult to find suitable support positions that can "take root". Only welding reinforcement bars outside the pump body support for reinforcement may have limited effectiveness. For safety reasons, it is best to conduct structural dynamic calculation and analysis before implementing a specific support and reinforcement plan, evaluate the effectiveness of the plan after implementation, and ensure that the plan can significantly increase the structural stiffness or change the natural frequency. The use of isolation pads and other vibration dampers is also a means of mitigating structural vibration. Choosing appropriate isolation pads can achieve good isolation and vibration reduction effects.

抑制变频运行风机组和泵组轴系产生扭转共振及其破坏的措施应从机械和电气两方面入手。机械方面要设计优化轴系结构，改变扭转固有频率，增加部件强度和阻尼，避免产生扭转共振。电气方面是要减小引发轴系扭振的激振源，即通过优化变频器与感应电机特性以及控制方法，尽量避免电动机电磁力矩中所含扭转固有频率的谐波成分，或减小其幅值。

The measures to suppress the torsional resonance and damage of the variable frequency operating fan and pump shaft system should start from both mechanical and electrical aspects. In terms of mechanical design, it is necessary to optimize the shaft structure, change the torsional natural frequency, increase component strength and damping, and avoid torsional resonance. In terms of electrical aspects, it is necessary to reduce the excitation sources that cause torsional vibration of the shaft system, that is, by optimizing the characteristics and control methods of the frequency converter and induction motor, to try to avoid the harmonic components of the torsional natural frequency contained in the electromagnetic torque of the motor, or to reduce its amplitude.

对于低负荷工况风机流量与系统阻力不匹配、不稳定振动问题，可进行烟风道整流、风机本体改造、优化风机沿程各系统等技术改造，同时加装风机在线监测系统，实时监测风机运行工作点及风机效率，指导风机运行，及时防止风机进入不稳定区。

For the problem of mismatched flow rate and system resistance, unstable vibration of the fan under low load conditions, technical modifications can be carried out such as rectification of the flue and air duct, modification of the fan body, and optimization of various systems along the fan path. At the same time, an online fan monitoring system can be installed to monitor the operating points and efficiency of the fan in real-time, guide the fan operation, and timely prevent the fan from entering unstable areas.

为防止灵活性运行中发电机转子线圈端部滑移受阻及匝间绝缘易失效问题，可对发电机局部结构进行升级，如升级绝缘瓦、楔下垫条、滑移层材料，进一步提高端部整体滑移顺畅性；采用多层瓦结构的转子护环绝缘瓦，提高其绝缘和适形性。

To prevent the end slip of the generator rotor coil from being obstructed and the inter turn insulation from easily failing during flexible operation, the local structure of the generator can be upgraded, such as upgrading insulation pads, wedges, and sliding layer materials, to further improve the overall smoothness of end slip; The rotor protective ring insulation tile adopts a multi-layer tile structure to improve its insulation and conformability.

2 转子裂纹和转动部件脱落Cracks in the rotor and detachment of rotating parts

2.1 故障机理和特征Fault mechanism and characteristics

2.1.1 转子严重裂纹Severe cracks in the rotor

机组频繁启停和深度调峰运行方式下，汽轮机转子表面承受较大的交变热应力。机组启动和加负荷时，转子表面承受热压应力，内部承受热拉应力，而减负荷和停机时转子表面和内部承受热应力的状况则相反，这种交变热应力载荷使转子发生热疲劳。转子缺陷处或孔、槽、角等应力集中较大的部位，在交变热应力及工作环境腐蚀性因素的作用下，促使转子裂纹萌生及发展。随着裂纹扩展，转轴上承受循环载荷的截面越来越小，而承受的局部应力越来越大。当局部应力超过转轴材料的强度，则剩余截面发生脆性断裂，最终导致转轴灾难性破坏。图1是某300 MW机组长期深度调峰运行后在汽轮机高中压转子调节级后应力释放槽处裂纹。覆盖超过3/4周长、最大深度超过194 mm的横向裂纹，该转子最终报废。

Under the frequent start stop and deep peak shaving operation mode of the unit, the surface of the turbine rotor bears significant alternating thermal stress. When the unit is started and loaded, the surface of the rotor is subjected to thermal compressive stress, while the internal is subjected to thermal tensile stress. However, during load reduction and shutdown, the surface and internal of the rotor are subjected to thermal stress in the opposite situation. This alternating thermal stress load causes thermal fatigue of the rotor. Under the action of alternating thermal stress and corrosive factors in the working environment, the rotor defects or areas with high stress concentration such as holes, grooves, and corners promote the initiation and development of rotor cracks. As the crack expands, the cross-section on the shaft that bears cyclic load becomes smaller and the local stress it bears becomes larger. When the local stress exceeds the strength of the shaft material, brittle fracture occurs in the remaining section, ultimately leading to catastrophic failure of the shaft. Figure 1 shows a crack in the stress relief groove of a 300 MW unit after long-term deep peak shaving operation at the regulating stage of the high and medium pressure rotor of the steam turbine. Covering transverse cracks exceeding 3/4 of the circumference and with a maximum depth exceeding 194 mm, the rotor was ultimately scrapped.

图1 某300 MW汽轮机高中压转子应力释放槽处裂纹

Figure 1 Cracks at the Stress Release Slot of the High and Medium Pressure Rotors of a 300 MW Steam Turbine

为提高大型电源点向电力负荷中心长距离输电的能力，常在交流输电中采用串联电容补偿和特高压直流输电技术，可能会引发机网耦合作用下的汽轮发电机组轴系扭振故障，如次同步谐振和次同步振荡。前者产生很大的交变剪切应力使转子出现低周疲劳，会在极短时间内造成转轴出现严重裂纹，甚至断裂；后者产生较小交变剪应力使转子出现高周疲劳，一段时间后造成转轴产生裂纹。图2是扭振作用下某600 MW机组发电机转子汽端联轴器裂纹示意，该机组仅投运约半年即产生裂纹。

In order to improve the ability of large-scale power points to transmit power over long distances to the power load center, series capacitor compensation and ultra-high voltage direct current transmission technology are often used in AC transmission, which may cause torsional vibration faults of the steam turbine generator unit shaft system under the coupling effect of the generator network, such as sub synchronous resonance and sub synchronous oscillation. The former generates significant alternating shear stress, leading to low cycle fatigue of the rotor, which can cause serious cracks or even fracture of the shaft in a very short period of time; The latter generates relatively small alternating shear stress, which leads to high cycle fatigue of the rotor and, after a period of time, causes cracks in the shaft. Figure 2 is a schematic diagram of cracks in the rotor end coupling of a 600 MW unit generator under torsional vibration. The unit only started operating for about half a year before cracking occurred.

2.1.2 转动部件脱落Rotating parts falling off

机组频繁启停、深度调峰运行不但使转轴本身承受较大的交变热应力，同时也使转轴上的汽轮机叶轮、末级长叶片和发电机护环等大质量转动部件出现明显的交变热应力。如果这些部件存在划痕、毛刺、尖角等加工质量缺陷，则在长期运行中承受的交变应力作用下会产生疲劳裂纹，并且高温状态下的部件容易出现蠕变损伤。不利的环境因素，如含盐水质、汽轮机末级湿蒸汽、水击、发电机漏氢等，都会加速应力集中部位裂纹的扩展。裂纹扩展发展到最后阶段，部件则产生断裂、脱落。与汽轮机动叶叶冠、围带、拉筋以及施加的动平衡块等脱落不同，当发生汽轮机叶轮或整根末级长叶片、发电机护环或风扇环等非转轴大质量转动部件断裂时，会造成数十千克甚至上吨质量的严重失衡，产生剧烈的不平衡振动，转子振动幅值可能高达数毫米或数十毫米，不仅造成振动超限停机，而且导致动静部件严重碰摩、固定结构连接螺栓松动或断裂、润滑油泄漏、发电机氢气泄漏或氢爆、发电机电气故障、现场着火、设备损毁等重大事故，造成巨大的经济损失。

The frequent start-up and shutdown of the unit, as well as the deep peak shaving operation, not only causes the shaft itself to bear significant alternating thermal stress, but also causes significant alternating thermal stress on the large rotating components such as the turbine impeller, last stage long blades, and generator retaining ring on the shaft. If these components have machining quality defects such as scratches, burrs, sharp corners, etc., fatigue cracks will occur under the alternating stress during long-term operation, and components under high temperature conditions are prone to creep damage. Adverse environmental factors, such as saline water quality, wet steam in the final stage of the steam turbine, water hammer, and hydrogen leakage from the generator, can accelerate the propagation of cracks in stress concentration areas. When the crack propagates and develops to the final stage, the component undergoes fracture and detachment. Unlike the shedding of turbine blade crowns, shrouds, tie bars, and applied dynamic balancing blocks, when non rotating components such as the turbine impeller or the entire last stage long blade, generator guard ring, or fan ring break, it can cause severe imbalance of tens of kilograms or even tons of weight, resulting in severe unbalanced vibration. The amplitude of rotor vibration may reach several millimeters or tens of millimeters, not only causing vibration exceeding the limit and shutdown, Moreover, it leads to serious collisions between dynamic and static components, loose or broken connecting bolts of fixed structures, lubricating oil leakage, hydrogen leakage or explosion of generators, electrical faults of generators, on-site fires, equipment damage, and other major accidents, resulting in huge economic losses.

图2 某600 MW机组发电机转子汽端联轴器裂纹

Figure 2 Cracks in the Steam End Coupling of a 600 MW Unit Generator Rotor

2015年3月13日某热电厂1台165 MW机组运行中发生严重的氢爆、着火、轴系破坏事故。其原因是汽轮机低压转子第20级叶轮1/2部分及其动叶突然断裂、飞脱。汽轮机低压转子第20级1/2部分叶轮及叶片断裂和事故破坏现场如图3所示。

On March 13, 2015, a serious hydrogen explosion, fire, and shaft system damage accident occurred during the operation of a 165 MW unit in a thermal power plant. The reason is that the 1/2 part of the 20th stage impeller of the low-pressure rotor of the steam turbine and its moving blades suddenly broke and flew off. The fracture and accident damage site of the 20th stage 1/2 impeller and blades of the low-pressure rotor of the steam turbine is shown in Figure 3.

a) 叶轮impeller

b) 事故现场Accident scene

图3 低压转子第20级叶轮和叶片断裂及事故现场

Figure 3: Rupture of the 20th stage impeller and blade of the low-pressure rotor and accident site

2021年3月12日某320 MW机组运行中发生严重氢爆、着火、轴系破坏事故，其原因由发电机励端护环突然开裂、脱落所致。开裂的发电机励端护环和事故现场如图4所示。

On March 12, 2021, a serious hydrogen explosion, fire, and shaft system damage accident occurred during the operation of a 320 MW unit. The cause was sudden cracking and detachment of the generator excitation end protective ring. The cracked generator excitation end guard ring and accident site are shown in Figure 4.

a) 励端护环Exciting end guard ring

b) 事故现场Accident scene

图4 开裂的发电机励端护环和事故现场

Figure 4 Cracked generator excitation end guard ring and accident site

2.2 防范措施Preventive Measures

长期服役和频繁启停以及深度调峰机组，汽轮机转子经常承受剧烈的温度变化和交变热应力，致使其寿命损耗过快，影响机组整体使用寿命。因此 应开展汽轮机转子热应力的数值计算分析研究，探究循环应力对转子疲劳寿命损耗的影响，开发并安装汽轮机转子寿命损耗在线监测系统。

Long term service, frequent startup and shutdown, and deep peak shaving units often result in severe temperature changes and alternating thermal stress on the turbine rotor, resulting in rapid life loss and affecting the overall service life of the unit. Therefore, numerical calculation and analysis of thermal stress in steam turbine rotors should be carried out to explore the impact of cyclic stress on rotor fatigue life loss, and an online monitoring system for steam turbine rotor life loss should be developed and installed.

对于交流输电采用串补装置和特高压直流输电等受机网耦合扭振潜在威胁的大型汽轮发电机组，应加装扭振监测保护装置（TSR）和扭振在线监测分析系统（TVMS），以连续测量各种机电扰动下轴系扭振响应，估算对应的扭转疲劳寿命损耗，并保护机组轴系安全。

For large steam turbine generator units that use series compensation devices for AC transmission and ultra-high voltage direct current transmission, which are potentially threatened by coupled torsional vibration of the power grid, torsional vibration monitoring and protection devices (TSR) and torsional vibration online monitoring and analysis systems (TVMS) should be installed to continuously measure the torsional vibration response of the shaft system under various mechanical and electrical disturbances, estimate the corresponding torsional fatigue life loss, and protect the safety of the unit shaft system.

由于转子较深裂纹对其振动特性有明显的影响，而且大多在役机组普遍安装有振动在线监测和分析（TDM）系统，以及先进的离线振动测量分析仪表的广泛使用，可以通过转子的异常振动分析来识别和判断转子裂纹故障。经验表明，虽然振动分析方法可以诊断出转子存在的裂纹，但当出现明显的振动异常时，通常转子裂纹已经扩展到相当深的程度，且无法通过机械加工手段处理裂纹转子，可能造成价值数千万元的转子报废。尽管如此，转子裂纹故障的准确识别、及时停机检查可以避免机组继续运行存在的转轴断裂风险。

Due to the significant impact of deep cracks on the vibration characteristics of the rotor, and the widespread installation of vibration online monitoring and analysis (TDM) systems in most in-service units, as well as the widespread use of advanced offline vibration measurement and analysis instruments, rotor crack faults can be identified and judged through abnormal vibration analysis of the rotor. Experience has shown that although vibration analysis methods can diagnose cracks in the rotor, when obvious vibration abnormalities occur, the rotor cracks usually extend to a considerable depth and cannot be processed through mechanical processing, which may result in the scrapping of rotors worth tens of millions of yuan. Nevertheless, accurate identification of rotor crack faults and timely shutdown for inspection can avoid the risk of shaft fracture that exists when the unit continues to operate.

与转轴裂纹不同，当汽轮机动叶、叶轮以及发电机护环和风扇环出现一定裂纹时，轴系的平衡状态和转子刚度基本没有变化，在线监测的振动数值也就几乎没有反映，因而不会引起运行人员的关注。只有当这些部件裂纹发展到相当深的程度，裂纹出现明显的张口或部件出现明显的变形，这时轴系的平衡状态才会发生明显的变化，导致产生相应的振动响应。由于部件裂纹的扩展呈非线性特征，最后阶段发展速度极快，通常当轴系振动有明显变化时，这些部件的裂纹可能已经发展到即将断裂的时刻，事故将会瞬间发生。因此，部件断裂脱落前往往没有故障征兆，振动状态也多为正常，导致机组运行中无法提前预警或故障诊断，运行人员无法进行应急操作。

Unlike shaft cracks, when certain cracks appear on the turbine blades, impellers, generator retaining rings, and fan rings, the balance state of the shaft system and rotor stiffness remain basically unchanged, and the vibration values monitored online are hardly reflected, thus not causing concern to the operating personnel. Only when the cracks in these components develop to a considerable depth, with obvious opening or deformation of the components, can the equilibrium state of the shaft system undergo significant changes, leading to corresponding vibration responses. Due to the nonlinear characteristics of crack propagation in components, the final stage of development is extremely fast. Usually, when there is a significant change in the vibration of the shaft system, the cracks in these components may have developed to the point where they are about to fracture, and accidents will occur instantly. Therefore, there are often no signs of failure before the components break and fall off, and the vibration state is mostly normal, resulting in the inability to provide early warning or fault diagnosis during unit operation, and the inability of operators to carry out emergency operations.

机组停机检修中对部件金属探伤检测是发现裂纹的重要手段，但有时可能无法及时检测出已出现的裂纹。究其原因，一方面是金属技术监督文件中并非规定每一部件任何位置都需要进行定期探伤检测，这就可能造成存在裂纹的部件或位置出现漏检；另一方面是有些情况下部件裂纹发展很快，还未等到机组停机检修，裂纹已发展到即将断裂、严重影响机组安全运行的危险程度。尤其是当前发电企业广泛开展设备状态检修，尽管其对于提高检修效率、减小检修费用发挥重要作用，但有时延长检修周期会增加部件裂纹扩展甚至断裂的风险。因此，应根据不同机组设计的结构特点、运行方式、服役年限、同型机组已出现过的部件断裂故障等，完善金属技术监督导则中对金属探伤检测的要求，并且优化状态检修导则，确定合理的检修周期，针对性地加强关键部件的金属探伤检测以发现潜在的裂纹，避免运行中大质量部件突发性断裂最终酿成重大事故。

Metal flaw detection of components during unit shutdown maintenance is an important means of discovering cracks, but sometimes it may not be possible to detect existing cracks in a timely manner. The reason for this is that on the one hand, the metal technical supervision documents do not stipulate that every component at any position needs to undergo regular flaw detection, which may lead to missed detection of cracked components or positions; On the other hand, in some cases, component cracks develop rapidly, and before the unit is shut down for maintenance, the cracks have developed to a dangerous level that is about to fracture, seriously affecting the safe operation of the unit. Especially at present, power generation enterprises widely carry out equipment condition maintenance. Although it plays an important role in improving maintenance efficiency and reducing maintenance costs, sometimes extending the maintenance cycle increases the risk of component crack propagation or even fracture. Therefore, it is necessary to improve the requirements for metal flaw detection in the metal technology supervision guidelines based on the structural characteristics, operating methods, service life, and component fracture failures that have occurred in the same type of unit design. The condition based maintenance guidelines should be optimized to determine a reasonable maintenance cycle, and targeted metal flaw detection of key components should be strengthened to detect potential cracks, To avoid sudden rupture of large quality components during operation and ultimately lead to major accidents.

加强对关键部件的运行参数调整对于防止部件开裂、脱落也是十分有益的。如运行中严格控制发电机内氢气湿度，可减小护环应力腐蚀程度。

Strengthening the adjustment of operating parameters for key components is also very beneficial for preventing component cracking and detachment. If the hydrogen humidity inside the generator is strictly controlled during operation, the degree of stress corrosion of the protective ring can be reduced.

3 汽轮机长叶片振动和腐蚀Vibration and corrosion of long blades of steam turbines

3.1 故障机理和特征Fault mechanism and characteristics

汽轮机低压缸末级叶片在极高的离心力和湿蒸汽腐蚀的环境中工作，承受了很大的蒸汽力作用。机组在深度调峰及低负荷运行过程中，随着汽轮机级内容积流量的减小，低压缸末两级叶片构成的级内流动状态会发生较大变化，主要表现为产生进汽负攻角，在叶片压力面上形成流动分离，在叶根处产生扩压流动并形成脱流，诱发叶片颤振，导致动应力水平突增。同时，末级叶根汽流倒流带入的水滴对动叶出口边背弧产生侵蚀，致使高应力水平的末级叶片强度被削弱。这些变化不仅直接影响汽轮机的运行效率，诱发的叶片颤振和水蚀加剧也会威胁机组安全运行。

The last stage blades of the low-pressure cylinder of the steam turbine operate in an environment of extremely high centrifugal force and wet steam corrosion, and withstand a significant amount of steam force. During the deep peak shaving and low load operation of the unit, as the volumetric flow rate inside the turbine stage decreases, the flow state inside the stage composed of the last two blades of the low-pressure cylinder will undergo significant changes, mainly manifested as the generation of negative inlet angle, the formation of flow separation on the blade pressure surface, the generation of expansion flow at the blade root and the formation of detachment, inducing blade flutter, and leading to a sudden increase in dynamic stress level. At the same time, the water droplets brought in by the backflow of the last stage blade root steam erode the outlet edge and back arc of the moving blade, causing the strength of the last stage blade with high stress levels to be weakened. These changes not only directly affect the operational efficiency of the steam turbine, but also threaten the safe operation of the unit by inducing blade flutter and intensified water erosion.

供热机组进行低压缸零出力改造后，进汽流量更少，小于末两级叶片的最小冷却流量，在汽轮机低压通流区域的汽流将不再推动叶片做功，而会以惰性形态被动叶扇动排挤出叶片通道，出现鼓风摩擦现象。鼓风摩擦会导致汽轮机叶栅通道局部出现高温区域，严重时将使内缸受热变形，影响动静部件的同心度，进而威胁机组的安全运行。同时，低压喷水的开启，蒸汽的卷吸作用会造成末级叶片出汽边水蚀。由于运行工况严重偏离设计值，在汽流负攻角冲击作用下，流场紊乱，涡系复杂化将导致末级叶片颤振，叶片动应力增大。极端工况下，供热甩负荷之后，大量供热抽汽又会瞬间进入低压缸，对于低压转子以及叶片存在瞬时冲击，严重时甚至造成叶片断裂、飞脱。

After the zero output transformation of the low-pressure cylinder of the heating unit, the inlet steam flow rate is less, which is less than the minimum cooling flow rate of the last two stages of the blades. The steam flow in the low-pressure flow area of the turbine will no longer push the blades to do work, but will passively fan out the blade channel in an inert form, resulting in blowing friction phenomenon. Blast friction can cause local high-temperature areas in the turbine cascade channel, and in severe cases, it can cause thermal deformation of the inner cylinder, affecting the concentricity of the dynamic and static components, and thus threatening the safe operation of the unit. At the same time, the opening of low-pressure water spray and the entrainment of steam will cause water erosion at the outlet edge of the final stage blades. Due to the severe deviation of operating conditions from the design value, under the impact of negative attack angle of steam flow, the flow field becomes disordered, and the complexity of the vortex system will lead to the flutter of the final stage blades and an increase in blade dynamic stress. Under extreme operating conditions, after heat rejection, a large amount of heat extraction steam will immediately enter the low-pressure cylinder, causing instantaneous impact on the low-pressure rotor and blades, and even causing blade fracture and detachment in severe cases.

尽管小容积流量工况下末级叶片失效和低压排汽区域导流及回流蒸汽涡动冲刷对叶片的水蚀机理不完全明确，但叶片产生裂纹、断裂、腐蚀的隐患一直存在。事实上，近年来一些深调机组和低压缸零出力机组检修中发现末级叶片严重腐蚀和出现裂纹。如调峰运行的某350 MW机组汽轮机检修中发现低压转子调端末级叶片背弧出汽侧水蚀严重，如图5所示。

Although the mechanism of water erosion caused by the failure of the last stage blades and the vortex erosion of the low-pressure exhaust area and the return steam under small volume flow conditions is not fully clear, the hidden dangers of cracks, fractures, and corrosion of the blades have always existed. In fact, in recent years, severe corrosion and cracks have been found in the last stage blades of some deep adjustment units and low-pressure cylinder zero output units during maintenance. During the maintenance of a 350 MW unit steam turbine during peak shaving operation, it was found that the last stage blade at the end of the low-pressure rotor had severe water erosion on the back arc outlet side, as shown in Figure 5.

图5 某350 MW机组汽轮机末级叶片背弧出汽侧水蚀

Figure 5 Water Erosion on the Exit Side of the Back Arc of the Last Stage Blade of a 350 MW Unit Steam Turbine

2021年11月19日，调峰运行某600 MW机组启动过程在2 976 r/min时低压2转子电端1根末级叶片从根部突然断裂（图6），引起剧烈振动导致跳机和轴系破坏事故。

On November 19, 2021, during the start-up process of a 600 MW unit under peak shaving operation, at 2976 r/min, a last stage blade at the electrical end of the low-pressure 2 rotor suddenly broke from the root (Figure 6), causing severe vibration and causing a trip and shaft system damage accident.

图6 某600 MW机组汽轮机末级叶片断裂

Figure 6: Last stage blade fracture of a 600 MW unit steam turbine

3.2 防范措施Preventive Measures

为防止小容积流量工况末级叶片振动、强度下降和腐蚀，可从设计制造方面入手。如通流设计采用较高的根部反动度，增加动叶的压力梯度，延缓脱流的发生；在末级后部装设喷水冷却装置，降低末级和排汽缸的温度；设计末级动叶时采用增加叶片弦长，选用外形粗壮和功角适应性好的大头叶型，减小叶片高度，整圈围带布置，选用衰减性大和耐水性好的材料等，以增加叶片的强度和阻尼。另外，通常对叶片进行喷涂处理以提高表面强度和抗水蚀能力。运行方面可设置合理的低负荷运行方式，控制机组排汽压力在适当的范围内，使排汽容积流量不低于规定值。

To prevent vibration, strength reduction, and corrosion of the final stage blades under low volume flow conditions, design and manufacturing can be started. If the flow design adopts a higher root reaction degree, increasing the pressure gradient of the moving blades and delaying the occurrence of flow separation; Install a water spray cooling device at the rear of the final stage to reduce the temperature of the final stage and exhaust cylinder; When designing the final stage moving blades, increasing the chord length of the blades, selecting large head blade shapes with robust appearance and good power angle adaptability, reducing the height of the blades, arranging the entire circumference of the shroud, and selecting materials with high attenuation and good water resistance to increase the strength and damping of the blades. In addition, blades are usually sprayed to improve surface strength and water corrosion resistance. In terms of operation, a reasonable low load operation mode can be set to control the exhaust pressure of the unit within an appropriate range, so that the exhaust volume flow rate is not lower than the specified value.

对于切除低压缸供热的汽轮机，可优化末级、次末级叶片设计，保证其在高温下也能满足强度要求，并具备良好的抗水蚀性能；通过优化设计保证中排抽汽供热工况中压末几级叶片和隔板的强度。同时，加强运行管理，精确分析小流量下叶片可能出现的颤振点，在运行中注意避开。

For steam turbines that cut off the low-pressure cylinder for heating, the design of the last and second last stage blades can be optimized to ensure that they can meet the strength requirements at high temperatures and have good water corrosion resistance; By optimizing the design, ensure the strength of the last few blades and baffles in the middle exhaust steam extraction and heating conditions. At the same time, strengthen operation management, accurately analyze the possible flutter points of blades under low flow rates, and pay attention to avoiding them during operation.

此外，应加强对深度调峰运行和低压缸零出力等非设计工况汽轮机末级叶片的在线状态监测。通过对末级叶片周向振动响应、振动固有特性和温度等参数的连续监测，能够对叶片健康寿命状态进行实时评估，并进行叶片裂纹等故障诊断，提前故障预警和振动超限保护。

In addition, online monitoring of the final stage blades of steam turbines under non design operating conditions such as deep peak shaving operation and zero output of low-pressure cylinders should be strengthened. By continuously monitoring parameters such as circumferential vibration response, inherent vibration characteristics, and temperature of the final stage blades, real-time evaluation of blade health life status can be carried out, and fault diagnosis such as blade cracks can be carried out. Early fault warning and vibration overload protection can be provided.

4 进汽阀门卡涩和振动Inlet valve jamming and vibration

4.1 故障机理和特征Fault mechanism and characteristics

超（超）临界汽轮机运行中进汽阀门阀杆表面会形成致密氧化层，其膨胀系数与阀杆材料的膨胀系数存在差别。在机组启停和宽负荷运行中，进汽阀门阀杆持续动作以及进汽温度的波动，会导致氧化皮增厚并从阀杆表面剥落，氧化皮卡在阀杆与阀套之间环缝中易造成阀门卡涩。进汽阀门卡涩影响机组的正常运行和负荷调节，严重时还会造成阀杆断裂。进汽阀门卡涩若发生在停机或甩负荷过程 中，还会引发机组超速等严重事故。2019年8月，某电厂超超临界1 000 MW机组运行中因电气故障跳闸、汽轮机甩负荷，由于汽轮机主蒸汽阀门、调节阀卡涩导致阀门无法关闭，致使汽轮机最高转速达3 848 r/min，严重影响机组的安全性。

During the operation of ultra supercritical steam turbines, a dense oxide layer will form on the surface of the inlet valve stem, and its expansion coefficient is different from that of the valve stem material. During the start-up, shutdown, and wide load operation of the unit, the continuous action of the inlet valve stem and fluctuations in the inlet steam temperature can cause the oxide skin to thicken and peel off from the surface of the valve stem. The oxide skin gets stuck in the circumferential gap between the valve stem and valve sleeve, which can easily cause the valve to jam. The jamming of the inlet valve affects the normal operation and load regulation of the unit, and in severe cases, it can also cause the valve stem to break. If the inlet valve gets stuck during shutdown or load rejection, it can also cause serious accidents such as unit overspeed. In August 2019, a 1000 MW ultra supercritical unit of a certain power plant tripped due to electrical faults and turbine load rejection. Due to the jamming of the main steam valve and control valve of the turbine, the valve could not be closed, resulting in the highest speed of the turbine reaching 3848 r/min, seriously affecting the safety of the unit.

随着大机组调峰加剧，使得高压调节阀将长时间处于小开度和变开度运行中。小开度下高压调节阀节流严重，阀内不稳定流动极易引发高压调节阀振动。高压调节阀振动会导致机组负荷波动，阀杆螺纹滑丝、断裂，调节阀LVDT杆断裂，DEH油管路系统破坏，汽轮机振动，严重时还会造成机组的非正常停机。如果阀内流体激振力的频率与阀芯、阀杆等阀门部件、阀门支撑系统或者阀门相连的管道等结构的固有频率重合，则会引发结构共振。如某1 000 MW机组深度调峰运行半年后发现高压调节阀至高压缸进汽管道晃动明显，2号高压管道晃动最严重，且2号高压调节阀内伴有明显异音。2号高压调节阀振动测试表明该调节阀振动呈现撞击特征，解体检查发现阀芯的固定销断裂导致阀芯部件脱落，引发了管道振动。

As the peak shaving of large units intensifies, the high-pressure regulating valve will be in operation with small and variable opening for a long time. Under small opening, the high-pressure regulating valve is severely throttled, and unstable flow inside the valve can easily cause vibration of the high-pressure regulating valve. The vibration of the high-pressure control valve can cause fluctuations in the unit load, thread slippage and fracture of the valve stem, LVDT rod fracture of the control valve, damage to the DEH oil pipeline system, turbine vibration, and even abnormal shutdown of the unit in severe cases. If the frequency of the fluid excitation force inside the valve coincides with the natural frequency of valve components such as the valve core, valve stem, valve support system, or pipeline connected to the valve, it will cause structural resonance. After six months of deep peak shaving operation of a 1000 MW unit, it was found that there was significant shaking in the steam inlet pipeline from the high-pressure control valve to the high-pressure cylinder. The shaking was most severe in the No. 2 high-pressure pipeline, and there was a significant abnormal sound inside the No. 2 high-pressure control valve. The vibration test of the No. 2 high-pressure regulating valve showed that the vibration of the regulating valve exhibited impact characteristics. Upon disassembly inspection, it was found that the fixing pin of the valve core was broken, causing the valve core components to fall off and causing pipeline vibration.

对于需要中联门参调进行供汽的机组，由于原有中联门仅考虑启机情况下使用，其油动机的出力较小，参调时存在突然关闭的风险。此外，中联门的口径相对较大，调节性能差，参调时前后压差大，节流情况下容易引起中联门振动，威胁机组的安全运行。对于通过中低压缸连通管打孔供汽的机组，在大流量供汽情况下需要连通管蝶阀关至较小的开度，容易引起连通管蝶阀振动和膨胀节裂纹。某超临界600 MW机组因连通管膨胀节频繁产生裂纹，每2年需更换膨胀节，影响机组长期安全运行。

For units that require intermediate gate adjustment for steam supply, due to the fact that the original intermediate gate was only considered for use under startup conditions, the output of its hydraulic motor is small, and there is a risk of sudden closure during adjustment. In addition, the diameter of the intermediate gate is relatively large, and its adjustment performance is poor. When adjusting, the pressure difference between the front and rear is large, which can easily cause vibration of the intermediate gate under throttling conditions, posing a threat to the safe operation of the unit. For units that supply steam through holes in the connecting pipes of the medium and low pressure cylinders, it is necessary to close the butterfly valve of the connecting pipe to a smaller opening under high flow supply conditions, which can easily cause vibration of the butterfly valve of the connecting pipe and cracks in the expansion joint. A certain supercritical 600 MW unit needs to be replaced every 2 years due to frequent cracks in the expansion joints of the connecting pipes, which affects the long-term safe operation of the unit.

4.2 防范措施Preventive Measures

为了防止阀门卡涩事故发生，需在汽轮机带负荷情况下，定期（每周）对汽轮机的高、中压主蒸汽阀和调节阀进行活动试验，以保证阀门安全运行。超（超）临界机组在阀杆等关键间隙表面采用喷焊司太立合金等抗氧化皮处理措施也可有效减缓氧化皮的生成。

In order to prevent valve jamming accidents, it is necessary to conduct regular (weekly) activity tests on the high and medium pressure main steam valves and control valves of the turbine under load to ensure safe operation of the valves. The use of anti oxidation skin treatment measures such as spray welding of Stellite alloy on the surface of key gaps such as valve stems in ultra (ultra) critical units can also effectively slow down the generation of oxide skin.

针对小流量工况下阀内流体不稳定流动，可进行阀门型线和结构优化，减小深度调峰时阀门所受到的激励力。对于中联门参调的大流量供热汽轮机，应配置更大提升力的油动机，同时优化阀门型线，避免参调时发生阀门突然关闭和振动。

To address the unstable flow of fluid inside the valve under low flow conditions, valve profile and structure optimization can be carried out to reduce the excitation force on the valve during deep peak shaving. For large flow heating steam turbines with intermediate gate adjustment, a hydraulic motor with greater lift should be equipped, and the valve profile should be optimized to avoid sudden valve closure and vibration during adjustment.

为掌握运行中联门的振动状况，可对阀门振动进行在线监测。由于阀门内蒸汽的工作温度较高，采用常规接触式的测振方法难以测量阀门振动。推荐使用非接触式的测量，如激光测振仪进行测量。目前已开发出阀门振动在线监测系统，并在一些中联门参调的大流量供热汽轮机上实施应用。图7为阀门振动在线监测系统。

To understand the vibration status of the connecting valve during operation, online monitoring of valve vibration can be carried out. Due to the high working temperature of the steam inside the valve, it is difficult to measure valve vibration using conventional contact vibration measurement methods. It is recommended to use non-contact measurements, such as laser vibration meters. At present, an online monitoring system for valve vibration has been developed and applied to some large flow heating steam turbines with intermediate gate adjustment. Figure 7 shows the online monitoring system for valve vibration.

图7 阀门振动在线监测系统示意

Figure 7 Schematic diagram of valve vibration online monitoring system

5 结 论Conclusion

1）火电机组在实施节能降耗各项措施、大流量供热和工业抽汽改造、灵活性运行后，运行的安全可靠性明显下降，可能出现主辅机轴系振动、转子裂纹和转动部件脱落、末级叶片振动和腐蚀、进汽阀门卡涩和振动等问题，应引起高度重视。

1) After implementing various energy-saving and consumption reduction measures, large flow heating and industrial steam extraction renovation, and flexible operation, the safety and reliability of thermal power units have significantly decreased. There may be problems such as vibration of the main and auxiliary machine shaft system, rotor cracks and detachment of rotating components, vibration and corrosion of the final stage blades, and jamming and vibration of the inlet valve, which should be highly valued.

2）加强机组振动控制，合理调整汽轮机径向和轴向间隙，对刚度较弱的低压缸进行加固，适当降低凝汽器真空，合理控制运行中轴封供汽温度等，都有助于减缓或消除启机过程和低负荷运行时汽轮机出现动静碰摩。

2) Strengthening the vibration control of the unit, adjusting the radial and axial clearances of the steam turbine reasonably, strengthening the low-pressure cylinder with weaker stiffness, appropriately reducing the vacuum of the condenser, and controlling the steam supply temperature of the shaft seal during operation can all help to slow down or eliminate dynamic static friction of the steam turbine during startup and low load operation.

3）加强灵活性运行发电机转子局部结构升级，采用多层瓦结构护环绝缘瓦以提高绝缘可靠性和适形性，升级绝缘瓦、楔下垫条滑移层材料以提高端部整体滑移顺畅性，避免或减缓大负荷工况发电机线圈膨胀受阻产生的转子热弯曲。

3) Strengthen the flexibility of the local structure upgrade of the generator rotor during operation, adopt a multi-layer tile structure with protective ring insulation tiles to improve insulation reliability and adaptability, upgrade the insulation tiles and sliding layer materials under the wedge to improve the overall smoothness of end sliding, and avoid or slow down the thermal bending of the rotor caused by the expansion and obstruction of the generator coil under heavy load conditions.

4）加强灵活性运行汽轮机转子热应力的数值计算分析研究，探究循环应力对转子疲劳寿命损耗的影响，开发并安装汽轮机转子寿命损耗在线监测系统。

4) Strengthen the numerical calculation and analysis of thermal stress in steam turbine rotors for flexible operation, explore the impact of cyclic stress on rotor fatigue life loss, and develop and install an online monitoring system for steam turbine rotor life loss.

5）加强汽轮机末级叶片补强和防水蚀设计，同时对末级叶片进行喷涂处理，高压调节阀和参调供热的中联门进行阀门型线和结构优化，减小深度调峰和大流量供热时阀门所受到的激励力。

5) Strengthen the reinforcement and waterproof design of the final stage blades of the steam turbine, and spray paint the final stage blades. Optimize the valve profile and structure of the high-pressure control valve and the intermediate gate involved in the regulation and heating, to reduce the excitation force on the valve during deep peak shaving and large flow heating.

6）加强设备的振动故障诊断，充分利用现场普遍安装的TDM系统，根据机组启停机、带负荷运行中振动频谱、伯德曲线等振动特征的变化，提早诊断转子裂纹故障，及时停机检修，防止发生突然断裂事故。

6) Strengthen the diagnosis of equipment vibration faults, fully utilize the TDM system commonly installed on site, and diagnose rotor crack faults in advance based on changes in vibration characteristics such as vibration spectrum and Bode curve during unit startup and shutdown, load operation, and timely shutdown for maintenance to prevent sudden fracture accidents.

7）加强机组运行中容易出现故障部件的状态监测，如加装汽轮机末级叶片在线状态监测系统、中联门振动在线监测系统等，评估末级叶片和中联门的工作状态，提早发现存在的潜在故障。

7) Strengthen the status monitoring of components that are prone to faults during unit operation, such as installing online status monitoring systems for steam turbine final stage blades and intermediate gate vibration, evaluate the working status of final stage blades and intermediate gate, and detect potential faults in advance.

8）加强设备优化检修，在状态检修的基础上，针对深度调峰、灵活性运行、切缸供热等机组，应加大汽轮机末级叶片、高中压转子和叶轮、发电机转子、护环及低发联轴器等部件的金属探伤频次，及时发现存在的裂纹，防止运行中突然断裂、脱落。

8) Strengthen equipment optimization and maintenance. On the basis of condition based maintenance, for units such as deep peak shaving, flexible operation, and cylinder cutting and heating, the frequency of metal inspection for steam turbine final stage blades, high and medium pressure rotors and impellers, generator rotors, retaining rings, and low engine couplings should be increased to timely detect existing cracks and prevent sudden fracture and detachment during operation.

文献来源Source

张学延, 何国安, 曾立飞, 等. “双碳”目标下火电机组故障及应对措施综述[J]. 热力发电, 2022, 51(12): 10-17.

ZHANG Xueyan, HE Guoan, ZENG Lifei, et al. Overview of thermal power units’ faults and the countermeasures under the target of “carbon neutrality and carbon peaking”[J]. Thermal Power Generation, 2022, 51(12): 10-17.