非同期并列时机组轴系扭振的时频分析

三维有限元模型能较好地描述轴系的复杂结构,精确地反映倒角、凹槽等应力集中截面的扭应力情况。以某660 MW汽轮发电机组轴系为研究对象,介绍了应用ANSYS软件求解轴系扭振响应的过程,分析了机组非同期并列时的轴系扭振特性。分析表明：非同期并列时,各截面扭应力幅值迅速达到最大值,之后逐渐振荡衰减,故障对低发间转子危害较大;扭应力主要包括前两阶扭振固有频率和少量的工频成分,不同截面处各模态分量所占比例不同;120°和180° 2种非同期并列情况时的扭振响应特性基本相似,前者的扭应力响应大于后者。研究结果有助于提高机组安全管理水平。     

短路故障时汽轮发电机组轴系弯扭耦合振动分析

简要介绍了用于分析机组弯扭耦合振动的增量传递矩阵方法,利用该方法,分析了发电机出口端两相短路和三相短路故障时轴系弯扭耦合振动特性,并与三相短路重合闸以及非同期并网故障的耦合振动特性进行了比较。分析表明:发电机出口端发生短路故障时,各转子都很快被激励出扭振来,由于耦合作用,各转子弯振也发生一定的变化,但弯振的变化明显滞后于扭振;弯振受短路故障影响较为明显;各转子扭角与扭矩变化特征相似,其频率成分包含了工倍频及前三阶扭振固有频率;各种电气故障下,各转子弯振幅值都增大了,发电机转子增加最为明显;三相短路及重合闸故障不论是对高、中、低压转子,还是对发电机转子的弯振、扭振以及扭矩幅值影响都最为显著。     

非同期并列时汽轮发电机组轴系的扭振及其主动控制

非同期并列是大型汽轮发电机组常见的电力系统故障之一,对机组的安全运行甚为关键。该文计算了非同期并列时汽轮发电机组产生的电磁转矩,分析了其影响因素,并以一台２００ ＭＷ 汽轮发电机组为例,建立了汽轮发电机组轴系扭振主动控制系统模型,并用二次型全局最优控制算法对非同期并列时产生的扭振进行主动控制模拟计算,取得了满意的效果。     

并列操作对大型汽轮发电机组轴系扭振的影响

并列操作是系统运行中很经常的一项操作。过去只注重并列冲击电流产生的危害，而对轴系扭振缺乏研究。针对某电网600MW汽轮发电机组，研究准同期并列、自同期并列、非同期并列对轴系扭振的影响，并从轴系扭振角度，对并列操作提出一些看法，供大型汽轮机发电机组并列时参考。     

质量不平衡转子的弯扭耦合振动分析

对Jeffcott质量不平衡转子建立弯扭耦合振动方程。利用小参数法,得到该耦合振动方程的解析解,并给出数值仿真结果。理论分析与计算表明:弯振与扭振是相互耦合的,质量偏心是耦合的前提;转子在圆频率为ω1的外部激励作用下,通过弯扭耦合,主要激发出频率为|Ω-ω1|的扭振。当转子有频率为ωT1的外扭矩作用时,将主要激励产生|Ω±ωT1|频率成分的弯振;转速Ω等于转轴扭振固有频率ωt0与弯振固有频率ω0之和或之差时,可能发生弯扭耦合共振;当外激励的频率为弯振(或扭振)固有频率时,也会激发出较大的扭振(或弯振);弯扭耦合共振导致转子损坏的可能性很小,可为故障诊断提供有益的信息。     

非同期并列对汽轮发电机组的危害

分析了汽轮发电机组非同期并列时的电流和电磁转矩特性，推导了汽轮发电机组在与系统角度差为１２０°附近时并网电磁转矩最大这一结论，并对一非同期并网事例进行了分析。     

大型汽轮发电机组轴系扭振仿真与分析

基于场路耦合方法，对大型汽轮发电机组轴系扭振进行了仿真与分析，考虑了动态饱和特性和转子本体涡流特性的影响。对一台６００ＭＷ汽轮发电机组在单机无限大系统中，由于突然短路故障，非同期并网以及重合闸管电力系统扰动引起的轴系扭振进行了仿真计算，结果令人满意。     

300MW汽轮发电机组扭振的模拟试验研究

对东方３００ＭＷ汽轮发电机组的扭振进行了模拟试验研究,设计并制造了扭振模拟机及其扭振试验与测试系统,测试并分析了该模拟机的扭振特性。试验结果表明,扭振模拟机的前几阶扭振固有频率和振型与被模拟对象基本吻合,可以用来研究被模拟对象的扭振响应特性及其与电系统的耦合互作用规律。     

一起发电机的180°非同期并列事故

一起发电机的１８０°非同期并列事故北京热电总厂钱振华非同期并列为电力系统五大恶性事故之一。发生非同期并列事故，不但引起电网振荡，破坏稳定，大量甩负荷，而且对电气设备的安全构成威胁，甚至扩大为发配电设备事故。而发电机的１８０“非同期并列又是在非同期并列...     

水电机组转子轴承系统弯扭耦合振动影响因素研究

建立了水电机组转子-轴承系统的弯扭耦合振动模型,应用数值算法求解了不同导轴承刚度情况下,转子的弯振和扭振响应时程曲线,研究了轴承集中刚度和阻尼、陀螺力矩及转动惯量等对转子轴承系统弯扭耦合振动的影响.结果表明,轴承在弯曲方向上的集中刚度和阻尼对转子的弯振和扭振均有重要影响,而扭转方向上的阻尼对弯振和扭振影响相对较小,陀螺力矩中的扭转力矩对系统的响应起主要的影响作用,转动惯量增大使得系统的弯振和扭振响应降低.     

基于阻尼器的双馈风力发电系统扭振抑制策略

由风速扰动或网侧的电气扰动所引发的风机传动轴扭振现象会导致轴系机械零件疲劳过载,甚至损坏。提出一种对网侧电气小扰动引发机网扭振的抑制策略。该策略通过在转子侧逆变器功率控制环节引入阻尼器,当轴系发生扭振时,利用发电机转速波动信号产生阻尼功率,再附加到逆变器有功功率参考值上,使系统额外输出有功功率来增大系统阻尼,从而抑制轴系扭振。建立系统小信号稳定模型,分析扭振抑制原理,观察引入阻尼器后,系统主导扭振模态的特征根变化;并利用Bode图分析阻尼器对轴系扭振模态的抑制效果。最后,在Matlab/Simulink上进行仿真验证。结果表明,所提出的阻尼策略可以显著增大双馈风力发电系统的阻尼,增强对风力发电系统扭振尤其是低频振荡模态的抑制。     

汽轮发电机组轴系扭转振动的计算

本文以大型汽轮发电机组轴系为基础,利用传递矩阵解析地求解其扭转振动的固有频率和主振型,并根据主振型的正交条件进行坐标变换同时解耦。最后在主坐标下求解轴系在任意扭矩作用下的动力响应。算例和工程实际问题的计算结果与解析解完全一致。     

大推力推挽纵振弯纵复合直线超声电机

提出一种大功率夹心式纵弯复合直线超声电机。电机定子主体结构由2个小端相连的指数形变幅杆组成,并在连接处设有驱动足。纵弯振动叠加并在驱动足处产生具有驱动作用的椭圆轨迹。在经典变幅杆理论和变幅杆弯振的传递矩阵分析法的基础上,利用有限差分法,分析各结构参数变化对纵弯谐振频率变化的灵敏度,选取敏感度最大的参数作为设计变量,将电机的纵弯频率简并至27.476kHz。有限元仿真和阻抗特性测试结果与理论计算结果吻合。讨论分析了纵弯振动间的耦合作用并提出带耦合环节的等效电路模型拓扑结构,并利用单相驱动实验验证模型的正确性。电机样机的最大速度为1280mm/s,最大推力为45N。     

180°导通方式无刷直流电机换相转矩脉动研究

无刷直流电机(BLDCM)换相转矩脉动一直是业界关注的问题,但仅限于120°导通模式。文章研究了180°导通模式无刷直流电机在换相期间的转矩脉动变化,并与120°导通方式转矩脉动进行了比较。理论分析和仿真结果表明:电机在低速区域,120°导通模式比180°导通模式转矩脉动变化小,而在高速区域,180°导通模式比120°导通模式转矩脉动变化小。研究结果为无刷直流电机换相转矩脉动抑制提供了一种新的控制策略。     

Power links with Ireland-excitation of turbine-generator shafttorsional vibrations by variable frequency currents superimposed on DCcurrents in asynchronous HVDC links

The paper describes an in-depth analysis of excitation of shaft torsional vibrations in steam-turbine-generator-exciter shafts in close proximity to HVDC converter stations by variable-frequency ripple currents superimposed on the DC currents in asynchronous links. It extends earlier work to include an in depth analysis of system scaling factors for harmonic currents impressed on generators in Northern Ireland by an inverter and to investigate the phenomena for possible torsional vibrations in the generators by the link. It is concluded that variable-frequency ripple currents superimposed on the DC current in asynchronous links can excite sympathetic torsional vibrations in turbine-generator-exciter shafts. Subtransient generator reactances may be used to approximately proportion injected harmonic current to each machine of a multi-machine network. Very small noncharacteristic currents could result in serious damage to the machine although possibility of two power systems operating with fixed deviation in system frequencies long enough for the vibrations to build up is remote. Studies should be undertaken as routine on all machines in close proximity to HVDC converter stations to ascertain whether or not the machines are at risk     

真空泵用多台屏蔽电机模式切换与位置补偿偏差耦合同步控制

针对真空泵用多台屏蔽电机起动、突加随机扰动、突加周期性负载及单/多电机不同时刻故障停机过程,设计了模式切换与位置补偿偏差耦合同步控制系统,创新性地在速度补偿器中引入位置补偿器,同时在故障瞬间将偏差耦合控制方式切换为主从控制。将所提出的控制系统与传统的虚拟电机控制系统进行了对比。结果表明:当发生单电机故障以及双电机不同时刻故障时,在相同的模式切换和位置补偿条件下,所提出的控制系统位置误差分别为4.6°和4°,在5°的误差允许范围内,而传统虚拟电机控制系统的位置误差分别为15°和20°。     

纵振夹心换能器式圆筒型行波超声电机

提出一种纵振夹心换能器式圆筒型行波超声电机,该电机定子组件由定子圆筒和4个纵振夹心换能器组成,变幅杆和圆筒采用一整块硬铝合金加工而成。利用压电陶瓷片的纵向振动在夹心换能器中激励出纵向振动,实现两组换能器在定子圆筒上激励出2个幅值相等、在时间和空间上均相差p/2的弯振模态响应,2个弯振模态响应叠加在定子圆筒上形成弯曲振动行波,定子齿表面质点产生椭圆运动轨迹,进而通过和转子之间的摩擦耦合实现宏观运动输出。运用有限元法设计了定子圆筒和纵振夹心换能器,并实现了频率简并。测量结果表明,样机的最大转速为110 r/min,堵转力矩为0.5 N×m。     

Results from Investigations of Torsional Vibration in Turbine Set Shaft Systems

The article generalizes the results obtained from investigations of torsional vibration in the shaft system of the T-175/210-12.8 turbine set installed at the Omsk CHPP-5 combined heat and power plant. Three different experimental methods were used to determine the lowest natural frequencies of torsional vibration excited in the shaft system when the barring gear is switched into operation, when the generator is synchronized with the grid, and in response to unsteady disturbances caused by the grid and by the turbine control and steam admission system. It is pointed out that the experimental values of the lowest natural frequencies (to the fourth one inclusively) determined using three different methods were found to be almost completely identical with one another, even though the shaft system was stopped in the experiments carried out according to one method and the shaft system rotated at the nominal speed in those carried out according to two other methods. The need to further develop the experimental methods for determining the highest natural frequencies is substantiated. The values of decrements for the first, third, and fourth natural torsional vibration modes are obtained. A conclusion is drawn from a comparison between the calculated and experimental data on the shaft system’s static twisting about the need to improve the mathematical models for calculating torsional vibration. The measurement procedure is described, and the specific features pertinent to the way in which torsional vibration manifests itself as a function of time and turbine set operating mode under the conditions of its long-term operation are considered. The fundamental measurement errors are analyzed, and their influence on the validity of measured parameters is evaluated. With an insignificant level of free and forced torsional vibrations set up under the normal conditions of turbine set and grid operation, it becomes possible to exclude this phenomenon from the list of main factors influencing the crack formation processes in low-pressure rotors. The importance of experimentally confirming the fact that the shaft system has been detuned from resonances at the 50 and 100 Hz excitation frequencies is pointed out.     

A Damping Method for Torsional Vibrations in a DFIG Wind Turbine System Based on Small-Signal Analysis

Torsional vibrations present in the drivetrain excited by turbulent winds or grid disturbances (often manifesting as voltage sags) can produce severe stresses on the components of wind turbines. This study presents a damping method for the rotor side converter of a doubly fed induction generator (DFIG)-based wind turbine to improve system damping during small grid disturbances. Within the damping strategy, torsional damper is included into the power loop of the rotor side converter to provide damping for the system. During vibrations, a well-designed low-pass filter (LPF) is employed by the torsional damper to extract the dynamics of the generator speed and to generate a damping signal. To demonstrate the proposed damping approach, the small-signal stability model of a wind turbine connected to an infinite bus system is presented, and the eigenvalue analysis is conducted to verify the damping effect introduced by the torsional damper. In the case study, grid voltage sag at the point of common coupling (PCC) is applied to excite the torsional vibration of the wind turbine shaft. The validity and effectiveness of the proposed damping approach are testified by using the simulation results against theory analysis.