Coherency-based low order models for shaft systems ofturbine-generator sets

Accurate low order lumped models that represent the low frequency torsional motion of turbine-generator sets are needed for determining shaft torsional responses resulting from subsynchronous resonance conditions, electric power system faults and planned/unplanned switching actions in the electric network. This paper presents a coherency-based method that resolves a high order inertia-spring lumped model into a low order inertia-spring lumped model, while preserving the selected group of natural torsional frequencies and their associated mode shapes. Forced eigen-frequency matching and conservation of angular momentum form the basis of the iterative procedure developed in the paper. Numerical examples are included to illustrate the capabilities of the proposed method in determining accurate low order dynamic equivalents     

Turbine generator laboratory model tests to damp torsionaloscillations with supplementary signals

The improvement of generator stability by the use of supplementary signals into the voltage regulator and governor loops using discrete-time linear optimal control theory has been studied with particular emphasis on providing better damping for torsional oscillations. A multi-inertia laboratory model equipped with data acquisition and control computers was constructed to model the shaft dynamics of a 660 MW Drax turbine-generator. It is shown that the shaft torsional phenomena can be adequately simulated on a micro-synchronous-generator at least as far as the dominant shaft torsional modes of vibration are concerned. The practical implementation of multi-mode linear quadratic Gaussian (LQG) controllers has been shown to enhance system stability and provide better damping to the lower frequency torsional modes, which are those most susceptible to excitation     

Stochastic evaluation of turbine-generator shaft torsional torques

This paper presents a probabilistic approach to the evaluation of the maximum torsional torques induced in turbine-generator shafts during high-speed reclosing of system faults. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The results of these investigations are presented in the form of discrete probability distributions of the maximum torsional torques induced in the turbine-generator shaft sections     

Effect of adaptive short time compensation on the stochasticbehavior of turbine-generator shaft torsional torques

This paper presents a Monte Carlo based approach to evaluate the maximum torsional torques induced in turbine-generator shafts during high-speed reclosing following system faults. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. In the case of unsymmetrical faults, two switching schemes were considered in clearing and reclosing such faults, namely conventional (triple pole for line-to-line and double line-to-ground faults and single-pole for single line-to-ground faults) and selective-pole switching. In the latter case, the transmission system is balanced during the period between fault clearing and line reclosing using compensating capacitors. Moreover, an adaptive reclosing technique is used for reclosing the tripped phases. The effect of employing the adaptive short-time compensation and reclosing technique on the expected maximum torsional torques as well as their variances has been investigated. A risk index which reflects the likelihood that the torque induced in a turbine-generator shaft exceeds its design value is also presented     

The influence of shaft spring constant uncertainty on torsionalmodes of turbogenerator

The paper explores the dependence of torsional modes of turbogenerator on the uncertainty in the shaft spring constant (stiffness). The analysis is performed on a typical single machine infinite bus system. Small-signal stability analysis as well as large-disturbance analysis are performed on a five rotational mass mechanical system. Different operating conditions of the generator are examined. It is shown that the spring constant (stiffness) of the shaft can significantly influence damping and frequency of torsional modes. Effects on maximum torsional torques developed in the shaft following large disturbance in the electrical system are also analysed. The paper underlines the importance of accurate modelling of the turbine-generator shaft for studies of torsional oscillations and subsynchronous resonance     

Effect of adaptive single-pole reclosing on the stochastic behaviorof turbine-generator shaft torsional torques

This paper presents a Monte Carlo based approach to evaluate of the maximum torsional torques induced in turbine-generator shafts during high-speed reclosing of system faults. Two reclosing schemes were considered, namely simultaneous and adaptive reclosing. In the case of a single line-to-ground fault, single-pole reclosing is considered in clearing such a fault. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The effect of employing adaptive single-pole reclosing on the expected maximum torsional torques as well as their variances have also been investigated. A risk index which reflects the likelihood that the torque induced in a turbine-generator shaft exceeds its design value is also presented     

Impact of shaft torsionals in steam turbine control

Shaft torsional vibrations are discussed along with their effect on steam turbine-generator control following severe supply-network disturbances and the destabilization of shaft torsional modes through the action of high-speed electrohydraulic controllers. It is shown that shaft flexibility can exert a significant influence on steam turbine-generator response following a severe supply-system disturbance, particularly when the turbine has nonlinear valve stroking and fast valving. The effect can be minimized by the careful location of a speed sensor along the turbine shaft and by filtering speed or acceleration signals to reduce the speed input of troublesome low-frequency torsional vibrations to an insignificant level. The effect of shaft torsionals on control system response to an islanding situation and on the above mentioned destabilization is evaluated. Digital implementation of steam-turbine control systems in relation to quantization, sampling, response time in protection systems, and software integrity is examined     

Application of STATCOM for damping torsional oscillations in seriescompensated AC systems

This paper presents the results of a study on the application of the recently developed FACTS device, the static compensator (STATCOM), for the damping of torsional oscillations that occur in a series compensated AC system. The IEEE first benchmark system is considered for this study. In order to suppress unstable torsional mode oscillations, a STATCOM with a PI controller to regulate the bus voltage, and with an auxiliary signal derived from the generator speed deviations is employed at the generator terminal. The eigenvalue analysis technique is used for small signal analysis and optimization of the control system parameters is done through step response studies. In addition, dynamic performance of the nonlinear system with optimized STATCOM controller is evaluated under a three-phase fault. Results from the analytical and digital simulation studies reveal the technical feasibility of using STATCOM for damping of turbine-generator torsional oscillations in series compensated AC systems     

"Q因子"在超临界600MW机组设计中的应用

超临界600MW汽轮发电机组是国内首台大型超临界机组,设计分析难度很大,针对超临界600MW汽轮发电机组轴系,采用国际上通用的不平衡响应及共振转速峰值响应灵敏度Q因子(Q factor)进行计算和分析及评价。     

Analysis of shaft torsional phenomena in governing large steamturbine generators with non-linear valve stroking

The paper focuses on how shaft torsional problems can be initiated in some situations by the fast action of steam control valves. It demonstrates that shaft flexibility can exert a significant influence on steam turbine-generator response following severe supply system disturbances, particularly for large machines where the turbine has nonlinear valve stroking and fast valving. The effect can be minimised by careful location of the speed sensor on the turbine shaft and by filtering to reduce speed input or acceleration signals due to troublesome low-frequency torsional vibrations to an insignificant level. Digital implementation of steam-turbine control systems is described. Response for a range of control philosophies where digital control procedures are used are given. Two large machines where digital speed sensing and filtering techniques in steam valve control are implemented are examined     

Application of simultaneous active and reactive power modulation ofsuperconducting magnetic energy storage unit to damp turbine-generatorsubsynchronous oscillations

An active and reactive power (P-Q) simultaneous control scheme, which is based on a superconducting magnetic energy storage (SMES) unit, is designed to damp out the subsynchronous resonant (SSR) oscillations of a turbine-generator unit. In order to suppress unstable torsional mode oscillations, a proportional-integral-derivative (PID) controller is used to modulate the active and reactive power input/output of the SMES unit according to speed deviation of the generator shaft. The gains of the proposed PID controller are determined by pole assignment approach based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Dynamic simulations using the nonlinear system model are also performed to demonstrate the damping effect of the proposed control scheme under disturbance conditions     

Effect of field discharge resistors on turbine-generator shafttorsional torques

The possibility of reducing the torsional torques of turbine-generator shafts during disturbances by interrupting the generator excitation and switching in a field discharge resistor during the fault duration is discussed. The results of these investigations show that the use of such field discharge resistors reduces the turbine-generator torsional torques after the fault clearance. These results have been obtained through extensive parametric studies and are supported by simulation results     

A Methodology for Predicting Torsional Fatigue Crack Initiation in Large Turbine-Generator Shafts

This document presents results of a three-year program in which an analytical method was developed to estimate the cumulative fatigue damage sustained by a turbine-generator shaft system during a torsional transient. The work was conduted at the Steam Turbine-Generator Engineering and Manufacturing Department of the General Electric Company undr the sponsorship of the Electric power Research Institute (Proect RP1531-1). The product of this program was a methodology that used the results of analysis and torsional fatigue tests on 25.4 mm diameter laboratory specimens to predict the fatigue life of large-diameter shafts subjected to torsional transients. These predicted results were verified with 127 mm diameter specimens subected to simulated torsional transient load history tests. To account for complicated deformation cycles, range pair cycle counting and linear damage summation techniques were used. Notch root deformation response was characterized with a form of Neuber's rule. The results of tests of 25.4 mm and 127 mm diameter specimens showed that the proposed methodology characterized the torsional cumulative fatigue damage within a factor of two of the measured damage under laboratory conditions.     

电力系统扰动对汽轮发电机组轴系扭振的影响及其主动控制

采用线性定常二次型全局最优控制理论对电力系统扰动下大型汽轮发电机组轴系产生的扭振进行主动控制,较详细地阐述了三相短路和两相短路的故障原因,讨论了两种故障对最大电磁转矩的影响,计算了发电机组轴系产生的冲击转矩和扭振响应,并利用线性定常二次型全局最优控制理论对这两种故障进行扭振主动控制仿真计算。计算结果证明:采用扭振主动控制技术能有效抑制由于电力系统扰动而引起的大型汽轮发电机组轴系扭振。图7参8     

小机组液压调节系统的改造

随着汽轮机的发展和电网峰谷差的不断增大,对机组的调峰和调频要求越来越高。因此,降低运行成本,改善机组运行可靠性和控制灵活性,已成了各电厂特别是老电厂的当务之急。介绍了广州石化1号机组液压调节系统改造为数字式电液调节系统的改造方案,对比分析了机组调节系统改造前后的控制水平。     

空冷600MW汽轮发电机组轴系扭振特性分析

主要研究了空冷600MW汽轮发电机组轴系扭振特性、疲劳寿命损耗,并针对两个特定电厂的接入系统进行网机耦合次同步谐振特性分析。轴系扭振频率和响应计算采用连续质量模型,次同步谐振特性分析采用集中质量模型。计算结果表明,机组扭振频率避开了工频和倍频,轴系不会因共振而破坏;在短路故障轴系扭振是安全的;空冷600MW汽轮发电机组可以用于远距离输电在线路中进行串联电容器补偿。     

On the application of the complex torque coefficients method to the analysis of torsional dynamics

The complex torque coefficients method has been widely accepted for the analysis of the phenomenon of torsional interaction of turbine-generator units in power systems. This paper shows that, depending on the system parameters and the operating point, the complex torque coefficients method may exhibit limitations and not accurately and fully predict the system behavior in the frequency range of interest. These shortcomings consist of inability to i) predict monotonic instability due to real poles, ii) identify all electromechanical oscillatory modes, and iii)accurately predict damping (and consequently stability) of the oscillatory modes. This paper develops mathematical expressions to highlight the limitations of the complex torque coefficients method. Quantitative results based on three case studies, including a study on the first IEEE Benchmark System, are reported and results from eigenvalue analysis method, complex torque coefficients method, and time-domain simulation are presented and compared. This paper concludes that the complex torque coefficients method can be used only as a preliminary method for the investigation of torsional interactions and the results must be verified by other methods.     

350MW汽轮发电机组性能监测系统

】针对３５０ＭＷ汽轮发电机组的热力性能介绍了一种性能监测系统,该系统选用常规测点作为机组性能监测的基本数据,采用了易于评价机组性能和指导运行调整的性能分析方法。现场运行情况表明,整个系统的设计和实施是合理的,对指导现场的机组运行发挥了重要作用。     

某电厂3号汽轮发电机组异常振动的分析处理

介绍了某电厂3号机组振动情况,分析了机组振动的主要原因,精确分析出机组振动的原因是轴系上有部件脱落,以及不平衡重量出现的部位,及时消除了机组的振动故障,振动达到优良水平,保证了机组的安全投产运行。     

Analysis of torques in large steam turbine driven inductiongenerator shafts following disturbances on the system supply

The paper first summarises the advantages of steam turbine-driven induction generators over conventional generators such as low cost, less maintenance, rugged and brushless rotors (squirrel cage type, no need for synchronisation, etc.), together with problems concerning excitation (VAr compensation at loads etc). A mathematical model of the induction generator simulated in direct-phase quantities where saturation of the magnetising reactances is simulated and saturation of stator and rotor leakage reactances is ignored is developed and employed for detailed simulation of the machine. Discrete-mass models of the machine shaft where both steam and electrical viscous damping is simulated are employed in comparing transient shaft torsional response evaluated by time domain simulation and frequency domain analysis following incidence and clearance of severe system faults. The paper then investigates torsional response following incidence and clearance of severe supply system disturbances, when the rotor is stationary and when running at close to synchronous speed unexcited, and following malsynchronisation when excited by a controlled VAr source, together with torsional response following bolted stator-terminal short-circuits at full-load and no-load following switching in of the induction generator onto the system supply. It examines precision of predicting torque in turbine-generator shafts by frequency domain analysis not analyzed for induction generators in the literature heretofore following incidence and clearance of worst-case disturbances on the supply. Effect of steam and electrical damping on maximum shaft torques predicted by frequency domain analysis is also illustrated. The results illustrate there is no tendency for shaft torques to become more onerous as the fault clearing time is increased as is the case for shaft torques in large synchronous machines. Three large two-pole machines of rating of up to a few hundred MWs are analysed