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     

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     

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     

Torsional system parameter identification of turbine-generator sets

Accurate low order linear models that represent the torsional motion of turbine-generator sets are needed for determining shaft torsional responses resulting from subsynchronous resonance conditions, electric system faults and planned/unplanned switching actions in the electric network. This paper outlines the theoretical background and the methodology used for identification of linear state-space models of turbine-generator systems. These analytic mass-spring-damper models are lumped-parameter approximations, which in reality represent a continuous nonlinear system. For transient torque studies these models are adequate representations of the torsional dynamics of interest. Reduced analytic models of any particular turbine-generator unit, however, usually do not match precisely the behavior of the real machine. The paper describes an optimization method that can give a more precise representation of a particular turbine-generator based on actual plant tests and an assumed model of that unit. The parameter identification process is illustrated using plant test data from a 618 MVA turbine-generator unit     

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     

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     

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     

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     

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     

Torsional Model Identification for Turbine-Generators

A method for identifying the parameters of a turbine-generator torsional model from measured data is presented. The method is based on the use of trajectory sensitivities and least squares to compute changes in model parameters. This method is illustrated by identifying the shaft stiffness and inertia constants of a torsional model from data collected by a Torsional Vibration Monitor.     

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     

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     

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.     

300 MW汽轮发电机组在机电耦合作用下的扭振

大型汽轮发电机组轴系扭振是电网系统和机械系统相互作用的结果.以1台300 MW汽轮发电机组扭振模拟机为对象,对轴系扭振和机电耦合次同步谐振的耦合作用进行了模拟试验.结果表明:在三相短路故障激励下,具有串补电容的输电线路比无串补电容的输电线路对机组轴系扭振响应的影响更大;补偿度越高,电力系统中谐振电流明显增大,发生机电耦合次同步振荡的危险性越大.     

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.     

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     

汽轮发电机组轴系扭转疲劳性能估算方法的参数灵敏度分析

采用参数灵敏度分析方法,详细讨论了各相关参数对某汽轮发电机组轴系扭转疲劳性能指标的敏感性.结果表明:拉伸强度、尺寸系数和表面加工系数对疲劳性能的灵敏度相同,其灵敏度因子均为1;随着应力集中系数的增大,其灵敏度因子线性增大,当应力集中系数约大于1.68时,其灵敏度因子大于1,成为影响构件疲劳强度的最主要因素;疲劳缺口敏感系数对疲劳强度的影响最小;由于修正参数选取时的不确定性造成的寿命损耗估算偏差最大可达约15.5倍.     

采用落地轴承有利于提高某空冷600MW机组轴系的全裕度

某空冷600MW汽轮发电机组是国内首台完全自主开发设计的全新机组,本文针对某空冷600MW汽轮发电机组低压转子采用落地轴承结构,对轴系安全裕度的影响进行了计算和分析。计算结果表明：采用落地轴承有利于提高某空冷600MW机组轴系的安全裕度。     

"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。     

Measurement of torque in steam turbine-generator shafts followingsevere disturbances on the electrical supply system-analysis andimplementation

Phenomena that affects the performance of transducers that measure torque at positions along a turbine-generator shaft are reviewed, and the design of a transducer for precise measurement of torque at positions on a steam turbine-generator shaft that results from severe disturbances of the electrical supply system is discussed. Torque at shaft couplings following severe supply system events predicted using continuum models of turbine-generator shafts are analyzed and compared with that obtained over a section of the shaft by shaft twist and overall stiffness of the section. Algorithms for processing torque deduced from twist over a section to estimate true torque at specific shaft locations are discussed. Studies are performed for severe L-L-L short circuits with clearance. The design of a transient shaft torque transducer which uses disks with slits which are secured to the rotating shaft is described