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     

Analysis of torsional torques in starting of large squirrel cageinduction motors

The paper presents a comprehensive study of the starting process of a large squirrel cage induction motor driving an inertia load through an elastic shaft. The analysis of the electromagnetic torque of the motor has revealed that there are variable frequency components which interact with the torsional mode of the mechanical system and produce hazardous shaft torque. This torque may exceed the maximum yield of the shaft or it may accumulate and result in a cyclic fatigue fracture. The nature of the problem is explained and the factors which aggravate its impact are discussed. Furthermore, it is shown that the torsional torque can be substantially reduced by the proper coordination of the switching operations     

考虑轴系扭振抑制的双馈风电机组惯量控制策略

双馈风电机组惯量控制是通过建立发电机转子转速与电网频率之间的耦合关系,调整机组有功输出以适应电力系统频率波动。惯量控制直接快速地调节有功会对机组轴系小干扰稳定性造成负面影响,不利于轴系扭振的抑制。文章分析了不同惯量控制响应特征及其对轴系阻尼特性的影响,设计一种以转差率为输入信号的附加惯性与阻尼转矩的惯量控制策略,提出了含轴系稳定性约束的附加惯性与阻尼转矩惯量控制参数整定方法。仿真结果表明,所设计的双馈风电机组惯量控制策略不仅有良好的惯量控制效果,还能有效增大轴系等效电气阻尼,提高了轴系的稳定性。     

Recent development of large electrolytic hydrogen generators

An overview of the history and market of large electrolysis units is presented. The historical background introduces and explains the thought process behind a new design of Teledyne's Electra Cell alkaline electrolysis hydrogen generators.The new design enables construction of modules capable of 1.6 ton per day of hydrogen. The cost of hydrogen is used as a criterion for the selection of optimum performing cells as a function of user parameters. It is suggested that due to cell costs, the highest efficiency cell does not always produce the cheapest hydrogen.     

A survey of shaft voltage reduction strategies for induction generators in wind energy applications

Common mode voltage generated by PWM inverters and the parasitic couplings of the machine structure in high frequencies create a model for the system which leads to an induced voltage on the shaft. Shaft voltage became a dominant side effect of power electronic converters since they are widely used in wind turbine applications to prepare desirable frequency and suitable control on active and reactive power. This voltage is known as the main cause of many unwanted problems such as leakage current, ball-bearings damages and reduction of generator's life time. In this paper, pulse width modulation strategies have been presented for two-level and three-level back-to-back AC–DC–AC converters in order to reduce or eliminate common mode voltage of these converters for reduction or elimination of shaft voltage in squirrel cage and doubly fed induction generators. Applying these techniques lead to complete elimination of shaft voltage for squirrel cage Induction generator with back to back AC/DC/AC converter and a 66 percent reduction of the shaft voltage generation in the Doubly Fed Induction Generator. Simulation results and mathematical analysis have been presented to investigate proposed techniques.     

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     

Implementation of large scale shadowgraphy in hydrogen explosion phenomena

The purpose of this study is to determine the performance of a portable large-scale shadowgraph system for use in hydrogen combustion experiments. Previous large-scale shadowgraph and schlieren implementations have often been limited to background-oriented techniques which are subject to noise. The system built is based on a large-scale shadowgraph technique, developed by Settles, which allows for noise-free visualization. We performed jet release, unconfined flame and detonation experiments in hydrogen mixtures. Shadowgrams taken were compared to a Z-schlieren system. Large-scale shadowgraphy offered high-quality visualization of hydrogen explosion phenomenon.     

A robust H∞ power system stabilizer with noadverse effect on shaft torsional modes

The H^∞ optimal control theory has been used to design a robust power system stabilizer (PSS) to improve transient and dynamic stabilities of a turbogenerator connected to an infinite busbar. It is demonstrated that the effects of disturbances in the machine output can be minimized and sufficient closed-loop stability margins (robustness) can be obtained to tolerate variations in the loop transfer functions, such as those which might arise from unmodeled low-damped high-frequency modes of oscillations. The resulting controller would effectively enhance the synchronizing and damping torques of the machine without the risk of exciting the shaft torsional modes. This is in marked contrast with the unstable performance of linear quadratic (LQ) optimal controllers under similar conditions. The H^∞ design methodology also ensures a satisfactory performance of the PSS under a wide range of system operating conditions     

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     

Interaction of fluid dynamics phenomena and generator efficiency in two-phase liquid-metal gas magnetohydrodynamic power generators

The two-phase-flow (liquid-metal and gas) magnetohydrodynamic (LMMHD) generator and its associated thermodynamic cycle offer a promising alternative to conventional means of electrical power generation. Several advantages can be gained from its application. The LMMHD cycle can be applied to a very wide range of operating temperatures (heat sources) either alone or as a topping or bottoming part of a binary cycle. The potential is high for extreme design simplicity and reliability, because the need for high-speed rotating machinery, as used in turbine power plants, is eliminated. The electrical conductivities, proportional to the power densities, are higher by three or four orders of magnitude than in plasma MHD generators; thus, generator efficiency is potentially higher. Also, because of the intimate contact between liquid-metal and gas in the generator, the expansion process is nearly isothermal (an ‘infinite reheat’ turbine). Therefore, with proper heat regeneration, the cycle is a quasi-Ericsson cycle. The choice of working fluids may be either an ideal gas (e.g. helium, argon) or a condensible fluid (e.g. steam, CO₂).This paper relates the potential loss mechanisms in the LMMHD generator to various fluid dynamic phenomena that are discussed. Among these are effects resulting from velocity slip, vorticity generation and suppression by the magnetic field, wall friction, and shunt currents in liquid boundary layers. Experimental data relating to the internal flow phenomena and to overall generator performance are shown.The relative importance of these effects is discussed in relation to experimental evidence and known theory. It is concluded that the slip loss, resulting from a churn-turbulent flow pattern, is the major source of loss. A proposed means of creating a stable, homogeneous foam flow with virtually no slip, using the surface active properties of liquid metals, is discussed. Means are also suggested for reduction of wall shunt and frictional losses. The effects of end losses in two-phase flows are also described.     

Reducing inefficiency and emissions of large steam generators in the United States

Combustion process modifications to reduce inefficiency and emissions in contemporary large boilers are constrained by a number of important design and operating considerations such as steam temperature, ash fusion and material limitations. Plant efficiency gains, obtainable by further increasing combustion heat release efficiency, are in many cases negligible. However, depending upon standard operation, a large potential exists for increasing overall efficiency by lowering excess air levels, while at the same time decreasing pollutant emissions. Dramatic increases in fuel prices have now made investment in such improvements more attractive in the United States than it was in the past. Reduction of excess air level can in addition effect reductions in emissions of NO_x and SO₃, and even of particulates, through equipment and operating improvements. High fuel prices have also made investment in air preheaters and economizers attractive for a larger number of boilers than ever before.Air pollutants can originate from components of the fuel, from incomplete combustion, or even through complete combustion processes. These various forms of pollution can be controlled in varying degrees during the combustion process by wet ash handling, SO₂ to SO₃ conversion minimization, or mixing and temperature control in the case of combustibles and nitric oxide. NO_x reduction techniques, applied to a large gas-fired utility boiler, resulted in NO_x emissions of 33 ppmV or less at power outputs up to 355 MW. For coal- and oil-fired boilers, NO_x scavenging by ammonia injection, recently developed, can give dramatic reductions in NO_x emissions without affecting the combustion process.     

Short-circuit test based maximum likelihood estimation of stabilitymodel of large generators

This paper presents a time-domain statistical identification method for synchronous-machine linear parameters from the standard line-to-line short-circuit test. The measurements are recorded on a 13.75-MVA hydrogenerator at Hydro-Quebec's Rapide-des-Quinze generating station. A complete mathematical model for synchronous machine asymmetrical test analysis is proposed. An efficient algorithm is built to accurately calculate the standard equivalent circuit from time-constants and operational inductances. The maximum likelihood estimator derived from the generalized least-squares method is then used for parameter identification. Validation of the estimated model response against the measured running-time domain data confirms the effectiveness of the proposed estimation technique     

Unsteady and non-linear aeroelastic analysis of large horizontal-axis wind turbines

Analysis results, obtained from numerical simulation, for non-linear and unsteady aeroelastic behavior of large horizontal-axis wind turbines are presented in this paper. Simulations are carried out using a partitioned scheme of weak interaction that allows dealing with the fluid–structure interaction problem by using one method to solve the structural-dynamic problem and another method for the aerodynamic problem.     

Analysis of parallel-operated self excited induction generators

The paper presents an iterative solution for the problems related to steady state performance of self-excited induction generators operating in parallel. The analysis is based on voltage and current balance equations derived from an inverse-model for the steady state equivalent circuit of induction machines. The nonlinearity in the magnetization characteristics has been taken into account by piecewise linearisation. The proposed method is general and can be applied for analysis of any number of parallel connected machines. Theoretical predictions and experimental results are presented to study different performance characteristics of the system     

Analysis of torsional oscillations using an artificial neuralnetwork

A novel approach using an artificial neural network (ANN) is proposed for the analysis of torsional oscillations in a power system. In the ANN those system variables, such as generator loadings and the capacitor compensation ratio, which have major impact on the damping characteristics of torsional oscillation modes were used as the inputs. The outputs of the neural net provided the desired eigenvalues for torsional modes. Once the connection weights of the neural network have been learned using a set of training data derived offline, the neural network can be applied to torsional analysis in real-time situations. To demonstrate the effectiveness of the proposed neural net, torsional analysis was performed on the IEEE First Benchmark Model. It is concluded from the test results that accurate assessment of the torsional mode eigenvalues can be achieved by the neural network in a very efficient manner     

Analysis of self-excited induction generators using an iterativemethod

This paper describes the steady-state analysis of self-excited induction generators (SEIG) using an iterative method. By considering the conductances connected across the air gap nodes, an iteration procedure is developed for the determination of the self-excited per-unit frequency, which enables the equivalent circuit to be completely solved. The proposed method involves only simple algebraic calculations, but the accuracy is good and convergence is rapid. The method is subsequently extended to include core loss effects and the analysis of SEIG with series capacitance compensation. Very good agreement between experimental and computed results has been obtained on a 2 kW laboratory machine     

Methodology development for estimation of armature circuit andfield winding parameters of large utility generators

This paper presents a methodology to estimate armature circuit and field winding parameters of large utility generators using the synthetic data obtained by the machine natural abc frame of reference simulation. First, a one-machine infinite bus system including the machine and its excitation system is simulated in abc frame of reference by using parameters provided by the machine manufacturer. A proper data set required for estimation is collected by perturbing the field side of the machine in small amounts, The recursive maximum likelihood (RML) estimation technique is employed for the identification of armature circuit parameters. Subsequently, based on the estimates of armature circuit parameters, the field winding and some damper parameters are estimated using an output error estimation (OEM) technique. For each estimation case, the estimation performance is also validated with noise corrupted measurements. Even in case of remarkable noise corruption, the agreement between estimated and actual parameters is quite satisfactory     

直驱型风电系统Boost变换器控制策略分析

以目前直接驱动型风电系统中最典型的单相boost DC/DC电路拓扑为对象,对单周控制、滞环电流控制、滑模控制、重复控制、双环控制等几种比较有效的控制策略作了深入剖析.最后选双环控制作了仿真分析.给出了仿真波形.     

Analysis of electromagnetic characteristics of typical faults in permanent magnet wind generators

Due to the harsh actual operating environment of the permanent magnet wind turbine, it is easy to break down and difficult to monitor. Therefore, the electromagnetic characteristics identification of major fault types of large-scale permanent magnet wind turbines is studied in this paper. The typical faults of rotor eccentricity, stator winding short circuit and permanent magnet demagnetization of permanent magnet wind turbines are analyzed theoretically. The wavelet analysis algorithm is used t...     

660 MW发电机漏氢原因分析与处理对策

鸳鸯湖电厂1号发电机为QFSN6602型汽轮发电机,采用水氢氢冷却方式,正常运行时发电机内氢压高于定子冷却水压力;当定子线棒存在裂纹并发生泄露时,将会导致定子冷却水含氢量急剧升高,从而使定子冷却水进入发电机造成发电机烧损.定子冷却水箱安装氢气泄露检测仪,在线检测定子冷却水箱内氢气含量,当氢气浓度达2%时就会报警.讨论了发电机定子冷却水箱内检测仪报警后的原因分析及处理,为同类机组类似故障处理提供参考.