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     

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 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     

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     

The design of turbine-generator optimal controllers including theeffect of torsional modes of oscillation

Optimal linear control has been suggested for designing supplementary signal controllers for turbine-generators. It is shown that the design of the controller should include consideration of the torsional modes of oscillation of the rotor to obtain the best performance. The exciter voltage ceiling is shown to limit the sum of the synchronizing and damping torques. Practical designs normally require that tradeoffs be made. It is shown how advantage would be gained by using the supplementary signal. Normally fed to the speed governor controlling the main steam valve, for a second governor that would merely act on a fast interceptor valve     

Heat propagation on a shaft due to transient torsional vibration

During transient torsional vibration of rotating shafts heat is generated due to material damping, which results in substantial temperatures. The problem of a cylinder of infinite length heated by way of a transient torsional vibration of variable amplitude is investigated and an expression of the maximum surface temperature is obtained. Diagrams with the appropriate dimensionless parameters are presented together with a numerical example. It is shown that substantial temperatures can be developed as a result of this mechanism of heat generation. This quantities the belief that this phenomenon was the reason for a major generator failure in a power system.     

Effect of torsional dynamics on salient pole synchronousmotor-driven compressors

This paper presents a rigorous treatment of the starting problem of a salient pole synchronous motor driving a complex multicompressor load. This is aimed at analysing the resulting torsional oscillations and calculating the different transmitted torques and twist angles of the multi-shaft assembly. For this purpose, the necessary mathematical models and corresponding digital simulation are developed. The results obtained show that there is a pressing need for taking care of the torsional effects on the different shafts during the design stage, otherwise serious problems could arise     

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 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     

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     

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     

抗侧滚扭杆对车辆动力学性能的影响分析

利用SIMPACK软件建立了车辆整车动力学模型,分析其线性临界速度及非线性临界速度,结果显示其临界速度完全满足设计要求。通过改变抗侧滚扭杆扭转刚度来考察其对于车辆运行性能的影响,进一步分析了该型车在直线及曲线状态下的性能。     

Effect of stochastic thermal input on elastic and thermal properties of an infinitely long annular cylinder

Random elastic and thermal properties for an infinitely long solid conducting circular cylinder are investigated under the effect of random thermal input. The problem is considered in the context of a generalized thermoelasticity theory with one relaxation time. The lateral surface of the solid is traction free and subjected to known stochastic temperature, driven by an additive Gaussian white noise. Laplace transform technique is used to obtain the solution in the transformed domain. Statistically, we derive and analyze the mean and variance for temperature, displacement and stress. Numerical inversion of the transformed solution is carried out, represented graphically and discussed.     

Numerical study on pressure drop factor in the vent-cap of CDQ shaft

In CDQ （Coke Dry Quenching） shaft, the vent-cap with complex structure is installed in the cone-shaped funnel under the cooling chamber. It acts to introduce cooling gas and support the descending coke in the chamber. The designing and installation of vent-cap aim to get relatively uniform gas distribution, to reduce the temperature fluctuation of cokes at outlet and realize stable operation of CDQ apparatus. In this paper, the turbulent flow of gas in vent-cap of 1：7 scale CDQ experimental shaft is numerically simulated by using CFD （Computational Fluid Dynamics） software, CFX. The velocity field, the outlet flux distribution and the pressure drop factor of each outlet under three kinds of vent-cap （called high vent-cap, low vent-cap and elliptic vent-cap） are analysed and compared. The results turn out that the pressure drop factor of elliptic vent-cap is larger than the other two vent-caps, and that the pressure drop factors of high vent-cap and low vent-cap almost have the same value. While for a specified vent-cap, the pressure drop factor with pressing brick is larger than that without pressing brick. The work in this paper is valuable for the designing of vent-cap for large-scale CDQ shaft.     

气烧石灰竖窑的节能与降耗

本文主要介绍新钢公司石灰厂气烧石灰竖窑在节能降耗方面的一些成功技改方法。     

Effects of eccentricities on shaft signals studied throughwindingless rotors

Shaft signals of electric rotating machines offer potentials for defect detection. The signals are affected by many factors. This study specifically focuses on how eccentricities affect shaft signals through theoretical predictions and tests conducted on windingless rotors. Windingless rotors imply currentless rotors. For symmetrical synchronous machines running at steady synchronous speeds, the induced rotor currents are zero, while harmonics are neglected. One advantage in experiments for this study is that air gaps can be shimmed accurately at standstill without end brackets; certain tests can be conducted at standstill without facing unmanageable locked-rotor currents for the test machines. Shaft signals decrease when the rotor of a machine closely situates at the center of stator bore. Shaft signals increase under greater eccentricities when stator and rotor axes are parallel. Tilted rotors reduce shaft signals. Even when there are no rotor windings, inherent positional characteristics exists. This characteristic produces cyclic shaft-signal components that are related to rotor revolutions     

内燃机过渡工况扭振特性研究

提出了一种去除过渡工况中趋势项的方法以提高内燃机轴系扭振幅频特性分析精度。利用过渡工况下扭振信号的各简谐成分实部和虚部等于该转速下稳定工况扭振信号各简谐成分实部和虚部与趋势项各简谐成分实部和虚部线性叠加的性质,可通过消去趋势项得到该转速下稳态工况的各简谐成分准确幅值。通过仿真和实验研究,不仅验证了所提方法的实用性,并且发现过渡工况中的趋势项具有对0.5、1.0等低简谐成分幅值影响最大,而对中、高简谐成分幅值影响相对较小的性质。     

Influence of the gasket materials on the clamping pressure distribution in a PEM water electrolyzer: Bolt torques and operation mode in pre-conditioning

To keep optimally connected, all electrolysis cell elements is one of the most important design criteria. The optimal distribution of the clamping points is crucial to increasing cell performance. In this work, the compression pressure distribution inside of a 25 cm² PEM electrolysis cell was evaluated, using different materials: Teflon®, Viton®, ethylene propylene diene monomer rubber (EPDM), and nitrile rubber. Sealing material evaluation was performed taking as performance indicators: total compressed area (%) and compression pressure, for different torques applied. Pressure distribution was obtained by using pressure-sensitive films, analyzing the distribution of pressure points from three-dimensional plots (3D), and quantifying intensities of the images obtained. Results showed that pressure points distribution depends on the stiffness and thickness of the gasket materials. For a tightening torque of 3.70 N m, a pressure of 2.23 MPa is obtained with 85% of the membrane area compressed using nitrile rubber-EPDM gaskets.     

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.     

汽车驱动桥半轴离合器的节能性研究

车辆在轻载滑行过程中,由于没有与动力源切断,往往会消耗大量的能源。对置于汽车驱动桥末端的一种新型机械节能装置——驱动桥半轴离合器进行了研究,并对其结构和工作原理进行了综合分析和性能实验。通过对汽车轻载滑行工况的研究分析,构建了汽车轻载时的滑行方程,并进行实际道路试验,分析了驱动桥半轴离合器半轴的强度和刚度。结果表明,半轴的强度和刚度并没有明显下降,且该装置具有显著的节能效果。