Analysis and Online Diagnosis on Plugging Fault of Servo Valve in Electro-hydraulic Regulating System of Steam Turbine

Through the study on the output signals of the electro-hydraulic regulating system in the thermal power plant, a novel method for online diagnosis of the plugging fault in the servo valve is presented. With the use of the AMESIM software, the changes of the piston displacement, the oil pressure, the magnitude attenuation and the phase lag of the system under different plugging states are studied after simulation. Besides, the influences of the symmetrical and unsymmetrical plugging on the system are also compared and the characteristic table is given. The duo-neural network is put forward to achieve an online diagnosis on the plugging fault of the servo valve. The first level of network helps to make the qualitative diagnosis of the plugging position while the second level is for the quantitative diagnosis of the degree of the plugged position. The research results show that plugging at different positions exerts different influences on the performance of the system. The unsymmetrical plugging mainly affects the regulation time while the symmetrical plugging leads to great changes in the magnitude attenuation and the phase lag.

Optimum Tilt Angle of Flow Guide in Steam Turbine Exhaust Hood Considering the Effect of Last Stage Flow Field

Abstract Heat transfer and vacuum in condenser are influenced by the aerodynamic performance of steam tur- bine exhaust hood. The current research on exhaust hood is mainly focused on analyzing flow loss and optimal design of its structure without consideration of the wet steam condensing flow and the exhaust hood coupled with the front and rear parts. To better understand the aerodynamic performance influenced by the tilt angle of flow guide inside a diffuser, taking a 600 MW steam turbine as an example, a numerical simulator CFX is adopted to solve compressible three-dimensional （3D） Reynolds time-aver- aged N-S equations and standard k-e turbulence model. And the exhaust hood flow field influenced by different tilt angles of flow guide is investigated with consideration of the wet steam condensing flow and the exhaust hood coupled with the last stage blades and the condenser throat. The result shows that the total pressure loss coefficient and the static pressure recovery coefficient of exhaust hood change regularly and monotonously with the gradual increase of tilt angle of flow guide. When the tilt angle of flow guide is within the range of 30~ to 40~, the static pressure recovery coefficient is in the range of 15.27% to 17.03% and the total pressure loss coefficient drops to approximately 51%, the aerodynamic performance of exhaust hood is significantly improved. And the effectiveenthalpy drop in steam turbine increases by 0.228% to 0.274%. It is feasible to obtain a reasonable title angle of flow guide by the method of coupling the last stage and the condenser throat to exhaust hood in combination of the wet steam model, which provides a practical guidance to flow guide transformation and optimal design in exhaust hood.

Numerical Simulation of Water Droplets Deposition on the Last-Stage Stationary Blade of Steam Turbine

Based on the method of discrete phase, the law of droplets’ deposition in the last stage stationary blade of a supercritical 600 MW Steam Turbine is simulated in the first place of this paper by using the Wet-steam model in commercial software FLUENT, where the influence of inlet angle of water droplets of the stationary blades is also considered. Through the calculation, the relationship between the deposition and the diameter of water droplets is revealed. Then, the amount of droplets deposition in the suction and pressure surface is derived. The result is compared with experimental data and it proves that the numerical simulation result obtained in this paper is reasonable. Finally, a formula of the relationship between the diameter of water droplets and the inlet angle is fit, which could be used for approximate calculation in the engineering applications.

Study on Valve Management of DEH for Steam Turbine

Valve management is one of the major functions of DEH for steam turbine. It has an important practical significance for the security and economy of the steam turbine. This paper starts from the valve configuration figure of the domestic-type 300 MW steam turbine, and then makes a simple comparison between the two types of valve governing modes. In order to realize the valve control, the structure of control system has been established, in which the roles of the mathematical functions are discussed. On the basis of the experiment of valve flow characteristic, this article carries out a quantitative study on the functions of the valve management and the parameter tuning method. Through a serious corrections, the sequence valve flow characteristic curve is obtained, which can provide significant guidance on the research of valve management of the similar steam turbines.

Investigation of the steam-cooled blade in a steam turbine cascade

With the increasing demand for electricity,an efficiency improvement and thereby reduced CO2 emissions of the coal-fired plants are expected in order to reach the goals set in the Kyoto protocol.It can be achieved by a rise of the process parameters.Currently,live steam pressures and temperatures up to 300 bars and 923 K are planned as the next step.Closed circuit steam cooling of blades and vanes in modern steam turbines is a promising technology in order to establish elevated live steam temperatures in future steam turbine cycles.In this paper,a steam-cooled test vane in a cascade with external hot steam flow is analyzed numerically with the in-house code CHTflow.A parametric analysis aiming to improve the cooling effectiveness is carried out by varying the cooling mass flow ratio.The results from two investigated cases show that the steam cooling technique has a good application potential in the steam turbine.The internal part of the vane is cooled homogeneously in both cases.With the increased cooling mass flow rate,there is a significant improvement of cooling efficiency at the leading edge.The results show that the increased cooling mass flow ratio can enhance the cooling effectiveness at the leading edge.With respect to trailing edge,there is no observable improvement of cooling effectiveness with the increased cooling mass flow.This implies that due to the limited dimension at the trailing edge,the thermal stress cannot be decreased by increasing the cooling mass flow rate.Therefore,impingement-cooling configuration at the trailing edge might be a solution to overcome the critical thermal stress there.It is also observed that the performance of the cooling effective differs on pressure side and suction side.It implicates that the equilibrium of the cooling effectiveness on two sides are influenced by a coupled relationship between cooling mass flow ratio and hole geometry.In future work,optimizing the hole geometry and cooling steam supply conditions might be the solutions for an equivalent cooling effectiveness along whole profile.

Catastrophe Model of Steam Flow Excitation Vibration in Steam Turbine Governing Stage

汽流激振是影响大型汽轮机组安全运行的主要故障之一。根据突变理论、非线性振动理论以及流体动力学，从机理分析的角度出发，对汽轮机调节级在部分进汽下导致的汽流激振突变性能进行了定量分析。建立了部分进汽情况下调节级气流激振力模型，以及考虑汽流激振力的调节级非线性动力学模型，通过基于突变理论的推导，得到了调节级汽流激振的尖点突变流形和分岔集，确定了系统汽流激振突变的影响因子，讨论了振幅突变与影响因子的相关性，划分了系统工作的突变区域。最后，利用数值计算方法对汽流激振的幅值响应进行了分析，分析结果验证了基于突变理论的汽流激振突变分析方法的正确性。研究成果为汽轮机汽流激振突变性能的研究提供了一条新的途径。

Fault Detection and Isolation Based on Neural Networks Case Study: Steam Turbine

The real-time fault diagnosis system is very important for steam turbine generator set due serious fault results in a reduced amount of electricity supply in power plant. A novel real-time fault diagnosis system is proposed by using Levenberg-Marquardt algorithm related to tuning parameters of Artificial Neural Network (ANN). The model of novel fault diagnosis system by using ANN are built and analyzed. Cases of the diagnosis are simulated. The results show that the real-time fault diagnosis system is of high accuracy and quick convergence. It is also found that this model is feasible in real-time fault diagnosis. The steam turbine is used as a power generator by SONELGAZ, an Algerian company located at Cap Djinet town in Boumerdes district. We used this turbine as our main target for the purpose of this analysis. After deep investigation, while keeping our focus on the most sensitive parts within the turbine, the weakest and the strongest points of the system were identified. Those are the points mostly adequate for failure simulations and at which the designed system will be better positioned for irregularities detection during the production process.

Theoretical and Numerical Analysis of the Mechanical Erosion in Steam Turbine Blades. Part I

The methodology of calculation of the velocity distribution for the stream frictionless and the drops in the flow line, on the basis of the frictionless, two-dimensional, stationary, transonic and homogenous flow is established. The knowledge of conditions that govern the low pressure section of steam turbines in the last stage to have an approximate movement of the droplets in the blade cascades and the accumulation of droplets on the stator blades, flowing through the steam, is presented. This study is used for developing a code in Fortran about the velocity distribution in the output of stator blades that have flow conditions of wet steam, in order to understand the causes that originate the erosion on the blades of the last stages in the low pressure section of steam turbines.

Modeling and Optimization of the Steam Turbine Network of an Ethylene Plant

In this paper,we developed a hybrid model for the steam turbines of a utility system,which combines an improved neural network model with the thermodynamic model.Then,a nonlinear programming(NLP) model of the steam turbine network is formulated by utilizing the developed steam turbine models to minimize the total steam cost for the whole steam turbine network.Finally,this model is applied to optimize the steam turbine network of an ethylene plant.The obtained results demonstrate that this hybrid model can accurately estimate and evaluate the performance of steam turbines,and the significant cost savings can be made by optimizing the steam turbine network operation at no capital cost.

Research on new type of fast-opening mechanism in steam turbine regulating system and optimization of operation tactic

With the analysis on regulating system in 200 MW steam turbine, the necessity of appending the fast-opening function to the original system is set forth and a new type of fast-opening mechanism is devised. The mathematical model of system is built up. With the use of AMESIM software, the displacement curve of the piston, the force curve of the cartridge valve spool, the pressure curve and the flux curve in the regulation process are obtained based on simulation. The performances of three fast-opening systems composed of cartridge valves with different diameters are compared. Based on the analysis on factors that affect the execution time of fast-opening, the dead zone of the fast-opening system is put forward. To overcome the defect, dif- ferent operation modes are adopted for different zones. The result shows that with the increase of the valve diameter, the regulating time in the dead zone significantly exceeds the fast-opening time in the whole journey. Accordingly, the optimization operation tactic in the dead zone and the qualification conditions are brought forward. The fast-opening system composed of 32 mm cartridge valves is taken as an example with use of the tactic. The simulation result shows that the maximum regulating time is shortened by 509 ms.

Sensitivity Analysis of Energy Consumption for Cylinder Efficiency of A 1 000 MW Steam Turbine Unit

以东汽1000MW汽轮机为研究对象，采用汽轮机组定功率变工况计算方法，对汽轮机各汽缸效率在THA、70％THA、50％THA、40％THA滑压工况进行敏度分析，得到相应工况下各汽缸效率变化对汽轮机热耗率和机组发、供电煤耗率的影响规律。分析表明，缸效率的能耗敏度随缸效率变化基本呈线性关系；低压缸效率的能耗敏度最大，高压缸效率次之，中压缸效率较小；随机组负荷降低，高压缸效率的能耗敏度增加，中、低压缸效率的能耗敏度变化较小。在THA工况下低压缸效率下降1％，供电煤耗敏度绝对值增加1．246g／（kW·h），相对值升高0．433％；高压缸效率下降1％，供电煤耗敏度的绝对值增加0．44g／（kW．h），相对值升高0．154％；中压缸效率下降1％，供电煤耗敏度的绝对值增加0．352g／（kW．h），相对值升高0．122％。分析结果可对同类型机组进行节能诊断，进而指导机组的优化运行。

Finite Element Analysis of Steam Turbine Diaphragm

Thediaphragmofsteam turbine isoneofthemainpartsofthepassageunitfor air flowing.For studying its working conditionand performance, the three-dimensionalfinite element model（FEM）with thesoftware ANSYS10.0 isestablished according to theactualworking parameters. With the model, the deformation resultsand stress field resultsare analyzed andthe maximum displacement and stress value are calculated, meanwhile,theircorrespondingpositions are found. It provides a good foundationfor solving the problem inproduction.

Correlation Dimension in Fault Diagnosis of 600 MW Steam Turbine Generator

GP algorithm of correlation dimension computation is ameliorated which overcomes the shortage of traditional one. Improved process of GP algorithm takes the influence of temporal correlative pairs of points on correlation dimension into account and promotes the computational efficiency prominently. Iterative SVD method is applied to remove the influence of noise on the result of correlation dimension. The faults of steam flow turbulence and oil film disturbance which occur in 600 MW Steam Turbine Generator are analyzed and whose correlation dimensions are computed. More distinct quantitative index than FFT is gained to distinguish two faults and it’s of little importance to apply correlation dimension to study the influence of various factors on steam flow turbulence fault for nonexistence of convergent floor in correlation integral curve, which presents a new way to learn the operational function of large capacity steam turbine generator and carry out comprehensive condition monitoring.

On-line Failure Diagnostics for Steam Turbine Hydraulic Governing System

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The Density and Momentum Distributions of 2-Dimensional Transonic Flow in an LP-Steam Turbine

Within turbine blade rows, particularly for cascades of high deflection angle, cross-channel gradients of steam properties may be appreciable. To determine the effects on spontaneous condensation of gradients of supersaturation normal to streamlines, the conservation equations can be incorporated in a two dimensional calculation procedure. With the help of program FORTRAN 90 a developed computational program of calculations is accomplished, whose results are communicated to the pressure and Mach number distribution, direction of flow and streamlines in the field and the drops distribution in the outlet of the stator blade mesh. The procedure contains a program section, which avoids difficulties in the strongly curved profile of the leading and trailing edge by a developed computational mesh construction.

Application of new techniques to renovation of 200 MW steam turbine

Presents the new techniques leading to the improvements in aerodynamics of 200MW steam turbine high pressure cylinder and mid pressure cylinder, discusses the rear loaded profile and blade bowing, and concludes from numerical simulation and experimental results that the application of rear loaded profile and blade bowing has improved the performance of 200 MW unit.

Feasibility Analysis of Back-Pressure Steam Feeding Water Pump for Direct Air-Cooled Unit

As the performance of an air-cooled condenser is apt to be affected by the fluctuating ambient condition, some difficulties are brought to the use of a steam feeding water pump in an air-cooled unit. This paper introduces a new design of for steam feeding the water pump of an air-cooled unit using the back-pressure steam turbine as the prime motor. Using variable condition analysis on a 600 MW direct air-cooled unit, and with consideration of the effect on the ambient conditions, the feasibility, economy, and adaptability of the design are verified.

Calculation of the Choked Back Pressure for Steam Turbines with Air Cooled Condensers

The choked back pressure characteristic of the steam turbine unit with air cooled condenser is very different with the unit with wet cooling technology, and the understanding of the choked back pressure performance change with operation load is important to guide the economic operation of the unit. One simplified Variable Operation Condition Analysis Method was put forward for calculation of the unit output-turbine back pressure characteristics. Based on this method, the choked back pressure for each operation load can be determined. An example was given for a super-critical, regenerative single-shaft, 2-casing with 2-exhaust steam turbine generation unit with air cooled condenser. The calculation result was provided and compared with the result of the unit with wet cooling technology.

Calculation of Thermal Stress and Fatigue Life of 1000 MW Steam Turbine Rotor

The paper calculated the temperature and stress fields of 1000 MW ultra-supercritical steam turbine rotors which start in cold condition using the finite element calculation program (ANSYS). After getting rotor stress field, the paper use the general slope method to estimate the low cycle fatigue life loss, the rest of the conditions can be calculated in this method.

Theoretical and Numerical Analysis of the Mechanical Erosion in Steam Turbine Blades. Part II

In the low pressure section of the steam turbines the damages are pronounced becoming remarkable in all the stages, since the generation of water liquid microparticles implies the impact on the blades having majors problems of erosion in the last stages by the increase of the humidity. In the first part of this work, the calculation presented of the transonic velocity field for the stream frictionless and the drops in the flow line, on the basis of the frictionless, two-dimensional, stationary, transonic and homogenous flow, give an approximate movement of the droplets and its accumulation on the stator blades, flowing through the steam. In order to understand the causes that originate the erosion on the blades of the last stages in low pressure section of steam turbines, the previous procedure is developed in a code in Fortran and the obtained results of velocity distribution in the output of blades that have flow conditions of wet steam are presented.