Main Steam Valve Research Articles

A novel adaptive backstepping design of turbine main steam valve control

The problem of transient stability for a single machine infinite bus system with turbine main steam valve control is addressed by means of a novel adaptive backstepping method in this paper. The recursive design procedure of the proposed controller is much simpler than that of the existing controller based on conventional adaptive backstepping method. In the system, the damping coefficient is measured inaccurately, and the reactance of transmission line also contains a few uncertainties. A nonlinear robust controller and parameter updating laws are obtained simultaneously. The system does not need to be linearized, and the closed-loop error system is guaranteed to be asymptotically stable. The design procedure and simulation results demonstrate the effectiveness of the proposed design.

New Coordinated Control Design for Thermal-Power-Generation Units

A nonlinear model combining boiler-turbine-generator dynamic characteristics for a thermal-power-generation unit is first introduced. Based on the nonlinear model, a new coordinated control design is proposed using the backstepping method incorporating the coordinated passivation approach that considers the entire boiler-turbine-generator system as a whole. The control design consists of three subcontrollers, namely, a main steam valve controller, an excitation controller, and a fuel flow controller. It is shown that the proposed coordinated control design can ensure asymptotical stability of the closed-loop system and improve the electric power regulation performance. Simulation results based on a practical thermal-power-plant model are presented to show the effectiveness of the proposed control design.

1020 主蒸気止め弁に発生するホールトーンの騒音低減方法(OS10-5 流体関連振動・騒音,オーガナイズドセッション)

There was a possibility that hole-tone was generated in a main steam stop valve (MSV) and caused the vibration and sound noise in the main steam line of the thermal power plant. To reduce the sound noise and vibration, scale air tests were conducted in the present study. Hole-tone broke out in Mach number more than 0.18. Low height slant tubs installed in the MSV seat completely suppressed the sound noise due to hole-tone.

Inelastic Deformation and Crack Growth Behavior of CrMoV Cast Steel after Long-Term Service at High Temperature

For the purpose of residual life prediction of high-temperature components after long-term service, both stress-strain behavior for evaluating fracture mechanics parameters and crack growth behavior were examined using CrMoV cast steel taken from a main steam valve served for 155,000 hours at 811K under 216 start-stop cycles. Firstly the influence of cyclic softening and thermal aging history on the stress-strain curve was examined. As a result of comparison between virgin and long-term served material, a possibility of predicting the stress-strain behavior of the long-term-served material from that of virgin material was discussed. Secondly creep and fatigue crack growth behavior of long-term served material were experimented and compared with those of virgin material. Finally creep-fatigue crack growth tests under displacement-controlled condition were carried out with structural model specimens made of the long-term served material. The crack growth behavior of the tests was simulated using the method proposed by the authors on the basis of the monotonic stress strain curve and the stress strain curve of half-fatigue life of the material. Comparison with the test results showed that the simulation using the monotonic stress-strain curve of the material gave the conservative prediction of the crack growth behavior.

Prediction of crack growth in CrMoV cast steel after long-term service at high temperature

A simplified prediction method is presented that uses fracture mechanics parameters for displacement-controlled conditions, which had been proposed by the authors. This method was applied to the CrMoV cast steel taken from a power plant that was in service as a main steam valve for 155,000 h at 811 K under 216 start-stop cycles. The possibility of predicting the stress–strain behavior of the long-term-served material was examined by considering the inelastic strain and thermal aging history of the material. Crack growth tests were also carried out with structural model specimens taken from the above component, and the crack growth behavior was predicted using the proposed method. Comparison with the test results showed that the proposed method was successfully applied to the prediction of the crack growth behavior of the long-term-served material.

A new adaptive backstepping method for nonlinear control of turbine main steam valve

A new approach for nonlinear adaptive control of turbine main steam valve is developed. In comparison with the existing controller based on “classical” adaptive backstepping, this method does not follow the classical certainty-equivalence principle in the design of adaptive control law. We introduce this approach, for the first time, to power systems and present a novel parameter estimator and dynamic feedback controller for a single machine infinite bus (SMIB) system with steam valve control. This system contains unknown parameters such as reactance of transmission lines. Besides preserving useful nonlinearities and the real-time estimation of uncertain parameters, the proposed approach possesses better performances with respect to the response of the system and the speed of adaptation. The simulation results demonstrate that the proposed approach is better than the design based on “classical” adaptive backstepping in terms of properties of stability and parameter estimation, and recovers the performance of the “full-information” controller. Hence, the proposed method provides an alternative for engineers in applications.

Evaluation of DBTT and Creep Properties of Aged Main Valve Casing by Using Small Punch Specimens

Both the change in DBTT and the degradation of creep properties of the aged CrMoV cast steel which had been actually used as a main steam valve were evaluated from the conventional SP test and the SP creep (SP-C) test using by SP test specimens. The CVN DBTTs of the virgin and aged steels were estimated to be 280 and 369 K by the conventional SP test, respectively. This increase in DBTT after the long-term service exposure was considered to be caused by carbide-induced embrittlement due to coarse carbides. The SP-C test results revealed that the creep rupture strength of the aged steel was inferior to that of the virgin steel. The ratio, F / s , between the load of the SP-C test (F) and the stress of the uniaxial test ( s) was determined to be 2.4 for the same value of the Larson-Miller parameter in the creep rupture data. This linear relationship enables us to convert the results of the SP-C test into those corresponding to a conventional uniaxial creep test. Consequently, the SP testing method is expected to be appropriate tool for the determination of material deterioration and, in turn, the assessment of remaining-life of high-temperature components.

Approach to residual life assessment of large steam turbine components

Ansaldo has manufactured and installed in Italy and all over the world, since 1909, medium and large steam turbines under its own design and various licence agreements, such as General Electric, Westinghouse, and, more recently, ABB. Since 1986 residual life assessment research programs have been implemented with a big effort, and a special approach to residual life assessment has been defined with our main customer, the ENEL Company, for the activity to be carried out in order to get the optimum balance between safety and cost consideration. The paper will illustrate this approach as well as the techniques developed for residual life investigations. In the paper are presented examples of the documentation for data acquisition, examples of the application of investigation techniques such as computer echotomography, boresonic and material sampling on rotors, and finite element analysis on critical main steam valves.

A case study and damage assessment of some heavy section components operating for more than 100 000 h in fossil-fired power plants

A main steam pipe T-piece, a main steam stop valve and a reheater steam piping Y-piece have been taken out of three different power boiler plants that have seen each an accumulated service life of over 100 000 h, involving more than 500 start-and-stop operations, and their states of degradation examined. The degradation was assessed in terms of the changes found in the mechanical properties and the metallographic structure, the flaws actually detected in them, and analyses of the distributions of temperature and stress for start-and-stop operations as well as steady state were calculated on the basis of the service histories. Detailed stress analysis afforded information to indicate the portions that sustained large damage, and on which damage assessment calculations were conducted. The remaining service lifetime calculation was conducted on the basis of analyses of propagation of the defects and showed that the component had sufficient allowances for continued service under severe operating conditions.

Disturbance Identification Method of Pressurized Water Reactor Plant Operated with Automatic Frequency Control by Applying Projection Operator Technique

The identification method applying the projection operator for less small disturbances which do not instantly lead the alarm initiation has been extended to diagnose PWR plants operated with automatic frequency control. The authors previously proposed the non-linear transformation of the observed signals to satisfy with the linear relationship between the disturbances and the observed signals by utilizing several additional observed signals which are closely related with the non-linear characteristics of PWR plant. In addition, a method is proposed to compensate the fluctuation of observed signals due to automatic frequency control by utilizing both the input signal of the main steam valve control system and the input signal of the control rod control system. The effectiveness of the extended method has been examined by several computer experiments using a simple PWR plant simulation code.

Disturbance identification method of pressurized water reactor plant operated with automatic frequency control by applying projection operator technique.

The identification method applying the projection operator for less small disturbances which do not instantly lead the alarm initiation has been extended to diagnose PWR plants operated with automatic frequency control. The authors previously proposed the non-linear transformation of the observed signals to satisfy with the linear relationship between the disturbances and the observed signals by utilizing several additional observed signals which are closely related with the non-linear characteristics of PWR plant. In addition, a method is proposed to compensate the fluctuation of observed signals due to automatic frequency control by utilizing both the input signal of the main steam valve control system and the input signal of the control rod control system. The effectiveness of the extended method has been examined by several computer experiments using a simple PWR plant simulation code.

Diagnostic monitoring of solid particle erosion in steam turbines

An in situ wear measurement system has been demonstrated for steam turbine applications. The diagnostic technique can measure the wear and erosion damage caused by solid particle erosion (SPE) on a main steam stop valve bypass valve disc (SVBV). The technique consist of weakly activating the areas on the disc subject to wear by placing the disc in an ion accelerator beam. The induced radionuclides emit specific gamma rays in strengths safe for personnel, but strong enough for detection. The change in activity can be accurately correlated to the amount of erosion. The results of the field testing and associated economic evaluation indicate that the erosion monitoring system will allow Dayton Power and Light to plan SVBV disc replacement intervals based on actual measured erosion rates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The design of turbine-generator optimal controllers including the effect 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. >

Microcrack initiation and growth behavior under creep-fatigue in a plain specimen of degraded CrMoV cast steel.

Microcrack initiation and growth behavior were observed on the surface of nondegraded and degraded CrMoV cast steels under various strain wave shape loadings at high temperature. The degraded steel was taken from the inside of a main steam valve casing after 140 000 hours of service. No signigicant difference in crack growth behavior was observed under low cycle fatigue for either steel. However, the crack growth rate in the degraded steel was higher than that in the nondegraded one under creep-fatigue resulting from slow/fast straining. This was caused mainly by grown and coarsened grain boundary carbides. A residual life assessment method, based on microcrack growth and the statistical properties of microcrack length distribution, closely predicts the experimental results.

Micro-crack initiation and growth behavior under creep-fatigue in plain specimen of a degraded CrMoV cast steel.

Micro-crack initiation and growth behavior were observed on the surface of nondegraded and degraded CrMoV cast steels under various strain wave shape loadings at a high temperature. The degraded steel was taken from the inside of a main steam valve casing after 140 000 h of service. No significant difference in crack growth behavior was observed in low cycle fatigue in both steels ; however, the crack growth rate in the degraded steel was higher than that in the nondegraded one in creep fatigue under S-F straining. This was caused mainly by coarsened grain boundary carbides. A residual life assessment method, based on micro-crack growth and the statistical properties of micro-crack length distribution, gives an estimation close to the experimental results.

RETRAN-02 Analysis of Loss-of-Fluid Test Experiments L9-3 and L9-4

Two simulations of pressurized water reactor (PWR) anticipated transient without scram (ATWS) sequences were performed in the loss-of-fluid test (LOFT) facility. These were designated as tests L9-3 and L9-4. Test L9-3 is a loss-of-feedwater transient, while L9-4 simulates an ATWS accompanied by loss of off-site power. In the latter case, the main steam valve and primary circulation pumps are tripped at the beginning of the experiment, along with the steam generator feedwater flow. The behavior of these experiments was analyzed with the RETRAN-02 computer code in order to evaluate the capability of the code to predict ATWS behavior against the experimental evidence exhibited by LOFT. The complex sequence of events, which occurs in L9-3, creates a difficult system modeling problem. The primary influence on the entire system response is the steam generator heat transfer rate (given core power as a boundary condition). Results of the analysis demonstrate how the course of the computer calculation is influenced by the steam generator model and its initial conditions. Test L9-4 does not contain the thermal-hydraulic complexity of test L9-3 due to the immediate isolation of the steam generator. Nonetheless, it reinforces the general conclusion that RETRAN-02 will produce an adequate simulation of PWR more » ATWS behavior if the initial and boundary conditions are completely defined. « less

Advance Turbine-Generator Controls

Advanced turbine-generator controls contribute to the utility industry's goal of producing reliable electric power at low cost. This paper describes how the microprocessor-based controllers and monitors aid turbine-generator .Operational flexibility, load cycling, two shift position .Network stability, fast recovery from load rejection .Operator guidance or relief from critical duties Specifically, microprocessor-based controllers calculate critical thermal quantities in the turbine, make and implement decisions, and control turbine startup, loading, and unloading through the positioning of main steam valves.

Theoretical and Experimental Dynamic Analysis of the H. B. Robinson Nuclear Plant

AbstractA mathematical model for predicting the dynamic response of the H. B. Robinson pressurized water reactor plant was formulated and compared with results from measurements made during full-power operation of the plant. The model was based on the basic conservation laws for neutrons, mass, and energy; design data from the safety analysis report were used to evaluate the necessary coefficients. The model included representations for point kinetics, core heat transfer, piping, pressurizer, and the steam generator. The experiment involved perturbations in control rod position and main steam valve opening. Periodic binary input signals and step inputs were used. Theoretical and experimental frequency responses were obtained from the model and the test data. The comparison showed that the model was capable of good predictions for reactivity perturbations and fair predictions for steam valve perturbations. A method was also demonstrated for using the test data for at-power determination of the differential...