Main Steam Valve Research Articles

Coordinated control strategy for concentrated solar power systems considering active defocusing

With an increasing proportion of renewable energy in the energy structure, concentrated solar power plants are required to respond rapidly to automatic generation control (AGC) commands, to ensure the grid stability when connected to the grid. Active defocusing affects the collecting capacity of the collector, which not only serves as a safety protection measure for system operation, but also improves the system load shedding rate and provides the possibility of system participation in the auxiliary service of grid frequency regulation. In this paper, a coordinated control strategy for parabolic through concentrated solar power (PTCSP) system considering active defocusing of collector is proposed. The coordinated controller utilizes four manipulated variables, including mass flow rate of heat transfer oil in the collector, active defocusing angle, mass flow rate of molten salt in the heat storage system, and main steam valve opening, to regulate three output variables, namely, collector outlet temperature, turbine power, and main steam pressure. By integrating the steady-state defocusing angle in the optimization function, the controller can utilize the extra control freedom degree to improve the control effect, and ensure that the final steady-state defocusing angle to be small, which reduces the unnecessary heat collection loss. The proposed control strategy improves the power response rate and also avoids excessive heat transfer oil temperature and main steam pressure. In the simulations featuring two 20% variations in load target value, the root mean square error of the outlet temperature of the collectors is reduced by 0.094, and the heat storage is reduced by 0.99 MWh.

A new assessment mechanism of primary frequency regulation capability for a supercritical thermal power plant in deep peaking

AbstractWith the rapid development of renewable energy, the primary frequency control (PFC) is becoming more critical and significant to ensure the stability of the electrical power system. As the main role of PFC, the thermal power unit tends to in a wide operation interval, and the changes in PFC characteristics along with working conditions are inevitable. By decomposing and quantifying the dynamic energy conversion process, this paper proposes a novel mechanism to evaluate the PFC capability for the supercritical thermal power plants that covered 30%–100% of the rated load. In the mechanism, a refined steam turbine model is established to reflect the short‐term dynamic response of PFC by combining it with the coupling characteristics of the main steam valve and main steam pressure in the later phase. Meanwhile, as a new prior assessment index, the equivalent electricity has been put forward to quantify the PFC capability for the power plant. In a case study of a 600 MW supercritical power plant, the capacities of PFC under 30%–50% of the rated load are quantified for the first time. Comparison results between theoretical calculation and real PFC test show that the proposed PFC capability assessment mechanism has acceptable accuracy of 96.1%, which could be effective to assess the frequency response reserve and stability margin in the grid.

Dynamic simulation and analysis of steam dump valve failure using secondary side model of PWR

The safety system reliability is a key issue for the nuclear power plant (NPP), and the steam dump system (SDS) is an important pressure stabilizing system used in Hualong Pressurized Reactor (HPR1000) to enable nuclear steam supply system to accept loss of load without incurring a reactor trip and to remove stored energy and decay heat following a reactor trip without actuation of the steam generator safety valves. The SDS is consisted of many steam dump valves, and its reliability is dominated by the reliability of steam dump valves. During the steam dump interlock inspection test of a NPP, the pressure of the main steam pipe in the second loop appeared shock, which triggered the protection signal because of the high main steam pressure difference between the second and other main steam pipes. The purpose of this study is to simulate the failures and explore the mechanism of SDS failure process. A dynamic simulation model is developed with APROS version 6.10, which includes components between the steam generator (SG) and the main steam valves of NPP. The compressed air leakage failure for the steam dump valve, which causes valve position reduction (0%, 10% and 20%) and adjust speed change, is included in the dynamic simulation, and it causes fluctuations and steady-state errors in system parameters such as the main steam pressure and valve opening position. In the case of 10% and 20% valve position reduction, the main steam pressure fluctuates between 7.3 MPa and 7.45 MPa, and the steady-state errors are about 0.02 MPa. Then, the safety valve will jump in the fluence of water hammer due to the unsteady mass flow rate of condensate water. The pressure can drop to 6.75 MPa caused by safety valve jump, and the safety injection system will be triggered to form a serious accident reaction if the take-off action sustains over 0.13 s. Results of this study would be helpful for the understanding of the SDS failures process and dynamic characteristics of the SDS for nuclear power units, and provide guidance for failure identification and safety system improvement work.

Dynamic characteristics analysis of pilot valves with different inlet diameters installed on the main steam valve set

The Main Steam Valve Set (MSVS) is the key protection device for nuclear power plants, whose dynamic characteristics are directly related to the security of the secondary circuit system especially under overpressure conditions. Dynamic mesh technology is used in this work to capture the dynamic characteristics of the interconnected pilot valves on the MSVS with different inlet diameters. The research results show that increasing inlet diameter can significantly reduce the opening time of the pilot valves, but it will also increase the fluid force of valve stem during the opening process as well as the movement speed at the maximum opening. The pressure of the pilot valves during the opening process is then analyzed. It can be seen that changing the inlet diameter will affect the inlet annular throttling area, thereby changing the pressure rise speed in the external chamber of the valve stem and the inner cavity of the valve body, thereby affecting the total response time. This work provides a reference for the selection of the pilot valve diameter in MSVS and helps to improve the overpressure protection capability of MSVS.

Dynamic Characteristics Analysis of Pilot Valves with Different Inlet Diameters Installed on the Main Steam Valve Set

Dynamic Characteristics Analysis of Pilot Valves with Different Inlet Diameters Installed on the Main Steam Valve Set

Optimization control of a 330 MW drum boiler unit based on DMC algorithm and DEB strategy

This paper firstly established a nonlinear dynamic model of a 330 MW drum boiler unit, which has a clear physical meaning and is conducive to the design of coordinated control system (CCS). On this basis, the boiler energy storage coefficient is calculated, and its relationship with that in direct energy balance (DEB) strategy is analyzed. Secondly, this paper proposes a CCS based on dynamic matrix control (DMC) algorithm and DEB strategy, in which: (1) energy demand and status signals of DEB are taken as the setting point and process value of DMC controller, so as to overcome the internal disturbance of the boiler; (2) a compensation signal is constructed as the feedforward input of DMC controller, so as to overcome the external disturbance of the turbine and realize the timely utilization and supplement of boiler energy. Simulation shows: (1) there is a certain deviation in main steam pressure when the energy demand and status signals are taken as the setting point and process value, but this is an illusion of insufficient energy, and in fact the energy status can already meet the demand; (2) compared with the main steam valve, the constructed compensation signal takes into account more operating parameters of the unit, which greatly improves the accuracy of the compensation. Practical application shows: the grid dispatch order can be well tracked by the unit, the maximum deviation of main steam pressure is ±0.6 MPa in constant pressure mode, and that is ±1.2 MPa in sliding pressure mode, thereby improving the control performance of the unit under high, medium, low, and overall load conditions.

Analysis of dynamic characteristics and influencing factors of steam dump conditions of marine nuclear power plant

Objectives Based on the operation requirements of steam bypass exhaust system of marine nuclear power plant, the dynamic characteristics and influencing factors of bypass exhaust conditions are analyzed. Methods According to the functional characteristics of the steam bypass exhaust system, the mathematical and physical models of the matching operation of the steam generator, steam system, bypass system and main steam turbine are established. The dynamic operation characteristics and the coupling matching characteristics of the primary and secondary circuits under extreme working conditions such as quick closing of the main steam valve and load rejection of the steam turbine are analyzed to verify the accuracy and universality of the simulation model. Results The simulation results show that when operating under bypass exhaust condition, the appropriate bypass exhaust valve, main steam valve and their matching action time should be selected according to the power self-regulation capacity of the marine reactor, and the safety problems such as overpressure of the steam header and overspeed of the steam turbine unit should be comprehensively considered. At the same time, the steam demand of other equipments on the ship should be met. Conclusions The research results can provide reference for the safety control of side exhaust conditions and the optimal design of side exhaust system of nuclear power plant.

Transient simulation model and process simulation analysis of fast cut back process in thermal power plant

Fast Cut Back (FCB) technology of large thermal power plant can maintain the isolated operation of auxiliary power after the units are disconnected from the power grid. FCB unit can immediately cut off all external loads without turbine or boiler shutdown in case of large power grid failure, and supply power immediately as the external power grid fault eliminated, which has a very important impact on improving the stability and the recovery speed of the power grid system. Therefore, it is necessary to establish a dynamic mathematical model of thermal power plant to simulate FCB process. According to the principle of mass and energy balance, a dynamic mathematical model of 1050 MW thermal power unit was established. The model considered the change trends of main steam pressure and temperature caused by the action of main steam valve and high-pressure (HP) bypass valve in FCB process, and the action characteristics of safety valve and pressure control valve (PCV) valve in FCB system. This model provides a reference for the simulation and control of FCB process in thermal power unit.

Primary Frequency Control Ability Evaluation of Valve Opening in Thermal Power Units Based on Artificial Neural Network

With the development of new energy, the primary frequency control (PFC) is becoming more and more important and complicated. To improve the reliability of the PFC, an evaluation method of primary frequency control ability (PFCA) was proposed. First, based on the coupling model of the coordinated control system (CCS) and digital electro-hydraulic control system (DEH), principle and control mode of the PFC were introduced in detail. The simulation results showed that the PFC of the CCS and DEH was the most effective control mode. Then, the analysis of the CCS model and variable condition revealed the internal relationship among main steam pressure, valve opening and power. In term of this, the radial basis function (RBF) neural network was established to estimate the PFCA. Because the simulation curves fit well with the actual curves, the accuracy of the coupling model was verified. On this basis, simulation data was produced by coupling model to verify the proposed evaluation method. The low predication error of main steam pressure, power and the PFCA indicated that the method was effective. In addition, the actual data obtained from historical operation data were used to estimate the PFCA accurately, which was the strongest evidence for this method.

Analysis of Causes of Valve Rod Fracture of Steam Turbine High Pressure Main Steam Valve

A 300MW sub-critical coal-fired thermal power plant steam turbine generator set # 1 high pressure steam valve stem is fractured. The turbine unit has been running 46000 hours before the crack happened. The chemical component was examined which was in the standard range. they observed the metallographic structure of the broken stem to find the nitriding treatment of fine grain martensite structure at surface area and lath martensite at central section, healthy structure condition. they also found the existing of circumferential oxidized cracks with white corrosion production. According to that, they believe it was caused by residual stress when grinding. Finally, SEM was used to observe the fracture to further confirm our ideas.

Design method of nonlinear adaptive controller for the main steam valve of turbogenerator set considering state constrain

Aiming at the main steam-valve control of turbine generator unit with amplitude constraint and parameter uncertainty, adaptive backstepping is implemented on the main steam valve controller. The controller not only has an adaptive ability to uncertain parameters of the system and a good transient response performance, but also does not linearize the system. Meanwhile, the problem of state limit in the main steam-valve control of turbogenerator is effectively solved by using the Lyapunov function with constraints. Simulation results are presented to show the performance of the adaptive backstepping control.

Experimental and numerical study on loss characteristics of main steam valve strainer in steam turbine

In this paper, a kind of filter screen with special structure used in steam turbine’s main stop valve is simplified, and the three-dimensional modeling software is applied to build the filter screen test rig. The loss characteristics of it are investigated by using the method of wind tunnel test. Through the correlation analysis, a simple expression that reflects the total pressure loss of the strainer is obtained. The grid division and numerical simulation are performed on the minimum repeating unit (single crystal cell) which is taken from the whole strainer model and we compare the simulation results with the test data. Then the whole filter screen is simplified into a model of porous media and the feasibility is verified. The experimental results show that the loss coefficient of the strainer with different wind speed changes in a very small range under the same flow deflection angle. At the same wind speed, strainer loss coefficient will rise with the increasing angle, and when the angle varies from 0° to 25°, the increase amplitude of the loss coefficient is small; while it is great when the angel changes from 25° to 65°. Besides, the circumferential rotation angle of the strainer has little effect on its own drag performance. Through the numerical simulation of the single crystal cell of the strainer, its resistance characteristics can be qualitatively obtained. But there are still some deviations between the calculating results and the test data. While the value and variation of the loss coefficients obtained by using the porous media model for numerical simulation are almost identical to experimental data, indicating that the porous media model can better reflect the loss characteristics of real strainer.

Continuous fixed-time convergent regulator for dynamic systems with unbounded disturbances

This paper presents a novel continuous fixed-time convergent control law for dynamic systems in the presence of unbounded disturbances. A continuous fixed-time convergent control is designed to drive all states of a multi-dimensional integrator chain at the origin for a finite pre-established (fixed) time, using a scalar input. The fixed-time convergence is established and the uniform upper bound of the settling time is computed. The designed control algorithm is applied to fixed-time stabilization of two mechatronic systems, a cart inverted pendulum and a single machine infinite bus turbo generator with main steam valve control.

Co-simulation design and experimental study on the hydraulic–pneumatic-powered driving system of main steam and feed water isolation valves for CAP1400

CAP1400 is an advanced large passive nuclear power technology under research and development, and related electromechanical equipment should be improved to guarantee the safety. The driving systems...

The optimization methodology research on the motion performances of the driving device of main steam and feed water isolation valves

The driving device of the main steam and feed water isolation valves is one of the most important electromechanical equipment in nuclear power plants, and its motion performances are related to the safety of nuclear power plants. This article proposes an optimization methodology to research the motion performances. In the methodology, inputs are the motion performance indexes and the major influencing parameters with no need for complex mathematical models of the electromechanical equipment; the co-simulation model or the prototype are adopted to illustrate the influence rules of major parameters on the motion performance indexes; objective functions for optimization, which combine motion performances with weight factors, can reveal the influence rule curves. Then based on the methodology, motion performances of the equipment are analyzed and the key indexes are selected. Besides, the maximum pressure of the driving device is chosen as the major parameter and a dimensionless objective function synthesizing the motion performance indexes is proposed. Finally, the influence rule curve where the dimensionless function varies with the maximum pressure is obtained by the co-simulation and the experimental study on the prototype verifies the results, which provides references for the further research and development in the engineering application. For other electromechanical equipment, the method is an efficient tool to design, verify, and optimize the performances.

화력발전소 터빈 본관의 환풍기 위치 및 용량 최적화에 관한 연구

화력발전소 터빈 본관 내부는 고온의 스팀 배관, 탈기기, 스팀 저장 탱크, 수증기 차단 밸브 등의 존재로 터빈 본관 작업 공간의 공기가 고온으로 올라가서 작업자가 장시간 작업하기 곤란한 경우가 발생한다. 터빈 빌딩 작업공간의 공기를 냉각하기 위해 터빈 빌딩 창문을 개방하여 외부의 찬 공기로 냉각하고 상부에 환풍기를 설치하여 외부로 배출한다. 이렇게 한 경우에도 국부적으로 고온의 영역이 존재하여 작업 공간의 냉각을 위한 추가적인 환풍기 설치가 필요하고, 이 경우 환풍기의 위치와 유량에 대한 최적화가 필요하다. 본 연구는 여러 가지 경우의 열 유동 해석을 통해 쾌적한 작업환경을 위한 추가적인 환풍기의 위치와 용량을 최적화한 방안을 제시 하는 것을 목적으로 하였다. 본 연구를 통해 기존 환풍기 위치와 용량을 기준으로 터빈 본관 내부의 고온 영역인 탈기기 영역근처의 열원을 배출하는 환풍기를 추가로 설치하는 것이 전체온도를 <TEX>$3.0^{\circ}C$</TEX>, 가장 고온의 영역인 탈기기영역의 온도를 <TEX>$4.2^{\circ}C$</TEX> 저감할 수 있었다. The existence of high temperature equipment such as steam pipe, deaerator, steam storage tanks and main steam stop valves makes relatively higher workplace temperature in a power plant of the turbine building. In order to cool down the air temperature in the turbine building, the outside air flow with lower temperature passes through the window and the hotter air in the building is extracted to the outside by installing the ventilation fan on the roof. Nevertheless, higher temperature regions near the high temperature equipment still exist in the turbine building and additional fans for the temperature reduction in the higher temperature region should be examined for the optimal location and mass flow rate. The purpose of the present study is to suggest the optimized location and capacity of the additional ventilation fans for a comfortable working environment. From the present study, it has been elucidated that the additional ventilation fans might be located near the high temperature deaerator and it could reduce the mean temperature in the turbine building by <TEX>$3.0^{\circ}C$</TEX> and the temperature near the deaerator could be reduced by <TEX>$4.2^{\circ}C$</TEX>.

Nonlinear adaptive control for multi-machine power systems with boiler-turbine-generator unit

Summary This paper studies the stability of multi-machine power systems via simultaneous design of boiler fuel flow control, turbine main steam valve control and generator excitation control for the boiler-turbine-generator unit. Because the whole system is coupled among generators and has multi-parametric uncertainties, the decentralized adaptive coordinated controller design is considered and is based on the adaptive backstepping method. Moreover, in addition to the transient stability of the power angle and power oscillation, the voltage regulation is also an important property in power systems. Thus, the global control technique is used to simultaneously ensure both the transient stability and the voltage regulation. Furthermore, we improve the transient performance of power systems greatly by introducing the state-constrained control. Simulation results show the effectiveness and advantage of the proposed controller. Copyright © 2014 John Wiley & Sons, Ltd.

The Impact of the Power Plant Unit Start-Up Scheme on the Pollution Load

The typical problem in design of experiments methodology is to avoid risk of obtaining The article presents problems related to optimization of start-up and shut-down of the power unit located in a coal-based electric plant. The optimization includes minimization of the start-up and shut-down duration while maximum allowed stresses in the main steam valve are simultaneously taken into consideration. Such approach leads to increasing of overall efficiency of the power unit and as a result to reducing of environmental burden with the same amount of energy obtained.

RELAP5-3D transient modelling for NGNP integrated plant

The High-Temperature Gas-cooled Reactor (HTGR) is designed with outlet temperatures ranging between 750°C and 800°C. These high outlet temperatures enhance the power production efficiency and facilitate a variety of industrial applications. The objective of this study is to understand the response of the primary system to potential transients in the secondary system. For this analysis, the transient condition originates in the Intermediate Heat Exchanger (IHX) or Steam Generator (SG) of the HTGR-integrated plant. The transients analysed are: a loss of pressure; loss of feedwater flow; inadvertent closure of main steam valve; decrease in returning gas temperature and heat load step change. The results show a large dependence on the negative reactivity added to the fuel as a function of increased temperature. The returning gas temperature decrease transient resulted in the highest fuel temperature (1361°C). Fuel temperature was shown to be less than the 1600°C fuel limit for each case analysed.

Development of a thermal–hydraulic analysis software for a passive residual heat removal system

A series of reasonable mathematical and physical models for the thermal–hydraulic characteristic analysis of a passive residual heat removal system (PRHRS) in an integral pressurized water reactor were established. These models mainly include the core, once-through steam generator, nitrogen pressurizer, main coolant pump, and flow and heat transfer models. The flow and heat transfer models are suitable for the core with plate-type fuel element and the once-through steam generator with annular channel, respectively. A transient analysis code with Visual Fortran 6.5 has been developed to analyze the thermal–hydraulic characteristics of the PRHRS. Visual input, real-time processing and dynamic visualization output were achieved with Microsoft Visual Studio.NET 2008, which greatly facilitate applications in the engineering. The software was applied to analyze the effects of the heat transfer area of the PRHRS, the height difference between the residual heat exchanger center and the steam generator center, and the main steam valve turn-off time on the transient thermal–hydraulic characteristics of PRHRS. The obtained analysis results are significant to the improvement design of the PRHRS and the safety operation of the integral pressurized water reactor.