Table of Content

05 August 2019, Volume 52 Issue 8

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Cause Analysis of Colored Smoke Plume and Related Studies on Economic and Environmental Benefits of Its Treatment Technologies for Ultra-low Emission Coal-Fired Power Plants

ZHU Fahua, SUN Zunqiang, SHEN Zhiyong

2019, 52(8):  1-7,25.  DOI: 10.11930/j.issn.1004-9649.201905096

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The definition and causes of various colored smoke plume are introduced systematically in this paper. Colored smoke plume should be treated according to not only its exact causes but also the environmental and policy requirements. White smoke plume is commonly seen in ultra-low emission coal-fired power plants, while blue smoke plume appears in a small number of power plants burning medium and high sulfur coal. The article explores the treatment technologies, investment, operating costs as well as their economic and environmental benefits with the focus on blue smoke plume and white smoke plume. It turns out that the pollutant emission reduction and water-saving benefit from the treatment of white smoke plume are very limited, or it may even get worse by increasing the emission of pollutants. Therefore, it is not recommended to be widely promoted. For the treatment of blue smoke plume, it is necessary to strengthen the research and demonstration project of SO₃ detection and treatment technologies for flue gas, and publish the emission standards of SO₃ to make the treatment of the blue smoke plume in power plant follow the standard guidelines.

Bridge Average Value Model of Modular Multilevel Converter

CHEN Ning, QI Lei, BAO Meng, CUI Xiang

2019, 52(8):  8-15.  DOI: 10.11930/j.issn.1004-9649.201905116

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The speed-up simulation model of modular multilevel converter (MMC) is the basis for the research of voltage-source converter high-voltage direct-current (VSC-HVDC) system. Among many models, the bridge Thevenin model of MMC is the most widely used. In this paper, it is found that the simulation speed can be further improved. Based on the Thevenin equivalent circuit of MMC's bridge, a new bridge average value model (AVM) is proposed by using the idea of energy equalization. The proposed model significantly reduces the computational burden of Thevenin model and improves the simulation efficiency of the model. The simulation results show that the model can be applied to the application scenarios of circulating current suppression, AC/DC side fault simulation and so on, in which cases that do not pay attention to the capacitor voltage of sub-modules.

Influence of Package Parasitic Parameters on Transient Current Distribution of Paralleled IGBT Chips

SHI Hao, WU Pengfei, TANG Xinling, DONG Jianjun, HAN Ronggang, ZHANG Peng

2019, 52(8):  16-25.  DOI: 10.11930/j.issn.1004-9649.201805131

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High power IGBT usually use multiple chips in parallel to achieve large current. The consistency of the dynamic and static current distribution of parallel chips is essential to improve the current level and reliability of devices.At first, the difference of package parasitic parameters caused by inconsistent internal layout of paralleled IGBT chips is introduced in this paper. Secondly, combined with the equivalent circuit model of IGBT and its switching characteristics, the influence of parasitic parameters on the transient current distribution characteristics of parallel IGBT chips is analyzed. Then, the equivalent circuit model of parallel IGBT chip is established, and the simulation circuit is built by Synopsys Saber software. From the differences of package parasitic inductance parameters and package parasitic resistance parameters, the influence of parameters differences on the transient current distribution characteristics of parallel chip is analyzed. In this paper, the influence of various package parasitic parameters on the transient current distribution is considered comprehensively, which is of great significance for optimizing the transient current consistency of multi-chip parallel connection.

An Optimized Capacitor Voltage Balancing Control Strategy of Modular Multilevel Converter Based on Comparison of Variable Reference Values

GAO Fengyang, QIANG Guodong, GAO Yunbo, ZHANG Guoheng

2019, 52(8):  26-33,54.  DOI: 10.11930/j.issn.1004-9649.201807076

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The capacitor voltage balance of modular multilevel converter is the key to its stable operation, aiming at problem of large calculation amount and high switching frequency existing in traditional capacitor voltage balancing strategy. This paper proposes an optimized balancing control strategy of the capacitor voltage based on the comparison of variable reference values. The number of current input modules is calculated by the nearest level modulation, then the reference value is adjusted according to the number of input modules, and based on this reference value, the sub-module capacitor voltage sequences are divided into two groups. At the same time, the random scramble algorithm is used to sort the elements in the group. According to the direction of the bridge arm current, the sequencing order of the groups is determined, and the information of the input module is finally determined. Meanwhile, the permissible deviation threshold of capacitor voltage and the regulatory factor are selected by the optimization function of the capacitor voltage to achieve optimal control of the device's average switching frequency and capacitor voltage consistency. A simulation model of three-phase inverter based on MMC is set up in MATLAB/Simulink to verify the proposed strategy can significantly reduce the amount of calculations and the average switching frequency of the device under the premise of achieving a good effect of capacitor voltage balancing.

Research on Comprehensive Benefit Assessment Method of Medium and Low Voltage Distribution Network

QIN Zijian, SHI Jiying, WEI Wenhui, LIN Jikeng, ZHANG Xinlun, WU Lin

2019, 52(8):  34-44.  DOI: 10.11930/j.issn.1004-9649.201805055

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AC power distribution network is now the main form of the distribution network, which failed to cover three distribution form, AC, DC and AC-DC hybrid power distribution. The subjectivity of exiting distribution network assessment method is strong Thus, this paper proposes a set of assessment system to evaluate the comprehensive benefit of medium and low voltage distribution network, which includes five aspects:technology, power supply reliability, economy, sociality and environment protection, and each aspect is further subdivided into a number of specific indicators. Meanwhile, the comprehensive evaluation method based on fuzzy entropy weight is adopted to assess the comprehensive benefit of typical distribution mode of AC, DC and AC-DC hybrid power distribution network. The proposed method was verified by a few examples.

Evaluation of Interval Load N-K Contingency of Power System Based on DC Power Flow

HONG Shaoyun, XING Haijun, CHENG Haozhong

2019, 52(8):  45-54.  DOI: 10.11930/j.issn.1004-9649.201806152

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From the rigorous mathematical point of view,this paper evaluate K components of contingencies for generation and transmission system,which based on DC power flow system. There are many N-K contingent scenarios of interval load. In this paper, the optimal state and the minimum state with minimum load model of the N-K interval load are established from the optimization perspective. According to this, a bi-level optimization model is proposed for minimum load shedding of the worst state of power system considering generating unit contingency and interval load. The upper decision variables of the model is the state of units, lines and loads. The lower layer of the bi-level model is the minimum load shedding model based on DC power flow. In order to solve this model, the papers transforms the bi-level model to a mixed integer linear programming (MILP) by strong duality theory and linearized method. Finally, An IEEE standard system is used to testify the validity of the proposed model, in which the worst N-K case evaluation model of interval loads, units and lines (or transformers) faults are fully tested. Numerical results indicate that the method proposed in this paper is feasible and effective.

Restoration of Power Systems with AC/DC Conversion Terminal at Receiving-End Considering Parallel Transmission Lines

ZANG Erbin, GU Xueping, LI Pengfei, YANG Chao, LI Shaoyan, WU Chen

2019, 52(8):  55-63.  DOI: 10.11930/j.issn.1004-9649.201805143

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The path optimization method proposed in previous studies severely restricts the restoration of LCC-HVDC system. To overcome this weakness, this paper studies power system restoration with AC/DC conversion terminal at the receiving-end. In this paper, the characteristics of LCC-HVDC transmission systems under the condition of system restoration are analyzed. To ensure the efficiency and security of restoration, the system restoration optimization model considering parallel transmission lines is established by taking the ratio of total power generation and grid charging reactive power as the optimization goal. Then hybrid particle swarm optimization is adopted to solve the problem of power system restoration, which is characterized by various constraints. The effectiveness of the proposed method is demonstrated and validated by the optimization results on the modified IEEE 39-bus system and a practical power system in Southwest China.

Research and Application of Regional Power Grid Auto Transfer System for the Petal-Shape Distribution Networks based on HSR Network

LI Zhenghong, DING Xiaobing, FENG Baocheng, JIN Zhen, HOU Wei

2019, 52(8):  64-70,77.  DOI: 10.11930/j.issn.1004-9649.201810044

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In the petal-shape regional distribution network, the fast power recovery cannot be realized with the traditional auto transfer system when a power failure occurs at the non-standby-switch room. To solve this problem, based on the idea of real-time sampling, real-time data exchange, real-time judge, and real-time control, a regional power grid auto transfer system is proposed in the paper based on the high-availability seamless redundancy (HSR), which can be used in various complicated regional distribution network structures. The composition, communication structure and logic control strategies of the regional power grid auto transfer system are discussed in the paper. The field application of the developed devices of the regional power grid auto transfer system shows that the system can effectively realize the rapid recovery of power supply after failure of the petal-shape distribution network.

Closed Form Expressions of Self and Mutual Inductance of Disk Coils and the Optimal Value of Self-Inductance

ZHU Runhang, ZHAO Yating

2019, 52(8):  71-77.  DOI: 10.11930/j.issn.1004-9649.201804035

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The disk coils are the core element of energy coupling of the wireless power transmission system blooming in recent years. By introducing generalized hypergeometric functions _pF_q, the integral expression of self-inductance of disk coils is transformed into a closed form. Similarly, the closed form expression of mutual inductance of coaxial coplanar disk coils is obtained by establishing a relationship between the complete elliptic integrals and generalized hypergeometric functions. These closed form solutions can bypass the numerical integration of traditional methods for the inductance calculations. Furthermore, based on the obtained closed form solution the GPW (given piece of wire) optimization problem is analyzed and the maximum value of self-inductance is found for disk coils which are wound by a piece of given wire. It is also revealed that the ratio of the outer and inner radii of the optimal disk coils is independent of the geometric parameters of winding wires. Numerical results show the high consistency between existing methods and methods proposed in this paper.

Analytical Study on Electromagnetic Shielding Characteristics of Wire Mesh

WANG Yonghong, XIAO Bing, HE Ri, HU Yifan, JIAO Chongqing, XU Keqiang

2019, 52(8):  78-84.  DOI: 10.11930/j.issn.1004-9649.201807077

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Based on the surface impedance model of metal mesh and the full wave simulation software, in this article the applicable range of the formula for calculating the shielding effectiveness of metal mesh for plane wave is discussed.On this basis, when the shape of metal mesh is diamond, the shielding effectiveness of the metal mesh is calculated by using the full-wave simulation software, and then the mechanism of the wire mesh is analyzed. According to transmission line theory and the surface impedance of metal mesh, the transmission line model is equivalent to double-layer infinite metal mesh, and an analytical model for calculating shielding effectiveness of double-layer infinite metal mesh is proposed. Furthermore, shielding characteristics of the double-layer metal mesh and the difference between the single-layer metal mesh and the double-layer metal mesh are discussed.

Research on Method and Device for Measuring Unbalanced Current of High Voltage Capacitor Bank in Converter Station

WU Peng, ZHANG Yuan, SHI Lei

2019, 52(8):  85-90,119.  DOI: 10.11930/j.issn.1004-9649.201805174

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Complex electromagnetic field in converter station poses a serious interference to the field test of unbalanced current of high voltage capacitor bank, and the unbalanced current is too small to be accurately measured directly during the test. This paper proposes a new measurement method that the high frequency low voltage AC signal is applied to the capacitor bank, and the power frequency interference is removed through collecting the unbalanced voltage between the bridge arms and by use of the second-order high-pass filter, and then the unbalanced current value is calculated based on the equivalent impedance of the capacitor bank. The paper also presents the principle for developing measuring devices, and the measures taken for removing such interferences as power ripple interference, power frequency interference, discharge interference, thermal noise of the devices so as to achieve accurate testing results. The field test results show that the new method is correct in theoretical thinking and accurate in measuring the unbalance current.

An Online Pre-Decision Method for Security and Stability Emergency Regulation

BAO Yanhong, XU Taisha, ZHOU Hua, REN Xiancheng, LOU Boliang, WU Feng

2019, 52(8):  91-97.  DOI: 10.11930/j.issn.1004-9649.201810001

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With the development of UHV AC/DC power system, the security and stability characteristics are becoming more and more complex, preventive controls are needed to reduce the accident risk of multiple serious faults. For security and stability problems with low real-time requirement (minute level), timely post-fault manual emergency regulation measures can avoid the high cost of preventive control. In order to remedy the defects of offline manual emergency regulation plans and real-time decision calculation of corrective control, an online pre-decision-making method of manual emergency regulation is proposed in this paper. Based on medium and long term time domain simulation method with variable step size, the quasi-steady operation state is determined by amplitude of frequency fluctuation, and the pre-decision-making strategy is obtained by solving the optimization function with steady state security constraints. The manual emergency regulation is carried out after real fault through pre-decision-making strategy of matching the types of fault and security problem. The validity of the method is verified by a case study of the actual power system.

Research on Reactive Power Compensation Device in UHV AC Substation Connected Directly to 500 kV Busbar

GUAN Lan, LIU Fei, WEN Weibing, KANG Peng, HU Junhui, ZHAO Juan

2019, 52(8):  98-104.  DOI: 10.11930/j.issn.1004-9649.201903051

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Site selection is often difficult for the 1 000 kV UHV AC substation due to its many-grouped reactive power on the low-voltage side of main transformer and the large space occupation. A solution to this problem is proposed in the paper to directly connect the reactive power compensators to the 500 kV busbar. Based on a comparative analysis of various wiring modes of reactive power compensation devices connected directly to 500 kV busbar and an investigation of the device supply ability, different layout schemes for the connection are studied and compared in terms of life cycle. The results show that the solution can not only improve the capacity of the capacitor and reactor, and reduce the floor space of the reactive power compensation equipment, but also save the energy.

Coordinated Optimization of Generator Excitation System for Improving Transmission Capacity of Power System

WANG Guanhong, LI Ying, YU Yao, WANG Biao, TAO Xiangyu, LI Wenfeng, TANG Yong

2019, 52(8):  105-111.  DOI: 10.11930/j.issn.1004-9649.201703090

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For long-distance AC transmission system from energy base to load center, the system damping is insufficient when N-1 fault occurs, which leads to the reduction of transmission capacity. In order to enhance the dynamic stability of the transmission system and improve the constrained generating capacity of the generator units, the paper studies the coordinated optimization strategy of the generator excitation control system in disturbance. Aiming at above-mentioned problems, we firstly optimize the excitation system AVR main loop, the reactive current compensation and PSS parameters of generators, which reduces the lag time of generators and excitation system, decreasing the non-compensation phase frequency characteristic hysteresis by 10 degrees. And then we studies the phase compensation for PSS parameters, which brings the compensation characteristics closing to -90 degrees, substantially increasing the AC gain provided by PSS. The results show that the excitation system and PSS have important influence on the dynamic characteristics of the power grid, and under the existing parameter configuration, the delivery capacity of the power system cannot meet the full power generation requirements of generator units at the sending end. Tests have proved that under the optimized parameter configuration, the loading test results of generator units can meet the safe operation requirements of generator units and power grids, and the capacity of transmission system can be improved after N-1 fault occurs. Implementation of the optimization strategy will improve the delivery capacity of power grids for centralized power sources with high efficiency, safety and economy.

Relay Protection-Related Domestic and Foreign Standards for Interconnecting Distributed Resources with Electric Power Systems

WANG Zengping, YANG Guosheng, WANG Zhijie, LIU Yu

2019, 52(8):  112-119.  DOI: 10.11930/j.issn.1004-9649.201809002

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With the rapid development of distributed resources (DR) recently, more attention has been paid to the research and formulation of standards for interconnecting DR with grid, among which relay protection is an important part. Based on a comprehensive review of the relevant standards of relay protection for interconnecting DR with grid both at home and abroad, the important provisions and updates of the standards are analyzed in detail. Selecting North America, Europe, Australia and China as representative countries, a study is made on the voltage deviation, frequency deviation, island protection and low voltage ride-through, and some suggestions are given for standard revision. The results can be used as references for further improvement of the relevant regulations and standards of relay protection for interconnecting DR with grid in China.

Research on Abandoned Wind Heating System Based on Robust Disturbance Observer

LIU Qianwei

2019, 52(8):  120-125.  DOI: 10.11930/j.issn.1004-9649.201805062

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Considering the uncertainty of wind power generation, a control strategy of wind turbine power supply system based on robust disturbance observer is proposed for the large range of abandon the wind and global warming in this paper. Firstly, the detailed modeling of the wind turbine power supply system is made and the disturbance observer based on Taylor series expansion is used to eliminate the widespread parameter uncertainty and the unknown wind power fluctuation. Secondly, a distributed heating control method of electric boilers based on PLC and WinCC is applied. Finally, the effectiveness of the proposed method is verified by simulation.

Relative Robust Optimization of Coordinated Charging of Electric Vehicles based on the Consortium Blockchain Trading Platform

WANG Huizhou, YU Aiqing

2019, 52(8):  126-134.  DOI: 10.11930/j.issn.1004-9649.201807082

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To deal with uncertainties of electric vehicle (EV) charging and wind and photovoltaic power generation as well as risks of decentralized power trading, an EV charging trading platform based on the consortium blockchain technology and a coordinated charging strategy of EVs considering wind and photovoltaic power generation are proposed in this paper, and the relative robust optimization technique is used to deal with the uncertainties of wind and photovoltaic power generation. First, the consortium blockchain technology is used to build the EV charging trading platform. Second, the relative robust optimization technique is used to deal with the uncertain wind and photovoltaic power generation, and relative robust optimization models of coordinated charging of EVs considering uncertainties of wind and photovoltaic power generation are built. Finally, the optimization problem is solved by quantum particle swarm algorithm. The security analysis has proved the reliability and security of the trading platform, and the simulation results have verified the correctness of the models and the validity of the algorithm.

Comprehensive Energy Service Mode under the Replacement of Old Growth Drivers with New Ones

YANG Yongqi, XUE Wanlei, SHAN Baoguo, XU Nan, ZHAO Xin

2019, 52(8):  135-143,163.  DOI: 10.11930/j.issn.1004-9649.201806054

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This paper aims at developing the key support from comprehensive energy service to replacement of old growth drivers with new ones. This paper has sorted out basic structure of the replacement from policies and industries' development. Besides, the new pattern of energy supply and demand to support the replacement was analyzed. Moreover, the basic structure, operation mode and key technologies of comprehensive energy service have been presented to provide feasible thoughts and mode to the implementation of comprehensive energy service and the replacement.

Research of Electricity Price Cross Subsidy based on Demand Price Elasticity

ZHANG Chao, ZHAO Qian, XU Zhao, YOU Peipei

2019, 52(8):  144-148,156.  DOI: 10.11930/j.issn.1004-9649.201903070

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How to dispose the cross-subsidy of electricity price properly has become a key issue in advancing the reform of electric power system. In order to analyze the mechanism of electricity price cross subsidy intensively, this paper takes the demand price elasticity used into its theoretical model to introduce a classification standard for cross-subsidy of electricity price based on Opening Form. It founds that:compared with cross-subsidy among regions, cross-subsidy among different users distort the electricity price much more serious in China; and the Generalized Preference and Price-boosting Effect have caused the benefit spillover problems of electricity price cross subsidy. It provides theoretical support for precisely grasping the key issues of dealing with electricity price cross subsidy.

Research on the Reasons of the Growth of Electricity Consumption during the 13th Five-Year Plan Period and Medium- and Long-term Perspective

ZHANG Chenglong, TAN Xiandong, WENG Yuyan, SHAN Baoguo

2019, 52(8):  149-156.  DOI: 10.11930/j.issn.1004-9649.201903114

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China's electricity consumption has experienced an over-expected growth since the 13th Five-Year Plan period due to complicated factors. It is of great significance for the high-quality development of the power industry to deeply analyze the reasons of the rapid growth of power consumption, the influencing factors of medium-and long-term power demand, and scientifically forecast the trend of electricity demand growth. Based on the analysis of the reasons of the growth of electricity consumption during the 13th Five-Year Plan, this paper comprehensively considers the main factors affecting the medium-and long-term electricity demand under the new situations, and then adopts the medium-and long-term model to forecast the electricity demand from 2020 to 2050 in China. It is estimated that with the consideration of the accelerated electrification scenario, the electricity demand will reach to 7 700, 11 100, 12 200, and 13 900 TW·h in 2020, 2030, 2035, and 2050, respectively; and the average annual growth rates will be 6.1%, 3.1%, and 0.9% in 2015-2020, 2020-2035, and 2035-2050, respectively. In 2050, the electricity will account for about 45.2% in the terminal energy consumption.

Study on Forecasting Model of Maximum Daily Power Load in Beijing Area

SHI Yuheng, ZHAO Na, WANG Ling, XU Lijia, ZHOU Jie, LIN Qian, QIAO Yuan

2019, 52(8):  157-163.  DOI: 10.11930/j.issn.1004-9649.201811091

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The characteristics of maximum daily power load and the dependence of maximum daily power load on meteorological factors are analyzed in this paper based on the records of the power load and auto weather station meteorological data of Beijing from 2009 to 2013. A maximum daily power load forecasting model is established through multivariable linear regression. The results of the study indicate that the maximum daily power load occurs between 9 BST and 17BST, obviously correlating to the air temperature, with positive correlation with the air temperature below 18.7℃ and negative correlation above 18.7℃. The proposed model is verified using the data collected in 2013 with an accuracy of 91.6%, showing its good ability to forecast the maximum daily power load.

Thermo-economic Analysis on Four Regulation Schemes with Different Flexibilities for Primary Frequency Regulation Control in a Coal-Fired Power Plant

LUN Tao, E Zhijun, ZHANG Li, WANG Xin, ZHAO Yongliang, YAN Junjie

2019, 52(8):  164-172.  DOI: 10.11930/j.issn.1004-9649.201903017

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Achieving high operational efficiency and flexibility of coal-fired power plants is an effective way to improve the security of power grids. In this study, the dynamic model of a 660 MW supercritical coal-fired power plant is developed via the GSE software, and then the dynamic characteristics of the main thermo-economic parameters and heat storage using four regulation schemes during the primary frequency regulation process are explored. After the thermo-economic index is defined for the primary frequency regulation, the deviations from average standard coal consumption rate with respect to different time durations of the four regulation schemes are analyzed. It turns out that during the primary frequency regulation load ramping up process, the output power of steam turbine and the total efficiency of power plant get boosted sharply with all the four regulation schemes, whereas the standard power generation coal consumption rate goes down in an opposite way. The basic reason for those four schemes eligible to participate in primary frequency regulation is explained as the heat storage reduction of both the boiler and steam turbine systems. The deviation from the average standard coal consumption rate hit the minimum value of -22.15 g/(kW·h), when the scheme of throttling extraction steam from high-pressure heaters is applied with the primary frequency regulation time duration set as 90 s.

Determination and Interference Study of Trace ETA in Secondary Circuit of Nuclear Power Plant

ZHU Zhiping, ZHANG Yu, SHI Chun, SONG Xianzhi, LIU Zhifeng

2019, 52(8):  173-178,184.  DOI: 10.11930/j.issn.1004-9649.201812009

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Ethanolamine (ETA) has been selected as the pH control agent for the secondary loop water quality regulation in the third-generation nuclear power plant of China. Hence the determination and interference analysis of trace ETA in the secondary circuit is becoming one of the critical issues that have captured attentions. On the basis of a series of experiments it is discovered that these chromatographic columns (CS12A, CS16, CS18) can determine the concentration of ETA accurately without any other ions. Under the condition of simulated second-loop water quality in the nuclear power plant, the interference of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺ and morpholine was mainly discussed when using CS18 analytical column to determine the concentration of ETA. The results showed that through the optimization of the chromatographic conditions, the concentration of trace ETA in the second-line water quality of nuclear power plants can be accurately measured with gradient elution when the column temperature is 50℃, the inhibition current is 20 mA and the eluent flow rate is 0.36 mL/min.

Application Study on CPSO-FLN Model in the Steam Turbine Heat Rate Forecast

HU Jian, LIU Chao

2019, 52(8):  179-184.  DOI: 10.11930/j.issn.1004-9649.201903078

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The heat rate is one of the important indexes to assess the thermal economy of thermal power units. Regarding the difficulties in accurate heat rate calculation, this paper proposes a short-term heat rate forecast model based on optimized fast learning network (FLN) by cloud particle swarm optimization (CPSO). The cloud model based adaptive weight strategy is introduced into the particle swarm algorithm such that the weight of the particle swarm algorithm can be self-adaptively adjusted to improve the global optimization performance of the PSO algorithm by taking advantage of the randomness and stability of cloud droplets. Furthermore, the CPSO algorithm is used to tune the model parameters of FLN and establish the CPSO-FLN heat rate forecast model. Finally, the CPSO-FLN model is applied to predict the heat rate of a steam turbine with 12 controllable variables of strong correlation as the input parameters. Through the comparison of the results from the proposed model with those from standard FLN model and PSO-FLN model, the CPSO-FLN model has demonstrated higher accuracy and better generalization capacity, and hence is proved to be an effective forecast method.