Table of Content

23 September 2013, Volume 46 Issue 9

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Column of CFB Boiler

Numerical Simulation and Optimization of SNCR System for CFB Boilers

LI Jing-ji, YANG Hai-rui, LI Qiong, YANG Jian-hua, LU Jun-fu

2013, 46(9):  1-5.  DOI: 10.11930/j.issn.1004-9649.2013.9.1.4

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With the regulation on NO_x emission for power plants becoming more and more stringent, the DeNO_x devices have to be installed even for the low NO_x emission CFB boilers. NO_x emission of boilers can be effectively decreased by injecting the reductant, such as ammonia or urea, into the inlet of CFB cyclones to realize the SNCR at high temperature. In this paper, the flow field of the cyclone and attached flue of a 185-t/h CFB boiler is simulated by ANSYS Fluent^�� software and a SNCR DeNO_x system is designed accordingly. The simulation results show that it is preferable to install more nozzles at the inner side of the cyclone inlet to improve the uniformity of the distribution of reductant. Also, increasing the average atomized particle size and spray cone angle is helpful to enlarge the spray range of reductant, but the effect of the spray speed on the spray range is limited

Testing and Numerical Simulation of Temperature Field and Oxygen Field for CFB Boilers

HUANG Zhong, SUN Xian-bin, JIANG Jian-zhong, SHI Zheng-hai, XIAO Ping

2013, 46(9):  6-6.  DOI: 10.11930/j.issn.1004-9649.2013.9.6.0

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The test on furnace temperature field and oxygen field of one CFB boiler is conducted and the combustion process of the boiler is simulated by numerical simulation software. The results demonstrate that the temperature distribution along the furnace height is relatively uniform, therefore, the temperature in the dilute region can be represented with a fixed value during boiler design. In addition, the temperature 1 meter away from the furnace wall varies slightly and tends to be constant, so that, the temperature in the furnace center can be used as the reference temperature during boiler design. The oxygen concentration is lower in the center and at the wall surface and shows a M-shape distribution approximately along the furnace width. The numerical simulation results are consistent with the test data. The study is helpful to understand the CFB boiler temperature field and oxygen field distributionand improve the combustion efficiency. The research results can provide a reference for large CFB boiler design and theoretical studies.

Wear Proof Technology for EHE Heating Surfaces and Its Application

HU Chang-hua

2013, 46(9):  12-15.  DOI: 10.11930/j.issn.1004-9649.2013.9.12.3

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Aiming at the wearing, tube rupture and overheating phenomena existing in the external heat exchanger(EHE) of 300-MW CFBB units, mechanisms and reasons of the wearing are analyzed. A series of measures against abrasion and overheating, including the optimization of pipe clip structures and maintenance technologies; the monitoring of outlet steam temperature of EHE tubes, as well as the insulation capacity of high-calorific intensity tubes are proposed. The designed structure of EHE for 600-MW CFBBs is also presented in the paper and the wear proof measures for the 300-MW CFBB units are applied to the 600-MW units, which has improved the reliability of the unit with high efficiency.

Regulation and Load Variation Performance of the Domestic 330-MW CFB Boiler

SUN Xian-bin, SHI Bo, SHI Zheng-hai, WEI You-ling, CAI Ai-min, YU Wu-gao

2013, 46(9):  16-20.  DOI: 10.11930/j.issn.1004-9649.2013.9.16.4

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The first domestic proprietary 330-MW circulating fluidized bed(CFB) boiler is developed with a compact-type returning ash heat exchanger(CHE) attached. In order to ensure the stable and economical operation of this boiler, studies on its regulating scheme are performed. Based on the analysis of the methods to regulate the bed pressure, bed temperature, air flow rate and limestone rate, a control scheme and corresponding implementation plan are proposed. The control scheme is characterized by adopting the CHE to adjust the bed temperature and reheated steam temperature. The operation results show that the boiler regulation is quite reliable and flexible, and the temperature in the hot circulating loop is uniformly distributed. In addition, the boiler turns out to be of high combustion efficiency with excellent load variation performance.

Analysis and Measures of Secondary Air Gate Wearing in 300-MW CFB Boilers

XUE Wen-xiang

2013, 46(9):  21-23.  DOI: 10.11930/j.issn.1004-9649.2013.9.21.2

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Regarding the problem of secondary air gate wearing in 1 065-t/h CFB boilers with no external fluidized bed heat exchanger (HG-1065/17.5-LMG, single firepot and double air distribution plates) which is independently designed and implemented by Harbin Boiler Company Limited, different measures have been tried in practice through the analysis of the air gate structure and the wearing mechanism. Eventually by installing wear-proof devices at the secondary air gates, we are able to address the wearing problem effectively, which may cause the boiler tube rupture and affect the boiler’s safe long-term operation.

Energy-Saving Analysis for Startup Systems of Supercritical CFB Boiler

LI, Peng

2013, 46(9):  24-28.  DOI: 10.11930/j.issn.1004-9649.2013.9.24.4

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Nowadays large-scale supercritical circulating fluidized bed (CFB) boilers are still in the stage of development domestically and internationally. Therefore, it is very necessary to carry out quantitative calculation for the analysis of the starting system. Based on the technical characteristics of CFB boilers and taking the 600-MW supercritical CFB boiler for example, the cold start curve from ignition to loading by 30% of rated load is divided into four stages, and the heat loss of each stage is calculated respectively. In addition, economic comparison between flash box startup system and compound startup system is also conducted. The results show that although the investment and maintenance costs of flash box startup system are low, there exists big heat loss during startup as much as 42.19×10⁵ MJ for one cold startup of a 600-MW CFB boiler. With the cost of manufacturing and maintenance decreasing, the compound startup system is more economical, which is highly recommended for 600-MW supercritical CFB boilers.

Testing on 520-t/h CFB Boiler Firing Coal Slurry Mixture

LIU Zhi-qiang

2013, 46(9):  29-33.  DOI: 10.11930/j.issn.1004-9649.2013.9.29.4

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To study the performance of the combustion system fueled with different proportions of coal slurry mixture, three operating conditions, without peat blending, with peat blending at 25% main pump speed and with peat blending at 40% main pump speed, are tested on a 520-t/h circulating fluidized bed(CFB) boiler in one Power Plant. The results show that with the increase of peat blending ratio, the average bed temperature is significantly reduced and much closer to the optimum desulfurization bed temperature; the distribution of the furnace temperature field is more uniform so that will benefit the furnace combustion and heat absorption; the overheating of the platen superheater wall and the low boiler main stream temperature are substantially improved.

Generation Technology

Aging Precipitation Behavior of Solid-Solution Strengthened Nickel-Base Alloys

GUO Yan, HOU Shu-fang, WANG Bo-han, LIN Lin

2013, 46(9):  34-38.  DOI: 10.11930/j.issn.1004-9649.2013.9.34.4

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Aging precipitation behavior of the two solid-solution strengthened Ni-based alloys(617 and 625) has been investigated. The results revealed that the M₂₃C₆ and M₆C carbide particles precipitated both at the grain boundaries and inside grains, and the γ phase particles were situated at intragranular sites in the process of aging at 760 ℃ for two alloys. In addition, γ″ phase precipitated at grain boundaries and stacking faults in the aged alloy 625. The carbide particles discontinuously dispersed at grain boundaries after aging for up to 3 000 h for alloy 617; however, the 5 000 h aging induced the coalescence of the carbide particles. After aging up to 5 000 h, the size of precipitates inside grains remained basically stable for alloy 617. The carbides precipitates dispersed continuously at inter-granular site were observed in the alloy 625 aged for 3 000 h and an increase of aging time resulted in the growth of carbide particles. The size of intragranular particles kept almost unchanged after aging for up to 3 000 h for alloy 625; however, the presence of a number of M₆C particles was visible for alloy 625 after 5 000 h. The impact absorbed energy obviously declined for two alloys after aging. Aging embrittlement of the alloy 625 is greater than that of the alloy 617.

Forecasting the NO_x Emissions from Utility Boilers Based on Independent Component Analysis

SUN Bao-min, XIN Jing, YANG Bin, WANG Lan-zhong, WANG Chong

2013, 46(9):  39-43.  DOI: 10.11930/j.issn.1004-9649.2013.9.39.4

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There are many high dimensional input values in the modeling process for low NO_x combustion property of coal-fired utility boilers, Moreover, processing such a large amount of sample data may slow down the calculations and reduce forecasting accuracy. To solve these problems, the independent component analysis(ICA) is applied to data pretreatment and then the back propagation(BP) neural network model based on fastICA algorithm is established in this paper. The ICA-BP model is used to predict the NO_x emission from a 220-MW thermal power unit. The results indicated that the neural network model based on fastICA algorithm outperforms the one without data preprocessing. The relative error of the ICA-BP model was only about 2.5% between the calculation and the measured results, in which the ICA method is verified to be an effective tool for data pretreatment in system modeling in the aspect of lowering the dimensions while more original data characteristic information still retained simultaneously is.

Estimation of Auxiliary Power Consumption Rate with Load Ratio Method

NIE Jun, LIU Gang

2013, 46(9):  44-46.  DOI: 10.11930/j.issn.1004-9649.2013.9.44.2

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Generally, the estimated auxiliary power rate in design stage is greater than its actual value with relative error about 20%, which will influence the economic evaluation for project approval and the long-term economic benefits. Analysis indicates that the error mainly comes from the fact that the same factor K is adopted in the conversion factor method (CFM) for auxiliary power rate estimation and high-voltage auxiliary transformer capacity determination. The load ratio method proposed adopts a specified K_L for auxiliary power rate estimation. The K_L is critical to the new method and its determination is demonstrated through examples. The proposed method has been used in 12 projects. The average relative error is less than 2%, which shows that the estimation accuracy is improved almost by 90% compared to that of CFM.

The Operation Practices and Optimization of CEDI Equipment in Heyuan Power Plant

SHEN Jian, CAO Yun, LI Yuan-yuan, HE Zhen-kun

2013, 46(9):  47-51.  DOI: 10.11930/j.issn.1004-9649.2013.9.47.4

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The 2 series of Continuous Electro-deionization(CEDI) equipment of Heyuan power plant have been put into operation for four and half years, which is approaching the service life and the quality of the product water deteriorated frequently over the past year. The possible causes for the problem were investigated one by one and relevant measures were proposed respectively, including chemical cleaning, level regeneration, transformation of pipeline, rinse cycle, and replacement of individual membrane block. The results showed that the quality of product water of CEDI equipment returned to normal level after various measures had been taken. As a result, the steam quality of Heyuan power plant is guaranteed and the about-to-expire equipment can work normally, realizing security and economy.

Computational Analysis on the Influence of Dust Accumulation of Air-Cooled Condenser on Unit Outputs

GUO Min-chen, LI Mei-bao, PENG Xin-fei, FAN Xue

2013, 46(9):  52-55.  DOI: 10.11930/j.issn.1004-9649.2013.9.52.3

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The dust accumulation of air-cooled condensers determines whether the unit can be operated with enough security and high efficiency. With the ever-increasing installed capacity of air-cooled units in the areas rich in coal but short of water resources, it is necessary to study the relationship between the thickness of dust accumulation and unit outputs. In this paper, the heat exchanging coefficient before and after dust accumulation is calculated by taking advantage of the heat transfer theory and the principle of heat exchanger. Combined with the operation data of one 330-MW unit of a power plant, the correlation between the heat exchanging coefficient/unit back pressure and the fouling thickness is derived. In this way the influence of dust thickness on the unit output is concluded. The results show that for 330-MW units, a mere 1mm thick layer of fouling will reduce the unit output by 1.4%.

Power System

Analysis on the Electric Performance of 500 kV Tower with Insulated Cross-Arm

ZHANG Zhi-jin, YANG Chao, JIANG Xing-liang, HU Jian-lin, HU Qin

2013, 46(9):  56-60.  DOI: 10.11930/j.issn.1004-9649.2013.9.56.4

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The accelerated construction of UHV transmission lines by the state brings about, higher insulation performance requirements for the UHV transmission line towers. Based on an investigation of the research and application status of insulation towers, the paper proposes the structure pattern of insulation towers. By taking the insulated cross-arm tower as an example and with a reference to the 500 kV single circuit cup-type tower, the insulation level of the insulated cross-arm towers and the ordinary towers are calculated and the difference of their electrical performances are compared. The impacts of two factors, including reducing the number of insulators and shortening the length of insulated cross-arm, are analyzed on the electric performance of insulation towers. The results show that the towers with insulated cross-arms are superior over the common towers in terms of insulating margin under frequency voltage, switching overvoltage and lightning overvoltage. It can be concluded that number of insulators and the length of the insulated cross-arms may be reduced concurrently to achieve the unification of the safety and economy of insulation towers.

Selecting Method of FACTS Damping Controller Wide Area Control Signals Based on Dominant Mode Ratio

WANG Hua-xin, ZHAO Yong-xi

2013, 46(9):  61-64.  DOI: 10.11930/j.issn.1004-9649.2013.9.61.3

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The paper introduces the method of dominant mode ratio to solve the problem of FACTS damping controller design and proposes a method for selecting the FACTS damping controller wide-area control signals based on dominant mode ratio. The dominant mode ratio indicator is proposed in the model of single input and output system. The indictor of complex system is calculated by using the PRONY identification method. The method is proved feasible in the standard 3 machine system. A case study was conducted in Sichuan and Chongqing power grid to improve the practicability of the SVC damping controller. The simulation shows that the method can improve the power system’s dynamic stability.

Short-Term Forecasting of Wind Farm Groups in Beijing-Tianjin-Tangshan Power Grid

TIAN Chao, CHEN Ying, ZHANG Ben, ZHANG Tao, WANG Zhi-jia

2013, 46(9):  65-70.  DOI: 10.11930/j.issn.1004-9649.2013.9.65.5

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With large-scale integration of wind power, it is important for the safe, stable and economic operation of regional power grid to strengthen the power forecasting of the regional wind farm group. Based on the specific features of wind farm group in Beijing-Tianjin-Tangshan power grid, a short-term wind forecasting model is established by using the physical modeling method, and the statistical up-scaling technology is combined with the physical model to enhance its precision. A wind power prediction system is built with the three-layer architecture for Beijing-Tianjin-Tangshan power grid, and has been applied to the engineering project. It has been proved that this method can effectively predict the wind power of the Beijing-Tianjin-Tangshan region, and can significantly increase the wind power absorptive capacity of Beijing-Tianjin-Tangshan power grid, and improve the lean level of power grid dispatching.

Improvement on Single-Ended Traveling Wave Based Fault Location Through Singular Point Detection

XIN Chao-shan, LI Feng-ting

2013, 46(9):  71-74.  DOI: 10.11930/j.issn.1004-9649.2013.9.71.3

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The single-ended traveling wave based fault location became the focus of study due to the feature that it is not subject to communication constraints. Through wavelet transforming, the first wave head can be located precisely. But, in complex circuits, the second reflected wave will decay rapidly due to superimposed waveforms and cross transmission waves, which leads to the decrease of measuring accuracy. In this paper, based on the analysis of refraction-reflection law for different impedance line, the extraction of traveling waves and wavelet transformation, the method of averaging processing for the transformed second wave to improve the measuring accuracy is proposed. An improved scheme of traveling wave based fault location using single end electric parameters is established and simulation is performed in Matlab. The results show that, compared with the modulus maxima method, the updated averaging processing can significantly improve the fault location accuracy. The correctness and effectiveness of the new scheme are proved.

Transformer Fault Diagnosis Method Based on Bayesian Network and Rough Set Reduction Theory

LU Qi-shen, ZENG Hui-xiong, YAO Sen-jing, HUANG Rong-hui, ZHANG Hai-long

2013, 46(9):  75-79.  DOI: 10.11930/j.issn.1004-9649.2013.9.75.4

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The ability of Bayesian network to deal with uncertain problems can be a solution to transformer fault diagnosis when data is incomplete and reliable conclusions are difficult to be reached. By combining the Bayesian network classifier and rough set reduction theory, this paper set up a Bayesian network classification model based on expert knowledge and statistical data. The integral use of DGA and electrical test data as the input set of diagnosis realized the probabilistic reasoning and sequencing of the possible failure types, and as a result, improved the reliability of the diagnosis. Meanwhile the rough set reduction theory was used to make the minimization reduction of Bayesian network classification model, effectively reduced the complexity of network structure and the input of the model. Experiments proved that this method is an effective transformer fault-diagnosis method and has the ability to deal with the absence of information, the fault-tolerant features and high accuracy.

Adaptive Closed-loop Control System of Phase Selection Circuit Breakers

WANG Hai-yan, YUAN Duan-lei, HE Zhou

2013, 46(9):  81-85.  DOI: 10.11930/j.issn.1004-9649.2013.9.81.4

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In order to solve the problems in the traditional phase selection circuit breaker’s control system, such as complex relationships among compensation parameters, which vary randomly and dispersedly, an adaptive feedback closed-loop control scheme was proposed, which was combined with a new type of magnetic bodies. The hardware and software systems were designed according to the PID fuzzy control principle, and the new phase selection circuit breaker was tested under conditions of varied temperature, SF₆ gas density and control system voltage. The results show that the closed-loop control system can effectively track the changes in temperature, SF₆ gas density and control voltage with an error smaller than ± 1 ms.

Balancing Control Method of DC Voltage of Cascade STATCOM

ZHOU Yuan, XIA Ming-chao, REN Yi-biao

2013, 46(9):  86-91.  DOI: 10.11930/j.issn.1004-9649.2013.9.86.5

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This paper studies the unstable problem of capacitor voltage in the DC-link of STATCOM, and proposes a new control strategy with additional circuits, which are used to control charge and voltage stability. The use of additional circuit multi-winding transformer effectively isolates the direct electrical contact between the additional circuits and the main circuits of devices, and avoids the occurrence of instantaneous zero capacitance voltage when the additional circuits and the main circuits of devices are put into operation concurrently. This method makes the control strategy of additional circuit independent of the control strategy of the main circuit. The additional circuit can either connects to the large power grids, or use independent stand-alone power supply separated from the grid, or the large capacity UPS, which can preferably achieve devices starting, fast power switching and so on. In addition, the dynamic response of the devices can also be enhanced, and the STATCOM capacitor voltage stability and normal reactive output can be ensured at the same time, when the main circuits have larger voltage fluctuations.

Commissioning and Setting of Voltage-Injection Stator Ground Fault Protection for Large-sized Generator

WU Li, PNEG Jin-ning, YAO Li-xiao, NAI Hai-peng

2013, 46(9):  92-95.  DOI: 10.11930/j.issn.1004-9649.2013.9.92.3

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Generator capacity and stator winding capacity to ground per phase increasing cause large current circulating within the stator, which may result in severe damage to the stator insulation and earth faults in the stator. So higher requirements are needed for stator single-phase grounding protection of large generator.The paper introduces the basic principle of voltage-injection stator single-phase grounding protection and summarizes the field adjustment methods of the voltage injection scheme against the stator earth fault protection ,and gives the experimental results of adopting impedance angle mutation and transition resistance.The actual operating status for inoperative generator and that with 30% rated voltage commissioning are analyzed, and the results have verified the accuracy of setting the grounding transition resistance and selecting the fault generator.

Study on Power Frequency Electromagnetic Impacts of AC Transmission Lines on Paralleling Erected VSC-HVDC Transmission Lines

LI Jing-hui, GONG You-jun, CHEN Bing

2013, 46(9):  96-101.  DOI: 10.11930/j.issn.1004-9649.2013.9.96.5

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A model of power frequency electromagnetic impact of AC transmission lines on the parallel VSC-HVDC transmission lines and a DC bias current model on the converter transformer side are constructed by using the distributed parameters model of overhead transmission line and the voltage-current transport equation with consideration of the power frequency equivalent circuit on the side of DC system valve. In the end, based on the parameters of existing ±160 kV VSC-HVDC Transmission Lines and 110 kV AC Transmission Lines, the impacts of such factors as parallel distance, parallel length, AC transposition and DC transposition on bias current are analyzed.

An Initial Value Optimization Algorithm to Track Thevenin Equivalent Parameter

DING Lan, WANG Xian-hong, OU Zhi-le, ZENG Bo

2013, 46(9):  102-106.  DOI: 10.11930/j.issn.1004-9649.2013.9.102.4

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As interconnected power systems expand, the Thevenin equivalent is widely used in power system, which can reflect the operating conditions of system because of its clear, simple and rapid characteristics. Based on the parameter drift and tracking problems in obtaining the Thevenin equivalent parameter with existing method, an improved deviation correction algorithm is proposed in this paper to track the Thevenin equivalent parameter. The algorithm computes the initial value of parameter in case of constant Thevenin equivalent voltage amplitude and varied phase angle of the adjacent operating point. The deviation correcting mode is used to track the changing operation point of power gird. The combination of initial value optimization algorithm and deviation correction method can not only rapidly track equivalent parameters, but also avoid the numerical instability. At last, the tracking performance testing and four-machine two-area system simulation have proved the accuracy and applicability of the proposed algorithm for actual grid operation mode.

Power Emergency Resources Allocation Schedule Model Considering the Sequence of Loads

LUO Hua-feng, FANG Xin-yan, YU Guo-qin

2013, 46(9):  107-111.  DOI: 10.11930/j.issn.1004-9649.2013.9.107.4

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In dealing with the sudden power blackout caused by external factors, power emergency resources allocation schedule plays a very important role. This paper discusses the characteristics of local outages in a power system and the key points that need to be considered in formulating corresponding restoration strategies. To solve the integrated scheduling problems which includes multiple areas to be restored and multiple resource storehouses, the FAHP is used to sort out and sequence the areas to be restored according to the load importance and the priority is determine accordingly. An emergency resources allocation schedule model is established by taking the minimum total time, total cost and penalty cost as objective, and the priority of areas to be restored is added in the model in the form of weighting coefficient, so as to ensure the areas with higher priority to obtain emergency resources. In the end, a case study proved the feasibility and applicability of the model.

Design and Realization of a Testing System for Flexible HVDC Valve Control Equipment

HU Si-quan, JI Pan-pan, ZU Li-feng, FENG Min, LI Kun

2013, 46(9):  112-116.  DOI: 10.11930/j.issn.1004-9649.2013.9.112.4

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A testing system for modular multi-level converter HVDC flexible valve control equipment has been designed, which consists of simulation device for pole control, main circuit signals generator for converter stations, simulation device for valve sub-module and background monitor. This testing system can carry out the basic functional testing, including capacitor voltage reading and valve status monitoring, voltage sharing control, sub-module fault processing logic, valve control device fault processing logic and analog signal acquisition, of the modular and multilevel HVDC Flexible valve control device without the pole control system and converter valve. And it can meet the testing requirement of MMC HVDC flexible valve control device with different voltage classes or transmission capacity, by just adjusting the interface numbers of the simulation device for valve sub-module. A MVCE300 valve control device was tested and the testing result shows that the testing system can meet the testing need of modular multi-level converter HVDC flexible valve control equipment.

A New Type Noise Control System Structure for Indoor-Reactors

PU Qi-qi, JIN Xiao-gu, ZHANG Jiang-tao

2013, 46(9):  117-120.  DOI: 10.11930/j.issn.1004-9649.2013.9.117.3

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In dealing with the nuisance problem of an indoor-substation producing different frequency band noise when its reactors are in operation, a composite noise-suction technology is developed, which uses micro-perforated metal-fiber board-walls and soundproof doors coated with damping materials to block noise leakage. In order to improve the radiating efficiency of the reactors, the ventilation system with silencers is redesigned by using low-noise and automatic-cycle cooling technique to control noise transmits outward. By compare the noise data before and after reconstruction, the noise control effects and rationality of the new type structures are analyzed. The testing results show that, the noise of the substation control room basically meets the requirements of noise emission standards of class-Ⅱ-area after the restruction (i.e.≤50 dB ); the noise of the substation’s surrounding environment is nearly the same with background noise; the noise of the reactors’ room has also been significantly reduced. This study provides a basis for creating a quiet environment-friendly substations in smart grids.

Development and Application of Fire Fighting Water Storage & Supply Control System in Smart Substation

ZHOU Zhi-yong, HAN Ben-shuai, LI Yan-li, ZHANG Hang, ZHANG Da, ZHANG Fan

2013, 46(9):  121-125.  DOI: 10.11930/j.issn.1004-9649.2013.9.121.4

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In design of fire fighting water storage & supply in substation, a research is conducted on system integration, control mode, automatic inspection, fault analysis of fire fighting. Through integration of the water storage & supply system and the pressure stabilization system in design, a centralized control idea is put forward. An intelligent control device of water storage & supply is developed for fire fighting in substation, which can carry out real-time monitoring of the pressure, liquid level, flow, temperature of the water storage & supply system. An automatic inspection module is developed and used for the first time to replace manual inspection and a fault diagnosis module is developed to realize the equipment fault diagnosis and early warning. The engineering application shows that the system and equipment has high reliability, high degree of automation, good extensibility and stable operation. It is therefore has a broad prospect of application.

Random Distribution model of Photovoltaic Output Based on Non-parametric Kernel Density Estimation Method

WU Zhen-wei, JIANG Xiao-ping, MA Hui-meng, MA Su-liang, GAO Zhi-qiang

2013, 46(9):  126-130.  DOI: 10.11930/j.issn.1004-9649.2013.9.126.4

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The random characteristics of photovoltaic(PV) output is one of the significant factors affecting the stability of PV power generation. The influence of weather difference on the level of PV output was studied by statistical calculations and analysis of the historical operating data of a PV power plant. Meanwhile, the random distribution models of PV output were established under clear, cloudy, overcast and rainy or snowy weather conditions by non-parametric kernel density estimation method. The non-parametric kernel density estimation method can analyze the distribution features of the data without any additional assumptions, which is suitable to analyze the random distribution characteristics of PV output that is influenced significantly by weather conditions. The analysis indicates that these models are well consistent with the actual probability distribution of single day PV output under corresponding weather conditions.

New Energy

Dynamic Global Optimal Power Flow and its Two-Stage Control Algorithm of a Power Grid Integrated with Wind Power Farms

LUO Yu-lei, LI Yan, WU Kun

2013, 46(9):  131-137.  DOI: 10.11930/j.issn.1004-9649.2013.9.131.6

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In order to solve the fluctuation problems of wind power in a grid, the dynamic global optimal power flow analysis is conducted and a two-stage control algorithm and its mathematical model are presented. The algorithm sets the minimum grid power loss as the objective function in a period of wind power output, and optimizes the traditional control method (with the taps of transformers and numbers of capacitors in parallel as variables) and the fast response control method (with active and reactive power compensation) separately, to reduce the action times of the traditional control method and get the optimal control strategy which takes both methods’ advantages. For accurate simulation of wind power connected to the grid and fast convergence of the new algorithm, a modified Newton-Laphson power flow method with genetic algorithm for the dynamic global OPF is set up, in which the P-Q(V) equations are established and the Jacobi Matrix is modified with consideration of the double-fed and asynchronous wind generators connected to the grid. The method is suitable for power flow calculation of the grid integrated with wind farms, and can improve the accuracy of the two-stage control method. The reasonability and efficiency of the proposed algorithm are verified through its application in the analysis of the wind power integrated system in central China area, and comparison of the computed results with those of conventional multi-stage OPF method.

Scenery Storage Systems Connected to the Grid Optimization Control Strategy

LI Chun-ping, YANG Wan-qing, LIANG Ying-zhe, WANG Xiao-nan

2013, 46(9):  138-141.  DOI: 10.11930/j.issn.1004-9649.2013.9.138.3

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This paper describes the current major energy storage technologies, including electrochemical energy storage, physical storage, and electromagnetic energy storage; analyzes the structure and characteristics of micro-grid system of hybrid power; introduces the dynamic programming-based system control method and simulation results; proposes a model forecast-based control strategy for typical hybrid systems. The energy fluctuations or even intermittent problems caused by sudden change in weather can be solved, to a certain extent, through optimizing the distribution of wind, solar, battery energy storage function ratio, thereby improving system stability.

Energy Conservation and Environmental Protection

Speciation Analysis of Arsenic in Power Plant Coals

ZHU Xiao-yu, YUAN Chun-gang, ZHAO Yi

2013, 46(9):  142-144.  DOI: 10.11930/j.issn.1004-9649.2013.9.142.2

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It is necessary to understand the existing forms of arsenic in power plant coals so as to provide some basic data to bridle arsenic pollution caused by power plants. Sequential chemical extraction procedure was adopted to extract the arsenic in various forms from five coal samples, which are namely to be obtained as non-specific adsorbed arsenic, specific adsorbed arsenic, amorphous and weak crystalline iron and aluminum hydrous oxides arsenic, crystalline iron and aluminum hydrous oxides arsenic and residue arsenic. The contents of arsenic in various extraction liquids were determined by atomic fluorescence spectrometer. The results show that the distributions of arsenic are different in the different coal samples. Arsenic mainly exists in amorphous and weak crystalline iron and aluminum hydrous oxides arsenic form and residue arsenic form. The total amount of arsenic in different coal samples is almost consistent with that measured in the coal samples digested by HNO₃, which demonstrates that there is no significant loss of arsenic in coals during the extraction process and the method and operation adopted are proven to be appropriate.

Analysis of Mercury Species and Thermal Stability of Desulphrized Gypsum in Coal-fired Boiler

YIN Li-bao, GAO Zheng-yang, ZHONG Jun, ZHENG Shuang-qing, CHEN Chuan-min

2013, 46(9):  145-149.  DOI: 10.11930/j.issn.1004-9649.2013.9.145.4

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Identifying the Hg species and release characteristics have guiding significance for WFGD gypsum utilization. The X-ray fluorescence spectrometry(XRF) was used to make the composition analysis of the two gypsum samples of the coal-fired power plant. In order to determine the thermostability and species distribution of Hg in gypsum, the gypsum sample and gypsum residue sample were heated by two heating method and the gypsum weight loss and Hg contents were measured after heating treatment. The results show that the Hg release began at 100 ℃ and 200 ℃ respectively for the two gypsum samples; the rapid release occurred at the temperature between 200 ℃ and 400 ℃; the Hg release finished at 500 ℃for all the gypsum samples; the Hg in gypsum residue decreased and the main Hg compounds in WFGD were HgCl₂ and HgS.

EIA-Based Trend Prediction Method of Thermal Power Industry

WU Ya-nan, REN Jing-ming, DING Feng

2013, 46(9):  150-154.  DOI: 10.11930/j.issn.1004-9649.2013.9.150.4

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During the period of 2006-2012, the EIAs of 477 thermal power projects were approved by the state. Based on an analysis of the data of the approved environmental impact assessment(EIA) reports in terms of project investment, environmental protection investment and installed capacities and a contrast study of the approved investment and actual investment of the thermal project constructed during the 11th Five-year(2006-2010) period, an EIA-based trend predication method was proposed for thermal power industry development according to the time series analysis and grey correlation analysis. The research shows that it takes 3.5 years to complete the project construction after approval of project’s EIA. Accordingly the development trend and the resources and environmental pressure brought about by resource consumption and pollutant emissions of thermal power industry was forecasted for the period of 2013-2015.

Numerical Simulation of 3-D Velocity Field in Air Core of Gypsum Cyclones

YANG Yang, AN Lian-suo, LIU Chun-yang

2013, 46(9):  155-159.  DOI: 10.11930/j.issn.1004-9649.2013.9.155.4

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Gypsum cyclones are important equipments in wet limestone-gypsum flue gas desulfurization(WFGD) system in power plants. The air core phenomenon in gypsum cyclone operation may cause waste of energy, unsteady flow conditions, separation efficiency decrease and so on. The three-dimensional velocity field in the air core is simulated with volume of fluid(VOF) model in Fluent to study the characteristics of the flow field. The simulation results indicate that there is a spiral flow in the air core and a certain period of time is needed for the air entered from the two outlets developing into a steady air core. The velocity of the air changes with time obviously in axial but less in tangential direction. Also, the radial velocity is one magnitude order lower than the axial and tangential velocity.