Table of Content

05 January 2021, Volume 54 Issue 1

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A Self-commutated HVDC Circuit Breaker Based on Forced Zero Crossing Technology

LI Guoqing, WEI Pengcheng, LIU Yutong, BIAN Jing

2021, 54(1):  2-9,77.  DOI: 10.11930/j.issn.1004-9649.202003090

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In order to improve the breaking capacity of Hybrid DC circuit breaker and reduce the harm of DC short circuit fault to the system, we proposed a self-commutated HVDC circuit breaker based on forced zero crossing technology. The circuit breaker replaces the IGBT components with thyristors and diodes, and realizes the cut-off of the faults on both sides of the circuit breaker through a single precharge capacitor and forced zero crossing technology, which reduces the installation cost of the circuit breaker. In this paper, the topological structure and working principle of the DC circuit breaker are described in detail, and the parameter selection method of the components is analyzed through the action sequence and the equivalent circuit. Finally, the three-terminal ring network model is built by PSCAD simulation software and verified by simulation. The results show that the scheme can realize the reliable cut-off of the fault line, and the circuit breaker can recover the cut-off ability without recharging after one precharge, thus having good economy.

Air Clearance Calculation and Compacting Layout Design of Valve Hall in Converter Station of VSC-HVDC Grid with High Voltage and Large Capacity

FU Shouqiang, ZHANG Libin, LI Hongjian, CHEN Xiangyu, GAO Yang, CHEN Lei

2021, 54(1):  10-18.  DOI: 10.11930/j.issn.1004-9649.202004220

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The high voltage and large capacity VSC-HVDC grid project has significant difference in valve hall air gap and space layout from the previous one due to its installation of DC circuit breakers. According to the characteristics of high voltage and large capacity VSC-HVDC system, a study is made on the air clearance calculation and compacting layout design of valve hall. The g-parameter method is used to correct the discharge characteristics of air gap under non-standard meteorological conditions, and a method is given for obtaining the temperature and humidity of the valve hall at the maximum air clearance; a method is proposed for compacting layout design of high voltage and large capacity valve hall with DC circuit breakers. Taking Zhangbei converter station of Zhangbei ±500 kV VSC-HVDC demonstration project as an example, the temperature and humidity conditions for calculating air clearance of valve hall were corrected, and the air clearance values were obtained. A comparative analysis of the valve hall layout schemes show that under the condition for meeting the requirements of air clearance and maintenance space, the proposed compacting design method can significantly reduce the valve hall size.

Analysis and Test of Reverse Recovery Performance of Fast Recovery Diode in IGCT-MMC

LOU Yantao, SUN Xiaoping, LIU Qi, ZHOU Wenpeng, ZHAO Biao, YU Zhanqing, ZENG Rong

2021, 54(1):  19-24.  DOI: 10.11930/j.issn.1004-9649.202005037

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The reverse recovery characteristics of the diode plays an important role in IGCT-MMC. This paper firstly introduces the reverse recovery characteristics of the fast recovery diode. Then the switching behaviors of the fast recovery diode in the IGCT-MMC topology are analyzed. Finally a double-pulse experimental platform is built for IGCT-MMC testing, and the reverse recovery characteristics of three commercial fast recovery diode products are compared. The test results show that the reverse recovery peak current and power of the fast recovery diode have a linear relationship with di/dt, and the testing result at high temperature are higher than that at room temperature. While under the same di/dt and temperature conditions, different fast recovery diodes have different reverse recovery peak currents and powers in IGCT-MMC. As a result, it is necessary to choose a suitable di/dt according to the safe working area of the diode in IGCT-MMC.

A Review on Large Capacity Controllable Switching Current Source Converter Research

CHEN Longlong, XU Fei, WEI Xiaoguang, TANG Guangfu, CUI Xiang, GAO Chong, CHEN Qian

2021, 54(1):  25-36.  DOI: 10.11930/j.issn.1004-9649.202004222

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The controllable switching current source converter (CSC) is considered to have promising technological advantages over LCC and VSC. The rapid development of reverse blocking high-power semiconductor devices provides a new opportunity for the application of CSC to HVDC system. Firstly, the advantages and disadvantages of the existing CSC topology and modulation methods are investigated in this paper. And then, the LCC-CSC topology and specific harmonic elimination modulation methods suitable for HVDC system are analyzed. Finally, the LCC-CSC based hybrid HVDC system is comprehensively compared with LCC and VSC technologies, and the technical advantages, existing problems and future researches of LCC-CSC are summarized. This work can provide a research basis for application of CSC in high-voltage DC transmission engineering.

A Calculation Method for Line Harmonic Current Based on Three-Terminal HVDC Transmission System

CUI Jiaying, LIU Tianqi, WANG Shunliang, MA Junpeng, CHANG Pengfei

2021, 54(1):  37-46.  DOI: 10.11930/j.issn.1004-9649.202003179

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In view of the potential problem of harmonic current amplification of overhead transmission lines in three-terminal DC transmission system, a study is conducted on the harmonic current of bipolar overhead lines under different operating modes. Based on the theory of wave impedance, the symmetrical DC lines are simplified into the symmetrical component loops, and the unit length parameters are obtained. The calculation method for harmonic current of uniform line is analyzed. Based on the theory of wave refraction and reflection, a method for calculating harmonic current of hybrid transmission lines is proposed. By building the corresponding DC line model on the PSCAD/EMTDC platform for simulation, and comparing with the theoretical calculation results, it is shown that the proposed calculation method has a high accuracy in obtaining the line harmonic current under different operation modes of the three-terminal DC transmission system.

Optimal Configuration Method for DC Power Flow Controller Considering Power Flow Transfer Characteristics

CHEN Ruochen, ZHANG Yingmin, LIU Qilin, LIU Tianqi

2021, 54(1):  47-53,149.  DOI: 10.11930/j.issn.1004-9649.202003110

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The number of DC power flow controllable lines follows the N−1 principle. Installing DC power flow controller (DCPFC) on the line can improve the controllability of line power flow. The existing research on the configuration of DC power flow controller only focuses on its steady characteristics. Considering that the line overload may be caused by disconnection fault in DC system, a novel configuration method for DC power flow controller is proposed from the power flow transfer principle. A mathematical model of DC power grid with DC power flow controller is established. The installation position of DC power flow controller is determined by sensitivity analysis combined with power flow distribution. The power flow transfer entropy of DC system is proposed, and the DC power flow controller is optimized based on the weighted power flow entropy of DC system. The simulation results show that under different operation modes, the proposed method can not only improve the power flow distribution, but also optimize the power flow transfer characteristics of DC lines, and the average load rate of heavy lines after N–1 fault is significantly reduced, which verifies the effectiveness of the proposed method.

Experimental Modeling of Forward Recovery Characteristics of IGBT for DC Circuit Breaker

SHEN Hong, TONG Cuizhi, DONGYE Zhonghao, QI Lei, WANG Qian

2021, 54(1):  54-61.  DOI: 10.11930/j.issn.1004-9649.202006108

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DC circuit breaker is the main means to clear the faults in VSC-HVDC power grid. Before action of the hybrid DC circuit breaker, the IGBT in the transfer branch is in a state of zero voltage and zero current. When the current of the transfer branch begins to rise, and once the voltage overshoot of collector-emitter produced in the forward recovery process of IGBT meets the IGBT's over-current monitoring criterion, the protection will malfunction, consequently reducing the operating reliability. Aiming at the forward recovery phenomenon of IGBT, a high-current turn-on experimental platform of IGBT is built to obtain the IGBT’s collector-emitter voltage waveforms corresponding to different current waveforms. Based on the staged mathematical fitting, an I-U mapping relationship that reflects the forward recovery characteristics of the IGBT is established. Compared with the experimental results, the relative error of peak collector-emitter voltage is less than 10%, and the duration relative error of over-current monitoring threshold voltage is less than 15%. The model can help to reasonably formulate the over-current monitoring criterion of IGBT used in DC circuit breaker.

Hardware-in-the-Loop Test Method for Valve Base Controller of VSC-HVDC

LU Jianliang, HE Zhiyuan, TANG Rubin, DANG Qing, XIE Minhua, JI Ke, KOU Longze

2021, 54(1):  62-69.  DOI: 10.11930/j.issn.1004-9649.202004246

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The Zhangbei flexible DC power grid project is the world's first voltage source converter based high voltage direct current (VSC-HVDC) project, which brings higher requirements for the reliability of valve base controller (VBC). In order to comprehensively test the VSC-HVDC valve control equipment, a hardware-in-loop test method is proposed in this paper for the full-scale accessing of high voltage and large capacity VSC-HVDC VBC to the real-time simulation system. Through developing an I/O interface chassis, a full-scale access testing platform for VBC in Beijing Station was built based on RT-LAB, and the comprehensive test items and test methods for VBC were proposed. By studying the testing waveforms of several typical working conditions of the platform, the built platform is proved effective and accurate for VBC testing. This test platform has been applied in the certificate of analysis (COA) of VBC in Zhangbei VSC-HVDC Project, and it can also provide reference for the VBC testing in other VSC-HVDC projects.

Study on the IGBT Overcurrent Failure of VSC-HVDC Converter Valve

FENG Jingbo, LV Zheng, DENG Weihua, HU Rong, WANG Xinying

2021, 54(1):  70-77.  DOI: 10.11930/j.issn.1004-9649.202006217

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IGBT overcurrent failure, which is one of the important factors harming VSC-HVDC safe operation, can easily lead to module explosion, water cooling system leakage and even the converter valve shutdown. Based on the structural characteristics and operating conditions of the module multilevel VSC-HVDC converter valve, the paper analyzes the characteristics of three types of IGBT overcurrent failures of the VSC-HVDC converter valve, including short-circuit overcurrent, pulse over current, as well as fly-wheeling diode overcurrent. According to the working principle and characteristics of the MMC converter valve, three IGBT protection schemes and their parameter configuration methods are put forward. The IGBT (3300 V/1500 A) adopted in a converter valve of ±420 kV/1250 MW is used for overcurrent failure analysis and protection scheme verification, and the test results prove the correctness of the proposed overcurrent failure analysis method and the effectiveness of the overcurrent protection scheme.

Design Scheme and Simulation Verification of Suzhou Medium Voltage DC Distribution Project

SU Lin, ZHU Pengfei, YAN Anxin, MA Yalin, HE Mengxue, MEI Jun, WANG Bingbing, FAN Guangyao

2021, 54(1):  78-88.  DOI: 10.11930/j.issn.1004-9649.202006080

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With the development of medium voltage flexible DC distribution technology, the flexible DC distribution network based on power electronics technology has certain advantages over the AC distribution network in phase and frequency synchronization, flexibility of control, transmission line loss, etc., but still has deficiencies in the maturity and stability of technology, as well as the construction cost. For the medium voltage DC distribution network structure of Suzhou medium and low voltage DC distribution system project, a single-bus segmentation based " double-terminal ring " grid structure design scheme is adopted on the basis of comparison of the traditional ring structure and radiation structure. In order to meet the demand of active control of fault ride through and give full play to the flexible power supply modes of the improved grid structure, the design scheme of asymmetrical main station with half bridge converter station + mixed bridge converter station is proposed, and combined with the design of converter valve parameters and system grounding mode, a system simulation model is built on the PSCAD / EMTDC platform to verify the feasibility and fault handling ability of the engineering design scheme, which provides the analysis basis for the scheme design and equipment selection of the demonstration project.

A Review of Grid-Connection Impact and Control Technology of FCS Multi-type Application Modes

QUAN Hui, LI Xiangjun, ZHANG Yang, JIA Xuecui, HUI Dong, GUAN Minyuan

2021, 54(1):  89-95,103.  DOI: 10.11930/j.issn.1004-9649.202001105

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With the rapid construction of the energy internet, there will be increasing penetration of such mobile loads as electric vehicles, and fast charging stations (FCS) will operate in large-scale. As a result, the power grid is facing increasing controlling difficulties and instability risks because of its complex network structure and multi-agent regulation modes. Based on an investigation of the recent researches both at home and abroad on the influence factors of FCS grid-connection and the performance of involved grids, we focus on analyzing the three main challenges of large-scaled FCS to the grid. In addition, according to the novel application modes of "FCS+energy storage system (ESS)+other elements" in the energy internet, we also analyze the existing research progress and engineering experience in this field through a case study of integrated PV-storage-charging stations, and make a comparison of the similarities and differences between the large-scaled FCS and the integrated charging-storage/PV-storage-charging stations. Finally, from the perspectives of application prospect and key technologies, the future development of FCS with ESS is discussed.

Information Security Risk Assessment Method for Electric Vehicle Charging Piles Based on Fuzzy Analytic Hierarchy Process

WANG Weixian, SUN Zhou, PAN Mingyu, ZHANG Baoqun, LI Zhongwei, YE Lin

2021, 54(1):  96-103.  DOI: 10.11930/j.issn.1004-9649.202002053

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In order to quantitatively evaluate the information security level of the electric vehicle charging pile system and identify its vulnerability and hidden security risks, an information security risk assessment scheme and process is designed for electric vehicle charging pile system based on the fuzzy analytic hierarchy process; a security value hierarchical analysis model, a security threat hierarchic analysis model and an evaluation index system are established for the electric vehicle charging pile system assets. The assets of the electric vehicle charging pile system are divided into electric vehicle charging infrastructure pile asset, operation management platform asset, user asset and communication data asset, and they are quantified through investigation and expert opinions obtained by questionnaire surveys. The asset value weight and security threat weight are calculated based on the fuzzy analytic hierarchy process, and consequently the risk value of each asset is calculated. In this way, the fragile points and security risks of the charging pile system are effectively identified, and the corresponding security protection measures and recommendations are provided.

Review on Frequency Regulation Technology with High Wind Power Penetration

FU Hongjun, CHEN Huifen, ZHAO Hua, WANG Kaifeng, LU Zongxiang, QIAO Ying

2021, 54(1):  104-115.  DOI: 10.11930/j.issn.1004-9649.202003132

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In recent years, the global wind power penetration rate has continued to increase, and wind turbines have gradually replaced traditional synchronous units, which is one of the main reasons that cause power system frequency regulation difficulties and affect grid safety. By upgrading the control design, wind power can provide rotational inertia and frequency regulation capabilities, turn damage into benefits, and improve system frequency safety. Combined with the frequency regulation time scale, this paper details the principles and characteristics of each control method of wind turbine participation in frequency regulation, and analyzes the advantages and disadvantages of different methods and the adaptation process. The influence of high penetration caused by wind power grid integration on the frequency stability of the power system is analyzed. In combination with many recent power system frequency safety accidents involving wind power, it is pointed out that many countries and regions have raised the wind power frequency regulation technology standards. Finally, it is proposed that in-depth research should be conducted on issues such as technical and economic evaluation, market and access, in order to promote wind power to play important role in future power system frequency regulation.

An Integrated Control Strategy for Photovoltaic-Energy Storage System Participating in Frequency Regulation and Peak Shaving of Power Grid

DING Ming, SHI Jianxiong, HAN Pingping, LIN Zihao, ZHANG Yu

2021, 54(1):  116-123,174.  DOI: 10.11930/j.issn.1004-9649.201907198

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The increasing replacement of renewable energy for thermal power results in the decline of power grid frequency regulation capability. To solve this problem, a photovoltaic-energy storage (PV-ES) system model is established and a control strategy is proposed, which utilizes the idle capacity of the inverters to participate in peak shaving and frequency regulation. To ensure the two modes of peak shaving and frequency regulation of the energy storage battery operate coordinately, the energy storage battery is set into four types of state of charge (SOC) zones, including disable zone, frequency regulation zone, peak shaving charging zone and peak shaving discharging zone. The maximum output constraint coefficient of the energy storage battery is constructed based on SOC feedback to optimize the output and prolong the service life of the energy storage battery. Finally, a PV-ES system model is established in MATLAB/Simulink software. The simulation results and economic analysis for a typical case show that with the proposed control strategy, the PV-ES system has the ability to participate in peak shaving and frequency regulation of power grid by utilizing the idle capacity of the inverters.

Review of Application Research of Video Image Intelligent Recognition Technology in Power Transmission and Distribution Systems

ZHOU Junhuang, HUANG Tingcheng, XIE Xiaoyu, FAN Wenjun, YI Tingting, ZHANG Yongjun

2021, 54(1):  124-134,166.  DOI: 10.11930/j.issn.1004-9649.201912202

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The digital construction of the power grid has generated massive data. Video image intelligent recognition technology has attracted extensive attention for its powerful ability to extract image data value in application scenarios such as equipment and environmental video surveillance and unmanned inspection in power transmission and transformation systems, etc. In response, this paper first introduces the basic concept and research framework of video image intelligent recognition technology, and summarizes the common image recognition technologies that are commonly used in power transmission and transformation systems. Then from the two perspectives: intelligent inspection for power grid equipment and environmental safety monitoring, and intelligent patrol for personal safety monitoring, the four application research scenarios of video image intelligent recognition technology in power transmission and transformation systems are reviewed respectively. On this basis, three challenges faced by video image intelligent recognition in the application of power transmission and transformation systems are discussed, possible solutions and research ideas are put forward, and suggestions are given.

Overheating Defect Detection of Composite Insulator Based on Mask R-CNN

GAO Yi, TIAN Lianfang, DU Qiliang

2021, 54(1):  135-141.  DOI: 10.11930/j.issn.1004-9649.202003145

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Aiming at the problems of large workload and low intelligence of the current infrared image-based overheating defect detection techniques for composite insulators, and the poor accuracy and poor generalization performance of the traditional image segmentation methods in complex backgrounds, an overheating defect detection method is proposed for composite insulators based on instance segmentation network Mask R-CNN. Firstly, in order to improve the accuracy of segmentation, the Mask R-CNN network is improved according to the idea of Cascade R-CNN, and the data augmentation and transfer learning methods are used for model training to improve the network performance. Secondly, the result obtained by deep segmentation network is further optimized by using traditional image processing methods such as skeletonization, so that the final segmentation result only covers the core rod of the composite insulators. Finally, the temperature data in the infrared image is directly read and converted into the actual temperature value, and the grade of overheating defects is judged according to the relevant methods and criteria provided in DL / T664-2016 Infrared Diagnostic Application Specification for Live Equipment. The results show that the algorithm proposed in this paper has a high detection accuracy of 100% for the infrared images of composite insulators with serious and urgent defects, but has false detection occurrence for the infrared images without overheating defects or with general defects. On the whole, the accuracy rate of 93% is achieved in defect detection of test sets.

Full-Scale Testing and Theoretical Analysis of Influence of Tension Insulator Strings on the Sag of UHV Conductors

SONG Gang, SHEN Guohui, BAO Yunan, TENG Fei

2021, 54(1):  142-149.  DOI: 10.11930/j.issn.1004-9649.201907159

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In order to study the influence of tension insulator string’s weight on the sags and tensions of ultra-high voltage (UHV) conductors, full-scale testing and theoretical analysis are carried out. The full-scale testing of sags of a three-span transmission line are conducted using global positioning system (GPS) and total stations, and the sag’s distribution characteristics of tension insulator strings and conductors are obtained. A theoretical analysis method is developed with consideration of the correlation between tension insulator string’s weight and conductor’s sags, and the horizontal tension forces of transmission lines are fitted based on the full-scale testing data. The results show that both the conductors and tension insulator strings have a shape of catenary curve in sag. When the tension insulator string’s weight is not considered, the fitting results differ significantly from the testing results, with the maximum discrepancy of fitting tension between the strain section and the straight section reaching 27%. When the tension insulator string’s weight is considered, the difference between fitting results and testing results is quite small, with the maximum discrepancy of fitting tension between strain section and straight section being only 1.7%. It can be seen that the influence of tension insulator string’s weight must be considered in determining the sag of a strain section of UHV transmission lines.

The Potential Difference Characteristics between Two Points on Grounding Grid of Substation

WANG Yonghong, JIAO Chongqing, XIAO Bing, GUO Anqi, QIU Guizhong, BI Lipeng, XU Keqiang

2021, 54(1):  150-158.  DOI: 10.11930/j.issn.1004-9649.201907046

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With the intelligentization upgrade of power substations, a large number of secondary equipment are deployed dispersedly nearby the high-voltage primary equipment. The enclosures of these secondary devices are electrically connected to the grounding grid underground. When a fault current injection causes the potential rise in the grounding grid, there is a potential difference between any two points on the grounding grid conductors. For two secondary equipment located at different positions and connected by secondary cable, the potential difference can induce common-mode and differential-mode disturbance voltages at the ports of the secondary cable, which may interfere the normal operation of secondary system. In this paper, the grounding grid of a 220 kV substation is modelled and the corresponding potential difference is calculated by using the CDEGS software. Also, the effects of the grid density and size, soil resistivity, the positions of current injection and potential observation on the potential difference are investigated. The results are helpful for guiding grounding grid design and evaluating the influence of ground potential difference on secondary equipment.

An On-Line Preventive Control Method for Meeting the Power Supply Demand of Large-Scale Urban Power Grid

WU Feng, BAO Yanhong, ZHOU Hua, XU Taishan, LOU Boliang, REN Xiancheng, WANG Longfei

2021, 54(1):  159-166.  DOI: 10.11930/j.issn.1004-9649.201904067

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An on-line preventive control coordinated decision-making method is proposed considering different types of load reliability demands and accident risks in urban power grid, which is suitable for large urban power grid with diverse load characteristics and different reliability requirements of functional areas. Based on an analysis of the new demand for the development of the urban power grid and the shortages of the existing defense measures, a coordinated decision-making model is given considering the cost of measures and the risk of accidents. And then, the enumeration combination and cluster iterative computing are used to search the optimal preventive control strategies for partition load transfer and feeding user load shedding, which will lay the foundation for large urban power grid to realize meticulous, differential and integrated prevention of accidents. The correctness and feasibility of the proposed method are verified by simulation analysis of actual power grid operation data.

Security Transformation Technology for Electricity Metering Communication Protocol

REN Hui, LI Huifeng, ZHAO Hui, HE Feng, DOU Renhui, YAO Zhiqiang, ZHAO Guoqing

2021, 54(1):  167-174.  DOI: 10.11930/j.issn.1004-9649.202003037

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Network attacks are now penetrating into industrial control system. Acquisition of electricity energy data is related to the economic interests of all parties, so it is very important to obtain accurate electricity data in time. In the paper, security transformation is made to the 102 protocol based on IEC 62351. The TLS protocol is added in the transmission layer, and the HMAC is used in the application layer to verify the security of ASDU message, so as to realize such functions as the communication encryption, authentication and integrity verification between the main and sub stations of the electricity energy acquisition system. The key data indexes, such as the authentication time of the main and sub stations, the increase time of the single frame data before and after the 102 protocol transformation of the electricity energy acquisition system, are simulated and tested. The testing results show that transformation of the application layer consumes more time and can seriously affect the communication efficiency when message frames are large in numbers. It is concluded through comprehensive comparison that the overall performance is better when SM4 encryption suite is used for TLS protocol.

Application and Evaluation of Quantum Secure Communication in Electric Power Communication Networks

XIAO Lei, LI Bozhong, ZHANG Suxiang, LAI Junsen, LIU Lu, TIAN Zhaoyu

2021, 54(1):  175-181,202.  DOI: 10.11930/j.issn.1004-9649.201907143

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Quantum key distribution-based quantum secure communication (QSC) technology is one of the effective solutions to improve the level of information security protection. In recent years, related technology research, equipment development and demonstration applications have developed rapidly, but the standards for testing and evaluation of QSC system has not been completely established. On the basis of reviewing the progress of quantum secure communication technology and its application, the paper introduces the construction of electric power QSC demonstration network and the application of related equipment, and proposes a comprehensive evaluation scheme from different aspects such as quantum key distribution, management and application. The feasibility and technical effects of applying QSC technology in power communication networks are verified in the actual network environment. In the end, the prospect of QSC applications is given.

Experimental Study on Fine Particulate Matter Removal Efficiency and the Emission Characteristics of WESP under Different Loads

LIU Xipu, LI Dongyang, ZHANG Chao

2021, 54(1):  182-187.  DOI: 10.11930/j.issn.1004-9649.202005046

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In this paper, the dust mass concentrations and emission characteristics are tested using ELPI+ device at the inlet and outlet of a wet electric-static precipitator (WESP) under six different conditions, i.e., the combination of the boiler load at 100%, 75%, and 50%, with the WESP operated at high power and optimized energy-saving modes, respectively. From the experimental results, under 100% load and WESP energy-saving operation mode, significant increases are observed in the concentration of total dust emission, PM₁₀ and PM_2.5. Particularly, the total dust emission mass concentrations have even exceeded 5 mg/m³. However, under medium or low loads with WESP energy-saving operation mode, the total dust emission concentration still increases significantly, while the concentrations of PM₁₀ and PM_2.5 do not change much. The smaller the particle size, the less change of concentrations is noticed. Therefore, the energy-saving optimization test can provide technical assistance for the optimized unit operation mode with the goal of ultra-low emission also achieved at the same time. Additionally, PM₁₀ and PM_2.5 have little influence on the total dust emission under medium or low loads. The fly ash particles at the inlet and outlet of the WESP demonstrate the pattern of typical bimodal distribution. Under low or medium loads, the mass of the particles of 2~10 μm accounts for about 30% of all PM₁₀ particle mass if the WESP operates at high power mode, while that percentage jumps to 50% if it operates at energy-saving mode.

Experimental Study on the Characteristics of Rotating Spray Evaporation of Desulfurization Wastewater

LI Fei, CHEN Haijie, LIU Fengjun, GU Xiaobing, CHE Guangmin, BAI Yuyong, YANG Linjun

2021, 54(1):  188-195.  DOI: 10.11930/j.issn.1004-9649.202005143

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As a type of zero-discharge technologies, the rotary spray drying technology utilizes hot flue gas to evaporate desulfurization wastewater. In this paper, the evaporation test is carried out for both the raw wastewater with different suspended solid (SS) content and the concentrated high salinity wastewater. Specifically, the evaporation characteristics of the desulfurization wastewater in the drying tower are examined with the aid of visualization techniques. Moreover, the impacts of residence time duration, inlet flue gas temperature and gas-liquid ratio on the evaporation characteristics are also investigated during the spray evaporation process of the desulfurization wastewater. The results show that the rotary spray evaporation process has better adaptability to complex desulphurization wastewater components such as high salinity and high SS content. After sprayed from the rotary atomizer, the desulfurization wastewater evaporates rapidly mainly into the zone of 0.75~1.00 m below the atomization tray, and then the precipitated salt and the incompletely evaporated wastewater droplets are further evaporated until the moisture content is less than 2%. The residence time of the flue gas needs to last at least 20 seconds in the spray drying tower so as to ensure the moisture content of ash particles to be less than 2% at the outlet of the tower. The higher the temperature of the inlet flue gas, the lower the particle moisture content at both the bottom and the outlet of the tower. As for the wastewater with the gas-liquid ratio at 12 000 m³/m³ (standard state), the expected outcome of evaporation of wastewater droplets could hardly be guaranteed with the inlet smoke temperature at 280 ℃. However, if the inlet flue gas temperature is maintained at 340 ℃ and the gas-liquid ratio is greater than 10 000 m³/m³(standard state), the bottom ash moisture content is dropped down below 2%, which shows good evaporation effect.

Test Study on the Migration Characteristics of Slip Ammonia from the SCR System in the Coal-Fired Power Plant

ZHAO Hong, ZHANG Fajie, MA Yunlong, MA Baolin, TANG Xiao, XU Renbo, LUO Tongda, LI Chengbao, REN Chuanming, YU Jie, SUN Lushi

2021, 54(1):  196-202.  DOI: 10.11930/j.issn.1004-9649.202006114

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In this paper, the migration characteristics of slip ammonia were studied which passed through the various downstream equipments of the SCR system of a 350 MW coal-fired power plant. The field test concludes that the slip ammonia intercepted by the air pre-heater, low temperature economizer, and electrostatic precipitator accounts for 23%~26%, 9%~17%, and 56%~62% of the total slip ammonia, respectively, while that entering the desulfurization system accounts for less than 3% of the total slip ammonia. Raising the temperature of the low temperature economizer outlet flue gas will reduce its capture ratio of ammonia. However, the increase of the ammonia content in the fly ash from the electrostatic precipitator indicates the performance improvement of the electrostatic precipitator for the ammonia capture capability. Therefore, the overall capture ratio remains basically unchanged. Through the field test and data analysis, the relationship between the ammonia content in the fly ash from the electrostatic precipitation and the ammonia escape from the SCR outlet was also established. Nevertheless, whenever there are any significant coal quality changes or equipment modifications, etc., such relationship needs to be revised according to the actual situations.