Table of Content

05 April 2021, Volume 54 Issue 4

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Practice and Enlightenment of Ultra-low Emission and Energy-Saving Retrofit of Coal-Fired Power Plants in China

ZHU Fahua, XU Yueyang, SUN Zunqiang, SUN Xueli, WANG Sheng

2021, 54(4):  1-8.  DOI: 10.11930/j.issn.1004-9649.202102055

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Compared with the year 2013 when the ultra-low emission control had not been widely implemented, the installed capacity and actual power generation of thermal power sector in China increased by 36.7% and 19.5% respectively in 2019, but the emissions of smoke dust, SO₂ and NO_x decreased by 87.3%, 88.6% and 88.8% respectively. In the same period, the power consumption rate of plants for the thermal power sector in China remained at 6.01%, and the net coal consumption decreased from 321 g/(kW·h) to 306.4 g/(kW·h), which is equivalent to the reduction of CO₂ emission of about 270.15 million tons in 2019. That is about 1, 801 times of the designed capacity 150, 000 tons/year of the largest carbon capture project in China. In order to summarize the significant achievements of ultra-low emission and energy-saving retrofit of coal-fired power plants in China, as well as to provide guidance for the pollution control of other industries and promote the efficient and economic carbon peak and carbon neutrality, this paper systematically studies the critical impacts in terms of the strictest emission standard, enterprise demand, national attention, technological innovation and economic incentive policy on the successful practice of ultra-low emission and energy-saving retrofit of coal-fired power plants. The study concludes that in addition to the high investment, substantial operating cost should be take into account in ultra-low emission project and carbon capture project. The top-level design and continuous promotion is the key part of flue gas control project, while the technical breakthrough and normalized application ensure the success with the emphasis on the environmental protection electricity pricing and the related incentive policy. As far as the ultra-low emissions are concerned, economic incentive policies such as ultra-low electricity price should not be canceled even after the completion of ultra-low emissions retrofit. On the contrary, it should be further optimized to boost the high-efficient operation of ultra-low emission projects. In the process of implementing ultra-low emissions, by borrowing the successful experience from the electric power industry, other industrial sectors should formulate national environmental protection standards such as feasible technical routes and technical engineering, operation and management specifications. At the same time, relevant economic incentive policies shall also be issued to ensure the construction and operation of ultra-low emission projects to achieve real emission reduction effect. Upon the completion of energy-saving renovation projects, the operation of the projects have demonstrated not only certain economic benefits but also remarkable capabilities to reduce CO₂ emission. Constrained by carbon peak and carbon neutrality, coal-fired power plant should be prioritized first for energy saving retrofit project. Unless there are significant decrease of energy consumption, cost and risk, carbon capture project should not be popularized blindly.

Analysis of DC Cable Test Standards and Key Problems in the Test of ±535 kV Cable System

ZHAO Peng, OUYANG Benhong, CHEN Zhengzheng, CHEN Hong, RAO Wenbin, ZHAO Jiankang, ZHANG Hao

2021, 54(4):  10-18,25.  DOI: 10.11930/j.issn.1004-9649.202006164

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How to ensure the material quality, manufacturing process of DC cable and test the reliability of DC cable system effectively has become the focus of attention. In the past decade, the test method of HVDC cable has been developed in an all-round way. The established standards or specifications, including CIGRE TB 496, GB/T 31489.1 and IEC 62895, have made clear requirements for the test methods in the development of DC cable system. In this paper, based on the experience of development of ±535 kV DC cable in China, the background of the above standards are summarized, and the differences between GB/T 31489.1 and IEC 62895 are compared. What’s more, according to the electrical performance evaluation method of insulating materials during the development process of DC cable system and the type test of electrical performance in low temperature environment, some suggestions in the standardization work are put forward, which can be used as references for established the test scheme.

Impact of Different Pressures on Charge Transport in EPDM

HE Yifei, WU Kai, WU Yang, WANG Jinghao, ZHANG Chunyang

2021, 54(4):  19-25.  DOI: 10.11930/j.issn.1004-9649.202006016

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Ethylene-propelene-diene monomer (EPDM), as a high-quality insulation material, has been widely used in accessories of cable joints, but it bears a large compressive pressure in the working environment, which may affect its insulation performance. We conduct a study on the effect of pressures on charge transfer in EPDM by calculating the change of key parameters such as carrier mobility in EPDM at different pressures. By designing a unipolar carrier blocking experiment and using the improved pulsed electro-acoustic (PEA) measurement device, we calculate the mobility of electrons in EPDM at six pressures between 0.2 MPa and1.2 MPa (at interval of 0.2 MPa). In addition, an analysis of the mobility with hopping conduction model shows that the mobility in EPDM does not change significantly with different pressures, and the electron transition distance and the required energy also have no obvious variations. It is concluded that under normal working conditions, pressures do not affect the electrical performance of EPDM.

An Improved Location Method of 10 kV Cable Joints Based on Nuttall Self-Convolution Window

XU Xingquan, GUI Yuan, YAO Yuhai, WANG Zhihui, LI Rong, ZHOU Kai, XIE Min

2021, 54(4):  26-32.  DOI: 10.11930/j.issn.1004-9649.202006152

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In order to solve the problem of spectrum leakage and fence effect when using discrete Fourier transform (DFT) to analyze the input impedance spectrum of header point of cable, this paper presents an improved method of the joints location for the 10kV distribution cable based on Nuttall self-convolution window. First, the principle of the proposed method was briefly explained in this paper, including transmission line model for the power cable with an intermediate joint, input impedance spectrum of the cable, the locating principle of joints, and the windowed Fourier transform (WFT). Next, the window functions, i.e. Hamming window, Blackman window, four-iterm and third-order of Nuttall window, second-order of Nuttall self-convolution window, were selected to analyze their characteristics in detail. Then, through the simulation, the effects of the WFT algorithm with four window functions were analyzed and compared for the middle joint location. Finally, a 500 m long 10 kV cross-linked polyethylene (XLPE) cable was tested to verify the test results in the laboratory. The results indicated that compared with Hamming window, Blackman window and the four-iterm and third-order Nuttall window, the second-order of Nuttall self-convolution window had the best effect of suppressing spectrum leakage and fence effect. Besides, the proposed location method can identify and locate joints with higher sensitivity. The positioning error was less than 0.024%.

Review on the Research Status of the High Voltage XLPE Cable Buffer Layer Failure

MENG Zhengzheng, LI Xu, YU Yang, LI Zhijian, DU Xiaoyu, KONG Xiaoxiao, LI Jin, LI Qi, DU Boxue

2021, 54(4):  33-41,55.  DOI: 10.11930/j.issn.1004-9649.202011018

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Based on the analysis of the characteristics of the buffer material, this paper discusses the research status of buffer layer failure at home and abroad, and provides suggestions for future research. Summary studies show that discharge is the direct cause of ablation failure of the buffer layer, and the moisture of the cable is a necessary condition for such failures. Long-term exposure to moisture will induce the increase of the resistivity of the buffer layer and accelerate the production of high-resistance white powder. When there is an air gap between the aluminum sheath and the insulating shielding layer, the increase in resistivity of the buffer layer, the production of white powder and the impact of overvoltage will cause the local field strength in the air gap to exceed the breakdown field strength, which will eventually cause the discharge ablation. The results of the full text review summarized the causes of buffer layer failures and proposed corresponding preventive measures, which can provide as references for future research on buffer layer failures.

Application Status and Research Prospects of HVDC Extruded Cables

HU Ming, LIU Shujun, YANG Jianjun, XIE Shuhong, ZHANG Hongliang, YAN Zhiyu

2021, 54(4):  42-55.  DOI: 10.11930/j.issn.1004-9649.202006273

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HVDC extruded cable is one of the key facilities for long-distance and large-capacity power transmission lines. The currently widely used DC extruded cable is mostly insulated with crosslinked polyethylene (XLPE). An investigation is conducted on the HVDC XLPE insulated cable in terms of space charge and byproducts degassing. It is concluded that the ultra-pure XLPE material is currently the most feasible way to mitigate the space charge problem and manufacture extruded HVDC cable for large batches. The research on byproducts degassing problem should be based on the testing results of mini-samples to guide the degassing process for long distance and batch production of cables. Based on the extruded HVDC cable projects which have been put into operation or are under design both in China and abroad, it is proposed that future development of DC extruded cables should focus on improving the electrical insulation level of the insulation materials with a higher the operating voltage. Meanwhile, the allowable operation temperature of cables should be elevated to realize a larger transmission capacity. Besides, from the perspective of improving productive efficiency and recycling, it is suggested that the research on application of thermoplasticity insulation material in extruded HVDC cables should be enhanced.

Effect of DC Pre-stress on Space Charge and Electrical Tree in XLPE with Needle-Plate Electrodes

XU Xiaobin, LIU Aijing, LE Yanjie, LIU Hechen, GUO Zhanpeng, LIU Yunpeng

2021, 54(4):  56-62,71.  DOI: 10.11930/j.issn.1004-9649.202006270

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Space charge is one of the main factors that affect the electrical tree characteristics of HVDC cable insulation. Based on the bipolar charge transport model, this paper simulates the space charge distribution characteristics of the two-dimensional needle plate electrode model under ±20 kV、±22.5 kV and ±25 kV DC pre-stress with a duration of 3 600s, and makes a comparative analysis between the space charge distribution characteristics and the DC grounded electrical tree initiation characteristics. The results show that the space charge density and injection depth increase with the increase of the pre-stress and time, and the initiation length of DC grounded electrical tree increases with the increase of pre-stress duration and amplitude. There is a high similarity between space charge distribution characteristics and electrical tree initiation characteristics. The space charge distribution near the needle tip is the main reason for the difference in the initiation characteristics of the grounded electrical tree.

The Radial Gradient Effect of HVDC Extruded Cables in Manufacturing and Application

LI Fei, ZHONG Lisheng, LI Wenpeng, GAO Jinghui, REN Haiyang, ZHANG Chong

2021, 54(4):  63-71.  DOI: 10.11930/j.issn.1004-9649.202006208

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Extruded cables are widely used in HVDC projects, but the gradient effect in manufacturing and application affects their DC electrical performance significantly. The 500 kV XLPE DC cable was studied in this paper. Firstly, the field strength distribution in the uniformly insulated cable was simulated. Secondly, the temperature distribution of the insulation in the process of cross-linking and degassing was calculated, and the phase structure, by-product content and DC electrical performance of the insulation of cable at different radial positions were also measured. Finally, the field strength distribution of the insulation was simulated. The results show that there is a temperature gradient of cable insulation in the process of cross-linking and degassing, and the phase structure, and DC electrical properties of the insulation are non-uniformly distributed in the radial direction. The gradient distribution of the insulation conductivity in the radial direction results in the distortion of the field strength, in which the field strength of outer layer of insulation is greater than that of inner layer, and the field strength of the outer layer of insulation is greater than that the maximum electric strength in the uniform insulation.

Electromagnetic-Structure Transient Coupling Analysis of Large Cross-Sectional High Voltage Cables

SUN Na, LIU Shengchun, XU Aibin, SI Jiajun

2021, 54(4):  72-79.  DOI: 10.11930/j.issn.1004-9649.202006263

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The cable cleats play a role in fixing and supporting the cables. The cable cleats will withstand very large electromotive force when the grids are short-circuited. The deterioration of their mechanical properties may cause a serious threat to the stable operation of the grids. In this paper, the sequential coupling method of load transfer was used to establish the electromagnetic-structure finite element model of the cable cleats system. Based on Maxwell's electromagnetic theory and virtual displacement method, the transient electromagnetic field analysis of the cable was performed to obtain its magnetic field distribution and short-circuit electromotive force. As an excitation source, the transient dynamic analysis of the cable cleats was carried out to study its mechanical properties. The results show that the transient electromotive force of the cable changes periodically with the power frequency period, and the peak value of the electromotive force gradually reduced in every cycle. The stress of the intermediate phase cable fixture is the largest, and plastic deformation occurs at its corner of the fixture base mounting plate; Compared with the cable support, the stress of the cable fixture is less affected by the static and dynamic analysis methods. It recommended that the static analysis can be used for qualitative analyzing of the cable fixture stress while the transient dynamics method can be used for accurately quantitatively analyzing. As the calculated stress of the cable support is greatly affected by the analysis methods, so when the cable fixture is arranged in a horizontal linear shape, the transient dynamic analysis method should be used.

Design Method and Experimental Study of Water-Blocking Special-Shaped Wire Conductor for Submarine Cable

WANG Wenchao, XUE Chi, HU Ming, ZHAO Youlin, XIE Shuhong, WANG Haiyang, Ye Cheng, NIE Ying

2021, 54(4):  80-86.  DOI: 10.11930/j.issn.1004-9649.202009090

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The design and manufacture of water-blocking conductor is one of the key research topics in field of submarine cable. A new theoretical design method is proposed for trapezoidal wire water-blocking conductor with structures of constant cross section, which has strong versatility and high programmability, suitable for design and manufacturing of water-blocking conductor with a cross-section ranging from 50 mm² to 3500 m². The problems such as difficult design & manufacturing and unreasonable conductor size could be solved, with a filling coefficient of conductor reaching more than 0.96. Then, the rationality of the theoretical design method and manufacturing process is verified through water-blocking, mechanical and electrical performance tests. The trapezoidal wire conductor structure has no adverse effect on the cable’s overall performance, and the water-blocking glue conductor is better than that of the water-blocking tape structure. Finally, according to theoretical calculation, the outer diameter of the trapezoidal wire conductor for medium voltage submarine cables designed with the proposed method are 3.9% ~ 7.0% smaller than that of compact circular conductor, which can reduce the manufacturing cost by 1.1%. With the larger conductor cross-section, the structure optimization is more significant, which verifies the economy of submarine cables with trapezoidal wire conductor structure.

Comparative Experimental Study of Performance of Crosslinked Polyethylene Insulation Materials Used for HVAC Cables

OUYANG Benhong, LIU Songhua, WANG Shihang, LI Jianying, LI Shengtao

2021, 54(4):  87-93.  DOI: 10.11930/j.issn.1004-9649.202006176

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The crosslinked polyethylene (XPLE) insulation materials for HVAC cables are developed relatively late in China. At present, the domestic-made insulation materials for 220 kV voltage grade have not been applied in practical engineering. Based on three types of domestic and foreign made XPLE insulation materials used for HVAC cables, a comparative experimental study is made on their power frequency breakdown strength, dielectric constant, dielectric loss tangent, melting and crystallization properties, tensile properties, elongation at break, micro-morphology and crosslinking degree. The experimental results show that the domestic made XLPE insulation materials are not much different from imported ones in macro performance parameters, with the domestic-made insulation material samples even being better than the imported X1# samples in breakdown characteristics and mechanical properties. However, some shortcomings are also found for domestic-made insulation materials, such as poor stability of breakdown strength and large value of dielectric loss tangent. The results of this study can provide a data support for the development and performance improvement of domestic-made cable insulation materials.

Control Freedom Index of Integrated Energy System and Its Impact on Economic Dispatch

ZHENG Tao, DAI Zemei, YAO Jiahao, CAO Jing, WU Shuomin, ZHANG Kaifeng

2021, 54(4):  95-106,118.  DOI: 10.11930/j.issn.1004-9649.202007033

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Integrated energy system (IES) provides users with diversified energy supply services through the coupling conversion of multiple energy flows. Compared with conventional independent energy supply systems, the IES has greater degree of control freedom. In order to measure the degree of control freedom, this paper firstly proposes a convertibility index to characterize the mutual conversion ability of multiple energy flows, and a substitutability index to represents selection opportunities for alternative energy at the user side. In addition, the calculation methods for the convertibility index and the substitutability index are provided. Secondly, considering the influence of control freedom on the optimal operation of the IES, an economic dispatch model of the cooling-heating-power-gas IES is established. Finally, a case simulation is carried out, and the results shows that improving the two control freedom indexes of the convertibility and substitutability of the integrated energy system can reduce the economic dispatch cost of the system.

Scheduling Strategy for “Wind-Network-Vehicle” Joint Accommodation Based on Electric Vehicle Clustering

CHEN Yan, JIN Wei, WANG Wenbin, LI Huibin, HAN Shengfeng, WANG Yiming, ZHONG Jiaqing

2021, 54(4):  107-118.  DOI: 10.11930/j.issn.1004-9649.202005103

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In order to solve the large-scale real-time optimization scheduling problem of electric vehicles, a new method is proposed for dividing electric vehicles into several state clusters based on establishment of the electric vehicle state matrix. The power satisfaction and time satisfaction are defined in this paper, and their weighted sum is the user’s satisfaction. By taking the maximum economic benefit and satisfaction as the goal, a “wind-network-vehicle” real-time joint accommodation scheduling model is constructed based on the electric vehicle clustering. Aiming at the problem of grid-connected wind farm output and the uncertainty of electric vehicle loads, this paper studies the fusion of credibility theory and fuzzy opportunity constraints, introduces credibility measures, and makes clear and equivalent treatment of fuzzy opportunity constraints. Finally, a particle swarm optimization algorithm with a shrinkage factor considering the outlier penalty function method is used to optimize the scheduling model, and a case is used to verify the superiority of the model and its scheduling strategy.

A Multi-objective Robust Planning Method for Thermal-Electrical Coupling Micro-energy System Considering the Uncertainty of Renewable Energy

ZHANG Min, WANG Jinhao, CHANG Xiao, YANG Chaoying, LI Ran, SUN Changwen, FAN Rui

2021, 54(4):  119-129,140.  DOI: 10.11930/j.issn.1004-9649.202010037

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Due to the high randomness and intermittency of renewable energy, the large-scale connection of renewable energy to the power grid will seriously affect the security and stability of the power system. This problem can be solved by developing thermo-electrical coupling micro-energy systems. A multi-objective robust planning method is therefore proposed for thermo-electrical coupling micro-energy system with consideration of wind power uncertainty. With the minimum investment & operation cost and minimum system peak-valley fluctuation as the goal, a multi-objective robust planning model is established for thermo-electrical coupling micro integrated energy system. The multi-objective problem is solved using the combined NSGA-II and TOPSIS algorithm. The simulation results show that the proposed method can improve the utilization rate of wind power and increase the system economy, and has a certain value for engineering applications.

Evaluation Method for Park-Level Integrated Energy System Based on Electric Power Substitution

ZHAO Pu, ZHOU Man, GAO Jianyu, PAN Lezhen, LIU Zifa, XIE Haokai

2021, 54(4):  130-140.  DOI: 10.11930/j.issn.1004-9649.202006250

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According to the multi-energy coupling characteristics of the park-level integrated energy system (IES), the influencing factors of the IES construction are analyzed. Considering the positive impact of electric power substitution, an index system is built with such indexes as social benefits, energy utilization efficiency, reliability, economy and environmental protection, and a quantification model and calculation method for the indexes are proposed as well. A comprehensive evaluation method is proposed using combination weighting method to optimize the matter element extension model, in which the combination weighting method is used to integrate the subjective and objective weights according to the theory of minimum weight deviation vector, and the obtained expected combination weights are applied to the matter-element extension model to give the evaluation grades of the construction schemes. The case study has verified the scientificity and rationality of the proposed evaluation method, and demonstrated the positive effects of electric power substitution equipment on the construction of the park-level IES.

Two-Level Optimal Dispatching Strategy for Regional Integrated Energy System Considering Demand Response

ZHANG Haijing, YANG Yongqi, ZHAO Xin, XU Nan, LI Chenhui, XUE Wanlei

2021, 54(4):  141-150.  DOI: 10.11930/j.issn.1004-9649.202012014

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Demand response aggregator aggregates users’ transferable loads and reducible loads through demand response to improve the flexibility and economy of regional integrated energy system. Considering the interactive game relationship between the integrated energy system operators and the demand response aggregators, a two-level optimal dispatching model of the regional integrated energy system is established with consideration of the demand response. By taking the maximum economic benefits of the regional integrated energy system operators and the demand response aggregators as objective respectively for the upper and lower layers, the KKT conditions and linearization method are used to convert the two-layer model into a single-layer mixed integer linear optimization model for solution. The results show that using the time-of-use electricity price and the demand response compensation price to guide users to adjust their energy use plans can increase the profits of integrated energy system operators and demand response aggregators while achieving peak load shaving and reducing the impact on the safe and stable operation of the power grid.

Operation Relationship and Business Strategy of Stakeholders of Park-Level Integrated Energy Services

XU Wentao, LI Mingxuan

2021, 54(4):  151-157.  DOI: 10.11930/j.issn.1004-9649.202006014

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With the most applicable conditions in the field of integrated energy services (IES), the park-level IES has received more and more attention from industry and academia. Complex business and interest coupling exist among the stakeholders in the park-level IES, and it is urgent to study and sort out the operating relationships of the stakeholders to guide the healthy and orderly development of the park-level IES. The stakeholder operating relationship is obtained by analyzing of the energy flow, information flow, and capital flow of the park-level IES. By taking the grid enterprises as example, an operation strategy for the development of park-level IES is proposed. That is to expand the implementation of IES projects following the market development strategy of “proceeding from one location to a line or a region” and by taking the demonstration project as the guide.

Joint Expansion Planning of Energy Storage and Transmission Considering Power System Flexibility

LI Jiaming, LI Wenqi, LU Zongxiang, QIAO Ying, GAO Dongxue, LIU Shaolin

2021, 54(4):  158-167.  DOI: 10.11930/j.issn.1004-9649.202007062

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In order to accommodate high-penetration wind & PV power sources with strong fluctuation and randomness, the access of renewables and planning of transmission grids not only need to consider the balance of electricity, but also the balance of flexibility capacity. On this occasion, the conventional method of transmission expansion cannot economically realize the above-said objectives, thus joint expansion planning of energy storage and transmission becomes the new solution. A joint expansion planning method for energy storage and transmission based on quantitative assessment of flexibility is established. Firstly, from the perspective of flexibility, we qualitatively analyze the technical characteristics and advantages of the joint ‘storage-transmission’ planning in power balance and flexible adjustment capacity. Then, a joint storage-transmission planning model considering flexibility is established, and the solution method is given with combination of heuristic and mathematical programming. Finally, the feasibility of the proposed method is verified based on the modified Garver-6 system. The results show that under the scenario of high-penetration of renewable energy sources, the joint ‘storage-transmission’ planning has better economy. The energy storage can effectively improve the system’s up-regulation flexibility, but the cost is an important factor for restricting its planning capacity.

Key Technologies and Engineering Application of Converter Valve Monitoring System for Flexible HVDC

YANG Yuefeng, WANG Xiaohan, WANG Wei, SHI Xiuping, ZHAO Caiping

2021, 54(4):  168-174.  DOI: 10.11930/j.issn.1004-9649.202006024

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In order to monitor the operation status of the converter valve and the valve basic controller in the flexible HVDC transmission project and improve the operation safety of the converter valve, the role of flexible DC converter valve monitoring system is becoming more and more important. Based on the actual project requirements, and considering different application scenarios such as field subsystem debugging, converter valve maintenance, and normal operation and maintenance, a flexible HVDC converter valve monitoring system with dual network and dual redundancy architecture is developed, which uses the technology of automatic page layout and parameter matching for optimization, and the data caching mechanism of "memory + file" for massive data processing. The system has the functions of processing massive data with high-speed, displaying and storing telecommunicating and telemetry messages, recording high-frequency sampling fault and processing waveform. It can record information in real time with microsecond precision, and has the functions of remote control, modifying the status and key parameters of converter valve and valve control equipment at the same time. The system has been successfully applied in Zhangbei renewable energy flexible HVDC power grid demonstration project, and its performance meets the demand of monitoring and control of the converter valve and the valve basic controller.

Multi-Scenario Planning of Distribution Network in the Context of Integrated Energy

HU Yuan, XUE Song, YANG Su, TANG Chenghui, LIANG Cai, XIONG Tiangjun

2021, 54(4):  175-184.  DOI: 10.11930/j.issn.1004-9649.202002031

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With the development of energy utilization equipment, integrated energy system has become an important development direction for energy supply. Compared to the single form of energy supplies, the integrated energy supply system can provide users with a more economical, efficient, and diversified energy supplies, in which the distribution network that includes combined cooling heating and power (CCHP) units, electric refrigerators and other equipment is the main physical carrier. Based on this, we propose a multi-scenario planning method for coordinated planning of integrated energy system equipment and distribution network substation capacities with consideration of the uncertainties of new energy and the electricity, heat and cooling loads, to achieve efficient and reliable electricity, gas and heat supply. Firstly, according to the physical characteristics of CCHP units, electric refrigeration equipment and gas-fired boilers, a mathematical model for corresponding energy conversion is established. Considering the influence of numerous components in the integrated energy system on the node voltage of distribution network, the Distflow model is used to establish a AC power flow model. Secondly, in view of the impact of the uncertainties of renewable energy output and demand of electricity, gas and heat loads on the planning results, typical scenarios are used to describe the seasonal characteristics of electricity, gas, and heat loads, and the fluctuation of renewable energy output. Finally, a multi-scenario collaborative planning model for integrated energy system and distribution network is developed. The proposed model is tested on a reconstructed IEEE 33-node power distribution network system, and the results of the case study have verified the effectiveness and rationality of the proposed planning method.

The Current Releasing Characteristics of DC Vertical Earthing Electrode Forming an Elliptical Ring

CHEN Yang

2021, 54(4):  185-191.  DOI: 10.11930/j.issn.1004-9649.202009120

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The vertical DC grounding electrode forming an elliptical ring occupies a relative small land and has strong topography adaptability, which makes it worth to be widely applied. However, the nonuniformity of current releasing density caused by elliptical ring arrangement becomes a problem worth to be studied further. This paper carried out the analyses and comparison how those parameters of grounding electrode shape affect the electrode releasing characteristics. The shape parameters include ellipticity, circumference of pole ring, electrode length, electrode separation and the number of electrodes. The results show that the nonuniformity of current releasing density would be more significant on condition that with a higher ellipticity value, longer electrode length, shorter electrode separation and smaller electrodes number, moreover, the main factors by importance are in sequence of ellipticity, electrode length and separation distance, electrode number. The vertical grounding electrode should be arranged considering the nonuniformity of current releasing density between electrodes and that on a single electrode, so as to control the maximum error index of current releasing density at any point on the electrode.

Analysis of 2·15 Power Outage in Texas and Its Implications for the Power Sector of China

ZHANG Yue, XIE Guanglong, ZHANG Quan, HAN Xinyang, ZHU Rui, ZHANG Jun

2021, 54(4):  192-198,206.  DOI: 10.11930/j.issn.1004-9649.202103037

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Due to the extreme cold weather, a rotating power outage event occurred in Texas, USA, from February 15 to February 19, 2021, affecting more than 4.5 million residents. The Texas power grid entered the Level 3 emergency operation, with a maximum load shaving reaching 20000 MW, and the maximum real-time price surpassing 9000$(MW·h). According to published reports of Energy Reliability Council of Texas, this paper sorts out the outage process. Based on a proposed analysis structure of power outage, this paper analyses the outage causes and summarizes the implications for the power sector of China. It is proposed that we should bring into full play of the advantages of the "three-unified"(unified planning, unified dispatching and unified management)power system in China, pay attention to emergency power supply security in extreme scenarios, build a diversified supply system suitable for China’s future power system characterized with "double-high" (high-penetration of renewable energy and high-proportion of power electronics equipment), strengthen the physical basis for power security, and explore a electricity market model with Chinese characteristics.

Pilot Study of Flue Gas Moisture and Waste Heat Recovery Based on Ceramic Membrane Method

MI Dabin, GUO Jianglong, ZHANG Heng

2021, 54(4):  199-206.  DOI: 10.11930/j.issn.1004-9649.202010086

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In this paper, in order to study the dynamic performance of ceramic membrane in the applications of flue gas moisture and waste heat recovery in coal-fired power plants, a pilot apparatus was built in a 330 MW coal-fired power station in Hebei Province, in which the ceramic membrane module was integrated with 40 pipes of microfitration membrane. Then, the impacts of flue gas flow and cooling water inlet temperature on the moisture and heat recovery, as well as the latent heat and sensible heat release were studied. The study results show that with the flue gas flow at 9715 m³/h and the cooling water inlet temperature at 18.7 ℃, the moisture and heat recovered by the membrane module reach as much as 43.65 kg/(m²·h) and 106.31 MJ/(m²·h), respectively. The membrane modules have demonstrated remarkable recovery performance in actual industrial production environments and excellent potentials in industrial applications.

Evaluation of Wet Plume Treatment with Condensation-Reheat Process for a 330 MW Coal-Fired Unit

LIANG Xiujin, WEI Hongge, ZHANG Peng, WANG Fengji, ZHU Yue

2021, 54(4):  207-212.  DOI: 10.11930/j.issn.1004-9649.202012011

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Based on the testing and assessment result of the wet plume treatment system of a 330 MW unit with condensation-reheat process, its operational performance and unconventional contaminant removal effect are evaluated. The test results show that all parameters have reached the designed target value since the system was put into operation. Through the condenser, there are 23.93 t/h condensed water collected from the desulfurized flue gas with soluble solid of 93 mg/L, which can been reused into ultrafiltration treatment process directly such that the water processing cost is greatly reduced. As there are 4.47 kg/h soluble salt emission in dehumidified flue gas and 2.00 kg/h in condensed water from desulfurized flue gas, the soluble salt removal efficiency through flue condenser is calculated to be 30.97%. The study results show that for those units burning low sulfur content coal and with ultra-low emission already achieved, its potential of emission reduction is very limited because the total contents of soluble salt in the emissions are quite low. The component analysis exhibits high dependency of soluble salt removal efficiency on its solubility if its concentration is low in flue gas, which means the stronger solubility, the higher removal efficiency can be achieved.

Study on the Adaptability of Rotary Atomization Evaporation Technology to Desulfurization Wastewater and Flue Gas

LI Fei

2021, 54(4):  213-220.  DOI: 10.11930/j.issn.1004-9649.202011080

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In this study, the experiments on rotary atomization evaporation of desulfurization wastewater were conducted. The adaptability of this technology to wastewater quality and flue gas parameters were studied, and the methods to optimize the performance of evaporation were analyzed. The results show that the rotary atomization evaporation technology for desulfurization wastewater are highly adaptable to the total dissolved solids (TDS) and suspended substance (SS) of wastewater, as well as the temperature and dust concentration of flue gas. Under appropriate experimental conditions, it shows great evaporation effect in which the moisture contents of dusts from both the outlet and bottom of the evaporation tower can be reduced to below 2%, no matter whether TDS reaches as much as 200000 mg/L, SS reaches 6%, temperature≥300 ℃, or dust concentration reaches as much as 30 g/m³. In addition, increasing the gas liquid ratio or the sprayer rotate speed can effectively lower down the moisture contents, which makes it feasible to be applied for the optimization of wastewater evaporation.