Table of Content

25 December 2023, Volume 43 Issue 6

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Electricity Disaster Prevention and Reduction

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Application Scheme of Transformer Water Spray Fire Extinguishing Systems Adding Extinguishing Agent

CHEN Baohui, LIU Yu, ZHOU Tiannian, WU Chuanping, LI Bo

2023, 43(6):  1-5.  doi:10.3969/j.issn.1008-0198.2023.06.001

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In view of the problems existing in the transformer water spray fire extinguishing system, the transformer water spray fire extinguishing system with fire extinguishing agent and the fire and explosion prevention capacity improvement scheme of the fire pipe network are proposed, and the application technology are expounded. A fire extinguishing test platform using a real 110 kV transformer model is built to study the influence of extinguishing agent on extinguishing transformer oil fire by water spray fire protection system. The results show that the pure water spray is difficult to extinguish the transformer oil fire in the area where the water spray is not directly injected or semi-covered. After adding fire extinguishing agent, simulated transformer fire can be extinguished within 42 s. After 16.7% of the sprayers are damaged, the water spray system with extinguishing agent could still extinguish the fire efficiently within 40 s. The test results provide reference for the construction of transformer water spray fire protection system.

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Study on Lightning Damage Characteristics of Wind Turbine Blades Under Metal Mesh Protection

JIANG Lingfeng, JIANG Zhenglong, XIE Pengkang, FU Zhiyao, HUANG Xiaoqi

2023, 43(6):  6-10.  doi:10.3969/j.issn.1008-0198.2023.06.002

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Lightning damage of wind turbine blades is a difficult problem in the actual operation of wind power system. Metal mesh can be used as a supplementary method for lightning protection of blades. However, the lightning process and damage mechanism of high-amplitude lightning current after the blade is laid with metal mesh are not clear. In order to study the lightning protection method of wind turbine blade metal mesh and the lightning damage characteristics of blade composite materials, a test platform for lightning large current flashover of real wind turbine blades is built. Through the leader attachment test, the potential lightning strike position of the wind turbine blade is determined, and the direct damage effect of the lightning introduction point is observed synchronously. The test results show that the amount of lightning transfer charge and the flow capacity of the down lead are important factors for whether the blade is damaged by lightning. The pressure plate between the blade tip and the blade body has the risk of structural tearing. The type design of the discharge channel of metal mesh and the pressure plate should be optimized to improve the reliability of the blade′s lightning high current tolerance. The research results reveal the characteristics of large current damage of wind turbine blades under the lightning protection method of metal mesh, and guide its lightning protection design.

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Study on Composition Change Rule of Composite Insulator Silicone Rubber During Aging Process

NING Kai, JIANG Zhenglong, FU Zhiyao

2023, 43(6):  11-14.  doi:10.3969/j.issn.1008-0198.2023.06.003

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In order to study the variation rule of components in silicone rubber of composite insulators during aging process, various tests are conducted on unused silicone rubber as well as silicone rubber used for 2, 6 and 10 years. These tests includ scanning electron microscopy analysis, thermogravimetric analysis, differential scanning calorimetry analysis, Fourier transform infrared analysis, and X-ray spectroscopy analysis. The relevant results show that during operation, the integrity of silicone rubber molecular chains deteriorates, and more and more cracks and voids appear on the surface of silicone rubber. Additionally, the operation of silicone rubber is closely related to the variation and precipitation of aluminum hydroxide in its components, with aluminum hydroxide experiencing the most significant changes during operation. This study can better reflect the surface aging status of silicone rubber and is of great significance for the formulation design and aging failure analysis of composite insulators.

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Influence of Water Film on Power Frequency Discharge Characteristics of Short Air Gap for Sphere-Sphere and Rod-Rod Electrodes

DENG Jie, CHEN Baohui, FANG Zhen, ZOU Jiabin, XU Kai

2023, 43(6):  15-22.  doi:10.3969/j.issn.1008-0198.2023.06.004

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The short sphere-sphere and rod-rod gap are taken as the research models, and the effects of water films with different water conductivity and types of electrodes on the breakdown voltage of air gap are investigated. Research has shown that,the breakdown voltage of the both electrodes coated by water film is higher than that of the dry electrodes at the sphere-sphere short air gap,however when the gap length increases from 1 cm to 6 cm, the amplification of breakdown voltage decreases from 27.2% to 4.44%,the increase in breakdown voltage is due to the presence of a water film, which leads to an increase in the energy required for the initiation of secondary electron avalanches and photoelectrons,the increase in gap leads to an increase in the ionization region and and as a result the increase in breakdown voltage decreases with the increase of gap length.At the short rod-rod gap, the water film has no effect on the breakdown voltage of air gap. The water film has different effects on the discharge of the short sphere-sphere and short rod-rod air gaps. It is due to the fact that, at the sphere-sphere gap, the streamer is negative,the starting photoelectrons of the secondary electron collapse originate from the photoionization of the cathode, and at the rod-rod gap the streamer is positive, the starting photoelectrons of the secondary electron collapse are derived from the photoionization of air molecules, the rod to rod gap is longer, and the electric field distortion rate is smaller,and the conductivity of water has no effect on the breakdown voltage of the air gap.

Researches and Tests

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Research Progress of Green Hydrogen Preparation From Renewable Energy Electrolytic Water

BO Yanjun, HE Zhoulei, YANG Jingze, LIN Ziruo, YAO Hong

2023, 43(6):  23-30.  doi:10.3969/j.issn.1008-0198.2023.06.005

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Based on the potential role of producing green hydrogen from renewable energy electricity in peak shaving, valley filling, and power consumption, this paper introduces different types of electrolytic cell equipment, conducts research on green hydrogen production systems based on wind, solar, hydro, and geothermal energy, analyzes their application status and feasibility, and looks forward to the development direction of renewable energy electrolytic water production green hydrogen systems, providing suggestions for the development of the hydrogen energy industry.

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Study on Effects of Fuel Gas Parameters on Discharge Characteristics of Solid Oxide Fuel Cells

LIU Hanyu, JI Xuanyu, ZHOU Xiong, YANG Yu

2023, 43(6):  31-36.  doi:10.3969/j.issn.1008-0198.2023.06.006

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Solid oxide fuel cell (SOFC) technology is a clean and efficient power generation technology, and its high temperature characteristics make it easy to realize cogeneration, which has a good development prospect. In order to investigate the influence of different fuel gas parameters on the discharge characteristics of SOFC, a 500W SOFC experimental rig was built, and hydrogen discharge experiments, methane dry reforming discharge experiments, and durability experiments were conducted to analyze the influence of fuel gas flow rate and CH₄/CO₂ inlet ratio on the open-circuit voltage and electric power. The results show that with the increase of fuel flow, the open-circuit voltage of the battery, the power will increase, and the increase tends to stabilize at 2 L/min.When QCO₂/QCH₄=1∶1 and CH₄ flow rate is 2 L/min, the methane dry reforming discharge performance is the best. When Q_CO2/Q_CH4=1.5, the SOFC discharge performance is less affected by the flow rate, and under this inlet ratio, it is more conducive to achieve low fuel flow rate and high current density discharge to maximize the SOFC discharge power.

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Integrated Energy Management Approach for Photovoltaic Power Station-Thermal Unit-Aluminum Electrolysis Plant Islanded Microgrids for Multi-Time Scale

DU Shanzhou, HUANG Yongbo, LIU Ruiping, HAN Shuo, TANG Jianling, LIU Xubin, WU Jingbo

2023, 43(6):  37-44.  doi:10.3969/j.issn.1008-0198.2023.06.007

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Against the background of the gradually increasing proportion of new energy in microgrids, an integrated energy management method for light-fire-aluminum isolated microgrids with multiple time scales is proposed to address the problem of limited regulation capability of thermal power units in isolated microgrid systems containing electrolytic aluminum loads and the difficulty of new energy consumption. On the basis of the participation of the aluminum load in demand response, the dispatch model of the aluminum load is studied, and the carbon emission model of the aluminum load and the thermal unit in the isolated island microgrid system is analyzed based on the carbon tax policy. Finally, a low carbon economic dispatch model of the isolated island microgrid containing photovoltaic unit, thermal unit and electroytic aluminum load at multiple time scales is established. The simulation analysis is carried out with the example of a 9-node isolated island microgrid system to verify that the method can significantly improve the energy consumption of isolated island microgrids. The method can significantly improve the ability of the isolated island microgrid system to consume PV and make the system operate in a low-carbon and economic way.

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A Quasi-Z-Source Inverter Modulation Strategy With Low Voltage Stress and Inductor Current Ripple

YI Wenjing, LUO Chaokui, LUO Zhaoxu, CHENG Zhun

2023, 43(6):  45-53.  doi:10.3969/j.issn.1008-0198.2023.06.008

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The quasi-Z-source inverter has the advantages of simple structure and continuous input current compared with the conventional Z-source inverter. However, the quasi-Z-source inverter with simple boost control has the problems of high voltage stress of power devices, high capacitor voltage of the quasi-Z-source network, and high inductor current ripple. In this paper, the mean signal is determined by averaging the highest and minimum values of the three-phase sinusoidal modulation signal in the simple boost control. Additionally, the mean signal is injected into the three-phase sinusoidal modulated waveform and employed in the quasi-Z-source inverter, which can effectively reduce the voltage stress of power devices and capacitors as well as the inductor current ripple. The comprehensive performance of the two modulation strategies applied to the quasi-Z-source inverter is compared by MATLAB/Simulink simulation and the RT-LAB experimental platform, and the feasibility and superiority of the proposed modulation strategy are verified based on the theoretical study.

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Prediction Model for Coal Element Analysis and Its Application Based on GA-BP Neural Network

SHAO Zhixiang, LIU Zhu, KANG Yinhu, LU Xiaofeng, WANG Quanhai

2023, 43(6):  54-62.  doi:10.3969/j.issn.1008-0198.2023.06.009

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In response to the problem of long time and high cost in coal element analysis experiments, a GA-BP neural network is used to predict the results of coal element analysis. The GA-BP neural network model is constructed using 289 sets of typical thermal coal industrial analysis results as known quantity prediction element analysis. The prediction results are compared with the prediction results obtained from traditional multiple regression correlations, and the prediction results are evaluated through determination coefficients and root mean square errors.The results show that the determination coefficients of the GA-BP neural network prediction model for carbon, hydrogen, oxygen, nitrogen, and sulfur are 0.935, 0.811, 0.779, 0.430 and 0.051, respectively, with root mean square errors of 2.503, 0.458, 2.551, 0.245 and 0.824, which are better than the prediction results of traditional multiple regression correlations for each element. Finally, the element analysis prediction model is applied to calculate the boiler thermal efficiency and carbon emissions, and the error between it and the actual data obtained from element analysis is calculated. The average relative error of the boiler thermal efficiency is 0.19%, and the average relative error of carbon emissions is 3.56%.

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Research on Residential Peak-Valley Time-of-Use Electricity Price Scheme for in Hunan Province

HUANG Minqi, DAI Dandan, ZHANG Li, LIAO Jing, PAN Xin

2023, 43(6):  63-67.  doi:10.3969/j.issn.1008-0198.2023.06.010

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Aiming at the problem of power grid consumption structure in Hunan Province, the strategy of residential time-of-use electricity price scheme is proposed. Based on the residential electricity load data, the hierarchical clustering method is applied to divide the peak and valley periods of residents. Based on the heterogeneity of residential electricity demand, a demand price elasticity model is constructed, and on the basis of the current residential tiered electricity price policy, and with the goal of peak shaving and valley filling, a peak-valley time-of-use electricity price scheme for residents in Hunan Province is formulated.

New technology and Application

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Multi-Step Prediction of Wind Power Based on Long Short-Term Memory Network and Light Gradient Boosting Machine

LI Zhenhai, LI Yuyan, YI Zhigao, SU Sheng

2023, 43(6):  68-75.  doi:10.3969/j.issn.1008-0198.2023.06.011

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Wind power forecasting is important in power system planning and decision-making. However, accurately predicting wind power has always been a challenging problem due to the randomness of meteorological events. To solve this problem, this paper proposes a prediction model based on long short term memory(LSTM)-light gradient boosting machine(LGBM), which combines the advantages of LSTM and LGBM to improve the short-term prediction ability of future wind power. In this paper, the LSTM model is used to capture the timing patterns and trends of wind power and generate a hidden state containing sequence information, and the LGBM model is used as a supplement to the LSTM model to further predict future wind power by receiving the hidden state extracted by the LSTM as input. Experimental results show that the proposed LSTM-LGBM model is superior to other models in global training, which proves the temporal feature extraction ability of LSTM and the predictive performance of LGBM. The application of this model helps to improve the accuracy of wind power generation forecasts and provide effective support for the operation and resource allocation of power systems.

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Application of Improved Morphological Filtering in Voltage Sag Detection Algorithm

ZENG Jinhui, HUANG Mingxuan, ZOU Bin, HUANG Xi, NING Zhihao

2023, 43(6):  76-81.  doi:10.3969/j.issn.1008-0198.2023.06.012

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On the basis of traditional dq transform detection method, a voltage sag detection algorithm based on morphological filtering is proposed. This algorithm improves the problems of low real-time performance and insufficient accuracy of ordinary low-pass filters, and can also filter out the second harmonic component generated by coordinate transformation in traditional detection methods to quickly extract voltage sag features. Finally, a model is built on a simulation platform to verify the real-time and stability of the algorithm.

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Short-Term Load Forecasting of Long Short Term Memory Network Optimization Based on Variational Mode Decomposition- Permutation Entropy-Improved Pelican Optimization Algorithm

XIE Wenlong, ZHANG Lian, WANG Shibin, LI Duo, YANG Jiahao

2023, 43(6):  82-92.  doi:10.3969/j.issn.1008-0198.2023.06.013

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Aiming at the problems of modal decomposition aliasing and difficult selection of long short term memory network parameters in the traditional power load forecasting model, this paper proposes a new model, namely the long short-term memory network model based on variational modal decomposition and improved pelican optimization algorithm. Firstly, variational modal decomposition is used to decompose the power load data into multiple modes with low complexity, and the subseries are recombined by permutation entropy to reduce the prediction difficulty. Then, two strategies, logistic chaotic mapping, fusion Cauchy mutation and reverse learning, are introduced to improve the global optimization ability. Then, the improved pelican optimization algorithm is used to optimize the long short term memory network parameters to improve the generalization ability and practical operation of the model. Finally, the reconstituted submodes are predicted and superimposed respectively to obtain the final prediction results and compared with the prediction models of different optimization algorithms. Experimental results show that the long short term memory network model of variational mode decomposition-permutation entropy-improved pelican optimization algorithm has higher prediction accuracy and stability, and can effectively predict short-term power load.

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Collaborative Control Strategy of Hydropower and Stored Energy to Promote AGC Response Time Performance of Frequency Regulation Hydropower Plant

SAN Meiying, YAO Yangyang, QIU Yaming, QIN Huihui

2023, 43(6):  93-98.  doi:10.3969/j.issn.1008-0198.2023.06.014

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Northwest Power Grid is the regional power grid with the highest proportion of new energy installed capacity. Its “Two Articles” require that the AGC response time of hydropower units should be less than 10s. The AGC response time assessment of frequency regulation hydropower stations in the region is pretty severe. Based on the first frequency regulation hydropower power plant of Northwest Grid, the assessment and operational characteristics are analyzed. In addition, a suitable energy storage configuration scheme is proposed. Collaborative control strategy of hydropower and stored energy to promote the AGC response time performance is analyzed. The stored energy link is switched through electric break to regulate operation conditions whose AGC response time is less than 17s. Modeling and simulation are performed on Simulink platform,moreover economic analysis is carried out under hypothetical boundary conditions. The results show that through water storage collaboration, the AGC response time performance has been significantly optimized. Calculated based on a monthly reduction of 440 points, the internal rate of return reaches 18.7%, which can effectively alleviate the severe situation of AGC response time assessment in power plants and improve the economic benefits of power plants.

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Parameter Design and Power Flow Regulation Application for High-Voltage Phase Shifting Transformer

XU Shunkai, ZHU Jiran, TANG Haiguo, ZHAO Miao, ZHANG Di, DENG Wei

2023, 43(6):  99-105.  doi:10.3969/j.issn.1008-0198.2023.06.015

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For the transmission efficiency of some lines is insufficient under the natural distribution of power flow, this article provides a detailed analysis of the topology and working principle of the high-voltage phase shifting transformer, deduces its equivalent model, and conducts in-depth research on its power flow regulation theory and power improvement effect in a dual ended power supply system. The simulation results show that the active power flow regulation range at the end of the line is 90.19~1 524 MW. Finally, an equal proportion prototype is developed and a dual terminal power supply experimental platform is built for testing. The adjustment range of the experimental prototype for the active power at the end of the line was 24.86~214.83 W, which verifies the effectiveness and feasibility of the device.

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Summary of 5G Communication Technology Application in the Unattended Bucket Turbine

TAN Jianjun, LIU Wenzhe, HE Ye, ZHAI Linbo, MA Jinfeng

2023, 43(6):  106-110.  doi:10.3969/j.issn.1008-0198.2023.06.016

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Based on the practical application of 5G communication technology in the unattended system of coal yard of thermal power plant, this paper introduces the application of 5G communication technology in the complex environment of coal yard of thermal power plant, summarizes the operation experience of intelligent unattended coal yard with low delay and high reliability, and analyzes the feasibility of the application of 5G communication technology in the intelligent business application scenario of thermal power plant.

Experience and Discussion

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On-Site Installation Method of Fault Warning Equipment for 252 kV High-Voltage Circuit Breaker

HAN Chenlei, CHEN Hao, XIA Bing, ZHANG Ruowei, SUN Zichang, WANG Wei, WANG Ruihua

2023, 43(6):  111-115.  doi:10.3969/j.issn.1008-0198.2023.06.017

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In response to the high cost and poor real-time performance of traditional power outage detection methods for the operating status of high-voltage circuit breakers, an on-site installation method for a 252kV high-voltage circuit breaker fault warning equipment is proposed to achieve real-time monitoring and fault warning of the operating status of high-voltage circuit breakers. The on-site installation practice of the 252 kV circuit breaker fault warning equipment in a 220 kV substation in Jiangsu province has verified the effectiveness and feasibility of this method.

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Resilient Scheduling of Electric-Hydrogen Hybrid Energy Storage Microgrid Based on Stochastic Model Predictive Control

WU Xiaogang, JI Qingfeng, ZHANG Youxin, LIU Linping, CHEN Nan, YE Jieyang

2023, 43(6):  116-123.  doi:10.3969/j.issn.1008-0198.2023.06.018

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Microgrids have the potential to improve the power system′s flexibility within the framework of an energy paradigm centered on renewable resources. But when microgrids are included into the electrical market, the metrics used to evaluate their use mostly focus on economic factors, neglecting the resilience of the microgrid itself. This research offers a hybrid energy storage microgrid system optimization technique based on the resilience strategy through numerical simulation to improve the microgrid's resilience. In order to achieve a fast transition reaction, a hybrid energy storage system (ESS) made of batteries and hydrogen is built in this study. The problem is then controlled using the stochastic model predictive control (SMPC) technique. In addition to taking into account every sample moment at the dispatch level, the sample transition problem between grid-connected and islanded modes is also taken into account by the SMPC control mechanism. The suggested control approach takes into account the healthy operation of the hybrid energy storage system (ESS) in order to address the deterioration of energy storage devices.The practical tests show, although there is uncertainty in the main power grid,it is demonstrated that the microgrid can still supply the key internal loads at any sample instant during the occurrence in the event of a main grid outage, and that the devised control method maximizes the capacity utilization of each ESS.

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Hybrid Energy Storage Based on Fuzzy Control Stabilizes Wind Power Fluctuations

ZHAO Jianhong, DONG Xing, LIU Zhongwen, HAN Xu

2023, 43(6):  124-131.  doi:10.3969/j.issn.1008-0198.2023.06.019

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To suppress fluctuation in wind power grid-connected power and improve energy storage output level the dynamic distribution model of wind power grid-connected power, the output control strategy of energy storage system, and the dynamic model of wind power coupled hybrid energy storage system are proposed, and the simulation is carried out through Matlab/Simulink. The results show that the two-stage filtering and fuzzy control can effectively improve the rationality of power distribution, the overall fluctuation degree of power decreased by 43.82% from 0.227 16 MW to 0.127 61 MW, the average frequency deviation decreased by 15.03%, from 0.090 53 Hz to 0.076 92 Hz, and the frequency variance decreased by 34.59%, which effectively improves the stability and safety of wind power grid-connection, reduces the number of battery cycles to a certain extent, and effectively prolongs the life of hybrid energy storage system.

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Study of Lithium Batteries Optimal Discharge Strategy Based on Mechanism Model

WU Xinhua, LIU Linping, JI Qingfeng, DU Qianyun, LI Zuxin, ZHANG Feng

2023, 43(6):  132-137.  doi:10.3969/j.issn.1008-0198.2023.06.020

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As a clean and efficient energy storage device, lithium-ion batteries are widely used in energy storage fields such as new energy vehicles and microgrids. However, due to its complex degradation mechanism, the cycle life of the battery itself is affected. In order to optimize the discharge capacity and cycle life based on the unspecified optimal load current, a lithium-ion battery mechanism model is adopted, and the degradation mechanism related to low discharge current is studied through charge state and cycle number. The optimal discharge current and its variation pattern for general lithium-ion batteries are determined. The research results show that when the battery is a new battery, the optimal discharge current should be maintained at the 1C level at the beginning of the discharge cycle. When the charge state SOC reaches the point where the side reaction rate in the anode significantly decreases, the discharge current should be reduced. The research results have guiding significance for the optimization operation and design of the discharge process of lithium battery modules in energy storage stations or new energy vehicles.

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Research and Application of Inverter and Static Var Generator Reactive Voltage Control Strategy for Photovoltaic Power Plants

QIU Wenjun, LI Yuqi, ZHI Xiaochen, ZHANG Shunren, CHEN Xiaoyi, SHI Hongliang

2023, 43(6):  138-143.  doi:10.3969/j.issn.1008-0198.2023.06.021

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Based on the important role of automatic voltage control technology in reactive power support and safe and stable operation of the power grid, this paper introduces the mechanism of reactive power and voltage regulation in photovoltaic grid connection points. Taking inverters and static var generator (SVG) as research objects, the reactive power allocation strategy and SVG reactive power replacement method of photovoltaic power plants are studied and analyzed. The effectiveness of coordinated control and reactive power replacement of photovoltaic inverters and SVG is verified through on-site experiments in photovoltaic power plants,and it has reference significance for achieving automatic voltage control in regional power grids for new energy grid connected power stations.

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Research on Breaking Small Capacitive Current of Circuit Breaker Used in Ultra High Voltage Direct Current

XU Meng, CHEN Yu, GAO Yang, SHEN Fenghui

2023, 43(6):  144-150.  doi:10.3969/j.issn.1008-0198.2023.06.022

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In order to ensure that the type test of breaking small capacitive current of 800 kV AC SF₆ ciruit breaker in UHVDC transmission system of ±800 kV and ±1 100 kV is successfully passed and the products run reliably for a long time after being put into operation, the electric field strength and gas density of the circuit breaker under different conditions are calculated by finite element method, and it is concluded that the dielectric strength of the original circuit breaker and three optimized schemes and the position of the lowest point of dielectric strength during the circuit breaker opening process are not affected by the opening speed and inflation pressure. Under the optimized scheme, the average opening speed of the circuit breaker is increased by 5.7%, which can meet the dielectric strength requirement that the peak recovery voltage reaches 2 100 kV. The test passed smoothly, and there was no re-breakdown in the breaking process, which proved that the calculation method and optimization scheme adopted had practical guiding significance.

Faults and Analysis

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Multi-Fault Analysis and Diagnosis of Inverters Based on CGAN and LSTM

TIAN Rui, LIU Weike, WU Xun, ZHANG Xiaomin

2023, 43(6):  151-158.  doi:10.3969/j.issn.1008-0198.2023.06.023

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Inverter is widely used in UPS, motors, and renewable energy generation systems. Its safe operation is of great significance for converter systems. In harsh working environments, the power transistor and current sensor of grid connected inverter are prone to faults, and their fault characteristics are similar and coupled, posing great challenges to existing inverter fault diagnosis technologies. Therefore, this paper proposes a coupling fault diagnosis method based on conditional generative adversarial network(CGAN)and long short-term memory(LSTM)for inverters. First, the basic working principle of the inverter is analyzed and a digital model is established on the dSPACE platform. Next, the working modes under single power transistor open circuit fault, double power transistor open circuit faults and zero output fault of the current sensor are explored through the model. Then, three phase currents are used as diagnosis variables, and CGAN is utilized to obtain the fault data which is closed to the real operation conditions. The faults of switches and sensors are finally located by the LSTM network. The experimental data proves the effectiveness of this method.