Table of Content

25 February 2023, Volume 43 Issue 1

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Academician Message

Academician Message

2023, 43(1):  0-0. 

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Researches and Tests

Fault Location of Distribution Network Hierarchical Model Based on Improved Whale Algorithm

ZHANG Shangde, ZHANG Lian, ZHAO Mengqi, JIA Hao, XIE Wenlong, JI Hongyu, HUANG Wei

2023, 43(1):  1-7.  doi:10.3969/j.issn.1008-0198.2023.01.001

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After a large number of distributed power sources are connected to the distribution network, the dimension of the network structure and the uncertainty of the power flow direction when a fault occurs are increased. In view of the information distortion and the complexity of fault location when collecting or uploading fault current information, a fault location solution method is proposed, which establishes a mathematical model according to the network structure of distribution network, constructs a hierarchical model with the idea of hierarchical simplification, greatly reduces the variable dimension of distribution network, constructs a switching function and adds fault auxiliary criteria, and then improves the whale algorithm by population distribution, adaptive weight adjustment and cross-border treatment. The simulation results show that the proposed method can accurately locate the fault section and improve the efficiency and accuracy of distribution network fault solution under various working conditions, such as single fault, multiple faults, distorted current information or switching state of distributed generation.

Model Predictive Control Based on Quasi-Z Source Modular Multilevel Converter

ZHANG Yang, LUO Chaokui, YI Wenjing, CHENG Zhun

2023, 43(1):  8-16.  doi:10.3969/j.issn.1008-0198.2023.01.002

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In order to solve the problems of complex control structure, large fluctuation of DC-link voltage, poor AC output power quality and slow dynamic response when traditional carrier stack phase-disposition pulse width modulation (PD-PWM) is used in quasi-Z source modular multilevel converter (qZ-MMC), a model predictive control (MPC) for qZ-MMC is proposed in this paper. The control set of output voltage level is constructed according to the DC-link voltage, so as to predict the output current, without setting a PWM generator for each sub-module. At the same time, the mathematical model of inductor current and capacitor voltage of quasi-Z source network is analyzed, and the cost function of inductor current, capacitor voltage and AC output current is designed, so as to suppress the fluctuation of DC-link voltage and improve the power quality of output voltage. The effectiveness and feasibility of the proposed control method are verified on MATLAB/SIMULINK simulation platform.

Research on Hybrid Energy Storage Control Based on Improved Virtual DC Motor

BAI Penghui, QIN Bin, WANG Xin

2023, 43(1):  17-22.  doi:10.3969/j.issn.1008-0198.2023.01.003

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Aimed at the problem of bus voltage fluctuation caused by power fluctuation of load and distributed generation in DC microgrid, an expanded state observer (ESO) is introduced into the virtual DC motor (VDM) control and a hybrid energy storage frequency division control based on improved virtual DC motor (ESO-VDM) is proposed . Small signal modeling for VDM is conducted, the influence of inertia time constant H and damping coefficient D on the control system is analyzed, and the values of the two parameters are determined.In the case of power frequency division, the lithium battery is controlled by current closed-loop, and the ultracapacitor is controlled by ESO-VDM to improve its inertia and damping characteristics. The simulations with Matlab/Simulink are performed, and the results show that the proposed control algorithm makes full use of the advantages of hybrid energy storage device, smooths the output power of the battery, and improves the stability of the DC bus voltage.

Electrodynamic Calculation of Cable Short Circuit Based on Finite Element Electromagnetic Simulation

XU Binbing, CHEN Ziyao, LIU Yubin, LEI Jiacheng, QIN Rui, YANG Xin

2023, 43(1):  23-29.  doi:10.3969/j.issn.1008-0198.2023.01.004

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When a short-circuit fault occurs in the cable line, the mechanical properties of the cable bracket and hardware will be threatened under the action of short-circuit electric power. The traditional method of calculating cable short-circuit electric force is formula method. The formula method can only calculate the maximum short-circuit electric force, and there are limitations such as single solution object and inability to reflect the change of force with time. In this paper, the finite element calculation method based on electromagnetic coupling is used to establish the finite element calculation model of cable short-circuit electrodynamic force. Based on Maxwell 's electromagnetic theory and Gauss divergence theorem, the transient electromagnetic field analysis of the cable is carried out, and the change of short-circuit electrodynamic force on the cable with time is obtained. Compared with the calculation results of the formula method, there is only 2.11% error. The results show that the calculation method of short-circuit electrodynamic force based on finite element electromagnetic simulation can intuitively obtain the distribution and vibration frequency of electrodynamic force at each moment during short circuit. The electrodynamic calculation method of finite element electromagnetic simulation can be applied to short-circuit analysis of other fault types.

Research on Real-time Demand Response Strategy Considering Renewable Energy Uncertainty

HU Zhen, WANG Pan

2023, 43(1):  30-34.  doi:10.3969/j.issn.1008-0198.2023.01.005

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In order to solve the problem of uncertainty in renewable energy power supply, a method of establishing an optimal real-time demand response mechanism for power users managed by PMC is proposed. First, the electricity purchase model of a group of large scale electricity users managed by PMC is discussed, and its cost model and social welfare model are established. Then, with the goal of maximizing social welfare, an optimization algorithm based on real-time demand response is proposed to determine the PMC's day-ahead power and balance power purchasing decisions, as well as power users' real-time power consumption decisions. Finally, the proposed optimization algorithm is verified by simulation. The simulation results show that the algorithm can improve the social welfare of the power system while solving the uncertain power supply of renewable energy.

Comprehensive Evaluation Method of Regulation Performance of Industrial Load Participating in Power Grid Interaction

LIU Hanqing, SHEN Yangwu, LIAO Siyang, LEI Xiao, YUE Xuxin, SUN Jieyi, CHEN Yaling, XU Jian

2023, 43(1):  35-40.  doi:10.3969/j.issn.1008-0198.2023.01.006

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In order to evaluate the performance of industrial load participating in power grid regulation, a comprehensive evaluation index system is constructed, which includes three aspects: potential evaluation, economic evaluation and control effect evaluation. The evaluation index calculation method combining subjective and objective is put forward, which can reasonably calculate the index combination weight. The evaluation system is applied to three kinds of typical industrial loads, and the validity of the evaluation index and the proposed analysis method is verified.

New technology and Application

Non-destructive Identification Method of Transformer Windings Based on Multiple Points Temperature

DING Xiaofei, GUO Jing, TANG Haolong

2023, 43(1):  41-45.  doi:10.3969/j.issn.1008-0198.2023.01.007

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To ensure a fair market competition mechanism and avoid aluminum winding transformers from impersonating copper winding transformers, which affects the safety and stability of power system operation, it is important to identify transformer winding materials. To avoid transformer structure damage and identify winding material accurately and effectively, this paper proposes a non-destructive identification method of transformer copper and aluminum winding material based on multiple temperature points, which identifies the winding material based on the resistance coefficient method combining with the results of multiple test points. The experiment results on a copper winding transformer and an aluminum winding transformer show that the proposed method is accurate and effective, and can be further extended to large-scale engineering practice.

Research of Insulation Monitoring Methods for Electric Vehicle Power Battery Pack

DENG Yuanwang, YIN Huichun, E Jiaqiang, LIU Shuai, ZHU Hao

2023, 43(1):  46-49.  doi:10.3969/j.issn.1008-0198.2023.01.008

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As the demand for battery pack energy storage continues to increase and its voltage plateau rises, the real-time monitoring of the insulation performance of high-voltage systems becomes more and more important. In this paper, several common methods of insulation resistance detection are analyzed, the insulation resistance detection method of the balanced-unbalanced bridge is proposed, and Multisim is used to build a whole vehicle insulation simulation model to analyze the feasibility of the insulation resistance detection method of a balanced-unbalanced bridge.

A New Method of Ground Parameter Measurement and Grounding Fault Sensitive Perception for Distribution Network Based on Feeder Power

HE Shigeng, YANG Libin, YU Kun, ZENG Xiangjun, OUYANG Fan

2023, 43(1):  50-57.  doi:10.3969/j.issn.1008-0198.2023.01.009

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Aimed at the errors in modeling and principle of traditional measurement methods for grounding parameters, an accurate measurement method for grounding parameters of neutral ungrounded distribution network based on feeder power is proposed. By adding a controllable voltage source to the neutral point to regulate the zero sequence voltage, the active and reactive power of each feeder line is obtained, and combining the relationship between feeder line power and grounding parameters, the accurate measurement of the conductance and capacitance parameters of each feeder and system to ground are achieved. Furthermore, a sensitive sensing method of single-phase grounding fault based on feeder power is proposed, which can accurately identify whether the bus and feeder of distribution network are in fault through the difference of power factor angle characteristics between fault and normal feeder. This method can effectively solve the measurement problem of system to ground parameters, realize the sensitive sensing of single-phase ground fault, and accurately distinguish the bus and feeder faults based on the mathematical relationship between feeder power and ground parameters, power factor angle. The proposed method is simulated and verified in PSCAD/EMTDC simulation environment and 10kV real distribution network experimental field. The analysis results show that the method has high measurement accuracy, strong fault perception ability and certain engineering application value.

Principle and Implementation Method of Remote Standby Automation in Substation Based on 5G Communication Mode

YIN Chaoyong, LI Gang, LI Hui, XU Biao, LIU Weiliang, XIONG Shangfeng

2023, 43(1):  58-62.  doi:10.3969/j.issn.1008-0198.2023.01.010

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In order to solve the problems of high cost of optical fiber laying in medium and low voltage power grid and difficult application of remote backup automatic switching, this paper provides a principle and implementation method of remote backup automatic switching in substation based on 5G communication mode. By setting a 5G router in each remote backup automatic switching, the router realizes the point-to-point communication of remote backup automatic switching in GRE TAP mode, so as to realize the information exchange of remote backup automatic switching in substation. The simulation model built in RTDS proves the feasibility of the proposed remote backup automatic switching scheme based on 5G communication technology. This method does not need to change the original hardware and software of the remote standby self-switching device, and avoids the need of adding optical fiber channel and so on, which makes the remote standby self-switching device more convenient and reliable.The structure is simple, and anti-interference ability is strong, which greatly increases in the low-voltage power network application possibility.

Secondary Side Measurement Modeling Method of Voltage Fault Ride Through Model for Direct-Driven Wind Turbine

SHI Jiyin

2023, 43(1):  63-69.  doi:10.3969/j.issn.1008-0198.2023.01.011

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It is difficult to calculate the system stability margin and analyze the fault response accurately because of the lack of experimental verification for the crossing model of direct-driven wind turbine. In order to solve this problem, based on the analysis of the principle of secondary-side fault crossing model, the simulation system of secondary-side voltage crossing is designed, the waveform data is identified by the least square algorithm, and the model is verified. The results show that compared with the conventional primary-side voltage traversal test, the secondary-side measurement modeling method improves the test efficiency and has higher simulation accuracy.

Study on Initiation Characteristics of Low-Pressure Positive-Polarity 1 m Air Gap Impinging Stream Discharge

HU Jinyang, XU Xiaoyun, CHE Junru, ZHANG Wanxia, CHENG Chen, HE Hengxin

2023, 43(1):  70-78.  doi:10.3969/j.issn.1008-0198.2023.01.012

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Flow discharge is the first complete discharge stage in positive long air gap discharge. It is important to understand the mechanism of air gap breakdown and lightning flash process at high altitude to obtain the characteristics of low pressure flow discharge. Based on the critical volume model of flow discharge under impulse voltage, and considering the effect of gas pressure on the rate of negative ion desorption in critical volume, the initial discharge model is established, which considers many factors such as gas pressure, curvature radius of electrode and rise rate of voltage, etc. . A flow discharge experimental observation system based on a low pressure 1m air gap discharge chamber is designed and constructed, the distribution characteristics of the initial delay of flow discharge at 0.06 MPa, 0.08 MPa and 0.1 MPa are obtained, and the accuracy of the model is further verified. By using this model, it can be found that, under the constant condition of reduced electric field E/N, the effects of gas pressure, electrode size and voltage rise rate on the initial mean electric field and the dispersion of initial time delay of the discharge are calculated and analyzed. The research can provide guidance and reference for insulation coordination and lightning shielding performance evaluation of high altitude transmission and transformation engineering equipment.

Structural Strength Design of Outdoor Installation Protection Equipment

ZHANG Yuan, ZHU Lijuan

2023, 43(1):  79-83.  doi:10.3969/j.issn.1008-0198.2023.01.013

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The paper proposes a structural design method of sub unit, uses simulation software to analyze the structural strength design, and achieves the structural strength requirements through test verification, which has certain reference value for the subsequent device design under similar working conditions.

Experience and Discussion

An Improved Derivative Transform Detection Alogorithm for Voltage Sag

PENG Qingwen, LI Yujia, CHEN Baiyuan, SUN Jiangyueye, LYU Can, HU Xiangwei

2023, 43(1):  84-89.  doi:10.3969/j.issn.1008-0198.2023.01.014

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Voltage sag problems often bring huge losses to high-end manufacturing users, and the rapid and accurate detection of the typical characteristics of voltage sag is the key to compensating and controlling voltage sag. The key to managing voltage sags is to detect voltage sags quickly and accurately through small amounts of sampled data. In this paper, on the basis of the dq transformation method, a new type of improved derivative transformation method is proposed, which adopts different methods to construct d and q axis voltages, which can significantly reduce the detection delay of voltage sag, and only needs 2 sampling points to accurately detect the voltage phase and amplitude, which has good use value in engineering.

Study on Load Economic Distribution Method of AGC Scheduling Mode in Plant

WANG Chaosheng, SHAO Feng, TAN Rui, WANG Zhong′ao

2023, 43(1):  90-94.  doi:10.3969/j.issn.1008-0198.2023.01.015

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The application of plant AGC system in modern dispatching system can improve the operation speed of energy management system. However,due to the lack of scientific means of optimal distribution method of plant load. At this stage only AGC load is only evenly distributed among mutiple units. In order to solve this technical problem, this paper firstly studies the method of operation data mining, establishes the on-line optimal load distribution model, and finally realizes the on-line accurate calculation of unit energy consumption combined with the test method. The test results show that the energy-saving effect is obvious, which lays a theoretical and application foundation for the real-time optimal load distribution of thermal power units.

Development Status and Trend Analysis of Standard Digitization in Power Grid Enterprise

ZHANG Lan

2023, 43(1):  95-98.  doi:10.3969/j.issn.1008-0198.2023.01.016

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Standard digitization transformation facilitates standards in power grid enterprise to be more efficient, transparent, cooperative and smart, and will also make standard digitization in power grid to guide,regulate and support a healthy and ordered development of digital transformation in power grid. Based on the background of standard digitalization, this paper introduces the characteristics and status quo of standard digitalization of power grid enterprises, sorts out the problems faced by the standard digitalization of power grid enterprises, and analyzes the development trend of the standard digitalization of power grid enterprises.Some suggestions on the standardization and digitization of power grid enterprises are put forward.

Analysis of End Screen Dielectric Loss Measurement for Capacitive Current Transformer

CAO Wenbin, CHEN Ruizhen, LUO Wei

2023, 43(1):  99-102.  doi:10.3969/j.issn.1008-0198.2023.01.017

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The dielectric loss test of the end screen is of great significance for the detection of moisture defects in capacitive current transformers. The regulations stipulate that when the insulation resistance of the end screen of the current transformer cannot meet the requirements (less than 1 000 MΩ), the dielectric loss of the end screen to the ground should be measured to further judge its insulation status. In this paper, from the aspect of structure and dielectric loss test principle of capacitive current transformer, with the help of equivalent circuit, combined with actual test cases, the dielectric loss of current transformer is analyzed when the primary winding is suspended, the primary winding is grounded, and the primary winding is short-circuited and connected to the high-voltage shield. The dielectric loss measurement of the end shield in the three methods shows that the measurement results in the method of short-circuiting the primary winding to the high-voltage shielding method are the most accurate.

Three-Phase Load Imbalance Management Method Based on Improved Knapsack Algorithm for Manual Phase Change Station Area

ZHAO Ruolan, JIANG Fei, HE Zhenwu, YAO Peng, GUO Qi, PEI Xiangyu

2023, 43(1):  103-109.  doi:10.3969/j.issn.1008-0198.2023.01.018

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In view of the high degree of three-phase unbalance in the distribution station area and the low efficiency of the traditional manual phase change, a manual phase change optimization method based on the improved knapsack algorithm is proposed. The multi-objective phase change optimization model is constructed by considering the degree of three-phase unbalance and the number of phase changes. The phase change problem is abstractly transformed into a multi-pack model, and the algorithm is improved by introducing the idea of layered partitioned parallel search (LPPS). The actual data of a residential distribution area are used to analyze the case, and the improved knapsack algorithm is used to calculate the phase change scheme of the distribution area. Compared with the traditional knapsack algorithm, the number of phase changes is reduced while ensuring the treatment effect, which is conducive to improving the economic operation efficiency of the distribution area.

Research on Stator Bar End Electromagnetic Shielding for Pumped Storage Generator

NIE Liangliang, TAO Shidi, LI Tianwei, LIU Lei, LI Bin, WANG Qi

2023, 43(1):  110-115.  doi:10.3969/j.issn.1008-0198.2023.01.019

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Based on the analysis of the transient electromagnetic field for the electromagnetic shielding of generator stator bar, the model boundary is selected in theory, which can take into account both the calculation speed and the calculation precision. The calculation models of two wire rods in the same slot and multiple wire rods in different slots are established to calculate the influence of adjacent wire rods on the electric field distribution. At the same time, the three-dimensional calculation model of a single bar is established to calculate and analyze the distribution characteristics of the axial and normal field intensity of the bar. The results show that the surface potential of the end of the bar after leaving the notch is close to the phase potential, and the maximum field strength appears at the lap of the high and low stopbands. In order to improve the distribution of field strength and potential, this paper puts forward measures to improve the distribution of field strength on the surface, adding high-resistance materials to the original high-low resistance overlap layer to keep the same as the original design scheme, while the original high-resistance layer is coated with low-resistance materials, which can greatly suppress the field strength and potential at the end of the wire rod.

Faults and Analysis

Cause Analysis and Preventive Measures of Wind Turbine Blade Tower Sweeping

LUO Yanfei, XIAO Changyuan , SUN Maowen, LUO Shengxi, ZHANG Hualian

2023, 43(1):  116-120.  doi:10.3969/j.issn.1008-0198.2023.01.020

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In recent years, there have been a number of blade tower sweeping failures of wind turbine in China, which have seriously affected the safe operation of wind turbines, and also brought a lot of economic losses. This paper analyzes the causes of blade tower sweeping failure in a wind farm from the aspects of clearance design, hoisting maintenance, blade quality, unit operation control, site adaptability, simulation restoration, etc. It is determined that the blade tower sweeping in the wind farm are caused by turbulence overrun, negative shear, and blade installation angle dislocation. Preventive measures are given for different tower sweeping causes, and some suggestions are put up for the clearance design of new models.

Cause Analysis on Copper Shield Burst of 110 kV Cable Joint

LI Shaobin, XIE Shilin, PENG Yong, TANG Wenbo, ZHOU Hai, FAN Fangkun

2023, 43(1):  121-126.  doi:10.3969/j.issn.1008-0198.2023.01.021

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The copper shield burst caused by short-circuit breakdown of cable joints is prone to fire hazards in cable tunnels. This paper analyzes a typical 110kV cable joint copper shield burst accident and proposes that the copper shield burst of cable joints is caused by the compound action of two types of states, high temperature and high pressure, and the short-circuit breakdown process is accompanied by the cracking and ionization of insulating materials. The above viewpoint is verfied throgh the short-circuit high-current simulation test of the designed cable joint verifies the above viewpoint, the effectiveness of the current market mainstream use of the cable joint explosion-proof method is analyzed, and the design elements of the cable joint fireproof and explosion-proof are proposed.