Volume 46,Issue 11,2023 Table of Contents

1 Review of incipient insulation fault detection methods for power cables

REN Guangzhen , WANG Yunhe , CAO Junping , CHEN Weishao , CHENG Cheng , YONG Jing

2023, 46(11):1-12. DOI: 10.11835/j.issn.1000-582X.2022.212

[Abstract](328) [HTML](54) [PDF 1.86 M](1032)

Abstract:
Serious local insulation defects in power cables can cause distinct voltage and current disturbances. Precisely identifying these disturbances empowers utility companies to proactively manage cable maintenance and prevent unexpected power outages. This paper presents a comprehensive review of related research, detailing voltage and current disturbance waveforms across different systems. It categorizes existing incipient fault detection methods based on detection principles and data types, distinguishing between time-frequency characteristic threshold-based and artificial intelligence-based methods for transient power disturbances analysis. The study conducts a thorough comparison and evaluation of these methods. Drawing from existing research, recommendations are provided for further research on online detection technology for cable incipient faults.

2 Fault-tolerant control strategy for five-phase PMSM under adjacent two-phase open circuit fault

TAO Caixia , WANG Ranran , GAO Fengyang , WANG Weibin

2023, 46(11):13-25. DOI: 10.11835/j.issn.1000-582X.2022.204

[Abstract](216) [HTML](38) [PDF 2.18 M](500)

Abstract:
A two-phase open circuit fault in a five-phase permanent magnet synchronous motor (PMSM) can destabilize the entire drive system. In response to this fault scenario, a fault-tolerant control strategy utilizing space vector pulse width modulation (SVPWM) technology is proposed. Firstly, a mathematical model of the permanent magnet synchronous motor is constructed. To ensure smooth conversion of electromechanical energy, a reduced order transformation matrix is reconstructed, yielding the expression for fault-tolerant current in the residual phase. Subsequently, SVPWM technology is used to calculate the space voltage vector during the fault, delineate six sectors, synthesize the target vector, determine the action time of corresponding basic synthetic voltage vectors, and establish the selection order for space voltage vectors within the respective sector. Finally, MATLAB/Simulink simulations validate the correctness of the strategy by demonstrating consistency between simulation results and theoretical calculations. This approach significantly enhances the operation performance of the five-phase permanent magnet synchronous motor under fault conditions, ensuring its stability. A comparison with traditional current hysteresis tracking pulse width modulation (PWM) control confirms the superiority of the proposed strategy.

3 Corrosion characteristics and diagnosis technologies of grounding devices in power systems

DAN Yihua , ZHANG Ruixuan

2023, 46(11):26-41. DOI: 10.11835/j.issn.1000-582X.2023.11.003

[Abstract](200) [HTML](41) [PDF 1.19 M](895)

Abstract:
Grounding devices serve as essential foundations to ensure the safe and stable operation of power equipment and personal safety. Typically constructed with corrosive metal materials like carbon steel, domestic grounding devices are prone to issues such as corrosion fractures over time, leading to potential overvoltage and tripping accidents. Therefore, studying the corrosion characteristics and diagnosis technologies of these grounding devices becomes crucial in preventing power accidents caused by corrosion. From the perspective of the corrosion characteristics of grounding devices, in this paper, the corrosion mechanism of carbon steel grounding materials, corrosion characteristics of common grounding materials, soil corrosion characteristics, and effects of current on grounding device corrosion are reviewed. Various anti-corrosion measures for grounding devices are evaluated, and electrochemical corrosion diagnosis methods, electrical network diagnosis methods, and electromagnetic field analysis diagnosis methods are compared, with their pros and cons highlighted. Challenges faced by existing research in dealing with grounding device corrosion are summarized, and it is suggested that future studies focus on exploring corrosion interactions among different grounding materials, developing new corrosion-resistant grounding materials, quantifying actual corrosion levels in grounding devices, diagnosing potential corrosion faults, and swiftly identifying corrosion issues in ground lead conductors to prevent power accidents effectively.

4 Pressureless sintering performance and high temperature aging of formic acid-treated nano-copper

XU Yu , DAI Dongfang , YANG Renbin , CHEN Xianping , WANG Ping

2023, 46(11):42-48. DOI: 10.11835/j.issn.1000-582X.2023.204

[Abstract](282) [HTML](48) [PDF 1.43 M](653)

Abstract:
A pressureless sintering process of copper nanoparticle based on the copper formate pyrolysis reaction was developed. The aim was to address challenges faced by the existing copper sintering technologies, such as copper oxidation and the need for additional pressure. Copper nanoparticles (Cu NPs) were treated with formic acid solution to generate dense copper formate films, which, upon sintering, formed Cu-Cu joints. Quality tests confirmed that a formic acid reaction time of 10 min, PEG solvent, substrate surface polishing with 0.048 mm sandpaper, and a heating rate of 5 ℃/min were the optimal sintering conditions. This approach achieved pressureless sintering of copper nanoparticles, yielding joints with a shear strength of 16.18 MPa and low resistivity of 570 μΩ/m. Even after a 200 h high-temperature aging test, the joints maintained a shear strength of 9.38 MPa, which verified the reliability of the sintering process. Therefore, this method presents a novel approach for realizing reliable interconnections in third-generation semiconductor chips.

5 Research on the aging of oil-paper insulation based on continuous return voltage polarization spectrum

LIN Zhiyong , ZHANG Bo , ZHANG Damin , SU Ruohang , LIN Chaoming

2023, 46(11):49-55. DOI: 10.11835/j.issn.1000-582X.2023.11.005

[Abstract](150) [HTML](47) [PDF 904.89 K](375)

Abstract:
To address the issues of inaccuracies in traditional return voltage polarization spectrum, specifically the inaccurate representation of return voltage at various charging times and the challenge in determining the central time constant precisely, this paper proposes a novel drawing method of the continuous return voltage polarization spectrum. Firstly, this paper analyzes the relationship between the return voltage curve and the equivalent circuit parameters of the insulation system. It then builds a continuous return voltage polarization spectrum model, extracting a more accurate central time constant. By linking this central time constant with the micro-water content of the transformer, the paper establishes an effective method for determining the transformer’s micro-water content. Finally, this paper analyzes continuous return voltage polarization spectra using six transformers in different aging states. The results show that this method accurately determines the central time constant, significantly enhancing the accuracy of micro-water content determination in transformers. This approach offers a new method to accurately assess the aging state of transformer oil-paper insulation.

6 An incentive scheme of peak-valley price based on differential privacy

PANG Bo , ZHANG Linghao , TENG Yufei , CHANG Zhengwei , TANG Chao , HU Chunqiang , LIU Zewei , WANG Baolin

2023, 46(11):56-68. DOI: 10.11835/j.issn.1000.582X.2023.11.006

[Abstract](257) [HTML](47) [PDF 2.32 M](527)

Abstract:
To solve the problems of significant peak load variations and power supply shortages within smart grid systems, this paper proposes an incentive scheme for peak and off-peak time-of-use (TOU) pricing based on differential privacy. The scheme integrates differential privacy with the peak-valley TOU model, optimizing pricing strategies while safeguarding user data privacy. Differentiated pricing schemes are implemented to influence users’ behavior of electricity consumption, encouraging off-peak consumption habits and achieving a balanced power load across the system. Experimental analysis assesses the data utility following the introduction of differential privacy, evaluating the operation effectiveness of the proposed mechanism. Results show that this scheme successfully achieves load balancing throughout the whole power network while protecting user data privacy.

7 Prediction model of conductor icing based on basic environmental parameters

HAN Xingbo , CHEN Ziming , XING Bin , JIANG Xingliang

2023, 46(11):69-77. DOI: 10.11835/j.issn.1000-582X.2023.12.008

[Abstract](261) [HTML](43) [PDF 4.15 M](617)

Abstract:
Wind speed, temperature, air liquid water content, and median volume diameter of water droplets are the main environmental parameters influencing conductor icing. This paper establishes a “four-parameter” model for wire icing using principles from fluid mechanics and thermal equilibrium considering the motion, collision, and freezing processes of water droplets. Through numerical computations, the study analyzes the unique impacts of each environmental parameter on the growth rate of conductor icing. Additionally, empirical formulas for liquid water content and median volume diameter of water droplets are developed based on practical line monitoring data. Subsequently, a predictive model for conductor icing is devised, relying on readily obtainable sensor data. Research findings reveal that the influence of the median volume diameter of water droplets on the rate of conductor icing exhibits a saturation characteristic, while variations in air liquid water content correlate with wind speed, temperature, and humidity. These conclusions provide a theoretical foundation for predicting and early warning systems for icing on transmission lines.

8 Lithium battery remaining life prediction method based on improved grey wolf optimization least squares support vector machine

ZHENG Qinggen , YANG Xiangguo , LIU Dong , LI Xin

2023, 46(11):78-89. DOI: 10.11835/j.issn.1000-582X.2023.203

[Abstract](241) [HTML](50) [PDF 2.59 M](594)

Abstract:
To solve the problem of accurately predicting remaining life of lithium battery, this paper proposes an indirect prediction method based on improved grey wolf optimization least-squares support vector machine (IGWO-LSSVM). Three indirect health factors characterizing battery performance degradation are derived from discharge characteristic curves. To enhance prediction accuracy, the study incorporates a tent chaotic map, a nonlinear decreasing convergence factor, and a Levi flight strategy into the grey wolf algorithm. Combined with the LSSVM model, the lithium battery life prediction model with global optimization is formed. The proposed method is verified using the NASA data set and compared with GWO-LSSVM, PSO-ELM and BP algorithms. Experimental results show that the improved algorithm proposed in this paper outperforms other methods in terms of prediction accuracy.

9 Combined source magnetic field superposition imaging detection method for grounding grid topology

TIAN Weiguang , LIU Longhuan , LIAO Xian , Zhang Jing , WANG Haowen , FU Zhihong

2023, 46(11):90-101. DOI: 10.11835/j.issn.1000-582X.2023.208

[Abstract](182) [HTML](75) [PDF 4.58 M](482)

Abstract:
In response to the challenge of measuring weak magnetic field, this paper introduces a novel detection method, combining source magnetic field superposition imaging. The approach involves injecting current into the grounding grid through multiple down conductors in periodic rotation, each inducing different flow directions within the grounding grid. This variation ensures effective stimulation of measurement magnetic fields across different areas of the grounding grid. Integrated with an ultra-wideband positioning system, the method enables real-time location tracking of array sensing coil measurements in both x and y directions on the surface level. The induced magnetic field is scanned and abnormal data interference is eliminated using morphological filtering and Canny edge detection. Simulation and experimental results show that the proposed method effectively improve the imaging quality of grounding grid topology. Moreover, the positioning accuracy error for grounding grid conductors remains below 3%, validating the effectiveness of the proposed method.

10 Design Method of IGBT Module Condition Monitoring System for Submodule in High Power MMC system

LUO Dan , CHEN Minyou , LAI Wei , XIA Hongjian , LI Changsheng

2023, 46(11):102-118. DOI: 10.11835/j.issn.1000-582X.2023.214

[Abstract](172) [HTML](41) [PDF 8.57 M](566)

Abstract:
The insulated gate bipolar transistor (IGBT) module plays a pivotal role in the modular multilevel converter (MMC), making online monitoring essential for ensuring the MMC system’s safety, reliability, and cost-effectiveness. Addressing the challenge of real-time monitoring for multi-chip parallel IGBT modules in the MMC system, this paper presents a design method of condition monitoring system based on the relationship between the module’s case temperature distribution and its aging state, which enables adaptive evaluation and management of IGBT module under different operating conditions. Firstly, the impact of aging failure on the heat flow of IGBT modules in MMC sub-modules is analyzed, with case temperature selected as the characteristic parameter representing the module's state. Secondly, an aging state monitoring model for IGBT, based on neural network, is established. This model is adaptable to different working points, allowing for the characterization and identification of module states according to the demand preference of different application scenarios. Finally, the proposed condition monitoring system design method is verified on MMC test platform, demonstrating its feasibility and effectiveness. This paper provides an innovative solution for IGBT status monitoring in MMC sub-modules under high power operating conditions, offering a practical and effective approach to state maintenance.

11 Self-healing capability evaluation of smart distribution network after fault

ZHANG Xuefei , LI Zhiwei , JIANG Yinghan , TANG Xuejun , DONG Litong , SUN Liping , ZHOU Qiupeng

2023, 46(11):119-128. DOI: 10.11835/j.issn.1000-582X.2021.220

[Abstract](209) [HTML](44) [PDF 1.90 M](705)

Abstract:
The self-healing characteristic is a key aspect of smart grids and holds important research significance. However, a comprehensive measurement standard for assessing the self-healing ability of smart distribution networks has not yet been established. Existing evaluations of self-healing in smart distribution networks suffer from various issues, such as incomplete quantitative indicators and neglecting uncertainties in the process of self-healing. These problems leads to inaccurate evaluation and higher-than-actual results. To address these challenges, four quantitative indexes, namely, self-healing credibility, self-healing rate, self-healing speed and self-healing benefit are proposed. These indicators encompass factors such as the speed of load recovery, duration of sustainability, and economic benefits following faults in the distribution network. Being built upon these indicators, a comprehensive evaluation metric called “self-repair performance” is proposed using the method of information entropy. Uncertainty theory is introduced to quantitatively describe the uncertainty of self-healing so as to solve the problems of uncertainty and insufficient samples in the evaluation process. A simulation analysis is conducted on a constructed power distribution system with 7 sections to validate the effectiveness and accuracy of the proposed evaluation indexes and method.

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