LOW VOLTAGE APPARATUS

Research on Electromagnetic Torque Calculation Model of Polarized Magnetic System and Its Application

LIANG Huimin, LIU Guilin, CHEN Junfeng, WEI Zhen, HUANG Manyun

2022, 0(8): 1-7. doi:10.16628/j.cnki.2095-8188.2022.08.001

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Polarized magnetic systems are widely used in satellite and rocket electromagnetic relays due to their small size,light weight and low power consumption.At present,the parameter optimization of polarized magnetic system is mostly based on the experience and simulation results.The optimization cycle is quite long without theoretical basis.Firstly,the unified computation model for the electromagnetic torque of polarized magnetic system is established according to the equivalent magnetic circuit.The characteristics of electromagnetic torque curve under zero volt are analyzed.The relationship between the cross-sectional area of permanent magnet and the electromagnetic torque at 0 V release position and pick-up position is obtained.The adjusting method for the zero crossing position of electromagnetic torque curve under zero volt is achieved.Finally,the bridge polarized magnetic system is optimized by the above analysis results.Simulation and prototype test results show that the optimized structures can meet the respective optimization targets.The research can provide the theoretical basis and optimization direction for the parameter optimization and reliability improvement of the relay electromagnetic system.

Analysis and Optimization of Transmission Characteristics Of Wide Range Current Transformers Based on Multi-Objective Particle Swarm Algorithm

XIE Yunhao, WU Ziran, CHEN Wei, BAO Xiaozhong, XU Haibo

2022, 0(8): 8-17. doi:10.16628/j.cnki.2095-8188.2022.08.002

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The mathematical model of the current transformer considering material nonlinearity and secondary circuit parameters is established to calculate the transmission current waveform in a wide range.The vertical resolution of secondary current with high current value is used as evaluation index to analyze the influence of key design parameters on transformer transmission characteristics.In addition,the multi-objective particle swarm optimization algorithm is used to optimize the current transformer with 250 A rated current.On the premise of ensuring the measurement accuracy in the linear region,the vertical resolution in the deep saturation region is improved by 13.2%and the cost is reduced by 5.4%.

Research on a High-Efficiency Winding Self-Driven Synchronous Rectification Flyback DC/DC Converter

CHENG Ming, HUANG Ji, CHEN Lichuan

2022, 0(8): 18-22. doi:10.16628/j.cnki.2095-8188.2022.08.003

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Synchronous rectification technology is widely used in switching power supply.The rectification based on MOSFET with small R_ds(on) instead of schottky diodes can improved conversion efficiency.In order to solve the problem of complex shutdown control circuit for the self driving synchronous rectification,a winding self-driven synchronous rectification flyback DC/DC converter is studied.The influence of leakage inductance on the working state of synchronous rectification MOSFET is analysed.The optimal design of transformer leakage inductance is obtained by the transformer and circuit simulation.A 5 V/20 W output winding self-driven synchronous rectification flyback DC/DC converter with efficiency up to 89.7%is designed.It is suitable for the small volume synchronous rectification DC/DC converter to improve the power density.

Research on Forecasting Methods of Short-Term Load Based on Causal Relationship Analysis

ZHANG Guangru, MA Zhenqi, YANG Junting, ZHANG Jiawu, SU Juan, GAO Tian, DING Zeqi, FANG Shu

2022, 0(8): 23-32. doi:10.16628/j.cnki.2095-8188.2022.08.004

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With the high proportion of renewable energy and the rapid development of the electricity market,the uncertainty of the power system increases.In order to improve the accuracy of load forecasting in the market environment,a short-term load forecasting method based on causal relationship analysis is proposed.First,the grey correlation analysis method is used to quantify the correlation between meteorological factors and market factors and the load.Then,the optimal modal decomposition method is used to decompose the load mode,and the Granger causal analysis method is used to match the influencing factors with the modal subsequences.Finally,the subsequence is predicted using the differential autoregressive moving average (ARIMA) model and the bidirectional long-short-term memory (Bi-LSTM) neural network model.The prediction results are superimposed to obtain the short-term load prediction results.The simulation results show that the prediction accuracy of the proposed method can reach 92%,which can verifie the accuracy and effectiveness of the proposed method.

Research on Fault Location of Distribution Network Based on Edge Computing and Wavelet Neural Network

XU Xin, ZHANG Ying

2022, 0(8): 33-38. doi:10.16628/j.cnki.2095-8188.2022.08.005

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With the rapid development of the power internet of things,in order to further improve the accuracy of fault location in the distribution network,a method of distribution network fault location based on the edge computing and wavelet neural network is proposed.Firstly,the terminal is redivided into a collection terminal with calculation function and a collection terminal for fault information collection.Then,the fault current signal is subjected to wavelet transform and wavelet packet frequency band decomposition to obtain the fault feature vector.Finally,through the neural network training,the output diagnostic result the is obtained.The simulation results show that this method can reduce the time of fault diagnosis and improve the accuracy of fault location.

Thermal Analysis of SiC MOSFET Power Module Based on Die Package

WANG Haonan, CAO Yufeng, LAI Yaokang, HU Caixia, ZHANG Hongyu, WANG Zicheng, ZHAI Guofu

2022, 0(8): 39-43. doi:10.16628/j.cnki.2095-8188.2022.08.006

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SiC MOSFETs are widely used in the design of high-power solid-state power controllers due to the high temperature and high voltage resistance advantages.Aiming at the working conditions of solid-state power controllers,the die-packaged SiC MOSFETs are selected.The stacked structure of the power module is designed and its thermal resistance is analyzed.The selection and layout of the bonding structure is designed.The thermal influence of the package connection copper wire and copper tape is analyzed.Based on the packaging design,the thermal performance of the power module is evaluated by the finite element simulation.Finally,a platform for single channel thermal test is build.The results verify the accuracy of the simulation and the rationality of the packaging design.

Analysis on Temperature Rise Influence of Contactor Terminal

GE Shunfeng, LI Xinye, YANG Yunfei, WANG Maomao

2022, 0(8): 44-46. doi:10.16628/j.cnki.2095-8188.2022.08.007

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The terminal temperature rise performance of AC contactor is of great significance in safety.From the test comparison of different contact materials,different conductive plate materials and different contact working face shapes,the influence on the terminal temperature rise and the influence of the mechanical durability on the terminal temperature rise are analyzed.Finally the direction to improve the terminal temperature rise performance is provided.

Simulation Method of Permanent Magnet Circuit Breaker Closing Mechanical Characteristics

CHEN Jiaming

2022, 0(8): 47-50. doi:10.16628/j.cnki.2095-8188.2022.08.008

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The closing mechanical characteristics of permanent magnet circuit breakers are related to the important functions of the product.It is not only necessary to study the permanent magnet mechanism itself,but also to analyze the characteristics of the transmission structure.The simulation method of the closing mechanical characteristics of the permanent magnet circuit breaker is proposed.The displacement and force relationship of the transmission structure are obtained through the dynamic simulation.Then,the closing mechanical characteristics of the permanent magnet circuit breaker is obtained through the transient electromagnetic field simulation.Finally,according to the definition,the closing speed and time of the circuit breaker are calculated.The results are within a reasonable range,which can prove the rationality of the design of the circuit breaker's transmission structure and permanent magnet mechanism.

Design on On-Line Detection System of Partial Discharge in Cable Joints

XU Zhen, BAO Guanghai

2022, 0(8): 51-56. doi:10.16628/j.cnki.2095-8188.2022.08.009

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In order to solve the problem that the insulation fault of the cable joint is difficult to detect,the partial discharge on-line detection system for the cable joint based on the high-frequency current method is designed.The DSP and FPGA are taken as the core to collect the partial discharge signal coupled with high frequency current transformer (HFCT) installed on the ground wire of the cable connector through FPGA.The DSP is used to compile FFT and wavelet transform programs to suppress the white noise and narrow-band interference of the partial discharge signals,which can achieve on-line detection of partial discharge signals.Finally,the oscilloscope signal and MATLAB noise reduction processing results are compared with the on-line detection system.The comparison results are consistance,which can prove the effectiveness of this system.

Analysis on Stealing and Error Power Energy of Typical Sampling Circuit of Watt-Hour Meter

GUO Jiao, YUAN Ruiming, WANG Chen, LI Wenwen, JU HanJi

2022, 0(8): 57-60. doi:10.16628/j.cnki.2095-8188.2022.08.010

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Stealing power energy not only affects the economic benefits of users and electric power enterprises,but also affects the normal operation and high-quality service of the power grid.In order to solve this problem,the basic error test of the watt-hour meter is made by analyzing the working principle of a typical sampling circuit of the watt-hour meter,deducing the calculation formula of the power energy under the condition of stealing power energy and calculating the error power energy.Compared with the accumulated power energy,the theoretical data are consistent with the experimental data,which can be used to calculate the error power energy accurately and rapidly.

Selection and Design of Bimetallic Sheet of MCCB

XIAO Lin, JIANG Guping

2022, 0(8): 61-66. doi:10.16628/j.cnki.2095-8188.2022.08.011

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Thermal magnetic moulded case circuit breaker(MCCB) generally uses bimetallic sheet for overload tripping protection.The displacement of bimetallic sheet moves the operating mechanism through deformation to realize overload tripping protection.In the design,the thermal bending displacement of bimetallic sheet is the most important characteristic design.In addition,it is necessary to check whether the bending force can overcome the tripping force,and the heating of bimetallic sheet is required to reach a certain range.Finally,the design and selection method of bimetallic sheet are discussed through several examples.

Review on Development of Green and Low Carbon Standardization of Low Voltage Electrical Apparatus

ZHENG Jiexin

2022, 0(8): 67-70. doi:10.16628/j.cnki.2095-8188.2022.08.012

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The development background and demand of low-carbon green standardization in the field of low-voltage electrical apparatus in recent years are mainly introduced.The trends of standardization of low voltage electrical apparatus at home and abroad are analyzed.Finally,the main challenges of standardization development under dual carbon targets are put forward,and the green and sustainable development of low-voltage electrical apparatus in the future is prospected.

Introduction to Differences Between IEC 60947-1:2020 Low-Voltage Switchgear and Controlgear - Part 1: General Rules and GB/T 14048.1—2012

CHEN Xueqin

2022, 0(8): 71-75. doi:10.16628/j.cnki.2095-8188.2022.08.013

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To improve the development and design, manufacturing,testing and certification of low-voltage equipments,and guide users to correctly use domestic and foreign standards,the differences between IEC 60947-1:2020 Low-Voltage Switchgear and Controlgear - Part 1:General Rules and GB/T 14048.1—2012 were analyzed in the aspects of scope,terms and definitions,characteristics,product data and information,structure and performance requirements,test and annex.

Analysis on Application of Environmental Optimization SF₆ Alternative Gas in Medium and High Voltage Power Equipment

WANG Guangxian, ZHAO Ruiying

2022, 0(8): 76-80. doi:10.16628/j.cnki.2095-8188.2022.08.014

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In order to reduce greenhouse gas emissions,the research on environment-friendly SF₆ alternative gas should be carried out,and the timely evaluation and application should be promoted.At present,in terms of arc extinguishing,vacuum interrupter is widely used as the main breaking unit to replace SF₆ arc extinguishing medium for 40.5 kV and below voltage level switchgear.In terms of insulation,the great progress has been made in the research of using environmental protection gas instead of SF₆ as the insulation medium.The research focuses are mainly on dry air,N₂,C4-PFN (fluorinated nitriles) gas and its mixture,perfluorones (C_nF_2nO) gas and its mixture,etc.Through the analysis and comparison of their insulation,temperature rise,physical and chemical characteristics,their advantages and disadvantages and application status are summarized,and a certain gas or mixed gas is determined as an ideal alternative gas for SF₆ under a specific voltage level to carry out in-depth application research.

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