For the output of wind power system has the characteristics of randomness, volatility and intermittence, the voltage of wind power system fluctuates frequently and voltage sag is one of the most common voltage fluctua...For the output of wind power system has the characteristics of randomness, volatility and intermittence, the voltage of wind power system fluctuates frequently and voltage sag is one of the most common voltage fluctuations in wind power system. For the problem of voltage sag of wind power system, the limitations of the detection methods such as the square detection method, the half-wave RMS detection method and wavelet transform are summed up, and a new detecting method named Hilbert-huang Transform(HHT) is put forward in this paper, which can detect the voltage sag accurately and timely. In order to solve the problem of end effect in the process of empirical mode decompostion (EMD), a self-adaptive method named improved waveform matching is applied in dealing with the end issue. Voltage fluctuations are reflected by two parameters named voltage amplitude and frequency of each intrinsic mode function (IMF) in HHT. The practicality of the method is verified by Matlab simulation.展开更多
The surface flashover of epoxy resin(EP) composites is a pivotal problem in the field of highvoltage insulation.The regulation of the interface between the filler and matrix is an effective means to suppress flashover...The surface flashover of epoxy resin(EP) composites is a pivotal problem in the field of highvoltage insulation.The regulation of the interface between the filler and matrix is an effective means to suppress flashover.In this work,nano ZnO was fluorinated and grafted using lowtemperature plasma technology,and the fluorinated filler was doped into EP to study the DC surface flashover performance of the composite.The results show that plasma fluorination can effectively inhibit the agglomeration by grafting –CFxgroups onto the surface of nano-ZnO particles.The fluorine-containing groups at the interface provide higher charge binding traps and enhance the insulation strength at the interface.At the same time,the interface bond cooperation caused by plasma treatment also promoted the accelerating effect of nano ZnO on charge dissipation.The two effects synergistically improve the surface flashover performance of epoxy composites.When the concentration of fluorinated ZnO filler is 20%,the flashover voltage has the highest increase,which is 31.52% higher than that of pure EP.In addition,fluorinated ZnO can effectively reduce the dielectric constant and dielectric loss of epoxy composites.The interface interaction mechanism was further analyzed using molecular dynamics simulation and density functional theory simulation.展开更多
The detection of hydrophobicity is an important way to evaluate the performance of composite insulators, which is helpful to the safe operation of composite insulators. Image processing technology is used to judge the...The detection of hydrophobicity is an important way to evaluate the performance of composite insulators, which is helpful to the safe operation of composite insulators. Image processing technology is used to judge the hydrophobicity of composite insulators, which makes detection results more accurate and overcomes the subjective drawbacks of traditional detection methods.?As the traditional Canny operator requires manual intervention in selecting the variance of the Gaussian filter and the threshold, the paper presents a method of edge detection based on improved Canny operator. First, the adaptive median filter replaces the Gaussian filter, which can eliminate the impact from the variance of Gaussian filter and remove noise according to the characteristics of the image itself. Then the Ostu threshold method is used to select the best threshold automatically, which makes the edge detection be more continuous and reduce the presence of fake edges. The results show that the operator is applicable to all hydrophobic images.展开更多
Under the background of smart grid’s real-time electricity prices theory, a real-time electricity prices and wireless communication smart meter was designed. The metering chip collects power consumption information. ...Under the background of smart grid’s real-time electricity prices theory, a real-time electricity prices and wireless communication smart meter was designed. The metering chip collects power consumption information. The real-time clock chip records current time. The communication between smart meter and system master station is achieved by the wireless communication module. The “freescale” micro controller unit displays power consumption information on screen. And the meter feedbacks the power consumption information to the system master station with time-scale and real-time electricity prices. It results that the information exchange between users and suppers can be realized by the smart meter. It fully reflects the demanding for communication of smart grid.展开更多
The line side winding is under the fundamental frequency AC voltage, while the valve side winding contains not only fundamental AC voltage component, but also the DC voltage component, fundamental AC voltage component...The line side winding is under the fundamental frequency AC voltage, while the valve side winding contains not only fundamental AC voltage component, but also the DC voltage component, fundamental AC voltage component, and higher harmonic voltage components when the converter transformer is at its normal operating condition, and the electric field of converter transformer is a non-sinusoidal steady one. To analyze the non-sinusoidal steady electric field containing the DC component, fundamental AC and higher harmonic components, the voltage spectrum of the valve winding in a ±500 kV converter transformer is firstly analyzed, and the non-sinusoidal periodic steady electric field is obtained by the fast discrete Fourier transform. Different resistivity of the oil and oil-immersed paper is adopted to simulate the aging of oil paper insulation at operation, and get the non-sinusoidal steady electric field.展开更多
The surface insulation properties of insulating material under DC voltage are closely related to the characteristics of surface charge accumulation, and the surface roughness of these materials has a direct impact on ...The surface insulation properties of insulating material under DC voltage are closely related to the characteristics of surface charge accumulation, and the surface roughness of these materials has a direct impact on the surface charge distribution in vacuum. Therefore, it is significant to study their connection. In this paper, based on the secondary electron emission avalanche model, the surface charge accumulation on polymethyl methacrylate (PMMA) with different surface roughness was simulated by using particle in cell and Monte Carlo Collision method. The simulated environment was under the finger shaped electrode and in vacuum. The results showed that under the action of the electric field the electrons emitted from the cathode triple junction moved forward and collided with the insulating material, which may lead to the generation of secondary electrons or the accumulation of surface charge. The surface charge near the cathode was mostly negative since the effect of surface electron injection was greater than that of the collision ionization. Due to the change of electron energy and the influence of electric field distribution, the number of positive charge on the insulator gradually increased, reached the maximum, and then gradually reduced with the approaching of the anode. Moreover, when the surface roughness of the material increases or the secondary electron emission coefficient decreases, the amount of surface charge accumulated on the PMMA will reduce. This paper can provide some guidance for the practical application of insulating materials.展开更多
Aiming at the problem of abnormal data generated by a power transformer on-line monitoring system due to the influences of transformer operation state change,external environmental interference,communication interrupt...Aiming at the problem of abnormal data generated by a power transformer on-line monitoring system due to the influences of transformer operation state change,external environmental interference,communication interruption,and other factors,a method of anomaly recognition and differentiation for monitoring data was proposed.Firstly,the empirical wavelet transform(EWT)and the autoregressive integrated moving average(ARIMA)model were used for time series modelling of monitoring data to obtain the residual sequence reflecting the anomaly monitoring data value,and then the isolation forest algorithm was used to identify the abnormal information,and the monitoring sequence was segmented according to the recognition results.Secondly,the segmented sequence was symbolised by the improved multi-dimensional SAX vector representation method,and the assessment of the anomaly pattern was made by calculating the similarity score of the adjacent symbol vectors,and the monitoring sequence correlation was further used to verify the assessment.Finally,the case study result shows that the proposed method can reliably recognise abnormal data and accurately distinguish between invalid and valid anomaly patterns.展开更多
Fibre-reinforced polymer(FRP)/rigid polyurethane foam(RPUF)interface is susceptible to moisture intrusion in addition to natural ageing during operation.This study investigated the influence of moisture intrusion on t...Fibre-reinforced polymer(FRP)/rigid polyurethane foam(RPUF)interface is susceptible to moisture intrusion in addition to natural ageing during operation.This study investigated the influence of moisture intrusion on the FRP/RPUF interface under natural ageing using experiments and molecular dynamics(MD)simulations.Water absorption,shear strength,and leakage current tests were used to clarify the changes in the interface performance.The degradation mechanism of moisture intrusion at the interface under natural ageing was revealed by MD simulation and micro-characterisation.The results show that the natural ageing of interfacial materials will slightly reduce the quality of the interface but will reduce the water resistance of the material and promote the process of water intrusion into the interface.In addition,water mainly invades the interface through RPUF.After water penetration,the interfacial bonding strength and insulation performance significantly decreased.Plasticisation and hydrolysis of interfacial materials are the main reasons for decreased interfacial adhesion.Hydrolysis can cause irreversible damage to the interface,increasing interface defects and water absorption.The vicious cycle of material hydrolysis is the ultimate cause of interfacial debonding.The polar molecules produced by this process and the water absorbed by the interface caused the degradation of the interface insulation performance.展开更多
Establishing a long air gap discharge model considering the streamer-leader transition and randomness of the discharge path is of great signiflcance to improve the accuracy of discharge characteristic prediction and o...Establishing a long air gap discharge model considering the streamer-leader transition and randomness of the discharge path is of great signiflcance to improve the accuracy of discharge characteristic prediction and optimize external insulation design.Based on fractal theory and thermal ionization theory of streamer-leader transition,this work establishes a dynamic development model for the long air gap discharge streamer-leader system,which includes streamer inception,streamer development,leader inception,development of streamer-leader system and flnal jump.The positive discharge process of a 3 m rod plate is simulated to obtain the fractal distribution of the discharge path and the law of leader development for comparison with the discharge test results.The results show that the simulation model is similar to test results in the development characteristics of leader path distribution,each stage time and leader velocity.Finally,a simulation calculation of a 50%breakdown voltage of the rod-plate gap and ball-plate gap is carried out,with results fairly consistent with test data,proving the effectiveness and practicality of the model.展开更多
With the development of a smart grid,the automatic location of power equipment is becoming a trend.In this study,a method for automatic location identification and diagnosis of external power insulation equipment base...With the development of a smart grid,the automatic location of power equipment is becoming a trend.In this study,a method for automatic location identification and diagnosis of external power insulation equipment based on YOLOv3 is proposed.This deep learning algorithm is used to extract the characteristics of image data under the visible light channel of the insulator.It learns and trains the collected data to realise the rapid location identification and frame selection of the external insulation equipment and extract discharge characteristics of the target box under the ultraviolet channel.According to the number of photons and the spot area information,the operating status of the equipment is determined.The results show that the YOLOv3 algorithm with a training rate of 0.005 achieved a fast convergence of the location recognition model.The average recognition accuracy was 88.7%and the average detection time was 0.0182 s.The combination of visible light path insulator target recognition and ultraviolet light path diagnosis can realise a lean and intelligent diagnosis of power equipment.This method had good real-time performance,accuracy,and robustness to the background.It provides a new concept for intelligent diagnosis and location analysis of power equipment.展开更多
The roof arrester of electric multiple units(EMU)can efficiently limit the overvoltage,and ensure the safe operation of the EMU electrical equipment.In the process of high‐speed operation,the traction power supply sy...The roof arrester of electric multiple units(EMU)can efficiently limit the overvoltage,and ensure the safe operation of the EMU electrical equipment.In the process of high‐speed operation,the traction power supply system is often affected by overvoltage.In addition,roof arrester explosion accidents occasionally occur.In this paper,the on‐line voltage measurement system of the EMU arrester is developed.By analysing a large number of voltage waveforms,the abnormal voltage is divided into three categories:over‐phase voltage,high harmonic voltage and steep impulse overvoltage.The charac-teristics of abnormal voltage waveforms are then summarised.The electrothermal coupling simulation model of the arrester is developed,and the current response and temperature distribution of the arrester under abnormal voltage are calculated.The impact of the impulse voltage energy on the arrester temperature is studied by applying a triangular wave voltage to the model.Finally,some suggestions are proposed for the operation and maintenance of the roof arrester.展开更多
文摘For the output of wind power system has the characteristics of randomness, volatility and intermittence, the voltage of wind power system fluctuates frequently and voltage sag is one of the most common voltage fluctuations in wind power system. For the problem of voltage sag of wind power system, the limitations of the detection methods such as the square detection method, the half-wave RMS detection method and wavelet transform are summed up, and a new detecting method named Hilbert-huang Transform(HHT) is put forward in this paper, which can detect the voltage sag accurately and timely. In order to solve the problem of end effect in the process of empirical mode decompostion (EMD), a self-adaptive method named improved waveform matching is applied in dealing with the end issue. Voltage fluctuations are reflected by two parameters named voltage amplitude and frequency of each intrinsic mode function (IMF) in HHT. The practicality of the method is verified by Matlab simulation.
基金supported by Beijing Natural Science Foundation (No. 3222057)National Natural Science Foundation of China (Nos. 52277147 and 52007065)。
文摘The surface flashover of epoxy resin(EP) composites is a pivotal problem in the field of highvoltage insulation.The regulation of the interface between the filler and matrix is an effective means to suppress flashover.In this work,nano ZnO was fluorinated and grafted using lowtemperature plasma technology,and the fluorinated filler was doped into EP to study the DC surface flashover performance of the composite.The results show that plasma fluorination can effectively inhibit the agglomeration by grafting –CFxgroups onto the surface of nano-ZnO particles.The fluorine-containing groups at the interface provide higher charge binding traps and enhance the insulation strength at the interface.At the same time,the interface bond cooperation caused by plasma treatment also promoted the accelerating effect of nano ZnO on charge dissipation.The two effects synergistically improve the surface flashover performance of epoxy composites.When the concentration of fluorinated ZnO filler is 20%,the flashover voltage has the highest increase,which is 31.52% higher than that of pure EP.In addition,fluorinated ZnO can effectively reduce the dielectric constant and dielectric loss of epoxy composites.The interface interaction mechanism was further analyzed using molecular dynamics simulation and density functional theory simulation.
文摘The detection of hydrophobicity is an important way to evaluate the performance of composite insulators, which is helpful to the safe operation of composite insulators. Image processing technology is used to judge the hydrophobicity of composite insulators, which makes detection results more accurate and overcomes the subjective drawbacks of traditional detection methods.?As the traditional Canny operator requires manual intervention in selecting the variance of the Gaussian filter and the threshold, the paper presents a method of edge detection based on improved Canny operator. First, the adaptive median filter replaces the Gaussian filter, which can eliminate the impact from the variance of Gaussian filter and remove noise according to the characteristics of the image itself. Then the Ostu threshold method is used to select the best threshold automatically, which makes the edge detection be more continuous and reduce the presence of fake edges. The results show that the operator is applicable to all hydrophobic images.
文摘Under the background of smart grid’s real-time electricity prices theory, a real-time electricity prices and wireless communication smart meter was designed. The metering chip collects power consumption information. The real-time clock chip records current time. The communication between smart meter and system master station is achieved by the wireless communication module. The “freescale” micro controller unit displays power consumption information on screen. And the meter feedbacks the power consumption information to the system master station with time-scale and real-time electricity prices. It results that the information exchange between users and suppers can be realized by the smart meter. It fully reflects the demanding for communication of smart grid.
文摘The line side winding is under the fundamental frequency AC voltage, while the valve side winding contains not only fundamental AC voltage component, but also the DC voltage component, fundamental AC voltage component, and higher harmonic voltage components when the converter transformer is at its normal operating condition, and the electric field of converter transformer is a non-sinusoidal steady one. To analyze the non-sinusoidal steady electric field containing the DC component, fundamental AC and higher harmonic components, the voltage spectrum of the valve winding in a ±500 kV converter transformer is firstly analyzed, and the non-sinusoidal periodic steady electric field is obtained by the fast discrete Fourier transform. Different resistivity of the oil and oil-immersed paper is adopted to simulate the aging of oil paper insulation at operation, and get the non-sinusoidal steady electric field.
文摘The surface insulation properties of insulating material under DC voltage are closely related to the characteristics of surface charge accumulation, and the surface roughness of these materials has a direct impact on the surface charge distribution in vacuum. Therefore, it is significant to study their connection. In this paper, based on the secondary electron emission avalanche model, the surface charge accumulation on polymethyl methacrylate (PMMA) with different surface roughness was simulated by using particle in cell and Monte Carlo Collision method. The simulated environment was under the finger shaped electrode and in vacuum. The results showed that under the action of the electric field the electrons emitted from the cathode triple junction moved forward and collided with the insulating material, which may lead to the generation of secondary electrons or the accumulation of surface charge. The surface charge near the cathode was mostly negative since the effect of surface electron injection was greater than that of the collision ionization. Due to the change of electron energy and the influence of electric field distribution, the number of positive charge on the insulator gradually increased, reached the maximum, and then gradually reduced with the approaching of the anode. Moreover, when the surface roughness of the material increases or the secondary electron emission coefficient decreases, the amount of surface charge accumulated on the PMMA will reduce. This paper can provide some guidance for the practical application of insulating materials.
基金supported by State Grid Hebei Electric Power Co.,Ltd.(kj2020-040).
文摘Aiming at the problem of abnormal data generated by a power transformer on-line monitoring system due to the influences of transformer operation state change,external environmental interference,communication interruption,and other factors,a method of anomaly recognition and differentiation for monitoring data was proposed.Firstly,the empirical wavelet transform(EWT)and the autoregressive integrated moving average(ARIMA)model were used for time series modelling of monitoring data to obtain the residual sequence reflecting the anomaly monitoring data value,and then the isolation forest algorithm was used to identify the abnormal information,and the monitoring sequence was segmented according to the recognition results.Secondly,the segmented sequence was symbolised by the improved multi-dimensional SAX vector representation method,and the assessment of the anomaly pattern was made by calculating the similarity score of the adjacent symbol vectors,and the monitoring sequence correlation was further used to verify the assessment.Finally,the case study result shows that the proposed method can reliably recognise abnormal data and accurately distinguish between invalid and valid anomaly patterns.
基金National Natural Science Foundation of China,Grant/Award Number:52007065Fundamental Research Funds for the Central Universities,Grant/Award Number:2022MS071。
文摘Fibre-reinforced polymer(FRP)/rigid polyurethane foam(RPUF)interface is susceptible to moisture intrusion in addition to natural ageing during operation.This study investigated the influence of moisture intrusion on the FRP/RPUF interface under natural ageing using experiments and molecular dynamics(MD)simulations.Water absorption,shear strength,and leakage current tests were used to clarify the changes in the interface performance.The degradation mechanism of moisture intrusion at the interface under natural ageing was revealed by MD simulation and micro-characterisation.The results show that the natural ageing of interfacial materials will slightly reduce the quality of the interface but will reduce the water resistance of the material and promote the process of water intrusion into the interface.In addition,water mainly invades the interface through RPUF.After water penetration,the interfacial bonding strength and insulation performance significantly decreased.Plasticisation and hydrolysis of interfacial materials are the main reasons for decreased interfacial adhesion.Hydrolysis can cause irreversible damage to the interface,increasing interface defects and water absorption.The vicious cycle of material hydrolysis is the ultimate cause of interfacial debonding.The polar molecules produced by this process and the water absorbed by the interface caused the degradation of the interface insulation performance.
基金supported by the Natural Science Foundation of Hebei Province(No.E2021502025)。
文摘Establishing a long air gap discharge model considering the streamer-leader transition and randomness of the discharge path is of great signiflcance to improve the accuracy of discharge characteristic prediction and optimize external insulation design.Based on fractal theory and thermal ionization theory of streamer-leader transition,this work establishes a dynamic development model for the long air gap discharge streamer-leader system,which includes streamer inception,streamer development,leader inception,development of streamer-leader system and flnal jump.The positive discharge process of a 3 m rod plate is simulated to obtain the fractal distribution of the discharge path and the law of leader development for comparison with the discharge test results.The results show that the simulation model is similar to test results in the development characteristics of leader path distribution,each stage time and leader velocity.Finally,a simulation calculation of a 50%breakdown voltage of the rod-plate gap and ball-plate gap is carried out,with results fairly consistent with test data,proving the effectiveness and practicality of the model.
基金supported by the National Natural Science Foundation of China(51577069)the Fundamental Research Funds for the Central Universities(2015ZD19)the Headquarters Science and Technology Project of State Grid Corporation of China(SGTYHT/17-JS-199).
文摘With the development of a smart grid,the automatic location of power equipment is becoming a trend.In this study,a method for automatic location identification and diagnosis of external power insulation equipment based on YOLOv3 is proposed.This deep learning algorithm is used to extract the characteristics of image data under the visible light channel of the insulator.It learns and trains the collected data to realise the rapid location identification and frame selection of the external insulation equipment and extract discharge characteristics of the target box under the ultraviolet channel.According to the number of photons and the spot area information,the operating status of the equipment is determined.The results show that the YOLOv3 algorithm with a training rate of 0.005 achieved a fast convergence of the location recognition model.The average recognition accuracy was 88.7%and the average detection time was 0.0182 s.The combination of visible light path insulator target recognition and ultraviolet light path diagnosis can realise a lean and intelligent diagnosis of power equipment.This method had good real-time performance,accuracy,and robustness to the background.It provides a new concept for intelligent diagnosis and location analysis of power equipment.
文摘The roof arrester of electric multiple units(EMU)can efficiently limit the overvoltage,and ensure the safe operation of the EMU electrical equipment.In the process of high‐speed operation,the traction power supply system is often affected by overvoltage.In addition,roof arrester explosion accidents occasionally occur.In this paper,the on‐line voltage measurement system of the EMU arrester is developed.By analysing a large number of voltage waveforms,the abnormal voltage is divided into three categories:over‐phase voltage,high harmonic voltage and steep impulse overvoltage.The charac-teristics of abnormal voltage waveforms are then summarised.The electrothermal coupling simulation model of the arrester is developed,and the current response and temperature distribution of the arrester under abnormal voltage are calculated.The impact of the impulse voltage energy on the arrester temperature is studied by applying a triangular wave voltage to the model.Finally,some suggestions are proposed for the operation and maintenance of the roof arrester.
