Arc grounding faults occur frequently in the power grid with small resistance grounding neutral points.The existing arc fault identification technology only uses the fault line signal characteristics to set the identi...Arc grounding faults occur frequently in the power grid with small resistance grounding neutral points.The existing arc fault identification technology only uses the fault line signal characteristics to set the identification index,which leads to detection failure when the arc zero-off characteristic is short.To solve this problem,this paper presents an arc fault identification method by utilizing integrated signal characteristics of both the fault line and sound lines.Firstly,the waveform characteristics of the fault line and sound lines under an arc grounding fault are studied.After that,the convex hull,gradient product,and correlation coefficient index are used as the basic characteristic parameters to establish fault identification criteria.Then,the logistic regression algorithm is employed to deal with the reference samples,establish the machine discrimination model,and realize the discrimination of fault types.Finally,simulation test results and experimental results verify the accuracy of the proposed method.The comparison analysis shows that the proposed method has higher recognition accuracy,especially when the arc dissipation power is smaller than 2×10^(3) W,the zero-off period is not obvious.In conclusion,the proposed method expands the arc fault identification theory.展开更多
The reconstruction of emission coefficient is a key factor for the calculation of temperature field.However,most of the researches for determining arc plasmas are based on axisymmetric sources,little has been done to ...The reconstruction of emission coefficient is a key factor for the calculation of temperature field.However,most of the researches for determining arc plasmas are based on axisymmetric sources,little has been done to study non-axisymmetric arc plasmas.In order to reveal temperatures of a non-axisymmetric coupling arc,the distribution of emission coefficients must be reconstructed in advance.In this paper,the argon atomic line intensities of the coupling arc are obtained by using the imaging system that involves a high speed camera in conjunction with a neutral and a narrow-band filter.The converted programme between emission coefficients and emitted intensities is programmed based on MALDONADO＇s method.A displaced Gaussian model is used for evaluating the validity of the converted programme.Then,the emission coefficients of a free burning arc are reconstructed by MALDONADO＇s method and an Abel inversion,respectively,and good agreement is obtained.Finally,the emission coefficient profiles of the coupling arc are achieved.The results show that the distribution of emission coefficient for the coupling arc is non-axisymmetric.The emission coefficient profile is similar to an ellipse,and the short axis of the ellipse is in the direction that the two electrodes are arranged along.The peak temperature of the coupling arc is in the middle of both electrodes.There is a strong interaction between both arcs within the coupling arc.The proposed research solves difficulties for determining asymmetric arcs and enlarges the application scope of spectroscopic techniques.展开更多
Multilayered TiAlN/CrN coatings have been synthesized on stainless steel substrates by cathodic arc plasma deposition using TiAl and Cr targets.Influences of the bias voltage,cathode current ratio ITiAl/ICr,and deposi...Multilayered TiAlN/CrN coatings have been synthesized on stainless steel substrates by cathodic arc plasma deposition using TiAl and Cr targets.Influences of the bias voltage,cathode current ratio ITiAl/ICr,and deposition pressure on the hardness and friction coefficient of the coatings were investigated.The measurement revealed existence of two cubic phases,face-centercubic （Cr,Al）N and（Ti,Al）N,in the coatings deposited under various bias voltages except for the coating deposited at -400 V,which is amorphous.The hardness of the coatings was strongly dependent on the Itial/Icr ratio and deposition pressure,and reached a maximum of 33 GPa at an ITiAI/ICr ratio of 1.0 and a pressure of 1.0 Pa.The incorporation of the element chromium can reduce the density of pinholes in the coatings and assist the optimization of deposition conditions for high quality TiAlN/CrN coatings.展开更多
Cogging torque and electromagnetic vibration are two important factors for evaluating permanent magnet synchronous machine(PMSM)and are key issues that must be considered and resolved in the design and manufacture of ...Cogging torque and electromagnetic vibration are two important factors for evaluating permanent magnet synchronous machine(PMSM)and are key issues that must be considered and resolved in the design and manufacture of high-performance PMSM for electric vehicles.A fast and accurate magnetic field calculation model for interior permanent magnet synchronous machine(IPMSM)is proposed in this article.Based on the traditional magnetic potential permeance method,the stator cogging effect and complex boundary conditions of the IPMSM can be fully considered in this model,so as to realize the rapid calculation of equivalent magnetomotive force(MMF),air gap permeance,and other key electromagnetic properties.In this article,a 6-pole 36-slot IPMSM is taken as an example to establish its equivalent solution model,thereby the cogging torque is accurately calculated.And the validity of this model is verified by a variety of different magnetic pole structures,pole slot combinations machines,and prototype experiments.In addition,the improvement measure of the machine with different combination of pole arc coefficient is also studied based on this model.Cogging torque and electromagnetic vibration can be effectively weakened.Combined with the finite element model and multi-physics coupling model,the electromagnetic characteristics and vibration performance of this machine are comprehensively compared and analyzed.The analysis results have well verified its effectiveness.It can be extended to other structures or types of PMSM and has very important practical value and research significance.展开更多
TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating（CAIP）. The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning elect...TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating（CAIP）. The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning electron microscopy（FESEM） and X-ray diffraction（XRD）, respectively, and the morphologies, distributions of chemical elements and profiles of worn tracks were also researched using scanning electron microscopy（SEM）, energy disperse spectroscopy（EDS）, and optical microscope（OM）, respectively. The friction-wear performances of TiAlSiN coating under oil lubricated and dry fiction conditions were investigated, and the wear mechanisms of TiAlSiN coating were discussed. The experimental results show that the coating is primarily composed of（Ti, Al）N, AlTiN, and TiN hard phases, Si_3N_4 exists between the（Ti, Al）N crystal grains, increasing the coating microhardness to 3200 HV. The TiAlSiN coating has excellent performances of reducing friction and wear resistance, the average coefficient of friction（COF） of TiAlSiN coating under oil lubricated condition is only 0.05, lowered than the average COF of 0.211 under dry friction condition, the wear rate decreases by about 81.2% compared with that under dry friction condition. The wear mechanism of TiAlSiN coating under oil lubricated and dry friction conditions is composed of abrasive wear, fatigue wear, and abrasive wear, respectively. The internal friction of oil lubrication is a main factor of decreasing fatigue wear.展开更多
The TiN/Ni composite coatings were deposited on 7005 aluminium alloy by high speed jet electroplating and then processed with plasma transferred arc(PTA)scanning process.The microstructure,microhardness and friction c...The TiN/Ni composite coatings were deposited on 7005 aluminium alloy by high speed jet electroplating and then processed with plasma transferred arc(PTA)scanning process.The microstructure,microhardness and friction coefficient of PTA scanning treated specimens were investigated.It is shown that the PTA scanning treated specimens have a rapidly solidified microstructure consisting of the uniformly distributed TiN phase and fine Al3Ni2 intermetallic phases.The composite coating has an average microhardness of approximately HV 800.The friction coefficient of PTA scanning treated specimens(oscillated at around 0.25)is considerably lower than that of TiN/Ni composite coating(oscillated at around 0.35).The corrosion behavior of the composite coating in 3.5%NaCl solution at room temperature was also determined using a potentiostat system.In comparison with the corrosion potentialφcorr of-0.753 V for 7005 aluminium alloy,the corrosion potentials for TiN/Ti composite coating and PTA scanning treated specimen are increased by 0.148 V and 0.305 V,respectively.The PTA scanning treated specimen has the lowest corrosion current density Jcorr as well as the highest corrosion potentialφcorr,showing an improved corrosion resistance compared with 7005 aluminium alloy.展开更多
With advantages of high specific strength, low elastic module, good damping property et al., the magnesium alloys exhibit great potential applications in aerospace. But poor wear behavior results in limited use of mag...With advantages of high specific strength, low elastic module, good damping property et al., the magnesium alloys exhibit great potential applications in aerospace. But poor wear behavior results in limited use of magnesium alloy to static components. In this study, a 2 μm thick coating with 12 sub-layers of CrN and TiN is deposited alternately on the surface of magnesium alloy AZ91 by a novel method of arc-glow plasma depositing to improve its wear resistance. The composition and microstructure of the coating layer are analyzed by means of SEM, XRD and GDS. The friction coefficient is measured by ball on disc rubbing test, and the wear rates are also calculated. The results indicate that the friction coefficient is increased, but the wear rate is dropped sharply as compared with bare metal. The surface hardness is about HK0.01 1400.展开更多
Based on the wave radiation and diffraction theory, this paper investigates a new type breakwater with upper arcshaped plate by using the boundary element method(BEM). By comparing with other three designs of plate ty...Based on the wave radiation and diffraction theory, this paper investigates a new type breakwater with upper arcshaped plate by using the boundary element method(BEM). By comparing with other three designs of plate type breakwater(lower arc-shaped plate, single horizontal plate and double horizontal plate), this new type breakwater has been proved more effective. The wave exiting force, transmission and reflection coefficients are analyzed and discussed. In order to reveal the wave elimination mechanism of this type of breakwater, the velocity field around the breakwater is obtained. It is shown that:(1) The sway exciting force is minimal.(2) When the ratio of the submergence and wave amplitude is 0.05, the wave elimination effect will increase by 50% compared with other three types of breakwater.(3) The obvious backflow is found above the plate in the velocity field analysis.展开更多
The rate of electrification in rural areas in Zambia is very low, currently standing at less than 5% despite having abundant flowing water resources. Hydrokinetic technology is an alternative among other promising tec...The rate of electrification in rural areas in Zambia is very low, currently standing at less than 5% despite having abundant flowing water resources. Hydrokinetic technology is an alternative among other promising technologies for rural area electrification because of availability of abundant flowing Rivers and low population in rural settlement. In this paper, the author designed and numerically simulated a circular arc blade hydrokinetic turbine system. The design power for the horizontal axis hydrokinetic turbine was 3 kW at water velocity of 3 m/s with the tip speed ratio of 2.5, angle of attack of 10 degrees and power coefficient of 0.4. In this work, a numerical simulation was employed to characterize and develop the horizontal axis hydrokinetic turbine. The prototype circular arc blade horizontal axis hydrokinetic turbine was tested in one of stream in Zambia and the results were compared with the numerical simulation results.展开更多
Cold metal transfer with polarity⁃exchanging is a new integrated welding technology based on MIG.Due to the alternation of the positive and negative polarities of the wire,favorable control upon the deposition rate an...Cold metal transfer with polarity⁃exchanging is a new integrated welding technology based on MIG.Due to the alternation of the positive and negative polarities of the wire,favorable control upon the deposition rate and the welding shape coefficient was obtained in order to meet the desired joint design,and the related controlling principles and joint characteristics were reported.Droplet transfer physical behavior exhibited strong dependability on the studied welding parameters,such as welding voltage,welding current,wire feeding speed,and polarity⁃exchanging.This welding technology provides a new way for the welding of body⁃in⁃white(BIW)thin sheet with special demands.Moreover,the typical quality defects of MIG were greatly improved.Our study provides important technical information from the perspective of industrial application of MIG and sheds light on the higher application level of MIG in BIW welding.展开更多
基金This work was supported in part by the Natural Science Foundation of Henan Province,and the specific grant number is 232300420301。
文摘Arc grounding faults occur frequently in the power grid with small resistance grounding neutral points.The existing arc fault identification technology only uses the fault line signal characteristics to set the identification index,which leads to detection failure when the arc zero-off characteristic is short.To solve this problem,this paper presents an arc fault identification method by utilizing integrated signal characteristics of both the fault line and sound lines.Firstly,the waveform characteristics of the fault line and sound lines under an arc grounding fault are studied.After that,the convex hull,gradient product,and correlation coefficient index are used as the basic characteristic parameters to establish fault identification criteria.Then,the logistic regression algorithm is employed to deal with the reference samples,establish the machine discrimination model,and realize the discrimination of fault types.Finally,simulation test results and experimental results verify the accuracy of the proposed method.The comparison analysis shows that the proposed method has higher recognition accuracy,especially when the arc dissipation power is smaller than 2×10^(3) W,the zero-off period is not obvious.In conclusion,the proposed method expands the arc fault identification theory.
基金supported by National Natural Science Foundation of China (Grant Nos. 51175119,50775053)
文摘The reconstruction of emission coefficient is a key factor for the calculation of temperature field.However,most of the researches for determining arc plasmas are based on axisymmetric sources,little has been done to study non-axisymmetric arc plasmas.In order to reveal temperatures of a non-axisymmetric coupling arc,the distribution of emission coefficients must be reconstructed in advance.In this paper,the argon atomic line intensities of the coupling arc are obtained by using the imaging system that involves a high speed camera in conjunction with a neutral and a narrow-band filter.The converted programme between emission coefficients and emitted intensities is programmed based on MALDONADO＇s method.A displaced Gaussian model is used for evaluating the validity of the converted programme.Then,the emission coefficients of a free burning arc are reconstructed by MALDONADO＇s method and an Abel inversion,respectively,and good agreement is obtained.Finally,the emission coefficient profiles of the coupling arc are achieved.The results show that the distribution of emission coefficient for the coupling arc is non-axisymmetric.The emission coefficient profile is similar to an ellipse,and the short axis of the ellipse is in the direction that the two electrodes are arranged along.The peak temperature of the coupling arc is in the middle of both electrodes.There is a strong interaction between both arcs within the coupling arc.The proposed research solves difficulties for determining asymmetric arcs and enlarges the application scope of spectroscopic techniques.
基金supported by the Ministry of Industry and Information Technology of China(No.2009ZX04012-32)the International Cooperation Program of Ministry of Science and Technology of China(No.2011DFR50580)
文摘Multilayered TiAlN/CrN coatings have been synthesized on stainless steel substrates by cathodic arc plasma deposition using TiAl and Cr targets.Influences of the bias voltage,cathode current ratio ITiAl/ICr,and deposition pressure on the hardness and friction coefficient of the coatings were investigated.The measurement revealed existence of two cubic phases,face-centercubic （Cr,Al）N and（Ti,Al）N,in the coatings deposited under various bias voltages except for the coating deposited at -400 V,which is amorphous.The hardness of the coatings was strongly dependent on the Itial/Icr ratio and deposition pressure,and reached a maximum of 33 GPa at an ITiAI/ICr ratio of 1.0 and a pressure of 1.0 Pa.The incorporation of the element chromium can reduce the density of pinholes in the coatings and assist the optimization of deposition conditions for high quality TiAlN/CrN coatings.
基金supported in part by the National Natural Science Foundation of China under Grant 51737008.
文摘Cogging torque and electromagnetic vibration are two important factors for evaluating permanent magnet synchronous machine(PMSM)and are key issues that must be considered and resolved in the design and manufacture of high-performance PMSM for electric vehicles.A fast and accurate magnetic field calculation model for interior permanent magnet synchronous machine(IPMSM)is proposed in this article.Based on the traditional magnetic potential permeance method,the stator cogging effect and complex boundary conditions of the IPMSM can be fully considered in this model,so as to realize the rapid calculation of equivalent magnetomotive force(MMF),air gap permeance,and other key electromagnetic properties.In this article,a 6-pole 36-slot IPMSM is taken as an example to establish its equivalent solution model,thereby the cogging torque is accurately calculated.And the validity of this model is verified by a variety of different magnetic pole structures,pole slot combinations machines,and prototype experiments.In addition,the improvement measure of the machine with different combination of pole arc coefficient is also studied based on this model.Cogging torque and electromagnetic vibration can be effectively weakened.Combined with the finite element model and multi-physics coupling model,the electromagnetic characteristics and vibration performance of this machine are comprehensively compared and analyzed.The analysis results have well verified its effectiveness.It can be extended to other structures or types of PMSM and has very important practical value and research significance.
基金Funded by the Jiangsu Province Science and Technology Support Program(Industry)(BE2014865)
文摘TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating（CAIP）. The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning electron microscopy（FESEM） and X-ray diffraction（XRD）, respectively, and the morphologies, distributions of chemical elements and profiles of worn tracks were also researched using scanning electron microscopy（SEM）, energy disperse spectroscopy（EDS）, and optical microscope（OM）, respectively. The friction-wear performances of TiAlSiN coating under oil lubricated and dry fiction conditions were investigated, and the wear mechanisms of TiAlSiN coating were discussed. The experimental results show that the coating is primarily composed of（Ti, Al）N, AlTiN, and TiN hard phases, Si_3N_4 exists between the（Ti, Al）N crystal grains, increasing the coating microhardness to 3200 HV. The TiAlSiN coating has excellent performances of reducing friction and wear resistance, the average coefficient of friction（COF） of TiAlSiN coating under oil lubricated condition is only 0.05, lowered than the average COF of 0.211 under dry friction condition, the wear rate decreases by about 81.2% compared with that under dry friction condition. The wear mechanism of TiAlSiN coating under oil lubricated and dry friction conditions is composed of abrasive wear, fatigue wear, and abrasive wear, respectively. The internal friction of oil lubrication is a main factor of decreasing fatigue wear.
基金Project(0852nm01400)supported by Shanghai Municipal Developing Foundation of Science and Technology,ChinaProject(XK0706)supported by the Leading Academic Discipline of Shanghai Education Commission,China
文摘The TiN/Ni composite coatings were deposited on 7005 aluminium alloy by high speed jet electroplating and then processed with plasma transferred arc(PTA)scanning process.The microstructure,microhardness and friction coefficient of PTA scanning treated specimens were investigated.It is shown that the PTA scanning treated specimens have a rapidly solidified microstructure consisting of the uniformly distributed TiN phase and fine Al3Ni2 intermetallic phases.The composite coating has an average microhardness of approximately HV 800.The friction coefficient of PTA scanning treated specimens(oscillated at around 0.25)is considerably lower than that of TiN/Ni composite coating(oscillated at around 0.35).The corrosion behavior of the composite coating in 3.5%NaCl solution at room temperature was also determined using a potentiostat system.In comparison with the corrosion potentialφcorr of-0.753 V for 7005 aluminium alloy,the corrosion potentials for TiN/Ti composite coating and PTA scanning treated specimen are increased by 0.148 V and 0.305 V,respectively.The PTA scanning treated specimen has the lowest corrosion current density Jcorr as well as the highest corrosion potentialφcorr,showing an improved corrosion resistance compared with 7005 aluminium alloy.
基金Science foundation of Shanxi province, China (20041065)
文摘With advantages of high specific strength, low elastic module, good damping property et al., the magnesium alloys exhibit great potential applications in aerospace. But poor wear behavior results in limited use of magnesium alloy to static components. In this study, a 2 μm thick coating with 12 sub-layers of CrN and TiN is deposited alternately on the surface of magnesium alloy AZ91 by a novel method of arc-glow plasma depositing to improve its wear resistance. The composition and microstructure of the coating layer are analyzed by means of SEM, XRD and GDS. The friction coefficient is measured by ball on disc rubbing test, and the wear rates are also calculated. The results indicate that the friction coefficient is increased, but the wear rate is dropped sharply as compared with bare metal. The surface hardness is about HK0.01 1400.
基金financially supported by the National Key Basic Research Program of China(Grant No.2013CB036101)the National Natural Science Foundation of China(Grant No.11702054)
文摘Based on the wave radiation and diffraction theory, this paper investigates a new type breakwater with upper arcshaped plate by using the boundary element method(BEM). By comparing with other three designs of plate type breakwater(lower arc-shaped plate, single horizontal plate and double horizontal plate), this new type breakwater has been proved more effective. The wave exiting force, transmission and reflection coefficients are analyzed and discussed. In order to reveal the wave elimination mechanism of this type of breakwater, the velocity field around the breakwater is obtained. It is shown that:(1) The sway exciting force is minimal.(2) When the ratio of the submergence and wave amplitude is 0.05, the wave elimination effect will increase by 50% compared with other three types of breakwater.(3) The obvious backflow is found above the plate in the velocity field analysis.
文摘The rate of electrification in rural areas in Zambia is very low, currently standing at less than 5% despite having abundant flowing water resources. Hydrokinetic technology is an alternative among other promising technologies for rural area electrification because of availability of abundant flowing Rivers and low population in rural settlement. In this paper, the author designed and numerically simulated a circular arc blade hydrokinetic turbine system. The design power for the horizontal axis hydrokinetic turbine was 3 kW at water velocity of 3 m/s with the tip speed ratio of 2.5, angle of attack of 10 degrees and power coefficient of 0.4. In this work, a numerical simulation was employed to characterize and develop the horizontal axis hydrokinetic turbine. The prototype circular arc blade horizontal axis hydrokinetic turbine was tested in one of stream in Zambia and the results were compared with the numerical simulation results.
文摘Cold metal transfer with polarity⁃exchanging is a new integrated welding technology based on MIG.Due to the alternation of the positive and negative polarities of the wire,favorable control upon the deposition rate and the welding shape coefficient was obtained in order to meet the desired joint design,and the related controlling principles and joint characteristics were reported.Droplet transfer physical behavior exhibited strong dependability on the studied welding parameters,such as welding voltage,welding current,wire feeding speed,and polarity⁃exchanging.This welding technology provides a new way for the welding of body⁃in⁃white(BIW)thin sheet with special demands.Moreover,the typical quality defects of MIG were greatly improved.Our study provides important technical information from the perspective of industrial application of MIG and sheds light on the higher application level of MIG in BIW welding.
