This paper has researched the insulation characteristics of 10% c-C4F8/N2/CO2 mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of ...This paper has researched the insulation characteristics of 10% c-C4F8/N2/CO2 mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C4F8/N2/CO2 gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF6 and the comprehensive GWP is about 5% of SF6, and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF6, 10%c-C4F8/N2/CO2 gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.展开更多
This paper presents an approach to accurately forecast the yearly occurrence of flashovers caused by lightning-induced voltage in overhead power lines in the presence of layered ground.The aim is to improve the accura...This paper presents an approach to accurately forecast the yearly occurrence of flashovers caused by lightning-induced voltage in overhead power lines in the presence of layered ground.The aim is to improve the accuracy of flashover rate estimation by using the insulator volt-time model.In particular,two-layer horizontal ground structures are considered.A 3D finite element method is used to calculate induced voltages and a Monte Carlo simulation is applied to determine the annual flashover rate.Volt-time insulator characteristics are used to identify the flashover condition.The results are compared with those obtained by using the standard 1.5 times the critical flashover(CFO)threshold criterion.The results indicate that the conventional 1.5 times the CFO criterion may underestimate the rate of flashovers,particularly in regions with horizon-tally stratified soil,as the volt-time method offers a more accurate presentation of the flashover process.Furthermore,the effect of upper soil depth,upper soil conductivity,pole spacing,and different flashover distance calculation techniques on flashover rates are analysed.This paper presents a new mathematical formula for estimating yearly flash-overs based on the results obtained by the volt-time method in the presence of stratified ground.The derived analytical formula provides an insightful tool for power system engineers to evaluate the lightning performance of overhead lines and implement efficient mitigation strategies.展开更多
The electron swarm parameters including the density-normalized effective ionization coefficients（α-η）/N and the electron drift velocities V e are calculated for a gas mixture of CF3I with N2 and CO2 by solving the...The electron swarm parameters including the density-normalized effective ionization coefficients（α-η）/N and the electron drift velocities V e are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend（SST） experiment.The overall density-reduced electric field strength is from 100 Td to 1000 Td（1 Td = 10-17V·cm2）,while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%.From the variation of（αη）/N with the CF3I mixture ratio k,the limiting field strength（E/N） lim for each CF3I concentration is derived.It is found that for the mixtures with 70% CF3I,the values of（E/N） lim are essentially the same as that for pure SF 6.Additionally,the global warming potential（GWP） and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.展开更多
The performance of polypropylene film determines the reliability of capacitors.This paper studies the change of insulation characteristics of the insulation dielectric polypropylene of high-voltage capacitors during t...The performance of polypropylene film determines the reliability of capacitors.This paper studies the change of insulation characteristics of the insulation dielectric polypropylene of high-voltage capacitors during the long-term operation process.Moreover,the correction of the insulation failure model of polypropylene media is implemented.Some conclusions are drawn from a series of experiments.The breakdown strength of the insulation dielectrics decreases as the withstand time rises,with amaximum decrease of 37.91%compared to the polypropylene sample without withstand voltage.As the electric field increases from−20 to−100 kV/mm,the total amount of space charge,the trap energy level and the trap density inside the polypropylene increase by 524.15%,18.99%and 773.36%,respectively.In the capacitor simulation model,the electric field in the capacitor increases by 19.62%after presetting space charge relative to the nonspace charge.The experimental data are substituted into the inverse power model,and the trap parameters are used to modify the model.The results show that the ageing state of the polypropylene has a negative exponential relationship with the trap parameters.This paper provides an important reference for the study of the failure mechanism of polypropylene in high-voltage capacitors and the assessment of polypropylene ageing state.展开更多
Layered epoxy/paper composites that exhibit excellent insulating characteristics under elevated electrification and temperature conditions are essential components for power system insulation.Yet,inevitable charge acc...Layered epoxy/paper composites that exhibit excellent insulating characteristics under elevated electrification and temperature conditions are essential components for power system insulation.Yet,inevitable charge accumulation occurs at hetero interfaces between layers due to interfacial polarisation and interface barrier effect,bringing about local electric field distortion and potential risk of partial discharge.A fundamental challenge is either to obtain accurate interface charge behaviours of in-service multi-layer insulating composites,or to construct verified simulating models for replacing experiments.Herein,a modified bipolar charge transport model to simulate interface charge behaviours in layered composites is proposed.With model parameters directly originated from equivalent experiments(e.g.conduction current measurement,thermally stimulated depolarisation current testing,and ultraviolet-visible spectroscopy)of epoxy/paper composites,the simulated temperature-dependent interface charge characteristics match well with pulsed electro-acoustic results.Furthermore,electrical thresholds can also be accurately calculated using such models(maximum deviation of 8.44%from experimental results),providing references for optimised insulation structural design.展开更多
基金supported by National Natural Science Foundation of China (No. 51337006)
文摘This paper has researched the insulation characteristics of 10% c-C4F8/N2/CO2 mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C4F8/N2/CO2 gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF6 and the comprehensive GWP is about 5% of SF6, and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF6, 10%c-C4F8/N2/CO2 gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.
文摘This paper presents an approach to accurately forecast the yearly occurrence of flashovers caused by lightning-induced voltage in overhead power lines in the presence of layered ground.The aim is to improve the accuracy of flashover rate estimation by using the insulator volt-time model.In particular,two-layer horizontal ground structures are considered.A 3D finite element method is used to calculate induced voltages and a Monte Carlo simulation is applied to determine the annual flashover rate.Volt-time insulator characteristics are used to identify the flashover condition.The results are compared with those obtained by using the standard 1.5 times the critical flashover(CFO)threshold criterion.The results indicate that the conventional 1.5 times the CFO criterion may underestimate the rate of flashovers,particularly in regions with horizon-tally stratified soil,as the volt-time method offers a more accurate presentation of the flashover process.Furthermore,the effect of upper soil depth,upper soil conductivity,pole spacing,and different flashover distance calculation techniques on flashover rates are analysed.This paper presents a new mathematical formula for estimating yearly flash-overs based on the results obtained by the volt-time method in the presence of stratified ground.The derived analytical formula provides an insightful tool for power system engineers to evaluate the lightning performance of overhead lines and implement efficient mitigation strategies.
基金Project supported by the National Natural Science Foundation of China (Grant No. 51177101)
文摘The electron swarm parameters including the density-normalized effective ionization coefficients（α-η）/N and the electron drift velocities V e are calculated for a gas mixture of CF3I with N2 and CO2 by solving the Boltzmann equation in the condition of a steady-state Townsend（SST） experiment.The overall density-reduced electric field strength is from 100 Td to 1000 Td（1 Td = 10-17V·cm2）,while the CF3I content k in the gas mixture can be varied over the range from 0% to 100%.From the variation of（αη）/N with the CF3I mixture ratio k,the limiting field strength（E/N） lim for each CF3I concentration is derived.It is found that for the mixtures with 70% CF3I,the values of（E/N） lim are essentially the same as that for pure SF 6.Additionally,the global warming potential（GWP） and the liquefaction temperature of the gas mixtures are also taken into account to evaluate the possibility of application in the gas insulation of power equipment.
基金supported in part by the National Natural Science Foundation of China(Grant 52277153).
文摘The performance of polypropylene film determines the reliability of capacitors.This paper studies the change of insulation characteristics of the insulation dielectric polypropylene of high-voltage capacitors during the long-term operation process.Moreover,the correction of the insulation failure model of polypropylene media is implemented.Some conclusions are drawn from a series of experiments.The breakdown strength of the insulation dielectrics decreases as the withstand time rises,with amaximum decrease of 37.91%compared to the polypropylene sample without withstand voltage.As the electric field increases from−20 to−100 kV/mm,the total amount of space charge,the trap energy level and the trap density inside the polypropylene increase by 524.15%,18.99%and 773.36%,respectively.In the capacitor simulation model,the electric field in the capacitor increases by 19.62%after presetting space charge relative to the nonspace charge.The experimental data are substituted into the inverse power model,and the trap parameters are used to modify the model.The results show that the ageing state of the polypropylene has a negative exponential relationship with the trap parameters.This paper provides an important reference for the study of the failure mechanism of polypropylene in high-voltage capacitors and the assessment of polypropylene ageing state.
基金Science and Technology Project of State Grid Corporation of China,Grant/Award Number:SGLNDK00KJJS1900250。
文摘Layered epoxy/paper composites that exhibit excellent insulating characteristics under elevated electrification and temperature conditions are essential components for power system insulation.Yet,inevitable charge accumulation occurs at hetero interfaces between layers due to interfacial polarisation and interface barrier effect,bringing about local electric field distortion and potential risk of partial discharge.A fundamental challenge is either to obtain accurate interface charge behaviours of in-service multi-layer insulating composites,or to construct verified simulating models for replacing experiments.Herein,a modified bipolar charge transport model to simulate interface charge behaviours in layered composites is proposed.With model parameters directly originated from equivalent experiments(e.g.conduction current measurement,thermally stimulated depolarisation current testing,and ultraviolet-visible spectroscopy)of epoxy/paper composites,the simulated temperature-dependent interface charge characteristics match well with pulsed electro-acoustic results.Furthermore,electrical thresholds can also be accurately calculated using such models(maximum deviation of 8.44%from experimental results),providing references for optimised insulation structural design.
