电晕放电脉冲电流波形和相位分布的测量、分析与仿真(英文)

Partial discharge(PD) is one of the most important phenomenon in high voltage insulations.In most cases, the appearance of partial discharges is related to insulation defects.Understanding partial discharges is important for diagnosis on insulation condition.Corona discharges appear when extremely high electric field appears on the conductor surface exceeding the electric field strength of the gas.The high electric field may occur at around protrusion with very sharp tip.This paper reported a holistic approach of corona discharge investigation.The needle-plane electrode system was used.The medium between the electrodes was air.The needle was made from steel with radius of curvature of 3μm(Ogura needle).Sinusoidal as well as triangular applied voltages were used.The waveform of the corona discharges was measured using a digital oscilloscope.The corona discharge pulses were measured using a phase-resolved PD measurement system.The system was able to measure the magnitude(q) and phase angle position(φ) of each PD pulses,as well as the number of discharge pulses(n).The role of applied voltage was investigated using phase-resolved analysis of corona discharge pulses through pulse sequence,pulse magnitude and pulse number analysis. Experimental results indicated that corona discharge current waveform was an impulse with rise time of about several ns and the impulse width of about 100 ns.The Fast Fourier Transform analysis indicated that the corona discharge current waveform had several spectrum peaks at frequency of 7.8 MHz,85.9 MHz,109.4 MHz and 195.3 MHz.The experimental results also showed that discharge pulses were concentrated around the peak of applied voltage for both sinusoidal and triangular voltages.The discharge magnitude,as well as its probability of occurrence,was strongly dependent on the instantaneous applied voltage.The shape ofφ-n,as well asφ-q-n PD patterns,were strongly reflected by the shape of applied voltage.In order to get deep understanding of the corona discharge,by utilizing results of the phase-resolved analysis,electrical equivalent circuits of corona discharges were proposed.The electrical equivalent circuit contained capacitances and a spark gap.For deeply understanding of PD phenomenon,computer simulation was done by using the proposed electrical equivalent circuits.The similarity of the measured and simulated PD patterns was assessed by comparing measured and simulated theφ-q-n andφ-n PD patterns.The results indicated that simulated PD patterns similar to those obtained from experiment.     

空气中电晕放电与绝缘液体中流注放电的测量和分析

Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.     

气压对发电机定子线棒端部电晕放电特性的影响(英文)

According to the mechanism of corona discharge at the end of the generator stator bar,a model of stator bar end corona discharge is presented.In a closed corona cage at low atmospheric pressure,the corona discharge characteristics of the stator bar end model were observed using an ultraviolet imaging instrument and an oscilloscope.The influence of atmospheric pressure on the corona inception voltage and discharge intensity was analyzed.The results show that the corona inception voltage is lower under lower atmospheric pressure;the discharge intensity is stronger under lower atmospheric pressure.The particles swarm-optimized support vector machine was employed to analyze the impacts of air pressure and humidity on the corona inception voltage.Error between the calculated value of the established model and the experimental value is less than 5%.The established model can be used to calculate the corona inception voltage of the stator bar end model.     

高压下非均匀电场中局放机理的建模

Partial discharges in air in non-uniform electric field occur in surroundings made of high curvature elements.The equivalent electrode system,needle-plane refers both to external components of high voltage insulating systems and to micro sharpness in the internal structure of those systems.The ionization zone,accumulation of space charge and formation of corresponding current pulses depend on electrode configuration,voltage level,pressure,temperature and humidity of air.The assessment of pressure influence on discharge mechanism in non-homogenous electric field has been performed on the basis of empirical density distributions of discharge charges at different voltage levels,electrode distance,curvature of high voltage electrode and taking into account solid dielectric barrier in serial configuration.The measurement results obtained at variable voltage level yield the influence of electric field strength in the needle electrode zone.While increasing voltage,a deviation from normal distribution may be observed that reveals other forms of discharge.     

基于UV检测的UHV输电线路起晕电压的试验研究

Corona discharge is being detected by UV imaging detection technology at home and abroad in recent years.This technology is used in the corona tests of conductor bundles in this paper.In order to further research the corona characteristic,optimize geometry parameters and diameter of sub-conductor,and increase corona onset voltage of transmission lines,corona tests of three model conductors which are placed inside the outdoor corona cage are conducted.Corona cage could be used to simulate the corona activities on transmission lines under a low voltage and different conditions in an effective and economical way.Photon which was created by UV light as a result of corona discharge on conductors is detected by the UV detection apparatus.The photon number within unit interval,namely photon counting rate is adopted as the parameter of quantifying the intensity of corona discharge.According to the apparent change of photon number,corona onset voltage can be judged.All tests are conducted under almost same atmosphere condition.Using the method,corona onset voltage is acquired.The results indicate that the tests have a good repeatability,in other words,repeating same test twice same result can be aquired.The corona onset voltage can be acquired exactly from the curve of applied voltage vs.photon counting rate.Therefore UV detection apparatus can not only used to find discharge point exactly,but also applied on corona discharge research and live detection for power equipments.The method using in this paper is proved that is a new available method.     

空气中脉冲电压激励的表面微放电特性(英文)

The surface micro-discharge(SMD)excited by pulsed voltage in open air is experimentally studied by measuring its voltage,current,emission image,emission spectrum,and ultraviolet(UV)absorption spectrum.It is found that the SMD occurs intermittently in each cycle,and that it consists of many filaments on the surface of grounded electrode.While the applied voltage’s peak value Up increases from 1.75 kV to 7.25 kV,the discharge area keeps expanding until Up≈6 kV,when the discharge occupies all the available area.The emission spectrum of nitrogen metastable N2(C-B)and the density of ozone increase almost linearly.The ozone density decreases hyperbolically downstream of the grounded electrode due to the diffusion in open air.The characteristics of pulsed SMD are presented and analyzed as well,which may be referred by further investigations.     

30～200kV、上升沿1.5ns电压脉冲作用下常压空气中逃逸电子的产生(英文)

A pulse generator with a voltage rise time of～1.5 ns and voltage amplitude variable from 30 kV to 200 kV was designed for generating runaway electron beams in atmospheric pressure air with different interelectrode gaps.The influence of the voltage amplitude and gap length on the generation was studied.In the gas diode geometry under study,the gap voltage at which the generation of a runaway electron beam begins was determined.Decreasing the voltage pulse amplitude does not increase the beam current pulse width measured with a time resolution of～0.1 ns.It is shown that the escape of beam electrons to the downstream of the foil is sync in time with the voltage drop across the gap,and that the delay of beam current generation increases gradually from 1.1 ns to 2.6 ns as the voltage pulse amplitude across the gap decreases from～100 kV to 40 kV.     

大气条件下纳秒脉冲放电及其声特性分析(英文)

There was no well-resolved mechanism of audible noise caused by corona discharge on UHV transmission lines. Hence we measured the sound pressure of pulsed discharges between needle-plane electrodes under different discharge conditions in air, for revealing the intrinsic relationship between discharge and its audible noise(AN). The relationship between discharge parameters and audio characte- ristics was drawn from the analysis of the electric and sound signals obtained in experiments. Experiment results showed that nanosecond pulsed discharges produce the sound pressure with a microsecond pulse lagging behind the discharge pulse in their waveforms. The peak value of the sound pulse decreases and its high frequency component gradually attenuates, when the measuring distance from discharges increases. The sound pulses correlate with the discharge current and voltage significantly, especially the current. The audible noise produced by repetitive pulsed discharge increases with the strength, duration, and pulse repetition rate of discharge.     

大气压针板介质阻挡放电中微流注、电晕和辉光放电相互转换研究（英文）

To discuss the modes of dielectric barrier discharge(DBD) between needle-to-plane electrodes in air,DBD is generated and observed on a needle-to-plane device at atmospheric pressure air.Fast images of the DBD are taken by using a charge couple device(CCD) cinema with a macro lens,while the electrical and photo-electricity waveforms of the DBD are recorded.The current waveforms show that under an applied voltage of 3 kV,there are numerous short current pulses in both positive and negative half-periods of discharges.However,under 6 kV,there are still the numerous short current pulses in the positive half-periods,but only one wide current pulse in each negative half-period.This difference is also found in the photoelectric signals.The streamer,corona and glow discharges are observed from the images of the discharges at different applied voltages.The structure of glow discharge in the negative period is exactly the same as that of the low pressure glow discharge.However,in the positive period of discharge there is always a streamer.In the negative period of discharge,while the applied voltage increases,the transition from corona to glow discharge is observed.The progress of a transition between streamer and glow discharge at 6 kV during one period is analyzed.The glow discharge appearance is determined by two factors: the discharge current is limited to a certain extent by the dielectric layer; the charges deposited on the dielectric layer during the last half period enhance the intensity of the electric field.At an insufficient applied voltage,the cathode drop leads to no glow discharge,but Trichel pulses.     

振荡冲击电压下典型绝缘模型局部放电解析(英文)

The aim of this paper was to give an overview on partial discharges under oscillating impulse voltage.Three models(void in solid,needle-plate in air and oil) were presented,which describe the stochastic discharge process and represent internal discharges in solids and corona in air or silicon oil.Moreover,an air cored Rogowski coil and a sampling resistor for partial discharge(PD) measurement were developed and introduced in this paper.PD inception and extinction voltages(PDIV,PDEV) under single oscillating impulse voltage and AC voltage were investigated with different test samples.Experimental results firstly revealed that the PD inception voltage(PDIV) decreased with increasing applied voltage;secondly the PD inception voltage for three different insulating materials,showed an escalating trend with increasing frequency of the applied voltage.It was proven that the characteristics of PD under oscillating impulse voltage were identical to the features under AC voltage,which could be measured with the phase resolved partial discharge analysis(PRPDA) technique.Based on the reorganization and analysis of PDs under oscillating impulse voltage,the information about insulation defects was extracted from the measured data and used for estimating the risk of insulation failure of the equipment.     

线—板电晕放电电流体模拟方法研究（英文）

To simulate the electro-hydrodynamics of wire-plate corona discharge at different voltages accurately,a simulation method,which relates the definite radius and initial velocity of a jet source to the amplitude of discharge voltage,is developed.Firstly,a model of the electro-hydrodynamics is established by the Matlab software using the governing equations discretized with the finite difference method.Secondly,the electric field strength and current density are simulated and the radius and initial velocity of a jet source at different voltages are determined.Finally,the discharge electro-hydrodynamics is simulated using the determined boundary conditions.Compared with using a conventional method,using the proposed method can obtain a wind velocity with smaller errors from the experimental and theoretical wind velocities: the errors between simulated wind velocity and its theoretical counter part at 45 kV and 50 kV decrease from 9% and 6.25% to 1.7% and 1.56%,respectively.Thus,the proposed method is feasible for the existing discharge models.     

大气压下重复频率纳秒脉冲气体放电中X射线的辐射特性(英文)

Pulsed discharges can generate high power densities and high equivalent electric fields in plasma to emit X-rays,which is closely related to discharge mechanism.In this paper,discharge characteristics and X-ray emission of typical nanosecond-pulse discharges(corona,diffuse,spark or arc)are reviewed.Especially,the diffuse discharges are observed at pulse repetition frequencies up to 1 kHz.Factors influencing the discharge characteristics and X-ray emission are analyzed,such as the gap spacing,parameters of the applied pulse(amplitude,pulse repetition frequency),anode and cathode materials,and curvature radius of cathode.It is concluded that the maximum X-ray intensity is obtained in a diffuse discharge,and the X-ray intensity is affected by the pulse repetition frequency,applied voltage,anode material,and curvature radius of cathode.For example,X-ray intensity increases with the pulse repetition frequency and the atomic numbers of the anode material,but it decrease with the increase of curvature radius.It is also shown that the cathode material has no obvious influence on the X-ray intensity.     

Effects of Crosswind on an Automobile Under Dynamic Conditions

This paper presents results of a series of experiments carried out on models of a car and a truck in a wind tunnel to observe the pressure coefficient variation when the truck was overtaken by the car. However, conventional wind tunnels are not equipped to measure the yaw moment and side force created due to pressure difference created as a result of the interaction of two vehicles and the cross wind. An additional attachment for the wind tunnel was de-signed and built to measure the yawing moment and the side force experienced by the car when the cross wind is ap-plied. The attachment consists of a “top plate” which is independent from the wind tunnel frame and free to rotate. The car model is fixed to the “top plate” the top plate is connected to the base plate via a load measuring shaft which is connected to load cells that enable to measure the yaw moment. The pressure coefficient variation was measured by a series of pressure tapings provided by the circumference of the car. The two models were tested independently in the wind tunnel for their pressure coefficient variation. It was found that the pressure coefficient around the car varies substantially when it is overtaking the truck. It was also observed that when the cross wind is applied the yawing moment and the side force on the car increases with the air speed. The attachment was calibrated prior to the investigation and have been able to obtain consistent results. To relate the observations to real world conditions, fur-ther investigations are necessary.     

±1000kV特高压直流输电系统设备电晕特性(英文)

Corona performance is an important factor should be taken into consideration in power transmission project designs.Power equipments operate in various environments which will affect their corona inception voltages and thus influence the operation safety of transmission systems.In this paper,corona characteristic tests of bus bars,shielding rings,simulated eight-bundled conductors,and insulators were carried out in areas with different altitudes up to 4 300 m.Simulation tests of environmental factors were carried out in a HVDC corona cage.Based on site tests,it is concluded that corona inception voltages of both bus bar and shielding ball increase with their height to the ground or their dimensions.The influences of water droplet,wind,icing and surface contamination on corona inception voltage were also obtained from the simulation tests.The corona inception voltage of mist is higher than that in saturated water droplets.Conductivity of precipitation has little impact on corona discharges.Corona inception voltage decrease with increasing wind speed.The influence on corona current of glaze is the biggest,and that of hard rime is more than that of soft rime.The impact of pollution material on corona discharge depends on the size of pollution particle.Test results obtained in this paper are solid reference for design of UHV DC transmission projects.     

绝缘电极之间雷电冲击下油中放电特性分析(英文)

Looking at the problem of electrical discharge development in mineral oil, it is easy to see that most studies in this area focused on the setups of bare high voltage electrodes having a point-plane electrode arrangement. The setups with insulated electrodes are the mar- gin of these studies but it seems to be important to find the dependences between the paper insulation on high voltage electrode and parameters of the discharges initiated in the vicinity of this electrode. Hence, in this paper the results of researches intended to reveal the role of insulation wrapping on a HV electrode in the mechanism of electrical discharges in transformer oil under lightning impulse of both polar- ities are presented. This role is determined by analysis of the parameters characterizing the discharges (onset voltage, propagation velocity, time to initiation, rise-time of light impulses) and also by observation of their spatio-temporal development and oscillograms of the light emitted by their channels. The research was performed for two model electrode configurations: an electrode with paper insulation and a bare electrode which had the same outer dimensions as the insulated one. The most essential conclusion from performed experiment is related to times to initiation. These times, equal in the case of insulated electrodes and model bare electrode, indicate that the source of "weak points" of the paper-oil insulation system is the oil, not the surface of insulation wrapping or the metal.     

亚纳秒击穿产生超短雪崩电子束过程的动态特性(英文)

In this paper,subnanosecond-pulse and one-nanosecond-pulse generators are used to study the breakdowns in highly overvolted gaps in atmospheric pressure air.With different cathodes,we measured the applied voltage and discharge current to investigate the dynamic characteristics in the subnanosecond breakdown during the generation of a supershort avalanche electron beam.Especially,characteristics of dynamic displacement current are presented in the current paper,which is detected between the ionization wave front and a plane anode.It is shown that during a subnanosecond voltage rise time,the amplitude of the dynamic displacement current can be higher than 4 kA.It is demonstrated that the breakdown in the air gap is assisted by ionization processes between the ionization wave front and a plane anode.     

大气压氦气介质阻挡放电中交流驱动电压频率对击穿电压的影响(英文)

For dielectric barrier discharge(DBD)driven by AC voltage in helium at atmospheric,the relationship between the breakdown voltage and the driving frequency is experimentally investigated using a pair of parallel electrodes.The gap between the electrodes is 1 mm,4 mm,7 mm,and 10 mm,respectively.Meanwhile with an increment of 2 kHz,the applied AC voltage varies from 12 kHz to 30 kHz.In each experiment,the driving voltage increases slowly,till the helium-filled gap breaks down.Based on a number of experimental results and further analyses,conclusions are obtained as follows.(1)For a small gap(1 mm),the voltage that triggers the first breakdown(Uf)is close to the one that sustains steady breakdowns(Us).However,in the larger gaps(4,7,and 10 mm),Uf is obviously larger than Us.(2)For a fixed gap,Uf does not change significantly with the driving frequency,whereas in the gaps except the 1 mm one,Us drastically decreases with the increase of driving frequency.(3)The motion of residual space charges and the dissipation of positive column,two reasonable factors that explains asymmetrical discharges,are also main reasons for the effect of the driving frequency on the breakdown voltages.     

大气压下气流中小电流放电及其应用(英文)

The paper reviews the results of investigations of the low-current atmospheric-pressure discharges in gas flow.The attention is focused on the discharges in electrode systems of coaxial plasmatron and of so-called gliding arc.It is demonstrated that a considerable fraction of discharge current is carried by a plasma column operating in a regime of normal glow discharge with occasional transitions to spark.The nature of glow-to-spark transition is discussed.Beside the plasma column,a weakly ionized gas fills in the interelectrode gap and forms a plasma jet at the exit of electrode system.The jet contains the active chemical particles that play important role in different discharge applications.The applications in plasma assisted combustion systems,for surface treatment with a usage of plasma jet,and for biology and medicine are considered.     

Effect of Barrier Materials on Discharge Properties in Air at Low Pressure

Dielectric barrier discharge(DBD) is widely investigated in order to obtain uniform low-temperature plasma.Many studies have proved that some barrier materials,especially electrets,can improve the uniformity of discharge.It is regarded as an available way to get atmospheric pressure glow discharge(APGD).In this paper,discharge forms with 4 different barrier materials(alumina,quartz,PTFE and PET) are investigated,and the transition of discharge form depending on the air pressure are recorded to estimate the influence of barrier materials on discharge.By using electrets as barrier materials,homogeneous discharges can be obtained in a more wide pressure range.Under the same experimental conditions,discharges with electrets are more uniform or have larger uniform areas due to the storage and desorption of charges on the surface of electrets.The electrons deposited in the surface layer can be released on next half cycle when the polarity of the applied voltage changes,and provide a number of seed electrons,which makes the discharge more homogeneous.The capacitance and the permittivity of barrier materials have no effect on the discharge form directly.     

风沙条件下的平板模型直流沿面放电特性

The influence of sand dust on discharge of external insulation has caused widespread concern.At present,the research results show wind-sand electricity has a remarkable effect on the discharge characteristics of insulator and has little influence on the discharge characteristics of air gap.The flashover of insulator strings occurs along the insulator surface and air gaps,and the sand dust deposited on the insulator surface may affect the flashover characteristics of insulator strings.This paper studies the flashover characteristics of flat plate model under DC voltage in wind-sand condition.The experimental results show that under positive polarity voltage,the flashover voltage of the flat plate model has a maximum value,while under negative polarity voltage,the flashover voltage of the flat plate model has a minimum value with a certain degree of sand dust deposition.The wind or sand in sand-dust weather has an important effect on the flashover characteristics of the flat plate model.In certain variation range of electric charge,electric charge of sand dust has little effect on the flashover voltage of flat plate model under DC voltage.The deposition of sand has significant influence on the flashover process of flat plate model,which is related to the deposition density and moisture content of sand particle.