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.     

大气压下高压亚微秒脉冲激励产生的介质阻挡放电的实验分析(英文)

An experimental device is used to study the characteristics of dielectric barrier discharge(DBD)plasma excited by high voltage sub-microsecond pulse power in atmospheric air.Glass,polytetrafluoroethene(PTFE)and plexiglass are used as dielectric barrier materials.Comparatively homogeneous discharge is obtained within 130 mm diameter area in atmospheric air using the three dielectric materials with gap distances of 4.5 mm,6.5 mm and 6.5 mm,respectively.There is no filamentary discharge observed by naked eyes or by camera with the exposure time of 0.25 s.Gas gap voltage,discharge current,discharge power density,etc.are calculated by using Liu’s equivalent circuit model for pulsed DBD.These parameters are used to study the DBD characteristics.Typically,current varies from tens of amperes to hundreds of amperes in atmospheric air DBD excited by sub-microsecond pulses.The peak power can reach to MW order of magnitude.The average power surface density of 1.0 W/cm2and the average electron density of 1011cm 3can also be obtained in the discharge.Rotational and vibrational temperatures,approximately 400 K and 2 650 K,respectively,are obtained by using the emission spectrum of the discharge.This is the basic work performed for a better understanding of the characteristics of atmospheric air DBD plasma excited by high voltage sub-microsecond pulsed power source.     

大气压氦气与氩气等离子体射流形成机理的对比研究(英文)

To compare the formation mechanisms of He and Ar atmospheric pressure plasma jets(APPJs),an intensified charge-coupled device(ICCD)are utilized to observe the dynamic process of APPJ.The experimental results show that,He APPJ is first ignited,which is independent of the dielectric barrier discharge(DBD)between the two wrapped electrodes when the high voltage placed at the downstream.The intensity and APPJ length under positive discharge pulses are bigger than that under negative discharge pulses due to the space charge effect.The He APPJ is formed by the DBD development when the high-voltage electrode placed at the upstream side of tube.However,the plasma plume in Ar APPJ is formed by the propagation of DBD whatever the high-voltage electrode is arranged on upstream or downstream side of ground electrode.The difference in formation mechanism between He and Ar APPJs is mainly caused by the gas properties.Moreover,during the discharges,Ar tends to lead to thermal instability and electron Maxwellian instability.     

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.     

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.     

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.     

在共面介质阻挡放电中大气压等离子体射流的特性(英文)

Non-thermal plasma jet at atmospheric pressure has recently attracted lots of attention because of its applications in plasma bullet or plasma plume.Thus,we studied on generating plasma jet by coplanar dielectric barrier discharge in a device driven by sinusoidal voltage.The processes of plasma discharges in both positive and negative half cycles were recorded using a high-speed ICCD(intensified charge-coupled device)camera;based on the results we estimated the velocity of plasma propagation,and investigated the influence of gas flow on the plasma development.It is shown that the plasma bullets,which have velocity in the order of 103～104m/s,exist only outside the cathode.APPJ(atmospheric pressure plasma jet)is created by the electron beam from the cathode,and then sustained by a strong radial electric field near and outside the cathode.The gas flow influences the APPJ length in air but not the APPJ discharge,while the discharge is affected significantly by the applied voltage.     

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.     

裸露金属电极中的亚微秒脉冲常压辉光放电（英文）

In order to better understand the physical mechanism of sub-microsecond pulsed glow discharge with bare metal electrodes,using a one-dimensional self-consistent fluid model,the properties of the discharge at atmospheric pressure are numerically studied.The results show that,a discharge without dielectric layers,i.e.a barrier free discharge,is extinguished only with the decrease of the applied voltage.Only one positive discharge event occurs at the slope of the pulsed voltage.A stable glow of barrier free discharge can be achieved only in short durations of the pulsed voltage.The barrier free discharge always starts with a subnormal glow discharge and then evolves into a normal glow discharge.Moreover,to control the discharge stabilization better,the effects of pulse repetition frequency,pulse duration,rising(front) and falling(slope) times on the discharge characteristics are investigated systematically.It is found that the discharge is comparatively more sensitive to the repetition frequency and the pulse duration,while little affected by the rising and falling times.     

交直流复合电压油纸绝缘的沿面局部放电特性(英文)

The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.     

不均匀电场下加压气体中弥散放电和火花放电的形成(英文)

Diffuse and spark discharges are formed and studied during breakdowns with nonuniform electric field in nitrogen,air,and argon at elevated pressures and pulse repetition frequency of 400 Hz.Negative-polarity voltage pulses of the amplitude 20 kV,width at the base of 15 ns and rise time of 2 ns are applied to the electrode with a small radius of curvature.In the conditions of generation of runaway electron beams and X-rays,a CCD camera records the time of the diffuse discharge formation and its duration prior to its transition to a spark one.In all three gases,the diffuse discharge is formed during the time not exceeding 1 ns,when the bright spots appear on cathode in argon and air resulting in the beginning of the spark channel propagation.     

大气压下柱型微空心阴极放电(英文)

The mechanism of micro-hollow cathode discharge at atmospheric pressure is investigated through simulations using two-dimensional fluid model combined with a transport model for metastable atoms.In the simulations,electric potential,electric field,particle density,and mean electron energy of the discharge are calculated.The results show that the two characteristic regions of the discharge,i.e.cathode drop and negative glow can be distinguished in the simulation.The cathode drop is characterized by strong electric field and high mean electron energy,while quasi-neutral plasma of high density and exists in the negative glow.The peak value of electron density can reach the order of 1017cm-3.The electron temperature varies from several eV to tens of eV.The influence of cathode dimension on the discharge characteristics is also investigated.     

两相体中正脉冲放电分枝的现象和机理(英文)

Discharge branching is a general phenomenon in atmospheric-pressure air,dense gases,and two-phase mixtures(TPMs).In this work,an ultraviolet imaging device is utilized to investigate the branching of positive pulsed discharges in TPMs.Comparison among the captured images indicates that the branching is caused by the voltages and the macropartilces in the discharge channels combining together.The interaction of macroparticles with ions,electrons or photons is one reason for the branching behavior of pulsed discharges.The generation of electrons at the discharge front closely relates to the work function of dielectric macroparticles,which is a key parameter influencing the electron-emission ability of macroparticle surfaces.The electric field alteration under various applied voltage in TPMs,which is calculated by a two-dimension finite element method,is the other reason for the guiding effect of macroparticles on the streamers compared with in the air.     

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.     

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.     

局部放电射频信号与其视在放电量的关联分析(英文)

Radio frequency(RF) measurement has become a hot issue for partial discharge detection.However,its application is hampered by the difficulty to establish a relationship between the RF measurements data and apparent discharge quantity.In this paper,on the basis of an experimental model of metal protrusion,the relationship between the results of RF measurement and pulse current method(IEC 60270) was investigated.The energy,double integration,peak voltage,peak-peak voltage and the area of RF signals were plotted versus either the apparent discharge quantity or the square of the apparent discharge quantity in order to evaluate the optimal regression curve.At the same time,the impact of voltage and the distance between protrusion and plate were also investigated.The results indicate that the optimal match to a linear regression curve can be gained by plotting the RF signal energy versus the square of the apparent discharge quantity.The variation of voltage has no significant impact on the regression curve;that is,data from different voltages match one line.However,when the distance between protrusion and plate is changed,the slope of the regression curve changes accordingly;the same energy corresponds to a bigger discharge quantity.The results are significant enough to be applied in the estimation of the discharge quantity by measuring RF partial discharge signals.     

放电间隙导通过程中电流通道头部的加速效应（英文）

This paper is devoted to explanation of a phenomenon of current channels heads acceleration which bridges a discharge gap.This phenomenon was discovered experimentally during some works at investigating nanosecond streamer gas discharges of atmospheric pressure in the air and neon.Consideration of the bridging process of the discharge gap is presented in the framework of a model of microstructured current channel.In this case,the channel represents itself as a bunch of microchannels(up to 1 000 and more).Such consideration could be stipulated by the discovered earlier phenomenon of the current channels microstructuring that are realized in the nanosecond discharges of atmospheric pressure.The authors have developed the electro-technical model of the discharge gap bridging by the conducting channel.It is shown that the channel length dependence of the velocity is linear;this is similar to that of the model of the continuous(unstructured)channel.We considered and made estimations that stipulate a possibility of gas heating in the microchannels up to the temperatures of associative ionization beginning in the discharge gap bridging phase.In this case,increase of the charged particles concentration and,consequently,decrease of its resistance cause the head acceleration.It is shown that in case of the continuous channel it is impossible to realize the gas heating up to the temperatures of the associative ionization in these conditions.Obtained results reveal the physical reason of the current channels microstructuring as a consequence of the principle of least action manifestation in the area electric breakdown phenomena of the gases.     

氩气与氨气混合下的大气压介质阻挡放电(英文)

In this paper,the influence of ammonia admixture on argon discharge properties is investigated.Electrical measurements,as well as ten-nanoseconds-exposure photographs taken by an intensified charge-coupled device(ICCD)camera,are employed to confirm the existence of atmospheric pressure glow discharge(APGD)in Ar/NH3mixture.The breakdown voltage and transition voltage between APGD and filamentary discharge are studied at various ammonia concentrations.The results show that a small amount of NH3can lead to APGD due to the Penning ionization of NH3molecules by metastable argon,and the breakdown voltage increases with the growth in NH3concentrations owing to the electronegative feature of NH3.The optical emission spectrum of Ar/NH3APGD is analyzed.Besides,gas temperature is estimated at 327 K by the diagnoses of the OH(A-X)(0,0)band of the spectrum.     

多种试验条件下SF6放电及分解特性研究（英文）

Detection of gas decomposition products is widely used for condition diagnosis of SF6-insulated equipment because of its an- ti-electromagnetic-interference ability and high sensitivity. Previous investigations show that the volume of gas chamber influences the types and concentrations of SF6 decomposition products. Therefore using a newly developed dual gas chromatography (GC) detection sys- tem we investigated the discharge and decomposition of SF6 in a discharge chamber with its volume close to that of the real chambers in GIS. Tests in the chamber were performed with different applied voltage, different electrode arrangements, and different defect types. For discharge between needle-to-plane electrodes, the typical gas decomposition products are SO2F2, SO2 and S2OF10. A near linear growth with the increase of voltage duration is found in the concentration of SO2F2, whereas the growth rates of SO2 and S2OF10 concentration decrease with time. Concentrations of SO2F2, SO2 and S2OF10 at the same voltage duration decrease with the decrease of the voltage amplitude and the increase of the needle-to-plane distance. Change of the gas chamber volume affects the generation rates of SO2F2 and SO2, however not S2OF10. For insulator surface defects, the typical gas decomposition products are CF4, CS2 and SO2. Among which, the concentrations of CF4 and SO2 increase with the voltage duration almost linearly. Moreover, a new parameter that represents the degree of SF6 degradation, the SF6 deterioration ratio, is proposed. In the needle-to-plane case, SF6 deterioration ratio is positively correlated to the fitting value of an averaged discharge capacity. However, the maximum value of SF6 deterioration ratio varies with the defect type.     

采用多电极结构的大面积表面介质阻挡放电特性(英文)

Surface gas discharge(SGD)plasmas have potential applications in the fields of active flow control,gas purification,heat transfer enhancement,etc.In order to obtain a uniform,stable and large-area SGD at atmosphere,a multi-electrode SGD plasma generator is designed in this paper.The major features of this newly-designed SGD plasma generator is as follows:the air-exposed upper grounded electrodes are made of nine tungsten wires and flush mounted on the dielectric PTFE barrier layer,while the lower powered electrode is made of a copper foil and encapsulated inside the PTFE material to avoid the ignition of the gas discharges below the dielectric barrier layer.The measurements on the electrical characteristics,fast imaging of discharges and the preliminary numerical analysis on the electric field distributions suggest that the multi-electrode configuration of the plasma generator plays a crucial role in enhancing the local electrical field,and subsequently,leads to the stable,quasi-uniform and large-area surface discharges.