ElectricStep-APL-2011

Electric field step in air gap streamer dischargesRong Zeng, Chijie Zhuang, Zhanqing Yu, Zhizhao Li, and Yinan GengCitation: Appl. Phys. Lett. 99, 221503 (2011); doi: 10.1063/1.3665633View online: /10.1063/1.3665633View Table of Contents: /resource/1/APPLAB/v99/i22Published by the American Institute of Physics.Related ArticlesExpectation of ozone generation in alternating current corona dischargesPhys. Plasmas 19, 033513 (2012)Dynamic contraction of the positive column of a self-sustained glow discharge in molecular gas Phys. Plasmas 19, 033512 (2012)High power impulse magnetron sputtering discharges: Instabilities and plasma self-organization Appl. Phys. Lett. 100, 114101 (2012)A global model of the self-pulsing regime of micro-hollow cathode dischargesJ. Appl. Phys. 111, 053305 (2012)On the accuracy and reliability of different fluid models of the direct current glow dischargePhys. Plasmas 19, 033502 (2012)Additional information on Appl. Phys. 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Redistribution subject to AIP license or copyright; see /about/rights_and_permissionsElectric field step in air gap streamer dischargesRong Zeng,a)Chijie Zhuang,Zhanqing Yu,Zhizhao Li,and Yinan GengDepartment of Electrical Engineering,Tsinghua University,Beijing100084,China(Received10October2011;accepted14November2011;published online30November2011)Electricfield(E-field)in air gap streamer discharges under positive lightning impulse was measured by specifically developed integrated electro-optic sensors.An E-field step phenomenon was observed.The E-fieldfirstly agreed with the Laplacefield,then suddenly increased with a rise time of l s.The occurrence probability of this phenomenon increased as the applied voltage increased.The discharge current waveforms and photos taken by a fast camera prove the E-field step was caused by the space net charge.From the E-step rise time and the corona area range, the average electron drift speed under the experiment situation was estimated about0.2Â106–0.6Â106m/s.V C2011American Institute of Physics.[doi:10.1063/1.3665633]Electricfield near a streamer,with possible maximal magnitude of several hundreds kV/m,is a dominant parame-ter in streamer propagation and is widely used to describe the streamer models in air gap discharge simulations.1–3 Thus,measuring the E-field is one of the major means in gas discharge research and has been continuously studied by dif-ferent groups via different methods during the last four deca-des.In the1970s,large numbers of long air gap discharge experiments were carried out by the Les Renardie`res group and the E-field was measured by conventional probes.4Since 1980s,electro-optical sensors have been brought into E-filed measurement in the air gap discharge due to their large dynamic range(up to MV/m)and large intrinsic bandwidths (up to GHz or even more).5–8Among them,the integrated electro-optic sensors are much more compact,which result in a higher stability and less distortion to the E-field distribution.9Although the E-field strength of the gas discharge has been vigorously studied in the past,6–8the transient details of the E-field in an electrical discharge process are still not very clear.This letter developed a specific E-field sensor to measure the transient E-field of streamer discharges and an E-field step phenomenon was observed.In order to measure an E-field with huge magnitude(up to MV/m)and very short rise time,an integrated electro-optic E-field sensor with the mono-shielding electrode was specifically developed and carefully calibrated.10,11First,a lightning impulse and two parallel plate electrodes were used to calibrate the scale factor.The results measured by a voltage divider and the sensor agreed well[see Fig.1(a)]. Then,a dynamic response calibration system was established with parallel plate transmission lines and the simulated nuclear electromagnetic pulse(NEMP),with a1–3ns rise time and maximal amplitude up to100kV,was used as a cal-ibration wave.The rise time of the output waves measured by a voltage divider and the sensor is1.04ns and1.12ns, respectively[see Fig.1(b)].Both the calibration results of lightning impulse and NEMP demonstrate that the perform-ance of the adopted sensor is adequate for the measurement of the E-field in air gap discharges.After the implementation and calibration of the sensor,a rod-plane discharge experiment under positive lightning impulse was designed[see Fig.2].A rod with a semi-sphere tip of1cm in radius was hung1m above a well-grounded plate.An impulse generator worked as a power source to generate a lightning voltage impulse applied on the gap.E-field sensors were put in the gap,ranging from30cm to 70cm above the plane.A100X non-inductance resistor was connected in series at the high voltage side to measure the discharge current and the sampled voltage signal was trans-formed by an electro-optic modulator.Both the E-field and current signals werefinally connected to an oscilloscope.A high speed video camera(125thousand fps used in the experiment)took video of the discharge process.The camera was triggered and synchronized by the oscilloscope.Typical results are shown in Fig.3.When the applied voltage is low,the space E-field changed following the applied putations show the measured E-field agreed with the Laplacefield within less than5%error.When the voltage achieved a specific level(e.g.,above200kV under the experiment situation,this value also depends on d U/d t), the space E-field was distorted,the E-field strength suddenly increased D E and an E-field step with a rapid rise time was observed[see Figs.3and4(a)].The E-field step phenomena did not occur every time.Table I gives the statistical results of repeated experiments for different applied voltages.The prob-ability that the sensors detected the E-field step increased as the applied voltage increased.Tofind the formation reasons of the E-field step,the cur-rent waveform is investigated[see Figs.4(a)and5].At the beginning,the measured current was proportional to d U/d t and equaled to the displacement current.But it increased dra-matically once the E-field step formed.In proportion to d U/d t, FIG.1.(Color online)The normalized waveforms of the outputs in calibra-tion.(a)The response of lightning impulse.(b)The response of NEMP.a)Author to whom correspondence should be addressed.Electronic mail:zengrong@.0003-6951/2011/99(22)/221503/3/$30.00V C2011American Institute of Physics99,221503-1APPLIED PHYSICS LETTERS99,221503(2011)the displacement current is much smaller than the measured value and is impossible to cause such increase.Exclude the possibility of displacement current,this sudden increase in current must be caused by the movement of charge carriers produced by a discharge.Photos taken by the fast camera show that such streamers did exist once the E-field step appeared [see Fig.4(b)].The streamer discharge would produce a cloud of free electrons and ions in space and form a corona area.The free electrons drift to the positive electrode and would be absorbed when they reach the electrode,the ions are almost static since they move two orders of magnitude slower than electrons.Once the electrons and the ions are separated fromeach other,the E-field would be distorted due to the space net charge,and an E-field step is then formed.The total space net charge roughly equals to the charge injected into the electrode.The latter can be computed by integrating the discharge current over the time domain,provided the dis-placement current is eliminated from the total current.Under our experiment configuration,for positive lighting impulse with maximal magnitude of 200–300kV,the total net space charge is in the order of 1–3l C.As mentioned above,D E outside the discharge areas is caused by the space net charge.The space net charge,which is positive,reaches its maximal amount once all the free electrons are absorbed by the positive electrode,and so does D E .So the rise time of the E-field step consists of two parts:the period that streamer propagates to its maximal length and the time that all the free electrons in the corona area move to the electrode.The former can be omitted because in our experiments,streamer discharge occurred only once under every lightning impulse,and streamers develop and propa-gate much faster than electrons drift.Thus,the rise time of an E-field step roughly equals to the time that all the elec-trons move into the electrode.From the photos taken by the camera,under 200–300kV positive lighting impulse,the co-rona area ranged from 20to 30cm roughly.The rise time of typical E-field step is about 0.5–1l s (cf.Fig.4(a)).So the average electron drift speed under these situations is roughly 0.2Â106m/s–0.6Â106m/s.In summary,we report in this letter an E-field step phe-nomenon caused by the streamer discharge under positive lightning impulse.A streamer discharge leave in space a cloud of electrons and ions.The electrons move towards to the positive electrode and are absorbed.In our experiment,each time about 1–3l C space electrons is absorbed by the positive electrode.The electrons and ions separate from each other rapidly and cause the E-field step.From the rise time of the step and the corona area range determined by the fast camera,the average electron drift speed is estimated about 0.2Â106m/s–0.6Â106m/s under the experimentsituation.FIG.3.(Color online)Typical results of E-field at 70cm above the plane:(a)applied voltage 100kV;(b)applied voltage 150kV.FIG.4.(Color online)Typical results of measured discharge current wave-forms and photos.TABLE I.Statistical results of repeated experiments at different applied voltage magnitudes.Voltage magnitude (kV)200160130100Repeated experiment times20202010Times with detected E-field step181531FIG.2.(Color online)The configuration of a rod-plane electrical dischargeexperiment.FIG.5.(Color online)Typical measured current and computed displace-ment current.This work was supported by National Natural Science Foundation of China(Grant No.50777035)and National Ba-sic Research Program of China(973program)(Grant No. 2011CB209403).1S.Pancheshnyi,M.Nudnova,and A.Starikovskii,Phys.Rev.E71, 016407(2005).2A.Luque,V.Ratushnaya,and U.Ebert,J.Phys.D:Appl.Phys.41, 234005(2008).3C.Li,U.Ebert,and W.Hundsdorfer,put.Phys.229,200(2010).4Les Renardie`res Group,Electra53,31(1977).5C.Bulmer,W.Burns,and R.Moeller,Opt.Lett.5,176(1980).6N.Allen and A.Ghaffar,J.Phys.D:Appl.Phys.28,331(1995).7K.Hidaka,IEEE Electr.Insul.Mag.12,17(1996).8J.Santos,M.Taplamacioglu,and K.Hidaka,IEEE Trans.Power Deliv. 15,8(2000).9O.Ogawa,T.Sowa,and S.Ichizono,J.Lightwave Technol.17,823(1999). 10R.Zeng,Y.Zhang,W.Chen,and B.Zhang,IEEE Trans.Dielectr.Electr. 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