| Gas discharge is one of the fundamental problems in high-voltage engineering,which mainly includes four aspects:theoretical analysis,characteristic curves,discharge profile and numerical simulation.In recent years,the characteristics of gas discharge under low pressure condition is widely used in many areas such as air gap insulation coordination of power transmission and transformation equipment in the high-altitude area,electrostatic insulation design of space aircraft,the properties of vacuum circuit breaker and vacuum coating technique,and the discharge gap configuration is mainly in the form of extreme-nonuniform field.To meet the requirements of practical engineering application,most of the researches are limited to obtaining characteristic curves of high Pd range in the rough vacuum(103?105 Pa)and exploring the discharge mechanism at given Pd value.However,characteristic curves of low Pd range within the lower part of low vacuum to the upper part of rough vacuum and the relationship of discharge profile and Pd value have not been completely clearly.For these reasons,the author carried out laboratory investigations on discharge characteristics under extreme-nonuniform field in a low-pressure test platform,and analyzed the characteristic curves and variation of discharge profile within 10～3×104 Pa.Main results obtained by this thesis are as follows:A low-pressure-gas-discharge platform was designed and build.It contains power system,data collection system,test chamber,pressure control system,electrode system and optical image observation system.In the aspect of characteristic curves,the U-P curves and U-Pd scatterplots under different voltage mode(50 Hz power frequency,positive and negative DC voltage)with different rod tip(needle tip,conical tip and hemispherical tip)within 3.759×10-1～4.511×103 cm mmHg were obtained.The results show that the U-P curves under different experimental conditions have minimum obviously.The left branch of U-P curves are not sensitive to the shape of electrode but gap length will impact on entire morphology of U-P curves significantly.The U-Pd scatterplots have the form of Paschen curve but do not accord with Paschen rule.The dispersion of the left branch of U-Pd scatterplots are prominent,however,the right branch of U-Pd scatterplots under AC and negative DC voltage all have the Pd range which accord with U=f(Pd)function.By contrasting the U-P curves under positive and negative voltage,a typical polarity reversion pressure range is found.In terms of discharge profile,variation of discharge profile with Pd within 1.504～4.511×103 cm mmHg and the mechanism of discharge in different Pd ranges were obtained by the observation of gas discharge under AC,positive and negative DC voltage,and the concept of inflection point and profile-interval were proposed.Take 20 cm rod-plane gap as an example,four inflection points under AC and positive DC voltage divide 1.504-4.511×103 cm·mmHg into five major zone,striation zone,low-energy positive column zone,high-energy positive column conversion zone,single streamer zone and bifurcate streamer zone.The typical features of each zone are as follow:①Striation zone shows up as bright-dark striations which extend forward from anode within the left branch of U-Pd scatterplots.② The positive column in low-energy positive column zone belongs to a state of low energy,but the brightness of anode glow and cathode glow is more obvious than others.③In high-energy positive column conversion zone,positive column changes from low-energy state to high-energy state gradually which proportion increases with voltage magnitude.④There is no obvious branch in single streamer zone.⑤The streamer split into several branches in bifurcate streamer zone and the branching phenomenon increases with pressure value.Two inflection points under negative DC voltage divide observable Pd range into three major zone,low-energy positive column zone,pattern zone and single streamer zone.The discharge profile on both sides of the minimum of U-Pd scatterplots dose not show a clear change,but the self-organized pattern on the surface of mental plane electrode is the typical discharge phenomenon under negative DC voltage.The formation mechanism of striation in the left branch of U-Pd scatterplos was proposed.The result shows that electron density perturbation of the anode end of positive column exceed a stability threshold caused by heating effect of current and stepwise ionization of metastable atom is responsible for striation.The study shows that streamer constantly choose one of branches stem from effective bifurcation and the bifurcation stays still.It is found that the erosion trace on the surface of anode plane could be use to distinguish pattern property.Moreover,it is speculated that space charges in pattern which promoting the development of positive column is the reason for the reversion of polarity characteristic.Aiming to uncover the relationship between Pd with characteristic curves and discharge profile under low pressure condition,explorational experiments on various gap length ranged from 30 to 60 cm within 2～60 kPa were carried out by a self-organized polypropylene chamber.The study shows that when discharge gap is longer than 20 cm,the U-P curves under AC voltage represent a remarkable saturation characteristic which represent here just liner under positive and negative DC voltage.Moreover,with increasing gap length,streamer under AC voltage will has more bifurcates,branches and tortuous and the positive column will has more striations under DC voltage.There is obvious magnification effect of discharge profile characteristics thi*ough increasing gap length. |
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