Study On Needle-plate Corona Discharge And Migration Characteristics Of Ion Space Charge

Corona discharge is a typical form of partial discharge,which occurs frequently in the insulation problem of power system.Typical discharge models of corona discharge are needle-plate,rod-plate discharge model,and by studying this simplified model can reduce many problems caused by the complexity of the space charge distribution,from which we can get a better understanding of the physical process of corona discharge,and get a more accurate analysis result from the experimental phenomena.The duration of the electron avalanche is short.Because the low frequency band of the traditional pulse current method,it can not reflect the instantaneous characteristics of corona discharge,and the calculation results is not accurate due to the overlapping influence on the discharge when the discharge repetition rate is high.By using oscilloscope with both high storage and sampling rate and high-frequency non-inductance resistor in series with electrode,it is possible to accurately restore the single time-domain waveform of the corona discharge and analyze the single pulse characteristics during the short period of ionization.Because the alternately time of low frequency AC voltage is much shorter than the migration time of space charge,positive and negative corona discharging under the DC voltage and low frequency AC voltage is essentially the same.Corona discharge under low frequency AC can be seen as a corona discharge at different DC voltages.When the variation frequency of applied voltage is high enough that the migration time of space charge is same to its changing time,discharge characteristics will be affected both by the change of surface electric field and space charge field.Comparing the development process of positive and negative corona under the typical electrode spacing and same radius of curvature that we can understand the migration process of space charge more accurately.It is of great significance to analyze the characteristics of positive and negative corona discharge,which is in order to solve the problem involved by the space charge transfer law of gas discharge under the non-uniform electric field.There may be multiple negative ion clouds in the electrode gap in the process of Trichel discharge,and each negative ion cloud corresponds to the transmission of a single discharge pulse.But there is no accurate articles for the negative ion cloud migration and migration time.Based on the statistical data of pulse amplitude and repetition rate,the effect of single pulse discharge and the space charge generated in the migration region and the effect of discharge cloud on the needle electrode is calculated.Design different experiments to verify the migration of negative ions in the migration zone.The negative corona pulse of the needle plate satisfies the Trichel discharge pulse characteristic over a certain voltage range.As the voltage continues to increase,the negative corona pulse repetition rate will suddenly increase and the average amplitude of the discharge decreases rapidly.This paper preliminarily analyzes the causes of this phenomenon and the effects of different radius of curvature and the length of the gap on negative corona pulses.Discharge quantity of a single positive discharge is one order of magnitude higher than a negative one,which means that positive ions significantly weaken the electric strength of needle electrode.The positive ions in the zone will significantly affect the next discharge,making the positive corona discharge more likely to remove the positive ions in the migration zone.Therefore,there is a characteristic discharge repetition rate,which corresponds to the migration time of the primary discharge positive ions.In addition,pulses of a single positive discharge have secondary peaks.And peak to peak time is about 0.05 us,which reflecting the secondary electron avalanche of the positive corona discharge in the ionization moment.The ions generated by the corona in the migration area will diffuse into the surrounding space due to the distribution of ion concentration.While a single polar corona discharge last for some time,there will be a certain concentration of space charge of same polarity.In the confined space,this background space charge will have a significant effect on the discharge when the polarity of the electrode is reversed.And there is little mention of the influence of this kind of space charge on gas discharge.In this paper,the corona discharge of different applied voltages under the influence of background space charge is preliminarily studied.