Research On The Transition From Positive Corona To Streamer Discharge During Thunderstorms

Direct lightning strokes protection becomes a focus of power system security, and physics of lightning discharge is theoretical basis of protection design for direct lightning strokes. During thunderstorms, corona discharge initiated from grounded objects has an significant impact on the inception of upward streamers and leaders. At present, because of the lack of experimental observation on the transition from corona discharge to streamers in air, mechanisms of the transition is still not clear. So it is desiderated to carry out research on characteristics of the transition from glow corona to streamer discharge. This thesis focuses on positive corona and streamer discharge process in the plate-rod-plate gap, and makes a deep research on characteristics of corona discharge and its transiton to streamers.Based on analysis of conditions on the transition from corona to streamers, this thesis provides simulated experimental schemes of corona discharge and its transition to streamer discharge at the top of lightning rods during thunderstorms. A test loop of combined dc-impulse voltage is set up, with an integrated observation system of applied voltage, discharge current, discharge light intensity and image. Plate-rod-plate electrodes with the rod isolated to bottom plate is designed, which can generate different modes of corona, for simulating the spatial distribution of electric field around the lightning rod's top on the thundercloud electric field. The electrodes,test loop and integrated observation system combine to make up the integrated experimental platform for simulating point discharge of lightning rod during thunderstorms, realizing synthetic photoelectric observation of corona and streamer discharge.Using the integrated experimental platform, experimental research on characteristics of positive corona discharge during thunderstorms is developed, obtaining corona discharge process at the top of the rod electrode and characteristics of different modes of corona. Combined with discharge current waveforms and images, it is statistically analyzed including the change law of streamer corona current's front time, half-wave duration, peak value and glow corona current's DC component with variation on applied voltage and electrode structure parameters. Voltage and electric field criterions for different modes of corona is proposed, to lay a foundation of the conditions on transition from corona to streamers.Research on the characteristics of transition from positive corona to streamers is quantitatively performed. Typical image and light intensity of streamer discharge affected by glow corona are measured and compared to streamers without corona's effect. Under the influence of space charge produced by corona, streamers' inception voltage and electric field, as well as time delay and its dispersion of transition from glow corona to streamer are statistically analyzed with variation on corona current, rod electrodes' radius and the voltage rise rate. The transition probability with voltage rise rate increasing is experimentally obtained so as to analyze critical rise rate of voltage for transition from corona to streamers on the effect of corona current and rod electrodes' radius, contrastively verifying the theoretical conditions on the transition. Finally, according to measured results, the distribution characteristics of voltage peak value-rise rate of glow corona and streamer discharge on the effect of glow corona is analyzed.