Characteristics Of Lightning Current And Electric Field Of Triggered Lightning

Lightning has the characteristics of long distances,large currents,and strong electromagnetic radiation,which will seriously threaten the operation of transmission lines,power systems and control systems,and even affect the safety of human life.Studying the discharge process of lightning can guide the development of lightning protection.Rocket-triggered lightning technology has been used in Conghua,Guangzhou for two consecutive years to carry out triggered lightning experiments,and we have accumulated a wealth of optical,electrical,and magnetic observational data related to lightning.Through the synchronous measurement of current and electric field changes,there are obvious differences in the parameters of the initial discharge stage of triggered lightning with or without return strokes.In the initial stage of lightning without return stroke,there is an obvious silent period in the initial current variation,and the reconnection current pulse after the silent period has a relatively large amplitude(1237A)and rapid rise time(0.7?s),similar to the return stroke current.For the initial current variation of lightning with return strokes,there is no current silent period.The current pulse in the plasma channel reconstruction process is similar to the M component,with a smaller amplitude(172.8A)and a slow rise time(57.0?s).It is indicated that stronger initial stage discharge is usually accompanied by return strokes.The average number of triggered lightning flashes is 5.6.Compared with the subsequent return strokes of natural lightning,the return strokes in this article show a shorter rise time(0.6?s)and larger peak current(16.4k A),and the first return stroke usually has a larger lightning current amplitude and a slower rise time than the subsequent return strokes.The peak current of the return stroke has a strong power function correlation with the charge transfer within 1 ms and action integral within 1 ms.It has a certain linear correlation with the initial electric field peak value and the electric field amplitude of the return stroke.It also has a certain linear correlation with the leader magnetic field and the return stroke magnetic field.As the distance increases,the peak value of the magnetic field decreases.The analysis of all peak values of the magnetic field at different distances shows a linear relationship with r^-0.90.The 10-90%rise time of the magnetic field has a linear relationship with ln(r).The continuous current occurs after the return stroke,and there is still a current process of tens to hundreds of amperes or even k A in the return stroke channel,with a duration ranging from tens to hundreds of milliseconds.According to the continuous current duration,it can be divided into two types of continuous current less than 10 ms and greater than 10 ms,and present a variety of different waveforms.In the continuous current process,the existing pulse disturbance is called the M component.The current amplitude of the M component is smaller than the return stroke current pulse,and its geometric mean value is 401.5A.The 10-90%rise time and half-peak width are greater than the return stroke current pulse.The geometric average values are 120.8?s and 204.2?s,respectively,which are very similar to the initial continuous current pulse.Compared with traditional triggered lightning,the main difference of altitude triggered lightning is that the metal wire at the tail of the small rocket is not directly connected with the lightning rod.The initial positive change of electric field in the stage of bidirectional leader process is mainly affected by the upward positive leader.The light pulse(or recoil streamer)entered weakened discharge channel and made it re-emit.Then the ICCP or M-component was produced and corresponding electric field changed.With using the optical information,it is possible to assign certain pulses to certain branches.In the stage of leader-return stroke,the presented types of dart leader electric field waveforms are the result of processes in different branches.The formation mechanism of the slow front may be related to the breakthrough stage of the attachment process,through which the extended plasma channels of the upper and lower leader contact each other.Multiple discharge channel could influence electric field change of the slow front of the return stroke.