Research on the upward leader emerging from transmission line by laboratory experiments

The problem whether the upward leader can incept from the transmission lines in lightning shielding failure is still in question, since the upward leader emerging from transmission lines is difficult to be captured under natural circumstance. It is necessary to study the characteristics of upward leader. This paper presents some simulated experimental results of a 6-m long, combined plane-rod (PR) electrode to conductor (ground wire (GW)) air gap. A current measuring instrument with frequency response of DC-6.5 MHz was developed and used to measure the leader current. Besides, high speed CCD camera was used to observe the optical phenomenon of the whole process. In the experiment, upward leader emerging from bundle-conductors and GW was found. The velocity, surface electric field and charge of upward leader channel were obtained by analyzing the experimental data. Finally, the surface electric field of conductor for natural lightning circumstance was compared with the field in the experiment, in order to prove that the upward leader can emerge from transmission lines due to the downward leader of lightning.

► A new structure electrode is proposed in order to simulate the strong electric field produced by lightning.
► The characteristics of upward leader emerging from conductor or GW have been concluded.
► The average current of upward leader from conductor is smaller than upward leader from GW.
► The velocity of upward leader increases with the development of upward leader.
► The inception of upward leader from transmission lines due to the downward leader of lightning is possible.