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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-6.5MHz 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 …