Experimental Study on Surge Propagation Characteristics of Rail and Lightning Overvoltages on Level Crossing

Lightning protection measures are required for the railway signalling system because suspension and delays of trains due to lightnings may cause social confusion. Therefore, we carried out experiments on propagation characteristics of lightning surges along a rail, and injected a lightning surge current into the rail or wayside ground to raise their potentials, in order to measure the lightning overvoltages on a level crossing for the insulation design. There are no precedents that have carried out these experiments in the field until now. We could obtain the following results.

(1) The surge impedance of the rail is 56Ω and the surge propagation velocity in the rail is 55m/μs.

(2) The surge attenuation depends only on the duration of wave tail of the traveling lightning surge along the rail and decreases as the duration of wave tail becomes longer.

(3) Flashovers may occur at the terminals in the equipment of the level crossing in case 1) a 2kA lightning surge current is directly injected into the rail, or 2) a 10kA lightning surge current is injected into the wayside ground at a vertical distance of 2m from the rail.

(4) We can estimate the lightning overvoltages on the terminals in the equipment of the level crossing according to the vertical distance from the rail of the lighting stroke and the level of the stroke current.