Correction of Tunnel Clearance Insulation Gap at High Altitudes

Lightning damage is frequent in highland areas, thus the insulation performance of electrical devices is reduced. The correction of the tunnel clearance insulation gap is required in the construction of railway tunnels at high altitudes, in which the distance between the tunnel roof and the overhead catenary serves as an important criterion for determining the tunnel clearance insulation gap. The lightning impulse discharge voltage is the controlling factor in determining the minimum interval of this air gap. The existing domestical and international correction standards for high altitude areas are not applicable for areas above 3000 m. Therefore, taking the basic characteristics and principles of discharge into account, we built a typical railway tunnel structure in an artificial climate laboratory, and simulated the climate characteristics of high altitude regions to study the positive and negative lightning impulse discharge characteristics of five short gaps (300~700 mm) under five altitude conditions (243~4000 m). Based on actual atmospheric parameters, three methods for correcting the tunnel clearance insulation gap were proposed. It is recommended that the insulation gap between the tunnel and the overhead contact wire be corrected to 341 mm, 388 mm, and 442 mm, respectively, at altitudes of 2 km, 3 km, and 4 km. This method can provide guidance for the design and modification of electrification of railroads in high altitude regions, and has engineering application significance.