Aiming at lightning accidents in 35 kV substations in a certain region

U50% flashover voltage tests for the insulators on incoming line and field investigation were conducted

and severe defect in insulation coordination was found in the substations in this region

i.e.higher insulation level of transmission line and resistivity of the mountain soil cause the lightning invasion wave on the line not to attenuate sufficiently

and cause the lack of lightning discharge channel

which results in frequent lightning strike damages on the main transformers in 35 kV substations.In order to solve the lightning strike problem

a protection scheme is proposed in this paper by installing gap-adjustable lightning protection device in parallel on the insulators on incoming line and adopting arrester at substation.The insulation coordination of the device and insulator string as well as the design principle is analyzed

and the gap distance of the gap-adjustable lightning protection device for the region is designed through theoretical calculation and test.Simulation via the power system electromagnetic transient program ATP-EMTP shows that the gap-adjustable lightning protection device is feasible and effective.Considering that the gap is easy to induce clipped wave

which may significantly impact voltage

a reactor is concatenated to incoming line of transformer for inhibiting the effect of clipped wave over-voltage.