Study on Impulse Breakdown Characteristics of Internal-Gap Lightning Protection Device Applied to 35 kV Distribution Line

External environmental factors have no effect on the breakdown performance of the internal gap, leading to the anti-icing and anti-storm features of the internal-gap lightning protection device (ILPD). In this paper, a test platform is created to study the impulse discharge and arc erosion characteristics of the ILPD applied to a 35 kV distribution line. The 50% lightning impulse voltage and discharge stability of the ILPD are experimentally analysed. The results show that the ILPD has good discharge voltage repeatability under multiple impulses. Under a positive lightning impulse, the 50% breakdown voltage of the ILPD is 3.8–11.4% higher than that of the outer-gap lightning protection device (OLPD). A finite element simulation model is created for electric field analysis. The maximum electric field strength of the ILPD is 4.68% lower than that of the OLPD, leading to a higher lightning breakdown voltage. High-speed camera shooting shows that the discharge arc may lead to the erosion of the discharge tube, reducing its insulation performance. A large current impulse test platform is set up for arc energy analysis, which indicates that more than 90% of the energy is absorbed by the varistor during lightning stroke. The quality and leakage current of the discharge tube did not change significantly after testing. Given the current design of varistors, the per unit length energy of arc is less than 4.5 J/mm due to the numerical calculation, which is far less than the experimental arc energy (25.0 J/mm). Therefore, arc erosion will not cause the insulation performance of discharge tube to decrease when using the current varistor design.