VFTO (very fast transient overvoltage) has caused serious damage to the stable and safe operation of power equipment. Therefore, it is of great significance for accurate measurement of VFTO. Aiming at the widely used VFTO sensor based on coupling capacitance method, the 2 kV square wave calibration platform has been designed in this paper through using coaxial transmission cavity structure to simulate GIS busbar. The effects of different cavity structure parameters on the transmission characteristics of the square wave calibration platform are explored by simulation research, and the structure optimization scheme is given. The simulation results show that when the outer diameter of the inner conductor of the coaxial transmission cavity is 43.46 mm and the inner diameter of the outer conductor is 100 mm, the wave impedance of the coaxial transmission cavity is 50 Ω. The inner conductor insulation support shall adopt the tri-post insulator, and the square wave source has better transmission performance when the length of conical coaxial transmission line is 380 mm, and the end matching segment has an exponential shape with the length of 30 mm. Combined with the results of simulation research, the square wave calibration platform is built. The output amplitude is greater than 2 kV and the rise time is less than 1 ns, which meets the calibration requirements of VFTO sensor.
