On the basis of an analysis of lightning overvoltages in the circuit of an overhead line and high-voltage underground line, it is shown that, when installing non-linear limiters at the beginning and end of a 100-500 kV underground transmission line, the dimensions of the insulation of such a line of various designs (oil-filled cables, polyethylene-insulated cables, gas-insulated lines) can be chosen only on the basis of ensuring an acceptable operating electrical field intensity.