In 51 units t he permittivity of free space k0 is 8.85 X 10- 12 F/m (farads per meter). Relative
permittivity k, is the ratio of the actual permittivity k of a material of the permittivity of free space.
Thus, k, = kjk0 . For dry air k, is 1.00054 and is assumed equal to 1.0 in calculations for overhead
lines.