
384 Power System Transients
At a high conductivity of σ = 10
3
S/m, the depth d of penetration for an elec-
tromagnetic wave of frequency f into a medium of conductivity σ andper-
meability μ
0
is relevant for loss calculations. This depth is givenby
d
f
=
2
0
πσµ
(5.81)
For μ
0
= 4π × 10
−7
H/m, f = 30 MHz, and σ = 10
3
S/m, Equation 5.81 yields
d = 2 mm, which is close to the thickness of the semiconducting layer (3 mm).
Therefore, most of the axial current ows in the semiconducting layers rather
than on the core and sheath conductor surfaces. This results in signicant
signal attenuation and dispersion.
5.2.6 Air-Insulated Substations
In order to esti ...