Effective steady-state thermal resistance in the earth:

In order to evaluate the effect of a cyclic load upon the maximum temperature rise of a cable system, Neher observed that the heating effect of a cyclical load can be seen as a wave front which progresses alternately outward and inward in respect to the conductor during the cycle (1953). He further assumed that the heat flow during the loss cycle is represented by a steady component of magnitude plus a transient component. The steady-state component of the heat flow will penetrate the earth completely, thus the corresponding thermal resistance $T_{4ss}$ will be larger than its transient counterpart $T_{4et}$ which penetrates the earth only to a limited distance from the cable.

$T_{\mathrm{4db}} + T_{\mathrm{4iii}}$with backfill
$T_{\mathrm{4iii}}$without backfill
Used in