The transient period $\tau$ is the number of hours of the loading cycle, usually 24 hours.

With a period of 1 year, a soil diffusivity equivalent to the general and a load factor approaching unity, the current rating approaches steady-state load as defined by IEC. A longer transient period would reach a current rating below the steady-state value. Because we allow to select the soil diffusivity for each system separately, this may cause problematic effects for long transient periods. Therefore we limit the transient period to 1 year for buried cables.

Symbol
$\tau$
Unit
s
Used in
$\alpha_{\mathrm{t}}$
$\beta_{\mathrm{6}}$
$D_{\mathrm{x}}$
$\Delta \theta_{\mathrm{c_{\mathrm{t}}}}$
$\Delta \theta_{\mathrm{d_{\mathrm{t}}}}$
$\Delta \theta_{\mathrm{e_{\mathrm{t}}}}$
$\Delta \theta_{\mathrm{kp}}$
Choices
secondsof the transient period
60010 minutes
36001 hour
72002 hours
216006 hours
3600010 hours
4320012 hours
5040014 hours
8640024 hours
12960036 hours
315576001 year = 365.25 days