A three-core cable is represented as an equivalent single-core cable for long-term transients with duration $<PQ$.However, for very short transients with duration $<TQ$ where $TQ$ refers to a single core, the mutual heating of the cores is neglected, and a three-core cable is treated as a single-core cable with the dimensions corresponding to the one core. For durations between these two limits, the transient is assumed to be given by a straight line interpolation in a diagram with axes of linear temperature rise and logarithmic times.

$T_{\mathrm{A}}$

K.m/W

$T_{\mathrm{1t}}$ | long-term transients |

$\frac{T_{\mathrm{1t}}}{2 n_{\mathrm{c}}}$ | short-term transients |

$T_{\mathrm{1t}}$

$\delta \theta_{\mathrm{c}}$

$k_{\mathrm{t}}$

Temperature rise ratio [p.u.]

$M_{\mathrm{0}}$

$N_{\mathrm{0}}$

$T_{\mathrm{a0}}$

$T_{\mathrm{b0}}$