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Temperature screen/sheath

The formulae to calculate the loss factor for screen and sheath $\lambda_1$ use the resistance of the sheath $R_{sh}$ or screen $R_{sc}$ at its maximum operating temperature. Because the temperature of the sheath or screen is a function of the current, $I_c$, an iterative method is used for the calculation.

With crossing heat sources, a temperature rise of $\Delta\theta_{0x}$ applies at the hottest point.

Symbol
$\theta_s$
Unit
°C
Formulas
$\frac{\theta_{sc}+\theta_{sh}}{2}$average screen || sheath
$\Delta \theta_{c,t}-T_1 W_c$transient (approximation) CIGRE WG B1.72
Related
$\Delta \theta_{0x}$
Temperature rise by crossing heat sources [K]
$\Delta \theta_{c,t}$
Transient temperature rise conductor [K]
$T_1$
Thermal resistance conductor—sheath [K.m/W]
$\theta_{sc}$
Temperature screen [°C]
$\theta_{sh}$
Temperature sheath [°C]
$W_c$
Conductor losses (phase) [W/m]