Equivalent circuit for the thermal analysis of cables in non-vented vertical risers

This study presents an alternative methodological approach for thermal rating of power cables installed in vertical risers covered by unvented circular protective guards. An analogue thermal-electrical circuit is proposed for the thermal analysis of cables inside vertical risers. The proposed equivalent analogue model is verified by means of indoor experiments and finite-element simulations with various cable and riser geometries for various load currents. Single cable and trefoil configurations are studied. Analysis performed on measured, simulated and calculated data establish the validity of the proposed model. Computations performed using the proposed method give results within 5% of measured conductor temperature. It is concluded that increasing riser height has minimal or insignificant impact on conductor temperature, whereas, reducing riser diameter, holding other variables constant increases conductor temperature and therefore reduces cable ampacity.