PULLFLEX-new software for duct-cable pulling forces

This paper addresses the need to increase the section lengths of electrical distribution cables in underground duct by reducing the uncertainty of present analytical predictions for maximum pulling forces exerted on the cable during installation. New analytical models are proposed to take into account several additional effects related mainly to the bending stiffness of the cable. These bending effects, neglected by the classical Rifenburg-Smith model available to date, are in some cases responsible for substantial increases in pulling forces. The new models consider the geometrical and physical nonlinearity of the behavior of a cable stiff in bending and subjected to high tension. However, they are all fairly approximate in nature because they are based on simplifying assumptions aimed at obtaining conservative analytical results for the pulling forces to use in the line design. Based on these bending models, a new computer program, PULLFLEX, has been developed which is able to calculate and check all the mechanical limits of the cable, including pulling tensions and sidewall bearing pressures. The program was validated by comparison with field measurements taken on several underground sections, some built specially for testing and others part of real lines. All validations were done in typical Hydro-QuBbec conditions for a 25-kV three-phase cable with bare concentric neutral, installed without lubricant.