Study of mechanical behaviour of cables in integral-pipe water-cooled systems

The movement of cables in integral-pipe water-cooled systems, owing to the thermal expansion which occurs under load, has been studied theoretically. The axial thrust on the anchor joints and the strain variations in the cable sheath have been calculated for certain assumed cable configurations; e.g. the cable may be assumed to take up a helical configuration or to `snake¿ sinusoidally along the bottom of the pipe. The principle of minimum energy has been used to determine the percentage of total cable length taken up in a given configuration in those cases where a mixed, e.g. part helical part sinusoidal, configuration is considered, and to establish the preferred configuration (from amongst those studied) for a given temperature rise. The theoretical predictions have been compared with results obtained in two CEGB field experiments, a full report of the work is given in a companion paper, and the degree of agreement achieved has allowed certain general conclusions to be drawn concerning the effect of the various cable parameters, e.g. flexural rigidity, mass, dimensions and the pipe diameter, on the behaviour of cables in such systems. Particular attention has been paid to the problem of metal fatigue in the cable sheath due to cyclic strain variations which will follow the cable loading patterns. Finally, provisional design criteria for the mechanical design of such systems have been suggested.