Testing of mechanical joints in aluminium conductors for insulated cables

Abstract

The increasing use of aluminium conductors in insulated cables has created a need for a standardized testing procedure for the evaluation of joints in the conductors. The paper proposes electrical and mechanical evaluation tests which can be used as a basis for discussion preparatory to the formulation of a test specification. The tests are based on theoretical studies and practical experience relating to the mechanism of current transfer through an aluminium contact interface and of the thermo-mechanical stresses set up in the cores of insulated cables. For the electrical tests it is proposed that the joints should be subjected to 2000 load cycles at defined currents based on the maximum current loading likely to be experienced in service, followed by 12 short-circuit impulses of amplitude and duration dictated by the thermal limitations and bursting strength of the cables. It is recommended that a joint should be considered satisfactory if, at the end of the electrical tests, its resistance does not exceed 150% of the equivalent conductor resistance. In the mechanical test it is required that the joint should be capable of withstanding a tensile stress equal to 50% of the ultimate tensile stress of the associated conductor.