Joints and Clamps for Aluminum Conductors

Experience with conductor joints and clamps in a large transmission system is outlined with particular reference to aluminum-aluminum and aluminum-copper connections. Three investigations are described in which outdoor exposure tests were made on live-line tap clamps, U-bolt clamp connections between ACSR (aluminum cable steel reinforced) and copper cable, and various types of sleeve joints in ACSR. During the exposure period of five to seven years, they were subjected to a load cycle, and periodically, measurements of electrical resistance were made. Following the exposure, specimens were examined for corrosion, and subjected to heat runs and short-circuit current tests. Live-line tap clamps of the screw type were found superior to spring type. Preferred material for clamp surfaces in contact with ACSR was aluminum. Coatings of zinc or tin on bronze clamps retarded corrosion of the ACSR strands. In U-bolt clamps serious corrosion of ACSR strands occurred where they contacted clamp parts of copper, even though the copper was coated with zinc or cadmium. Aluminum separators between copper cable and ACSR maintained the lowest resistance and caused least corrosion. The use of No-ox-id lessened corrosion especially where dissimilar metals were in contact. Hydraulically-compressed sleeve joints in ACSR were superior to those pressed with hand tools or twisted sleeve joints. The resistance of twisted sleeve joints was affected more than compression joints by variations in type of filler. The application of these and other observations to field practice is discussed.