2001 Volume 42 Issue 1 Pages 21-25
To complement the electric characteristics of contact wires, additional feeder cables are installed in railways in Japan. To save installation costs, lightweight and inexpensive stranded aluminum wires are used as additional feeder cables. They are bridged to contact wires every 250 meters and some strands break by the compression sleeve which connects the copper bridge wire and the aluminum wire, often resulting in disconnection accidents. We have obtained samples of broken strands which were 38 years old, and performed current loading experiments and material analysis. Through these experiments and analysis we found that the uneven contact resistance between aluminum sleeve and strand concentrates their current at only a few strands, which results in the strands being cut off by the Joule heat. On the other hand, There is concern about a disconnection accident occurring when the compression sleeve, which connects the aluminum wire and copper wire on the main circuits of power supply system, is superannuated. We have obtained superannuated samples which were 27 years old, and performed current loading experiments. Through these experiments we found that Joule heat is caused by the contact-resistance between the aluminum wire and aluminum sleeve, then the heat melts or deteriorates the alloy between the copper wire and aluminum sleeve to increase resistance value and Joule heat, and then the sleeve is overheated and at last melted down.