Superannuated aluminum stranded wires often break at compression joints. It is said that the increase in the resistance between the compression sleeve and its inner strands generates Joule heat to cause disconnection of aluminum wire. The heated joints are generally detected by a red mark that appears on the thermo-rabel put on the compression sleeve when it is heated, which is not a complete method, however. In order to find and propose an improved method, therefore, we have had to explain the breaking process. Through current loading experiments and material analysis on old and damaged materials, we found two braking processes of damaged sleeve. One is that the uneven contact resistance between aluminum sleeve and strands concentrates their current into a few strands and their own Joule heat cuts the strands off themselves. The order is that the Joule heat generated by the contact resistance between compression sleeve and strands increases the temperature of the whole sleeve to melt it down. Then, we have built a new resistance measuring device.

Copyright (c) 2001 Railway Technical Research Institute