Joint Resistance of Bolted Copper - Copper Busbar Joints Depending on Joint Force at Temperatures beyond 105 °C

The long-term behaviour of bolted joints used in high current systems is influenced by different ageing mechanisms. One of these mechanisms is the degradation of the joint force depending on temperature and time. If the joint force falls below a critical value, the joint resistance, the thermal dissipation and thereby the temperature of the joint can increase to a critical level. According to IEC 61439-1 the highest accepted temperature of joints is 140 °C. The influence of the force reduction to the ageing of joints is tested on current-carrying, bolted Cu-ETP (CW004A) busbar joints utilizing washers und spring washers at temperatures up to 160 °C. The joint force and the joint resistance are measured time-dependent. The possible physical mechanisms are discussed regarding to the results of the long-term tests and analyses of the busbar material by microscopic investigations. Based on this experimental data an extrapolation of the lifetime of such electrical joints is discussed in relation to the practical operating lifetime of more than 50 years.