Aging of defective electrical joints in underground power distribution systems

Electrical joints can be weak points in an underground distribution supply system. Cyclic loads and the fact that electrical joints are inside premolded rubber cable joints both greatly affect their reliability. Within the framework of a preventive maintenance program, we have studied the life expectancy of underground cable joints with defective electrical joints. Three types of cable joints were subjected to cyclic current loads: elbow separable connectors, straight joints, and 'T' joints. These represent three kinds of electrical joints: bolted Cu to Cu, crimped Al to Al, and bolted Al to Al. These joints had slight to severe defective electrical contact (a defective joint is defined as one having an above than normal operating temperature). Temperature was monitored at several points both inside and outside the cable joints. Experiments were conducted until electrical breakdown or loss of electrical contact. Evidence of fretting and self healing are also reported in this paper.