A Fatal Accident Caused by Aeolian Vibration Induced Fatigue of an ACSR Distribution Line

摘要

A span of 7,200-volt electrical distribution line made of swanate ACSR failed by aeolian vibration induced fatigue. A resulting fatality led to litigation against the utility company which owned the span. In discovery it was revealed that, in a previous incident, a vehicle had driven into a down-guy supporting the pole where the fatigue failure occurred causing an overload failure where the conductor was gripped in a dead-end shoe. The failure was repaired by clamping the broken end back into the dead-end shoe and making up for the reduced length by inserting an extra insulator. The utility company did not deny that the failure which caused the fatality was caused by aeolian vibration but claimed that cracks had been created in the central steel strand of the ACSR during the prior incident, and that one or more of these had grown by fatigue to cause the failure. Thus the failure was not foreseeable and was not the result of negligence in the design or maintenance of the span. To support this defence the utility cited some experiments carried out for them by a consultant in which 12 inch (0.305 m) lengths of swanate ACSR were tested to failure and then retested after each broken end was reinserted in the grip. It was found that in the second test failure always occurred at an ultimate tensile load about 15% lower than in the first. These experiments were repeated by the writer and the same result was obtained. It was suspected at first that this effect was due to the change in specimen length or strain-rate in the second tests but further experiments showed that this was not the case. The problem was resolved when it was found that if both ends were remounted in their grips after the first test the 15% reduction in failure load was not observed. Thus, it was due to damage to the specimen at the grip remote from the failure sustained during the first test.