Research on the Strands Fracture Caused by Poor Compression in the Strain Clamp

Abstract

Poor compression in the strain clamp often makes the strands overheat and fracture. There exists a certain gap between conductors and the strain clamp if the strain clamp is compressed poorly. The ashes, oxide, corrosion and abrasion tend to gather and scale in the gap, forming scale layers of high resistivity. As the exposure time increases, the layers expand and thicken, which causes the worsening of conductive properties of current and heat, and leads to abnormal temperature elevation, the degradation of microstructure and properties and strands fracture at last. In consideration of this kind of strands fracture phenomenon and through FEM, non-uniform temperature field influenced by scale layer in the clamp has been analyzed and the quantitative relationship between the scale layer, peak temperature and current has been obtained. The results of material experiments show that the strands vary from each other in the roundness of shear lips. Serious erosion is found on the surface of outer Al (aluminum) strands attaching to the clamp, while there is almost no erosion mark on the surface attaching to inner Al strands. Erosion spots in Al strands surface attaching to the scale layer are the deepest, and each erosion pit is large and some of which have even developed into plaques. The interacting deterioration of scale and temperature causes the Al strands attaching to the scale layer to fail and then led to fracture-temperature domino effect of other strands. The longitudinal fibrous microstructure of steel strands disappeared as the temperature rose. The plasticity of strands increased after recovery and recrystallization. The rapid degradation of mechanics properties resulted in the drop accident of conductors.