Failure Analysis of Conductive Rod in Traction Transformer

Aimed at the fracture failure of the conductive rod in a locomotive traction transformer, chemical composition analysis, microstructure examination, fracture observation and mechanical properties testing were carried out to identify the failure cause. The results show that the chemical composition and tensile strength of the failed conductive rod meet the requirements, but the room-temperature elongation is only 7.5%, approximately one-third of that of a non-failed conductive rod from the same batch. Additionally, the grain size of the failed conductive rod is larger, up to level 3, while that of a non-failed conductive rod from the same batch is level 9. In the high-temperature endurance test conducted under conditions of 120 ℃ and 180 MPa, the sample of failed conductive rod fractured after only 42.8 hours of holding, and the fracture nearly has the same features as the original fracture, both presenting intergranular cracking features. Therefore, it can be deduced that the main failure process of the conductive rod is that with the temperature rising at the working conditions, the conductive rod cracked and disruptive discharge took place. The instantaneous high temperature caused by discharge led to the volatilization of high-pressure oil, triggering the alarm. High-temperature creep is the direct cause of the fracture of the conductive rod, and the coarse original grains are the root cause of the poor creep resistance and the failure.