Failure Analysis of Aluminum Alloy Terminal Board in Substation

The causes of terminal board cracking in a substation were analyzed comprehensively from the aspects of chemical composition, mechanical property, microstructure, fracture morphology and structural design. And preventive measures were proposed to avoid the recurrence of similar accident. The results show that the content of iron in the failed aluminum alloy terminal was higher than that in the standard aluminum alloy ZL108. A lot of brittle β phases (Al-Fe-Si) and hole defects existed in the microstructure of substrate, which significantly reduced the mechanical strength of the material. The unreasonable design of the terminal board structure caused stress concentration at the junction of vertical plate and bottom plate. And stress corrosion cracking was induced with cooperation of the oxygen and sulfur corrosion medium. The galvanic corrosion between the aluminum alloy and the capacitive voltage transformer (CVT) steel plate occurred through corrosive medium during service, which further reduced the strength of the aluminum alloy, accelerated the crack propagation, and finally led to the terminal board fracture.