Failure analysis on fusing of power cable in main transformer control circuit for nuclear power plant

The main transformer control circuit is used to control and distribute electric power, and its reliability plays an important role in normal and stable operation of a nuclear power plant. In this paper, an unexpected fusing failure occurring on one power cable inside the cabinet of the main transformer control circuit of a nuclear power plant was addressed. By means of comprehensive investigation including morphologies observation of the fused area, materials characterization of the copper conductor and polymer insulation sheath, and compositions analysis of the corrosion products, it was identified that the failure was mainly resulted from the multiple factors in the manufacturing, installation and operation procedures. Under this condition, the root cause and contributing factors of the failure were determined, and a vicious circle that was originated from mechanical damage, accelerated by electrochemical corrosion, and functioned via heat accumulation was proposed to describe the failure process and relevant mechanisms. Based on the analysis results, the countermeasures were proposed, which would have reference values for failure prevention of power cables serving under similar environments.