Research on the overvoltage of cable sheath caused by the closing of unloaded transformers and suppression measures

Abstract To study the development laws and influencing factors of closing overvoltage during the grid connection process of power plants, this paper takes a certain pumped storage power station as the simulation object. First, it analyzes the overvoltage on the cable sheath. Then, based on the Electro-Magnetic Transients Program (EMTP), it simulates the transient characteristics of overvoltage generated by asynchronous closing of a no-load transformer, analyzes the operating overvoltage and cable sheath overvoltage produced by closing different numbers of main transformers, studies the statistical characteristics of overvoltage, and proposes measures to suppress overvoltage. The results show that during the grid connection process of the power plant, operating overvoltage will occur at the cable terminal (no-load transformer), and the overvoltage on the cable metal sheath exceeds a certain limit. Measures such as using series closing resistors or reactors, grounding the cable sheath through sheath protection devices, and interconnecting sheath crossings can reduce the overvoltage on the cable sheath.