Suppression of Transformer Oil Surges Caused by External Short-Circuit Faults Using an SFCL

When an oil-immersed transformer experiences an external short-circuit fault, the current flowing through the windings increases abruptly. The large electromagnetic forces generated by this fault current can induce violent vibrations in the windings and subsequent oil surges. Once the Buchholz relay (BR) detects an oil flow velocity surpassing its threshold, it erroneously cuts off the transformer. Such BR malfunctions have resulted in successive widespread power outages and economic losses in recent years. Given that significant fault currents passing through windings are the root cause of intense oil surges, a novel approach for suppressing transformer oil surges under external short-circuit faults by superconducting fault current limiters (SFCLs) is proposed. Specifically, a sophisticated electromagnetic–mechanical–fluid coupling model, which allows for the quantitative calculation of the mechanical response of transformer windings and the transient oil surge characteristics, is developed to estimate the efficiency of the suggested approach. The results indicate that applying an SFCL to a transformer rated at 40 MVA can reduce the velocity of oil flow through the BR by approximately 60%, effectively preventing unplanned transformer shutdown.