Lightning overvoltage suppression to UHV power transformer by ferromagnetic ring

Lightning overvoltage protection is of great importance to the safety of devices in UHV GIS. In practice, insulation failure of UHV transformer due to lightning strike is often reported. The widely used UHV metal-oxide arresters can suppress the magnitude of lightning overvoltage but lack effectiveness on alleviating the steepness. A new protection method is proposed in this paper using ferromagnetic ring as supplement to the arresters in suppressing lightning overvoltage within UHV GIS. Moreover, equivalent model based on the characteristic of ferromagnetic material and factual dimensions of the ring is established. Simulation of an actual 1000 kV GIS is carried out to thoroughly evaluate the lightning overvoltage suppressing effect of ferromagnetic rings with different materials and structure parameters.

► An effective new way is proposed to suppress lightning overvoltage on transformer in UHV GIS by equipping ferromagnetic ring at terminal of power transformer.
► Good lightning suppressing effect (decreasing the magnitude by over 30%, and steepness over 50%), possible act as supplement to metal-oxide surge arresters.
► Proved nonlinear simulation model of the UHV ferromagnetic ring is established and validated.
► Simulation analysis presents the impacts of magnetic material selection and size of the ring on its suppressing effect.