To suppress very fast transient overvoltage （VFTO） on gas-insulated switchgea （rGIS）

a new approach was proposed by applying small and large magnetic rings. A test platform consisting of a VFTO generator and a real 500 kV GIS was employed to conduct a series of comparative experiments in the absence of magnetic ring

in the presence of 40 and 80 cm （in length） small ring string respectively

and in the presence of 80 cm small ring string together with 10 cm largering string. The charging voltage was 460

500

540 and 560 kV

respectively.The small rings were made of ferrite

and the large rings were made of nanocrystalline. Experimental data shown that combination of small and large ring strings can achieve better suppression effect on VFTO

and the longer the ring string

the better the suppression effect.