To reduce the cost of production and the difficulty of assembly

optimization design of a three-phase-inone-enclosure type current transformer used in 252 kV gas insulated switchgear（GIS）is carried out

and both the electricfield intensity（EFI）within the transformer chamber and the mechanical strength of its shell are calculated with Ansys. The calculation results show that:the electricfield intensity concentrates in the coaxial gap between conductor and shield. The outer side of the connector between small flange on transformer shell and enclosure is the weak stress region; both the shell strength and the electric field strength within transformer meet the design basis with certain margin. Compared with the original design

the optimization design reduces the total height of the current transformer by 340 mm

and makes it more compact

lighter in weight

and cheaper.