To analyze the corona onset around the conductor in a 750 kV substation in Gansu Province

an entire3 D model of single-pitch conductor is built with the software package Pro/E

and the whole electric field is calculated with finite element method. Then

the typical sub-models of such as jumper and fitting in the substation arebuilt individually

and the electric field is calculated more accurately by refine-meshing. Finally

the reason of on-set corona is analyzed and some suggestions of optimization are offered. Calculation result shows that:（1）the electricfield strength reduces with increasing split number of conductor

which is similar to that of 2 D model;（2）the maxi-mum field strength around jumper is optimized by replacing two-split conductor with four-split conductor

and themaximum value reduces from 2 512.54 V/mm to 2 410.36 V/mm

satisfying the limiting value;（3）compared with the T-mode six-to-two fitting

the improved six-to-two fitting reduces the surrounding electric-field strength by 1 174.79 V/mm

that is a reduction rate of 35.36%

which can effectively weaken corona phenomenon.