In past few years

the voltage level of HVDC transmission system has been increased dramatically andequipment in the valve hall has become denser. Therefore

insulation requirements should be more stringent

espe-cially for the ±1 100 kV UHVDC valve hall. To testify if the fittings can fulfill the insulation constraints

we get theelectric field distribution of the fittings by using finite element numerical calculation. However

the mixture of theDC and AC voltage in valve hall makes the problem very complex. We take both of the electrostatic and transient elec-tric field method

and the results have shown the transient electric field can be predicted by calculating the field in-tensity in the condition of direct voltage. For researchers

electric field computational results will give a guideline onhow to choose a proper fitting and how to optimize structural parameters of the fitting. Furthermore

in the process ofcomputation

main structural parameters that have a strong effect on field intensity can be concluded. By embeddingthe simulation calculation in the fitting design

the design period will be shorten and substantial cost reductions canbe attained at the same time.