The insulating sheath is wrapped in the busbar of the substation to play the role of anti-corrosion and insu-lation protection. However

when a foreign object is lapped on the busbar of the insulated sheath

the phase-to-phaseshort-circuit accident often occurs. The specific cause of the accident is not clear

which seriously affects the grid

safe and reliable operation. Based on the finite element method

the busbar model of the wrapped insulation sheathunder typical fault conditions（air gap defects and lapped foreign objects）is constructed. The three-dimensional pow-er frequency electric field calculation is carried out on the wrapped insulation sheath busbar

and the insulation pro-tection is analyzed. The internal and surface electric field distribution of the insulating sheath caused by the internalair gap defect and the external foreign matter overlap

and the influence of the thickness of the insulating sheath onthe electric field distribution is studied. The results show that when there is air gap defect inside the busbar wrappedwith insulating sheath and external foreign matter overlap

electric field distortion will occur in the inner and surfaceof the insulating sheath. The degree of electric field distortion is: lapped metal>lapped wet branch>lapped drybranches>heat shrinkable air gap;increasing the thickness of the insulating sheath will help to improve the electricfield distortion on the surface and the inner part of the insulating sheath caused by foreign matters

which is differentto the metal The distortion of electric field can be reduced by 68%.