In order to study the effect of strong vertical components of electric field in a transformer bushing on switching impulse discharge characteristics

three structures with different electric field distributions were tested. The curves of 50% discharge voltage were obtained under two different wavefront time conditions. The bushing model of a 110 kV oil paper capacitor transformer was established

and the electric field distributions of three structures were studied by simulation. The processes of switching impulse discharge of three structures were observed by a high-speed camera. The results show that the vertical electric field component can affect the switching impulse discharge voltage by changing the degree of electric field inhomogeneity. For the structure where the capacitance core is removed to strengthen the vertical electric field

the sliding discharge will occur under switching impulses

and the upward streamer-leader process of air gap breakdown will be replaced by the sliding discharge. Compared with standard bushing products

the switching impulse discharge voltage is expected to increase by about 11.1%

which is due to the improvement of electric field uniformity and the barrier of sheds to the sliding discharge.