The burr defects on the surface of a grading-and-shielding ball in the valve hall of a converter station will have a great influence on its discharge characteristics. In this paper

photoelectric integrated electric field sensor and photomultiplier tube are used to build a photoelectric combined detection system to measure the instantaneous optical power and space electric field during the discharge at the long air gaps of 3 m rod-plate

ball-plate

and ball-plate with burrs under positive standard switching impulse voltage. The test results show that the characteristic parameters of the three kinds of gap structures

such as the initial streamer start time

the initial streamer field strength jump value and the distorted electric field recovery time

are quite different. When the ball-plate gap is taken as a reference

the above three parameters of rod-plate gap decrease most obviously. When there are 3 mm micro burrs on the surface of the ball

the above parameters will decrease by 33.4%

68.7% and 68.8%

respectively

and are close to those of rod plate gap

thus the burrs will change the discharge characteristics of the ball-plate gap drastically. Therefore

it is necessary to strictly promote the surface processing and installation process of the grading-and-shielding ball to avoid burrs and other defects. The research achievements in this paper are of great significance to the understanding of the mechanism of long gap discharge process and improvement of the gap insulation performance.