Insulating tubular bus bars have been widely used as connecting lines in recent years. However

faults occur frequently in their service due to lack of effective regulation. In this study

a 35 k V insulating tubular bus bar in a substation was analyzed in terms of the structure design and the abnormal behaviours. Disassembly inspection and tests were conducted

and the results indicate that the abnormal operation of the bus bar is caused by mismatch of the semi-conductive layer and the folded copper strip. Simulation shows that the electric field concentrate sat the position where semi-conductive layer is worn off by the folded copper strip

and there is a positive correlation between the electric field at the worn position and the size of the position. Further

as the semi-conductive layer is weak in electric strength and flame resistance

this defect develops quickly to induce bulging

smoking and burning in the existence of partial discharge. In addition

structure design and materials of the bus bar

as well as their effects on electrical properties of the bus bar

are also discussed

and some suggestions on safe operation of the bus bar are given with respect to production

operation

and detection.