Research on shielding effect of background electric field for GIS bus with a conductive protrusion under impulses

Gas-insulated metal-enclosed switchgear (GIS) is an important switching equipment in modern power system. The lightning impulse (LI) test is particularly sensitive to abnormal field configurations and is recommended in IEC 62271-203 and GB 7674-2008 for voltage classes of 245 kV and above. Usually, the rod-plane electrodes system with different geometric parameters are adopted to simulate local field enhancement in GIS. But for GIS, the defects may occur in the high voltage bus. In this situation, it's not just the rod-plane electrode can be represented. In order to research the shielding effect of background electric field for GIS bus with a conductive protrusion under impulses, coaxial cylinder structure with conductive protrusion electrodes was used. Meanwhile, the classical rod-plane gap was also used to make a comparison. A generating system of double-exponential impulses with front times in the range of 0.08~15 μs and wave tail times around 50 μs was established to simulate different impulse test waveforms based on a fully enclosed oil-immersed Marx generator. The results show that when the gap distance is fixed, with the length of the needle increase, the 50% breakdown voltage decreases. Discharge characteristics under different electrode configurations are compared. It is found that the shielding effect of the bus on the defect changes the electric field distribution of the gap. The U50%-Tf curves of the bus with needle defects thereafter no longer show the U-shaped as the rod-plane electrode, but increase with the increase of wavefront time.