Investigations on the Path of Defect-Induced-Discharge in GIS under AC/LI Superimposed Voltage

Gas Insulated Switchgear (GIS) may withstand AC/lightning impulse (LI) superimposed voltage which enhances the probability of discharge and threatens the safety of GIS. To further investigate the discharge properties and mechanisms in GIS under AC/LI superimposed voltage, a multiocular vision system was employed to get the three-dimensional path of the discharge channel induced by a protrusion in high-pressure SF
₆
gap and the emission angle θ was also studied under different discharge conditions. It was found that the path of discharge channel presented two distinct modes, which dramatically affected the breakdown voltage
U
_s
. In Mode I, the discharge channel developed along the centerline of the protrusion and θ was ≤20°, where
U
_s
was lower than
U
_LI
. In Mode II, the discharge channel bypassed the millimeter-magnitude region in front of the protrusion and θ was 50°-70°, where
U
_s
increased by over 20% than
U
_LI
. When a LI was superimposed to AC
_φ=270°
the discharge path was basically all in Mode II, because the low-amplitude high-repetition partial discharge in negative phase could induce a strong corona stabilizing effect which restrained the development of discharge path. when LI was superimposed to AC
_φ=90°
-LI could enhance the electric field before the protrusion and promote the discharge, resulting in a Mode I and lower
U
_s
, while +LI would counteract the electric field and lead to an increase in
U
_s
. The results were helpful for understanding the discharge mechanism of defect-induced-discharge in GIS under AC/LI superimposed voltage.