The 3D Accumulation Characteristics of Surface Charges on Actual 550 kV GIL Tri-post Insulator under AC Voltage in SF6

Surface charge accumulation is one of the most important factors causing surface flashover of gas-insulated metal-enclosed transmission line insulators. Surface charges not only distort the local electric field intensity but also provide charges for creeping discharge, which finally leads to flashover. The tri-post insulator is the most common applied insulator in GIL, and whose insulating properties could make the most significant contributions to maintain the safe and reliable operation of GIL. Aiming at discovering the accumulation characteristics of surface charge on actual GIL tri-post insulator in SF6 under AC voltage, a 3D surface charge measurement device based on electrostatic capacitive probe is developed in this paper, which has a charge resolution of 0.02803pC/(m2•nV) and a space resolution of 3.9mm2. The accumulation characteristics of surface charge under AC voltages with different voltage amplitude and different voltage application times were carried out. The results show that, in the context of AC voltage, there appears with both positive and negative charges accumulating on the surface. With the voltage amplitude increasing and application time prolonging, there are more charge accumulating on the abdomen zone than pillar zone, which could be attributed to the field strength differences in there two zones.