Spacer Involvement in Conducting-Particle-Initiated Breakdown in Compressed Gas Insulated Systems

This paper describes the results of an investigation into conducting particle initiated breakdown in a 76/250 mm coaxial electrode configuration, representative of a 145 kV gas insulated transmission line (GITL) or gas insulated substation. A free moving particle is known to initiate breakdown through a sequential two-stage process. The involvement of an epoxy disk spacer in such a breakdown, when the particle is at a distance from the spacer, is studied through specially designed experiments. For 6.4 mm long, 0.45 mm diameter aluminum particles it is observed that the discharge path may involve the spacer surface even when the particle is several centimeters away from the spacer surface. However, the 60 Hz ac breakdown voltages for discharge paths involving the spacer surface are not significantly different from those without spacer involvement, if the particle-to-spacer distance is greater than 3 mm.