In the last decade, compressed Gas Insulated
Substations (GIS) and compressed Gas Insulated Bus Duct
(GIBD) have been already developed with using various SF6-gas
mixtures in order to reduce the disadvantages of using pure SF6-
gas. The presence of contaminating particles inside gas insulated
bus duct is one of the things that affect on the insulation design.
In this paper, the Finite Elements Method (FEM) is used to
evaluate the electric field distribution on and around multicontaminating
wire particles with presence of different shapes of
insulating spacers such as di-post and tri-post spacer inside gas
insulated bus duct. With di-post spacer, the effect of two
protrusions rested on the coating of earthed enclosure of GIBD
on the electric field values is studied. The effect of length and
radius of one protrusion at constant length and radius for
another protrusion and also with constant spacing from
insulating spacer on the electric field values are studied. With tripost
spacer, the effect of three stick particles at different height
from earthed enclosure on the electric field values is presented.
Breakdown voltage calculations for various SF6-gas mixtures
around multi-contaminating wire particles and protrusions with
various shapes of spacers are carried out. The effect of gas
pressure for all cases which mentioned above on the breakdown
voltage is studied. The optimum gas mixture which gives higher
dielectric strength with lower cost is determined. Finally, the
percentage of reduction in breakdown voltage due to presence of
two ground protrusions with different cases is carried out.