Gas Insulated Busduct (GIB) is the most preferred choice for high voltage(HV) applications to meet the power demand. The switching operations and manufacturing process can result in various flaws, such as delamination, protrusion, depression, void, etc., which lead to insulator failures in GIBs. These defects have a significant negative impact on the distribution of the field along the length of the spacer, which de-energizes the entire GIB system and causes a significant economic loss. A spacer of post type with Functionally Graded Material (FGM) is designed in this paper for a 3-phase GIB under delamination to mitigate the electric stresses along the length of the pacer.Aluminium oxide (Al2O3), Titanium dioxide(TiO2) and Silicon dioxide (SiO2) with Epoxy resins are combinedly used for fabrication in different types of FGM materials.Additionally, a particle has been added at high operating voltages to analyze the spacer's unfavourable behaviour, and the stresses have then been reduced by inserting metal pieces. The Glerekson’s finite element approach is used to evenly distribute the field throughout a material composed of FGM and filler material of varying permittivity. The proposed spacer is simulated for different operating voltages (72.5kV, 132kV and 220kV) with delamination and particle as defects. By adding a metal insert(MI) to the post-type spacer, the effect of aluminium particles with delamination is decreased, and the findings are then presented and studied.