In a number of GIS installations, the connection to the transformer is given through either SF6 / air bushing or SF6 / oil bushing. The VFTO generated internal to GIS may propagate to the transformer winding through the above capacitive graded bushing (generally 245 KV and above). The voltage distribution under very fast transients may be highly non-linear due to having frequency components in the range of 100 MHz and above. Further, continuous application of these oscillating, aperiodic over voltages to the capacitively graded bushing may cause discharges inside the bushing, which may progressively degrade its insulation strength. The voltage distribution across various layers of capacitively graded bushing has been estimated by representing the layers as an equivalent multi-stage ? sections with Pspice
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