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Very Fast Transient Over voltages (VFTOs) generate during operation of the disconnector switches or circuit breakers in a gas insulated substation (GIS). These transient voltages stress the insulation system in GIS and further result in mal-operation of the control circuitry as well as the secondary equipment connected to it. Since the VFTOs affect the reliability of GIS, it is necessary to mitigate them. This paper presents the mitigation of the very fast transient over voltages and the associated very fast transient currents (VFTCs) using the nano-crystalline rings in a 245 kV GIS. The mitigation in the peak amplitude of VFTOs and VFTCs at various locations in the GIS for various switching configurations are analyzed in this paper. The nano-crystalline rings of different geometries and permeabilities are considered to understand the damping effect being offered. The nano-crystalline rings are considered at all the possible switches of 245 kV GIS bays. An equivalent circuit model of the nano-crystalline ring is obtained through an iterative algorithm. The very fast transients have been calculated using Electromagnetic Transients Program software. Further, attenuation in the dominant frequency components of VFTOs and VFTCs at different GIS components is also studied for various switching configurations with nano-crystalline rings.

Suppression of very fast transients in 245 kV gas insulated substation