📖 ABSTRACT/OVERVIEW
This research develops a unified theoretical treatment of electromagnetic transients in gas-insulated substation equipment operating at 330kV in the Nigerian transmission system, making original contributions to the modelling of lightning and switching overvoltage propagation through GIS busbars and equipment under the specific insulation coordination conditions applicable to Nigerian substations. GIS technology is being deployed by the Transmission Company of Nigeria under its grid expansion programme at major new substations, yet the transient overvoltage stress characterisation required for optimised insulation coordination designs specific to Nigerian lightning flash density and switching operation patterns is absent from the existing literature. The theoretical contribution centres on the development of a novel distributed-parameter electromagnetic transient model for GIS busbars that incorporates the frequency-dependent dielectric properties of sulphur hexafluoride and its N2 gas mixtures, the geometric propagation characteristics of very fast transient overvoltages within GIS enclosures, and the coupling of VFTO energy to secondary equipment through apertures and penetrations. The model is implemented in a custom finite-difference time-domain solver validated against published GIS transient measurement data from European experimental programmes. The validated model is applied to characterise VFTO magnitudes and rise times at three TCN GIS substations under construction, using actual Nigerian lightning flash density data from the Nigerian Meteorological Agency and recorded TCN switching operation profiles. Design recommendations for surge arrester placement and GIS secondary equipment shielding are derived from the simulation results. Keywords: gas-insulated substation, very fast transients, overvoltage, insulation coordination, Nigeria.
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