A Non-Perturbative Approach to Modelling Electromagnetic Pulse Effects on Nigerian Power Grid Infrastructure

High-altitude electromagnetic pulse events, whether from solar coronal mass ejections or adversarial nuclear detonations, pose a potentially catastrophic threat to long-distance electrical transmission infrastructure. Nigeria's 330 kV and 132 kV transmission network, comprising several thousand kilometres of overhead line, is highly susceptible to geomagnetically induced currents and fast transient EMP coupling that could induce voltages sufficient to damage transformers and protection systems. This study develops a non-perturbative electromagnetic modelling framework for EMP coupling to Nigeria's transmission grid, overcoming the limitations of perturbative approaches that break down for large induced currents in non-linear ferromagnetic transformer cores. The framework integrates a full-wave time-domain finite integration technique model of EMP propagation in the Earth-ionosphere waveguide with a non-linear transformer circuit model employing measured magnetisation curves for Nigerian grid transformers. The complete Nigeria 330 kV grid topology is parameterised from NERC network planning data. Both E1 (fast pulse) and E3 (magnetohydrodynamic) EMP components are modelled for worst-case and median threat scenarios. Results demonstrate that 13 of Nigeria's 23 operational 330 kV transformers exceed peak geomagnetically induced current thresholds associated with core saturation damage under the worst-case E3 scenario. The study provides a technical basis for EMP protection investment prioritisation. Keywords: electromagnetic pulse, power grid, EMP modelling, geomagnetically induced current, Nigeria transmission