Transmission System Islanding for Grid Resilience Enhancement in Nigeria: A Spectral Clustering-Based Approach to Transmission Expansion Planning

Abstract Nigeria’s 330 kV grid suffered 564 collapses between 2000 and 2022 and eighteen more between 2024 and January 2026, each cascading into a nationwide blackout because the network operates as a single synchronous area without islanding capability. In April 2026 the Nigerian Independent System Operator (NISO) announced grid islanding as a strategic priority. This paper evaluates whether controlled islanding is feasible and specifies the transmission expansion required to enable it. A custom 48-bus, 63-line model was built from Transmission Company of Nigeria and regulatory datasets, with the 132 kV layer represented as net-load injections. Newton–Raphson power flow gave base-case losses of 7.1%, severe Ferranti over-voltage at the lightly loaded north-eastern radial endpoints and deep under-voltage in the north-west. N-1 screening classified 58 of 63 single-line outages as critical. Spectral analysis of the susceptance-weighted network identified eight natural electrical communities; engineering constraints on generation viability, inertia pooling and tie-line structure selected a six-island partition, confirmed by the eigengap of a coupling-weighted Laplacian and aligned exactly with the six geopolitical zones. Only two zones were viable in the base case (Island Self-Sufficiency Index, ISSI, 72.7%). A US$2.65 billion expansion comprising 1,310 MW of distributed generation, 17 circuits, five substations, six Static VAR Compensators (SVCs) and Supervisory Control and Data Acquisition (SCADA)/Phasor Measurement Unit (PMU) upgrades raised the ISSI to 96.0%, made all six zones viable, restored every bus to the statutory band, cut critical N-1 contingencies from 58 to 5 (91%) and reduced losses to 2.2%. The Delta islanding event of 29 December 2025 provides empirical support for the operational feasibility of the approach. The results constitute an evidence-based roadmap for NISO’s islanding programme under the Electricity Act 2023.