Design and Simulation-Based Verification of an 1100‑kV AC Grid Substation Supplying a 10‑GW Load

Abstract This paper presents the design of an ultra-high-voltage (UHV) ac substation with a highest voltage for equipment of 1100 kV that delivers 10 GW into a 400-kV network and verifies every rating-determining decision by simulation. Four 1100-kV feeders (2 × 280 km and 2 × 320 km, 8 × ACSR 630/45, surge-impedance loading 4203 MW) supply five banks of 3 × 1000-MVA single-phase autotransformers, and twelve 420-kV feeders on six double-circuit routes distribute it. One consistent set of models supports the design: Carson–Deri line parameters, a 24-bus Newton–Raphson load flow with N-1, N-2 and P–V analysis, IEC 60909 sequence-network short-circuit analysis, multimachine transient stability, a three-phase Bergeron electromagnetic-transient model with Monte Carlo switching, IEC 60287 and IEC 60076-7 thermal models, and a two-layer boundary-element grounding model. Simulation revealed six findings missed by a deterministic preliminary design: with solidly grounded neutrals the single-phase fault at a two-bank 420-kV section reaches the full 63-kA rating, which a 10-Ω neutral reactor reduces to 48.4 kA; 1600 Mvar of switched capacitors is needed to keep the STATCOMs in reserve; a stuck center breaker gives a critical clearing time of 108 ms, shorter than the 150-ms breaker-failure clearing, which 1.1-GW generation rejection raises to 166 ms; transformer-terminal and bay-located gas-insulated arresters are indispensable; the 420-kV transformer connections require gas-insulated lines in hot desert soil; and autotransformer neutral-current reversal makes the grid discharge 69.8 kA, more than the fault current. The verified design has 1800/2400-kV switching/lightning withstand levels with 3.7–8.5% and 15.5% margins, a 55% voltage-stability margin and 99.83% full-load efficiency.