Comparative Assessment of TCSC and STATCOM for Voltage Stability Enhancement under High Renewable Penetration: A Case Study of the Nigerian 330 kV Power Grid

Widespread penetration of hybrid renewable energy (HRE) sources with intermittent and non-dispatchable potential and little reactive power support into transmission networks comprised of weakly-structured transmission grids threaten voltage stability. This paper compares two FACTS controllers, the Thyristor Controlled Series Capacitor (TCSC), and Static Synchronous Compensator (STATCOM) in the long-term voltage and transient stability improvement of a renewable integrated network. Case study: Nigerian 330kV, 34 bus network. Based on identified renewable potential, Birnin-Kebbi and Kano buses are added wind and solar PV generation. Newton-Raphson power flows and continuation power flow (P–V curve) are combined with eigenvalue analysis to establish the steady-state stability. Three phase faults on the idealized network are used to analyse generator rotor angle and speed in transient stability. Pre-compensation in this weak renewable-based network illustrates severe undervoltage at Gombe (0.865 p.u.) and Jos (0.885 p.u.) buses, a critical loading limit of λ= 1.7337 and existence of a negative eigenvalue indicating some degree of latent small-signal instability.  Pre-compensation using TCSC (200% series compensation) during the critical loading marginally improved the Gombe and Jos bus voltages at 0.985 and 0.957 p.u., respectively, whereas STATCOM (200% shunt) improved voltages to 1.049 and 1.023 p.u.  With all bus voltages regulated within ANSI C84.1 norms. In a strongly renewable-based weak network, the STATCOM outperforms the TCSC in long-term voltage stabilization. Keywords: FACTS controllers; STATCOM; TCSC; voltage stability; transient stability; hybrid renewable energy.