Analysis of Power System Network Stability In Rwanda

Abstract

Power system stability is a critical requirement for ensuring reliable and secure electricity supply, particularly in developing power systems experiencing rapid demand growth and increasing penetration of renewable energy sources. This study evaluates the stability of Rwanda’s electricity grid with a focus on transient, voltage, and frequency performance under realistic operating and disturbance conditions. A detailed model of Rwanda’s national power system was developed using Power System Simulator for Engineering (PSS®E), incorporating actual network parameters for generation, transmission, substations, and load centres. The model was verified and validated against available SCADA measurements before being subjected to steady-state power flow analysis and time-domain dynamic simulations. Stability performance was assessed under peak and off-peak loading conditions, generator and line outages, and renewable generation disturbances. The results show that the transmission network is generally lightly loaded, with maximum line loading of approximately 25% during off-peak and 46% during peak conditions; however, localised infrastructure constraints exist at critical substations, where transformer loading reaches up to 96% under normal operation and exceeds 130% under N-1 contingencies. Voltage stability analysis reveals widespread off-peak overvoltage, with several 110 kV busbars exceeding 120 kV, while dynamic simulations indicate slow voltage recovery following disturbances. Transient stability assessment demonstrates adequate stability margins, with critical clearing times ranging from approximately 200 ms to over 1000 ms, exceeding typical protection clearing times. Frequency stability analysis identifies limited spinning reserve as a major vulnerability: system frequency drops to 48.83 Hz following loss of 6.5 MW of solar generation when only 4 MW of reserve is available, necessitating under-frequency load shedding for recovery. The study further demonstrates that targeted mitigation measures significantly improve stability. The installation of shunt reactive power compensation reduces overvoltage and improves post-fault voltage recovery, while increased local generation or reserve capacity mitigates frequency excursions and reduces dependence on load shedding. Overall, the findings confirm that while Rwanda’s electricity grid possesses adequate transient stability, its operational performance is constrained by reactive power management challenges, low reserve margins, and topology sensitivity. The study provides practical insights for system operators and planners on improving voltage and frequency stability through targeted network reinforcement and operational strategies