Simulation-Based Time-Domain Short-Circuit Fault Evaluation and Protection System Reliability Analysis in 300MVA Substations with 132kV Transmission Lines

This study conducted a simulation-based time-domain short-circuits fault evaluation and protection system reliability analysis in 300 MVA substations with 132 kV transmission lines in Asaba (Ibusa/Asaba), Delta State, Nigeria. The analysis focused on two primary parameters: protection system dependability and selectivity, to determine the conditions necessary for ensuring rapid fault clearance and stable substation operation under line-to-ground, double-line, and three-phase faults. Fault currents, voltages, and relay trip signals were generated and analyzed using MATLAB time-domain simulations. Results indicated that system dependability exceeded 97% and security surpassed 95% when total fault-clearing times remained below 120 ms. Relay coordination intervals of 0.2–0.4s, backup misoperation below 3%, and circuit breaker MTBF above 20,000 h ensured selective fault isolation. Extended fault durations beyond 120ms or improperly coordinated relay settings increased the likelihood of misoperation and voltage instability. It was concluded that uninterrupted substation operation depends on integrating time-domain fault evaluation, coordinated relay settings, and reliable breaker performance into protection management protocols. Accordingly, it was recommended that substation operators maintain precise relay coordination, implement continuous time-domain monitoring, and uphold breaker maintenance schedules. These actions will further enhance the protection reliability, reduce fault propagation risks and support safer, more stable operation of the 132 kV transmission network.