Development of an Optimal On-Load Tap-Changing Scheme for a Transformer to Improve Power Quality

Voltage instability remains a major operational challenge in large-scale transmission networks, particularly in developing power systems with increasing load demand. This paper proposes a coordinated on-load tap changer (OLTC) control strategy based on a Hybrid Particle Swarm Optimization–Grey Wolf Optimization (HPSOGWO) algorithm to enhance voltage stability and power quality. The proposed approach is validated on a practical Nigerian 56-bus, 330-kV transmission network using real system data obtained from the Oshogbo National Control Centre. Simulation results demonstrate that the proposed scheme restores all bus voltages within IEEE-recommended limits, achieving a 76.47% reduction in voltage deviation. In addition, active power deviation and reactive power loss are reduced by approximately 87% and 90%, respectively. Injection current analysis confirms balanced current distribution and safe system operation. The results validate the effectiveness and practical feasibility of the proposed HPSOGWO-based OLTC coordination scheme for real-world transmission networks.