Minimising transmission losses via coordinated deployment and control of phase shifting transformers: a case study on the IEEE 300-bus system

Phase Shifting Transformer (PST) offers a robust means of controlling power flows and effectively rerouting them away from heavily loaded transmission lines. Although PSTs are primarily deployed for congestion management, their ability to redistribute currents across parallel paths means they can also be used to reduce network I²R losses. This paper presents an optimisation framework for minimising active power losses in transmission networks through coordinated deployment and control of multiple PSTs. The problem is formulated as an AC optimal power flow with explicit representation of PST tap positions, yielding a mixed discrete–continuous and highly non-linear search space. To address this challenge, an enhanced DOL–Jaya–AEPI algorithm is developed, which eliminates parameter tuning and integrates elite seeding, dynamic opposition-based learning, and adaptive escape, improving robustness and search efficiency compared to conventional heuristics. The framework is tested on the IEEE 300-bus system using the MATPOWER platform, which provides a standard benchmark for large-scale AC power flow studies. Results show that the algorithm consistently identifies feasible solutions and achieves measurable reductions in losses, with the best outcome obtained using three PSTs, achieving a reduction of about 4% compared to the base case.