Transformer Protection in Large-Scale Power Systems During Geomagnetic Disturbances Using Line Switching

Geomagnetically induced currents (GICs) can increase the reactive power loss in transformers and potentially cause permanent damage due to overheating. This paper considers line switching as a remedial action to protect transformers from geomagnetic disturbances. The algorithm uses linear sensitivity analysis to find an effective switching strategy, which minimizes the number of opened lines subject to satisfying the transformer thermal limits. To reduce the computational complexity for large-scale power systems, the critical lines are identified through sensitivity analysis and the optimization is performed on the reduced system. Furthermore, the effect of GICs on the ac power flow solution is modeled and heuristic techniques are developed to provide sufficient security measures in terms of both GIC flows and ac analysis. Finally, a multiaction solution with an alternating schedule is developed for severe storms when the losses are significant and a single switching action cannot remove the stress from all transformers at a time. The actions are obtained through a recursive algorithm, which divides the original problem into smaller subproblems with fewer constraints and solves them recursively. The effectiveness of the proposed algorithm is demonstrated through numerical results using a 150-bus and a 2000-bus system.