The pressure drop during circulation of the refrigerant limits the distance for superconducting power transmission. Evaluation of the pressure drop with respect to the flow rate of the refrigerant is crucial, particularly for long transmission lines. A circulation test, including pressure drop measurements, was performed in the sixth cooling test with the 200-m-class superconducting dc power transmission system at Chubu University (CASER-2). Pressure drops were measured in the high-flow-rate region, up to 31 L/min, to simulate 1-km-class systems, unlike those used in the first five cooling tests. A pressure drop of 12 kPa at 31 L/min for the 200-m cryogenic pipe was obtained. The obtained results were compared with the calculated results and showed good agreement. The model used for the calculation can predict the pressure drop with sufficient accuracy, making the prediction for the pressure drop for long transmission lines possible.