Design of main transformer capacity for electrified railway power systems

This paper investigates the main transformer capacity of an electrified mass rapid transit (MRT) system. The motion equation of a train set is used to solve the mechanical power consumption along the main line according to the operation timetable, the passenger ridership, and various types of operation resistance. The dynamic load demand of traction transformers is derived by executing the DC load flow analysis for the network consisting of rectifiers, conducting rails, car-borne inverters, and three-phase induction motors. The AC load flow simulation is then applied to find the loading of main transformers in the substations. The unit commitment is applied to derive the proper transformer capacity to meet the annual system peak power demand and provide sufficient capacity reserve. To demonstrate the effectiveness of the proposed methodology, the Tamshui-Hsintien line of Taipei MRT network is selected for the design of MRT main transformers. It is found that the loading factor of main transformers has been enhanced dramatically and the cost effectiveness of transformer investment over the life cycle has been obtained