Optimal Expansion Planning of Traction Substations for an Electrified Mass Rapid Transit System

This paper is to investigate the proper expansion planning of traction substations (TSS) for an electrified mass rapid transit (MRT) system. The motion equation of train sets is used to solve the mechanical power consumption at each time snapshot according to the operation timetable, the passenger ridership and various types of operation resistance. The mathematical models of power converters in traction substations for different operation modes have been derived. With all train sets operated along the main line, the AC/DC load flow analysis is performed to find power demand of all traction substations for annual system peak operation over the study period. The objective function is formulated by considering both the voltage drop of train sets and investment cost of traction substations as the equivalent cost of all feasible states of each year. By performing the dynamic programming (DP) to minimize the objection function, the expansion planning of traction substations to achieve the minimum overall cost has been obtained by identifying the optimal capacity and locations of new traction substations to be committed at each year.