## 1 Introduction  
In recent years, MCSs have been introduced with outstanding advantages. They can meet the traffic capacity range that bus rapid transit (BRT) (from 5400 passengers per hour per direction (p/h/d) to 10,800 p/h/d) and light rail transit (LRT) (from 18,000 p/h/d to 24,000 p/h/d) provide, but cannot meet the requirements of mass rapid transit (MRT) (from 18,000 p/h/d and up), with construction costs being too expensive [1; 2; 3; 4]. The definition of an MCS varies due to their non-standard nature. MCSs have a capability of boarding around 20,000-30,000 passengers per hour per direction (p/h/d), and can even board up to 48,000 p/h/d [5; 6; 7; 8; 9; 10; 11]. Therefore, after an in-depth survey and analysis of the traffic flow of 29,595 motorcycles during peak hours in the direction of the Pham Van Dong (PVD) route, we proposed an average railway system model to guide and solve the traffic problems on the main road of PVD in the northeast of Ho Chi Minh City (HCMC), Vietnam, submitted in an article with the title \"Research on Medium Capacity Rail System: Case on Pham Van Dong Route in Ho Chi Minh City, Vietnam\" [11]. In this article, we continue to study the feasibility of a traction power supply system for system operations with the largest carrying capacity. In traction power supply, there are important issues that are of concern, including power supply, traction power, useful voltage at the pantograph, contact line systems, and supply schemes [12; 13; 14; 15; 16; 17]. Power supply, including a bulk supply substation and an internal power distribution system, must comply with national or regional voltage standards, and must be synchronized with the existing urban railway planning system. The traction power demand estimation must ensure reliability and flexibility in cases of normal operation, overload, fault, and the development of the prevention of load [18; 19]. In addition, the contact voltage must be suitable for the type of load, ensuring that the voltage can operate during peak hours with the largest service frequency, as well as at low voltage, according to the reliable standard EN 50468 [20]. The voltage in contact line networks has a great influence on the carrying line capacity [21]. The contact line system is required to ensure that the important factors of good electrical conductivity and low voltage drop. There are also other related issues, such as beauty, total installation and operation costs, and operating speed [22]. Finally, the supply scheme plays another important role in distributing the exit current that directly affects the reliability of supply and the quality of contact voltage when operating. Therefore, it is very important that the design of traction power supply for new systems carefully considers the above issues. At the same time, applying new technology is necessary to avoid obsolescence and wasting capacity, and to improve system reliability and quality [22; 23; 24]. In this study, we will calculate the capacity required for the system to operate in both normal and incident cases. At the same time, we will conduct an in-depth analysis of the power supply options, as well as the traction current distribution structure of the 750 V DC traction system with a third rail system, overhead catenary system (OCS) [25; 26; 27; 28], and ROCS [29; 30; 31; 32; 33; 34; 35; 36; 37; 38]. In particular, the choice of ROCS in this research is one that we hope will become common in the near future because of its outstanding advantages. Furthermore, this will be a transparent scientific basis for choosing an effective power supply structure for the synchronous and sustainable development of urban railway transport networks [39; 40; 41; 42; 43]. The rest of this paper starts with an explanation of the synchronization and reliability provided by the power supply system design. Then, the traction power distribution system is presented in Section 2. Section 3 outlines the system design and the design method for traction load. The results and discussion are presented in Section 4.