## 2 Synchronization and Reliability Provided by Power Supply System Design
### Traction Power Distribution System  
#### 2.3.1 Contact Line System  
In the urban railway system, for the 750 V DC voltage level, the third rail is commonly used for subway systems, while the OCS is preferred for the LRT systems because of their advantages and disadvantages [13; 14; 25; 26; 27; 28]. However, the recent emergence of ROCS requires further study for its application in this context. There are three options available for the power supply system for MCS at PVD, with the following main advantages and disadvantages (technical):  
Flexible OCS: One of the outstanding advantages is connecting the current collector devices continuously during level crossings and at crossovers. However, drawbacks include large voltage drops, contact wire sags, tensioning equipment, and complex catenary wires. Third rail system (3R): The primary advantage is its ability to withstand large load traction currents and a low voltage drop. However, a major safety concern is the interruption of current collection at level crossings and crossovers, posing a higher risk to human life compared to OCS. Rigid overhead conductor rail system (ROCS): This system comprises a treated aluminum body, in a clamp shape that holds the copper contact wire in place, providing greater stiffness and a greater circuit section that allows for the removal of parallel conductor cables at voltages ranging from 750 to 1500 V and can accommodate voltages up to 25 kV [22]. The ROCS comprises different elements described in the following figures, Figures 1 and 2, and the conductor rail profile in Table 1:The conductor rail of ROCS is manufactured by extrusion in aluminum alloy 6106 T5, thermally treated, according to EN 573-3:2009 [51] standards, in lengths of 10 m or 12 m or lower depending on the assembly conditions. It can be manufactured with two heights, normally 110 mm and 80 mm or similar, depending on the existing gauges, and cross-sections are 2202 mm\({}^{2}\) and 2223 mm\({}^{2}\). The structure includes the following components: a conductor rail, conductor inter-locking joints, a union plate, support and clamps, movable arms, a transition element, an electrical connection clamp, anti-creep clamps, earth clamps, a protection cover, a joint and end cap, a cable connection source, and an insulator [22; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38]. The ROCS converges on all the outstanding advantages of OCS and 3R, eliminating the limitations of both OCS and 3R [22]. It can be used interchangeably with the two types, OCS and 3R, because of the following advantages: \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**Height**} \\ \cline{2-3}  & **110 (mm)** & **80 (mm)** \\ \hline Profile Section (mm\({}^{2}\)) & 2220 & 2202 \\ \hline Moment of Inertia Iox (mm\({}^{4}\)) & \(338\times 10^{4}\) & \(164.26\times 10^{4}\) \\ \hline Moment of Inertia Iyy (mm\({}^{4}\)) & \(113.7\times 10^{4}\) & \(106.53\times 10^{4}\) \\ \hline Weight (kg/m) & 6.10 & 5.95 \\ \hline Equivalent Copper Section (mm\({}^{2}\)) & 1400 & 1234 \\ \hline Coefficient of Linear Expansion & \(24\times 10^{-6}\) & \(24\times 10^{-6}\) \\ \hline Young’s Modulus (N/mm\({}^{2}\)) & 69,000 & 70,000 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of the aluminum profile. Figure 1: Conductor rail of ROCS. Figure 2: Types of ROCS installation: (**a**). Cantilever; (**b**). Crossbar support, in which there are (1). Conductor rail; (2). Insulator; (3). Rear bracket/suspension structure; (4). Anchor bolt; (5). Bracket cantilever/suspension/tunnel ceiling; (6). Fixed or sliding hanger clamp; (7) Standoff. 1. Allows smaller tunnel cross-sections for new constructions;
2. Allowing lower support columns;
3. Allows a replacement electrification of tunnels and stations originally built for the third rail system;
4. Offers highly electrical cross-sections, so that additional feeders can be avoided;
5. Fire resistance is significantly greater than that of a catenary system;
6.