## 4 Result and Discussion
Simulation results for all stages and failure scenarios are summarized in Table 7, and a rough description of the system is shown in Figure 6.  
During operation, the aim is to fulfill the requirement of the system with the largest carrying capacity among systems of the same type in each phase. The MCS type, in particular, is characterized by operating with the highest service frequency. This study is simulated for the power of TPS and compares the values for mean useful voltage (U\({}_{\rm mu}\)) at the pantograph of the types of contact line systems, OCS, 3R, and ROCS, following single-end feeding and double-end feeding. The results of calculating the required traction power and the minimum values for mean useful voltage at the pantograph under normal operating and failure conditions are given in Tables 7 and 8. 1. [leftmargin=*]
2. Traction power  
In Table 8, the calculating result of the power of TPS for three stages of traffic demand in a normal case according to the rated current is 2.644 MW (P\({}_{\rm n}\)). In the next step, also calculated according to instantaneous maximum traction force (P\({}_{\rm R}\)), the result is 2.227 MW (Phase 1), 2.375 MW (Phase 2), and 2.525 MW in Phase 3. According to traffic demand, with a reserve coefficient of 1.1, the largest capacity in Phase 3 is 2.778 MW (P\({}_{\rm dR}\)). In the case of regenerative braking energy recovery, assuming a regenerative recovery system with a maximum capacity of 40%, the minimum power required is from 1.4701 MW to 1.666 MW calculated according to the maximum instantaneous traction force (P\({}_{\rm RRE}\)), and 1.584 MW calculated according to rated power (P\({}_{\rm RRE}\)). In case a failure occurs at any TPS, the two adjacent TPSs before (i - 1) and after (i + 1) must supply power to the breakdown segment; this time, the power of the TPS (i - 1) or TPS (i + 1) calculated according to the rated traction current (P\({}_{\rm fr}\)) is 3.966 MW. The maximum instantaneous power calculated in this case according to the traction force (P\({}_{\rm fr}\)) for Phases 1, 2, and 3 is 3.341 MW, 3.563 MW, and 3.788 MW, respectively. Thus, the maximum power of the TPS is chosen to be 4.0 MW (P\({}_{\rm TPS}\)) with two group rectifiers working in parallel (n = 2), each with rated power of 2.0 MW (P\({}_{\rm TSR}\)). In the normal working mode, one set is working and the other is in standby mode. The supplied power of the TPS in this case (2.0 MW) is larger than the smallest power in the case of the regenerative braking train P\({}_{\rm RRE}\) (1.6668 MW), but smaller than the largest 2.644 MW and 2.778 MW by 32.2% to 38.9%, corresponding to the overload power of 132% to 138%. However, it is less than the condition allowing continuous overload for two hours, which is 150%. In this case, the selected rated power of TPS meets rated power supply conditions during rush hour. Considering the fault conditions, at this time, both sets are working simultaneously; the supplied power P\({}_{\rm TPS}\) is 4.000 MW, which is larger than the instantaneous power  
Figure 6: Design and layout of traction power stations on PVD line. calculated in the fault conditions, which is 3.7882 MW, and approximately, the fault power calculated according to the rated power is 3.9662 MW. Thus, the capacity of the traction substation is greater than the fault condition, meeting the necessary conditions for selecting the capacity of the traction power station with duty level VI according to standards EN 50328, EN 60146-1-1, and IEC 62590, and load limits according to standards NEMA RI9 and IEC 60146-1-1. The TPS's power and the minimum mean useful voltage at the pantograph depend on the length of the power segment and electrical characteristics of the contact line installation. Thus, the longitudinal voltage drops due to the relationship between the contact network resistance and the traction current train, which draws on the power section of TPS.