*5.1. Case Study*

A real single-track railway line has been chosen as case study. It presents an electrified section at 3 kV DC and a non-electrified section, currently covered by diesel-powered trains. Therefore, passengers are obliged to transfer to a diesel-powered train at the end of the electrified section, in order to reach one of the following stops or stations. The attention is focused to the non-electrified section in order to determine the technical-economic convenience of electrification at 3 kV DC or the use of trains equipped with on-board energy storage systems. Figure 7 reports an overview of the case study.

**Figure 7.** Railway connection between City I and City II and possible scenarios.

The non-electrified section is about 16.5 km long and links Station A, at the end of the electrified section with Station B, at the end of the non-electrified section (City II), in about 30 min for each direction. Between Station A and B there are 5 stops, as shown in Figure 8.

**Figure 8.** Stops between Station A and Station B.

Figure 9 shows the plano-altimetric profile of the railway line. It is characterized by an average slope of 9‰, with a maximum slope of 24‰. There are 22 curves with a minimum bending radius of 200 m.

**Figure 9.** Track features: slopes (**a**) and curves (**b**).

For the non-electrified section, the following scenarios have been analyzed: 3 kV DC electrification, since it is the feeding system currently used in the preceding section; high autonomy ESS and ESS with recharge station. For the ESS it has been considered the use of power-oriented Li-ion battery cells (lithium iron phosphate, LFP) and, in the case of hybrid ESS, energy-oriented Li-ion battery cells (lithium nickel manganese cobalt oxide, NMC - lithium nickel cobalt aluminium oxide, NCA) accompanied by supercapacitors.

The electrification at 3 kV DC involves the installation of a catenary and traction power substation, to be located at Stop 2 (progressive km 5.29). Contrariwise, the use of trains equipped with high autonomy on-board ESS allows to minimize the capital costs since it involves the recharge of the battery and supercapacitor pack in the electrified section of the line. However, in this case the ESS weight is high. The installation of a charging infrastructure at Station B (progressive km 16.5), allows reducing the on-board ESS rated capacity and therefore, the total weight of the system. In this paper, it is considered for all the scenarios, the use of the same electric train, whose traction curve is presented in Figure 10.

**Figure 10.** Rolling stock traction curve.

The main characteristics of the lithium-ion and supercapacitor cells are illustrated in Tables 1 and 2, respectively. This data is used to size the ESS as reported in the Section 3 of this paper. Table 3 shows the main characteristics of the different components of the traction system: rolling stock, track, DC feeder system and on-board ESS.


**Table 1.** Li-ion cell features.

**Table 2.** Ultracapacitor cell features.



**Table 3.** Railway System Parameters.
