# Analysis, Evaluation and Simulation of Railway
## 3 Results and Discussion
### Evaluation and Characteristics of Aggregated Demand
Notice that Railway Power Systems (Table 18) presents very low LFs (or very high CFs) even at medium-high aggregation level (in our case at 66 kV sub-transport level of public power system, considering in this table the possibility that DC traction substation can exchange energy from a substation to other substations of the route; at present, a remote and complex possibility from technical and economic points of view). In this way, RPSs need some improvement in their use and management. \[LF(\%)=\frac{Mean(tractive-demand)}{Max(tractive-demand)}100;CF=\frac{ Peak\_resource(Capacity)}{Avg\_resource(Mean\_Use)}. \tag{8}\]  
The next index, EStB (Energy Savings through Braking), evaluates the amount of energy generated during braking of a railway unit that can be used for other units in the same section of the overhead line of the route (i.e., at the same catenary/electrical section or substations) during a day:  
\[EStB=\frac{\sum\limits_{24h}^{RPS}gen\_usable}{RPS}100. \tag{9}\]  
Finally, the potential (available theoretically) generation of energy through braking (kWh) with respect to traction demand (kWh) in a section of RPS (or modified KPI5), MKPI5 is also considered:  
\[MKPI5=\frac{\sum\limits_{24h}^{RPS}gen\_braking}{RPS}. \tag{10}\]  
Several scenarios have been considered for simulation purposes in this subsection:  
1. Railway traffic in the route fulfills its timetable: This is theoretically possible, but difficult to accomplish in 100% of trains. In this case, trains usually use resistive braking to avoid incertitude and the possibility of an increase of voltage in catenary. 2. Railway traffic present delays in some passenger and freight services (a delay from 1 to 5 min is considered with a uniform distribution) and average values of demand have been considered with the aggregation methodology described in Reference [56]. Trains use resistive braking as the main braking system. This case represents an average scenario from the point of view of the demand for planning and operation purposes. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Case/Scenario** & **Load Factor (\%)** & **EStB (\%)** & **MKPI5 (\%)** &
\begin{tabular}{c} **Peak and Peak** \\ **Clipping (MW, \%)** \\ \end{tabular} \\ \hline
1 & 11 & NA 1 & NA 1 & 14.35, NA 1 \\
2 & 16.58 2 & NA 1 & NA 1 & 9.56, NA 1 \\
3 & 9.72 & 19.35 & 27.19 & 14.35, 0 \\
4 & 13.66 2 & 39.4 2 & 27.19 & 9.56, 0 \\
3 + 5 & 18.72 2 & 39.4 2 & 27.09 & 8.47, 11.4 \\ \hline \hline \end{tabular}  
* NA: not applicable, 2 Maximum value.  
\end{table} 
Table 18: Aggregation of Substations from Alcazar to Chinchilla (AJ-CH). Railway traffic in the route fulfills its timetable, and electric trains use regenerative braking if the voltage remains around normal values. * Railway traffic present delays in some passenger and freight services (a delay from 1 to 5 min is considered again, and average values have been considered) and vehicles deploy regenerative braking: Average values of demand and generation have been considered. In this case, some delay can improve energy recovery indices. * Hybrid units (S-730) are able to change from conventional catenary supply to diesel-electric generator, in limited sections of the electrified route, to acts as a responsive load/generator (DER resource) for achieving an improved flexibility of demand and supply. * Wayside storage: Substations have a partial storage system to limit power in peak periods and reduce LFs. The load factor of the aggregated demand in Figure 22a has a very low value in all cases being considered (9.7 to 18.7). Notice that time windows (usually some seconds to one minute, due to dynamic train behavior) for the evaluation of energy and power needs from acceleration and braking are shorter than the time windows considered in Public Power Systems to compute some indices and record demand data (i.e., data aggregation acts as a high-pass filter). It should be noted that some peaks appearing on the load curve are in phase with S-730 demand.