# Development of Railway Protective Relay Simulator for Real-Time Applications
## 4 Case Study
\begin{table}
\begin{tabular}{c c} \hline
**Items** & **Parameters** \\ \hline \%Z of the SS & \(Z_{1}=1.1128+\overline{\text{$7.8827$}}\) [\%] at 100 MVA base \\  & \(Z_{0}=3.0157+\text{$\text{j}17.8050$}\) [\%] at 100 MVA base \\ \hline \multirow{3}{*}{Scott transformer} & \%Z = 10 [\%] at 30 MVA base \\  & Primary side: 154 [\(\mathrm{k}\mathrm{V}\)] \\  & Secondary side: 55 [\(\mathrm{k}\mathrm{V}\)] \\ \hline \multirow{3}{*}{Auto transformer} & \(Z=\text{$\text{j}0.45$}\) [\(\Omega\)] \\  & Primary side: 55 [\(\mathrm{k}\mathrm{V}\)] \\  & Secondary side: 27.5 [\(\mathrm{k}\mathrm{V}\)] \\ \hline \multirow{3}{*}{Impedance of the catenary system} & Trolley 0.1076 + \(\text{$\text{j}0.2645$}\) [\(\Omega\)/km] \\  & Rail 0.1052 + \(\text{$\text{j}0.4699$}\) [\(\Omega\)/km] \\  & Feeder 0.1180 + \(\text{$\text{j}0.4548$}\) [\(\Omega\)/km] \\ \hline \multirow{3}{*}{Length of the each section} & SS to SSP 10 [km] \\  & SSP to SP 10 [km] \\ \hline \end{tabular}
\end{table} 
Table 5: Parameters of the traction power-supply system (TPSS) model. Figure 14 represents the results for Case 1. The distance relay element and overcurrent element of the integrated protective relay were operated within one cycle owing to trolley-rail short circuit fault near the SS. Each relay was used as the main protective relay and the back-up protective relay in the TPSS. Figure 15 shows the input and output waveform information and relay operation information displayed on the simulator interface. It is possible to intuitively identify the relay elements that operate in response to a simulated fault. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Scenario** & **PSCAD/EMTDC** & **Digital Simulator** \\ \hline Case 1 & 0.1266 & 0.1267 \\ Case 2 & 0.1292 & 0.1293 \\ Case 3 & 0.1287 & 0.1288 \\ Case 4 & 0.1329 & 0.1327 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Simulation results—relay operation time (s). Figure 13: Simulation results using PSCAD/EMTDC: (**a**) Case 1; (**b**) Case 2; (**c**) Case 3; and (**d**) Case 4. Figure 16 shows the result for Case 2 and the simulator interface output screen. Similar to Case 1, it is confirmed that the proposed simulator imports the COMTRADE file correctly and displays the results appropriately after checking the protective relay behavior. Figure 14: Simulation results for Case 1: (a) Input current; (b) Input voltage; and (c) Protective relay signal. Figure 15: Simulation results in the digital simulator interface. Figures 17 and 18 represent the resulting waveforms corresponding to Cases 3 and 4, respectively, which are cases of feeder-rail short circuit fault near SS and SP, respectively. It was confirmed that identical to the previously simulated trolley-rail short circuit fault, the relay operated when an analog signal was input into the protective relay, and the result was accurately outputted from the simulator. Figure 16: Simulation results for Case 2: (**a**) Input current; (**b**) Input voltage; (**c**) Protective relay signal; and (**d**) Digital simulator interface results. Figure 17: Simulation results for Case 3: (**a**) Input current; (**b**) Input voltage; (**c**) Protective relay signal; and (**d**) Digital simulator interface results. Table 6 compares the operating time of the relay using the simulator with the relay operating time using the PSCAD/EMTDC. It is verified that both sides have been properly modeled with a smaller error in the operating time, and it is expected to be able to perform accurate simulations through cross-validation on both platforms when validating and testing the performance of protective relays later. The operating time of the relay shows the sequential operation of the protective elements, and the last operating protective element is time-overcurrent relay. The current of the TPSS contains harmonics owing to the switching element of the train, and the protective relay must not operate on these currents including the inrush currents of the transformer.