## 2 Modeling and Simulation of an Aircraft Electrical Power System (EPS)
### Fault Injection in the EPS Digital Twin
This can be observed in Figure 5 (the fault ids are mentioned in the red box, near their respective effects in the plots). For example, when the fault F5 is injected (circuit breaker connecting the power distribution node to TRU is tripped) at t = 2.5 s to t = 2.75 s as per Table 2, the fault cuts off the current supply to all the valves and nozzles in the DC circuit (Figure 5 middle column at t = 2.5 s to t = 2.75 s). However, when the faults F1, F2, F3, and F4 (scenarios of switch stuck open at the LRUs), are injected at their respective simulation times from Table 2, they affect the current consumed by the concerned LRU only. This can be observed from the left column second plot (Power_TRU) and the entire middle column of Figure 5. Likewise, when the fault F7 (circuit breaker tripped at the distribution node connecting the AC lamps) is injected at t = 3.5 s to t = 3.75 s as per Table 2, the current is reduced to both the AC instrument panel lamp and at the AC cabin window fluorescent lamp (can be observed in right column bottom two plots of Figure 5). However, the faults F8 and F9 (scenarios of switch stuck open at the LRUs) injected at the simulation times listed in Table 2, affect the current consumed by the respective LRUs only. These cases can be observed in the left column bottom plot (Power_ACLamp) and right column bottom two plots of Figure 5. In the case of faults in the AC motor, when the circuit breaker is tripped at the AC power distribution node (Fault F6 at t = 3.0 s to t = 3.25 s), the motor does not receive any power, and hence there is no speed and current (left column third plot (Power_FSPump) and right column top two plots of Figure 5). It is to be  
Figure 4: Fault injection in AC pump motor by reduced voltage supply (F10). noted that, in the top plot on the left column of Figure 5 (Power_total), only the effect of fault F6 is observed. This is due to the difference in magnitude of power consumed by Power_FSPump when compared to the Power_TRU and Power_ACLamp. In the case of fault F10, when the supply voltage is reduced, the rotor speed is lower than the nominal speed that is observed during the healthy case simulation. The reduced supply voltage scenario is shown in Figure 6. Thus, all the faults listed in Table 2 affect the overall power output from the simulation of EPS digital twin, along with the power consumption of the aircraft systems the EPS is connected to. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Fault\_Id** & **Type of Fault** & **Location** & **Fault Label** &
\begin{tabular}{c} **Timeline of Fault** \\ **Injection** \\ \end{tabular} \\ \hline F1 & Switch stuck open & DC supply to fuel system & FS\_Nozzle\_SwitchStuckopen & t = 0.25 s to t = 0.5 s \\ F2 & Switch stuck open & DC supply to fuel system & FS\_Valve\_SwitchStuckopen & t = 0.75 s to t = 1.0 s \\ F3 & Switch stuck open & DC supply to engine bleed & Eng\_BleedValue\_SwitchStuckopen & t = 1.25 s to t = 1.5 s \\ F4 & Switch stuck open & DC supply to ECS & ECS\_TCValve\_SwitchStuckopen & t = 1.75 s to t = 2.0 s \\ F5 & Circuit breaker trip & AC power distribution node & DC\_TRU\_B & t = 2.5 s to t = 2.75 s \\ F6 & Circuit breaker trip & AC power distribution node & FS\_ACMotor\_B & t = 3.0 s to t = 3.25 s \\ F7 & Circuit breaker trip & AC power distribution node & AC\_Lamp\_B & t = 3.5 s to t = 3.75 s \\ F8 & Switch stuck open & AC supply to Instrument & AC\_Instru\_Switchopen & t = 4.0 s to t = 4.25 s \\ F9 & Switch stuck open & AC supply to cabin window & AC\_fluoro\_Switchopen & t = 4.5 s to t = 4.75 s \\ F10 & Voltage reduction & Line supply voltage to AC fuel pump motor & FS\_Motor\_lowvoltage & Simulated separately \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Faults injected in the EPS Digital Twin. Figure 5: EPS performance during various fault scenarios (faults F1, F2,..., F9). Left column: Total power generated and power consumed by DC TRU, FS Pump, and AC Lamp (kVA). Middle column: Currents at DC Loads. Right column, top two plots: FS Pump characteristics.