## 2 Distribution System Testbed
### Substation and Grid Testbed  
This study uses the testbed demonstrated in Figure 2. The testbed has three rack units. The RTS rack has an RTS expansion box (to increase the number of analog/digital signals) with the current and voltage amplifiers. The relay/meter rack has relays and meters that are wired to the RTS. The synchronized clock with displays are wired to IEDs (relays and meters). The communication rack has a time clock and remote terminal unit. The time clock can generate the time signal with or without a global positioning system (GPS) antenna because it has an internal clock. The advanced electrical substation grid testbed was created and led by Dr. [PERSON] [44; 45; 46]. This advanced testbed has been used in different research areas like harmonics metering [44], distributed ledger technology [45], relays and meters commissioning in electrical grid testbeds [46], and electrical fault type detections. This advanced testbed has been used with different distributed energy resources (DERs). In [44], the testbed was used as a substation/grid with a wind farm to assess the measured total harmonic distortions for meters and relays with different sampling frequencies. In [45], the testbed was used as a substation/grid with a customer-owned wind farm using a cyber grid guard to monitor the power quality using distributed ledger technology. In [46], the testbed was used as a substation/grid without DERs to assess methods for commissioning relays, meters, and real-time simulator testbeds for different power system applications. In this study, the testbed was used as a substation grid with an IB-PV array farm, to assess the envelope- and machine learning-based electrical fault type detection algorithms. Table 1 shows the main research areas, electrical grid characteristics, references, and main deliverables of these studies, using the advanced electrical substation grid testbed. Figure 1: (a) Diagram of the testbed and (b) real captured photo of equipment rack. The layers of the testbed are shown in Figure 3. In this testbed, the data are recorded during the simulations. The data are generated by the RTS, and the relays and meters collect these data. The IEDs (i.e., relays and meters) produce the grid data that are synchronized with the time clock system. The testbed's architecture (Figure 3) have computers and a time clock system (Figure 3a). The physical layers of the electrical substation grid testbed are shown in Figure 3. Level 1 in the physical layers includes the loads, power lines, breakers, transformers, IB-PV array, feeders, and other grid elements. Level 2 is the protection/metering layer that contains the hardware (relays and meters). Level 3 is the automation layer, which includes the clock displays, and communication devices. Level 4 is defined as the control layer. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Main** & **Electrical Grid** & **References** & **Main Deliverables** \\
**Research** & **Characteristics** & & \\
**Areas** & & & \\ \hline High & Electrical substation & & Assessment of total harmonic \\ harmonics & grid with wind farm & [44] & distortions for meters and relays \\  & & & with different sampling frequency \\ \hline Distributed & Electrical substation & & Assessment of monitored power \\ ledger & grid and customer- & & quality using a cyber grid guard \\ technology & owned wind farm & & with distributed ledger technology \\  & with cyber grid guard & & \\ \hline Electrical & Electrical substation & & Assessment of method for \\ grid & grid feeders without & [46] & commissioning real-time simulator \\ testbeds for different power system & DERs & & testbeds for different power system applications \\ \hline Electrical & Electrical substation & & Assessment of envelope- and \\ Fault Type & grid with IB-PV array & \(*\) & machine learning–based electrical \\ Detection & farm & & fault type detection algorithms for \\  & & & an electrical distribution grid \\ \hline \hline \end{tabular}
\end{table}