The testbed 'PRIME" is implemented as a typical end-to-end SCADA hierarchy, from the substation to the control center, using a combination of a well-known power system simulator, power system control, hardware-in-the-loop (HIL) and industry grade EMS software. Other cyber-physical testbeds have similar modularity. However, they lack flexibility in swapping out the software used for EMS, FEP, and the hardware used for RTU and relays as the computational subsystems and the input/output (I/O) subsystems are tightly coupled and integrated. They tend to be tied to a single vendor. In our approach, the power system simulator and the hardware driver (analog output subsystems to drive HIL) are decoupled and are interconnected through communication protocols as an interface. This provides an additional level of modularity to the architecture creating an interoperable environment where power system simulators and hardware could be interchanged as long as they support streaming of measurements/commands. This allows several commonly used power system simulation software tools (both transmission and distribution system modeling tools) to be used. Hardware could be driven depending on the use cases considered. Proposed relaxation of an otherwise tight restriction greatly reduces the cost and improves flexibility by creating a modular solution. This capability of the PRIME to support Remote HIL (RHIL) is unique to the PRIME. In PRIME, field devices (e.g., protection relays, capacitor controllers) are integrated in the closed control loop and their communication with the EMS is implemented to match the real-world practices. This setup enables interactions among power systems model (simulator), power systems control (EMS) and field devices, and therefore provides an excellent platform to conduct interactive operator training, and for use in studying the impacts of communication impairments and cyber-defense work.