# Smart Grid Protection, Automation and Control: Challenges and Opportunities
## 3 Evolution of Substation Architectures and Digital Modernizations for Smart Substations
### Comparasion of a Conventional P&C Systems vs. CPAC Approach
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Criteria/Test Feature** & **Conventional P\&C System** & **CPAC Approach** \\ \hline Scalability & Limited scalability: expansions require significant hardware and software modifications at multiple points. & Facilitates the addition of new functions and system expansion with upgrades at strategic points. & Facilitates the addition of new functions and system expansion with upgrades at strategic points. \\ \hline Security and Cybersecurity & Inconsistent security, relying on individual device security. & Enhanced cybersecurity through centralized authentication, authorization, auditing, and system hardening measures. \\ \hline Factory Pre-Shipment Tests & Individual testing of each relay. & Tests are comparable to those conducted on conventional systems. \\ \hline Commissioning Tests & Individual on-site testing of each relay with secondary injection of currents and applied voltages. & Secondary injection is performed on the merging units (MUs), similar to conventional system testing. \\ \hline Periodic Maintenance Tests & Each relay is regularly tested throughout its operational lifespan. & Sampled value (SV) simulations and GOOSE messages enable maintenance testing without altering wiring or communication setups. \\ \hline Test Configuration & Test equipment is configured at each stage of the relay’s lifecycle. & Test equipment configuration remains unchanged, saving time in wiring and connecting equipment. \\ \hline Test Automation & Limited applicability in test automation. & Test process can be automated using GOOSE and SV simulation capabilities per IEC 61850 standards. \\ \hline Secondary Injection & Conducted directly on the protection relays. & Conducted on the MUs, allowing the CPAC to disregard actual MU values during testing in simulation mode. \\ \hline Time Synchronization & Information is distributed without facilitating synchronization. & Fault detection and analysis information is consolidated in a single location with built-in time synchronization. \\ \hline Alarm Notification & Alarm information is dispersed across multiple devices. & Trigger information from multiple feeders is consolidated on a single alarm notification page. \\ \hline Waveform Capture & Waveform capture is completed individually for each relay. & The same disturbance recorder function is used across all feeders, enabling waveform comparison from multiple feeders. \\ \hline Sequence of Events & Events are listed individually for each relay. & Events from multiple feeders are presented chronologically within the CPAC system for a clear and comprehensive view. \\ \hline SCADA System Cost & Additional investment required for SCADA system. & SCADA system advantages are provided at no additional financial cost. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._protection commands from the CPAC unit. This setup offers the advantages of decentralized and centralized protection schemes. As the research focused on hybrid architectures continues, Figure 13 presents another example of a hybrid architecture with an NPR. In this configuration, the NPR located in the individual bays is interfaced with the CPAC unit via an ethernet switch. This makes it possible for relays in the bays to offer basic local protection and handle advanced substation protection in the CPAC unit. Centralized protection requires this hybrid architecture to have a core CPAC, which allows new functionalities to be added to the substation. Its functional requirements, pros and cons are summarized in Table 2 for both the centralized and hybrid architectures of substations, with greater detail than their respective merits and demerits. Figure 11: Fully centralized architecture with PRP-based communication redundancy. Figure 12: Hybrid architecture example with numerical protection relays. Today, maintenance in electrical substations is somewhat complicated due to the use of different electronic devices from various manufacturers.