# Smart Grid Protection, Automation and Control: Challenges and Opportunities
## 5 Redundancy
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Standard/Regulation** & \multicolumn{2}{c}{**Descriptions**} \\ \hline IEC 61850 [77] & Standard for electrical network automation, including redundancy in communication and protection systems to ensure high availability. & Standard for electrical network automation, including redundancy in message communication. \\ \hline IEC 61850-3 [78] & General hardware requirements for devices in electrical substations. & \\ \hline IEC 61850-5 [4] & Performance and functionality requirements for automation and control devices in substations. & \\ \hline IEC 61850-9-2 [79] & Standard for the transmission of sampled values and synchronization data over Ethernet. & \\ \hline IEC 61850-90-4 [80] & Part of IEC 61850 addresses redundancy in network and communication systems. & \\ \hline IEC 61850-90-2 [81] & Standard for integrating communication systems in substation automation, including redundancy in message communication. & \\ \hline IEC 61508 [82] & Standard for the functional safety of electrical, electronic, and programmable systems, including redundancy requirements to ensure safety systems. & \\ \hline IEC 62439 [83] & Standard covering protocols for redundancy in industrial networks, including PRP and HSR. & \\ \hline IEC 62439-3 [84] & Part of IEC 62439 specifies PRP and HSR to ensure network availability. & \\ \hline IEC 62351 [85] & Security standard for communications in industrial automation and control systems. & \\ \hline IEC 60870-5-7 [86] & Security extensions for IEC 60870-5-104. & \\ \hline IEC 60870-5-104 [39] & Standard for remote control of electrical power systems over a network protocol. & \\ \hline IEC 1588 (PTP) [27] & Standard for time synchronization over Ethernet networks, may involve redundant mechanisms to ensure time precision and availability. & \\ \hline NERC CIP [87] & Critical Infrastructure Protection standards, including redundancy and security requirements for power grid control and protection systems. & \\ \hline DNP SA V5/6 [88] & Standard for security and authentication in distribution automation and control networks. & \\ \hline ISO 27001 [89] & Standard for information security management, may include measures for redundancy in handling critical data and systems. & \\ \hline TIA/EIA-942 [90] & Standard for data center design, covering redundancy in IT infrastructure to ensure high availability. & \\ \hline \hline \end{tabular}
\end{table} 
Table 20: Standards and regulations associated with redundancy. Deploying two CPAC or VPAC systems at the substation level enhances reliability and efficiency by ensuring continuous operation, even in the event of system failure. This redundancy allows for uninterrupted control and monitoring, optimizing investment in protection schemes without excessive costs. Redundancy is crucial for both local and remote control systems, ensuring continuous functionality during failures. It is vital to design both hardware and software redundancy to support standards like IEC 61850-0-2 and IEC 62351, ensuring smooth communication and system backup without disrupting protection functions. Different redundancy methods enhance the availability and resilience of the system, as summarized in Table 22 by comparing methods against their advantages and disadvantages and their general effectiveness [49]. Amongst the available redundancy methods, the parallel redundancy protocol is the most effective for digital substation communication, providing seamless failover on link failure without data loss in a link failure [91]. For station buses, PRP has emerged as a standard for implementing communication redundancy. In fact, this has combined with ring network architectures to provide an effective solution that ensures the availability and dependability of protection and control systems in digital substations.