# Smart Grid Protection, Automation and Control: Challenges and Opportunities
## 5 Redundancy  
The station-level assurance enables the substation to act as a single switchgear that is unified and reliable. Safety, backup, and redundancy are the major considerations. This includes monitoring and controlling substation components, assessment and mitigation of cybersecurity risks of substation devices, and taking corrective action. Process-level assurance targets the safe and efficient operation of the selected substation processes. Data are acquired and continuously monitored against predefined criteria to meet the process operation requirements by mitigating cybersecurity risks accordingly. Redundancy in virtualized systems invariably features two active VMs such that protection functions will be retained during failures. In this respect, to achieve effective redundancy, primary and secondary systems should be isolated, having different hardware and software vendors to avoid common failure modes. The physical separation of A and B redundant systems is basic for avoiding common failure due to local events. Standards like IEC 61850-90-4:2000 and IEC TC 57, e.g., PWI TR 61850-90-20, specify minimum requirements for redundancy and LAN within VPAC systems. The VPAC system can make use of the RCT in SV messages for higher error detection and correction capability in the fault-tolerance networks using PRP or HSR. Conformity to IEC 61850 and UNE-EN IEC 62439-3:2022 norms ensures \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \multicolumn{2}{c}{**Aspect**} & \multicolumn{1}{c}{**Descriptions**} \\ \hline Current Transducer Testing & Confirm the correctness of the PTP message correction field and verify the accuracy of current transducers under different traffic conditions. & **Application** \\ \hline Network Configuration and Topology & Verify that all network components are configured correctly and that all clocks are synchronized to the same time domain. & **General synchronization for various low-precision applications.** \\ \hline \end{tabular}
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Table 16: _Cont._ \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \multicolumn{2}{c}{**Synchronization Class**} & \multicolumn{1}{c}{**Precision (\(\mu\)s)**} & \multicolumn{1}{c}{**Sync. Error**} & \multicolumn{1}{c}{**Application**} \\ \hline TL & \(>\)10,000 & Low precision & General synchronization for various low-precision applications. & **General synchronization for various low-precision applications.** \\ \hline T0 & 10,000 & 10 ms & Event stamping with 10 ms precision. & **Event stamping with 10 ms precision.** \\ \hline T1 & 1000 & 1 ms & Event stamping with 1 ms precision. & **Event stamping with 1 ms precision.** \\ \hline T2 & 100 & 100 \(\mu\)s & Zero-crossing tagging and data for distributed synchronization checks. Waveform-based switching tags. & **Zero-crossing tagging and data for distributed synchronization checks. Waveform-based switching tags.** \\ \hline T3 & 25 & 25 \(\mu\)s & Various applications. & **Zero-crossing tagging and data for distributed synchronization checks. Waveform-based switching tags.** \\ \hline T4 & 4 & 4 \(\mu\)s & Sample tagging or synchronized sampling. & **Zero-crossing tagging and data for distributed synchronization checks. Waveform-based switching tags.** \\ \hline T5 & 1 & 1 \(\mu\)s & High-precision sample tagging or highly synchronized sampling. & **Zero-crossing tagging and data for distributed synchronization checks. Waveform-based switching tags.** \\ \hline \end{tabular}
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Table 17: Time synchronization classes according to IEC 61850-5.