Practical Challenges of Using IEC-61850 SAS for Remote Synchronization During Restoration from Remote Control Centre

Conventional synchronization : Conventional synchronization of power systems has been done using a synchronization trolley or a synchrocheck relay at the substation level. In both cases, the local operator has a good view of the synchrocheck display, which indicates the angular separation, frequency difference, and voltage difference across the synchronizing breaker. With the visualization of angular separation using a dial display or a digital synchroscope display, the operator can confidently close the breaker either manually or through a command from the synchrocheck relay. Chances of wrong synchronization in this process is low as local operator has synchrocheck display for monitoring the actual closing.

Remote synchronization : With the advent of IEC 61850-based substation automation systems, many substations are now being operated remotely from far away located remote control centre hubs. Under such scenarios, trained manpower may not always be available at the substation. In such cases, synchronization must be initiated from the remote control center (RCC).

The process of remote synchronization from RCC involves the following steps:

1. Update the settings in the synchrocheck relay at the remote substation as per the requirement based on island strength. This can be done via the RCC, which is controlling the substation via SAS.
2. The synchrocheck relay across the synchronizing breaker at substation will have inputs from two islands systems and will check the parameters of the systems to decide whether they are ready for synchronization.
3. The synchrocheck relay will have a LED indication and a digital output (DO) signal for readiness for synchronization based on meeting the set parameters. This digital output can be transferred via digital I/O to the RCC. This will involve a time delay due to the delay in data transfer from the synchrocheck relay input to the RCC.
4. Based on the readiness status output receipt at RCC, the RCC operator will execute a command for breaker closing via HMI. In general, this is a two-step process in SAS for better situational awareness and control, and thus will involve a time delay in actual breaker closing command execution.
5. Based on the RCC command execution, the command will be transferred to the remote substation for final execution. This will involve a time delay in command transfer and its execution at substation (SAS to BCU to Synch Check relay-Breaker)

So overall process is as given:

Thus, it can be observed that overall process will be having some delays from the time the synchrocheck relay is ready to the actual breaker closing at site when done from RCC. There is a high chance that with low system strength during restoration or islands synchronization, the closing command may be executed when the synchronization parameters, especially angular separation, have exceeded the set limits in synch check relay.

Furthermore, the time available from synchrocheck OK status to breaker closing will depend on the frequency difference between the islands. The slip between two frequencies will decide how much time is available for breaker closing after the parameters are met for synchronization. This aspect can delay the synchronization process when being done from remote.

Command execution : It is also important that the command to breaker closing as received from the RCC should be executed through the sync-check relay itself. This is so that if the sync-check parameters are out of bound when the command is received, the command does not get executed without any check. This aspect will be required for avoiding any wrong or delayed synchronization.

Based on the above, the following are the major queries:

1. Whether such synchronization of islands during restoration should be done from the RCC or it should be through local manpower? Current practices may be shared.
2. Is there any possibility to have a remote synchrocheck display at the remote control center based on IEC 61850? Any utility using RCC for substation operators can share.
3. Is there a ready available synchronization circuitry diagram or programmable scheme logic (PSL) for synchronization via synchro check relay ? This is more important when done from RCC.
4. What are the best practices for ensuring the safety and reliability of remote synchronization?
5. What are the future trends in remote synchronization?

Do Share you best practices, feedback, reference material, relevant report, solutions, precautionary documents, SOP, standards or any relevant materials which may help in making this remote synchronization process smooth