Watchdog information by MODBUS or IEC61850

[sesa38348]

Dear all,

Can we have also the watchdog information by communication Modbus or IEC61850 on the same way as sepam. In sepam we can have by communication "mayor fault" and "partial fault". What is available by communication for P3 and P5.

Thanks.

Frank

[Rudolf_Simon]

Hello Frank,

some thoughts about this topic: 

A watchdog operation indicates a fatal error (major fault) of the relay (or IED). Then the IED is usually forced into a fail-safe mode, where all protection and control functions are disabled (to prevent false operation).

If it is a "partial fault" (or “minor fault”), also P3 and P5 continue their operation and just alarm/inform about the defect detected from their self-monitoring.

From my understanding, it is a kind of “tradition”, that also the communication interfaces are turned into a “halt state” in case of a mayor fault (causing watchdog operation). Whether that is a must have or not can be debated and the outcome may depend on the usage of the communication link for protection schemes, too. Yet noteworthy, such watchdog operation may also result from loss of power supply. And obviously then a communication link gets broken.

Now, how to get aware about broken communication link?
If the communication link itself does not provide any “link available” status information (which is the case in serial Modbus communication link), we may think about using other indications of such condition. A simple way is to monitor the response to cyclic reading of data from the IED (e.g. measured values, or binary states). If no new messages were received (best after few repetitions/attempts to avoid misguidance from spurious communication channel problems), the “slave” IED is broken. Well precisely: the communication to the IED is broken. We will never know, whether it is just this specific communication link, or the IED itself. Unless we apply redundant communication links… But not sure, whether such effort pays back.

kind regards
Rudolf