WiseOwl^™
                                        The Secure Automation Developer's Resource

by John T. Tengdin -- Editor-in-Chief
March 2000

In our last editorial, we described the present situation – that a way has not yet been found to use an Ethernet LAN to synch the IEDs’ clocks to 0.1 millisecond. This level of precision is required to achieve station wide time tagging to 1 millisecond. As we all know, one millisecond time tagging has been the de facto industry standard for many years. No one questioned it when the time tagging was all done within one box – a sequence of events recorder or oscillograph. However, achieving this level of time tagging across a substation is not easily accomplished. As we pointed out, it does not appear that an Ethernet LAN can be used for clock synching, and that distributing the clock synch signals via a timing wire (actually a fiber) may be the best solution at this time.

Now a dissenting voice has been heard – that "this 1 millisecond time tagging requirement is over kill, that 10 millisecond time tagging should be adequate for all but the most critical substations". "And if the utilities would only accept this minor relaxation of the requirements, then clock synching of 1 millisecond (or thereabouts) could be achieved over the LAN". "That would mean the IEDs could be simpler, with no IRIG-B or GPS port, and a separate timing fiber would not have to be run to each IED". So says the dissenter.

From the time work began on EPRI Research Project 3599 back in 1996, this is the first we have heard of any suggestion that 10 millisecond time tagging is adequate. RP3599 has always specified 1 millisecond time tagging for all substations – not one level for most and a more demanding level for a few. That report – RP3599 – was a major input to the work now underway in the IEEE PES Substations Committee C2TF4. That task force is at work on IEEE P1525 titled "Draft Standard for Substation Integrated Protection, Control and Data Acquisition Communications". Today, the clock synching and time tagging requirements in P1525 are identical to RP3599. If there is any vendor, any utility, any consultant, anyone who feels that there should be – in addition – a 10 millisecond time tag category, then we encourage you to attend the next Substations Committee meeting in Vancouver, BC May 1-4, 2000 and make your case. It’s an open meeting. All are welcome. If you can’t attend, send your arguments to this editor and we promise they will be presented to the Task Force. Better yet, propose the language changes you would like to see in the present draft.

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