1744   Clarification of Start Times in StrTm.setCal

Created: 17 Dec 2020

Status: Discussion (red)

Part: Part 7-4 (2020; Edition 2.1)

Links: #1756 Event driven schedules – Extend description , #1755 Event driven schedules – Add DO to stop schedule by event

Page: 481

Clause: K.2

Paragraph: K2.4

Issue

In behalf of the German VDE/FNN project group (PG Steuerbox):

Applying the standard’s schedule definitions to practical use cases caused some discussion on how to interpret part 7-4.
IEC 61850-7-4 annex K.2.4 states: “In case, for whatever reason, the schedule cannot start at the time given by the occurrence of a start time setting, but afterwards, then the schedule will run sharply as if it has started at the time given by the start time setting. Said in other words, the schedule won’t shift the scheduled values based on the real-time start.”

German VDE FNN Project Group Steuerbox concluded that an enabled periodic schedule would run as if enabled with its most recent (periodic) start time, if it were still running from this start. Because it affects interoperability of the specified devices, we decided to discuss the issue with the community.

The attachment shows the issue with examples.

Proposal

Chapter K.2.4 of part 7-4 (2020) shall be amended:

A schedule assumes status 'running' from 'not ready', if the following conditions are true:
1) the schedule is well-formed (has starting times, output values etc.)
2) if a UTC Start time (setTm) is present, it lies in the past
3) if the schedule is cyclic, there exists a cyclic start time (last cyclic start Time from setCal, lcst), for which is
lcst <= now <= lcst + (SchdIntv * NumEntr).

Attachments:
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Discussion Created Status
Additional change is proposed:
in Table K.1 row "not event driven" --> "periodic" change first sentence from "Once it has been enabled and integrity is OK, the schedule run periodically, starting at first occurrence of the Calendar time and repeats with every re-occurence of the calendar time until it is disabled."
to
"Once it has been enabled and integrity is OK, the schedule run periodically, starting at first occurrence of the Calendar time or after the Calendar time, when the periodic schedule meets the condition to run, and repeats with every re-occurence of the calendar time until it is disabled."
05 Mar 21 Discussion (red)
I propose to confirm the understanding A and to state this tissue as editorial or future improvement. So it would not be necessary to change part 7-4 immediately. We have to improve description later. 15 Feb 21 Discussion (red)

 

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