Pat, (or any power expert listening)
For power system timing requirements, any idea what sort of accuracy is desired
or in common practice?
Without clues, as a starting point, my guess would be some combination of the
following:
1) For correlating meter readings across the grid for billing purposes.
(Perhaps 1 second would be good enough for this?)
2) For correlating significant events (like breaker trips) over the grid to aid
in determining the root cause of a failure. (Perhaps 1 to 10 mS would be good
enough for this?)
3) For correlating voltage and current phase angles over the grid. (At 60Hz,
4.6 uS would be 1/10 of a degree?)
But it seems like we should have some additional clues as to if these numbers
are reasonable and if these or other applications are what is actually needed
before adding specific requirements
Also, what sort of packet network would it need to maintain the accuracy over.
(On a LAN inside the substation, outside over a dedicated link, other?)
Regards,
Stuart
-----Original Message-----
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Message: 1
Date: Thu, 18 Sep 2008 00:44:01 -0700
From: [EMAIL PROTECTED]
Subject: Re: [TICTOC] Requirements draft - call for assistance
To: Yaakov Stein <[EMAIL PROTECTED]>
Cc: "[email protected]" <[email protected]>
Message-ID:
<[EMAIL PROTECTED]>
Content-Type: text/plain; charset=US-ASCII
Hi Yaakov,
I can comment on the electric power and instrumentation bit. Each power
grid sub-station has a large number of monitoring devices. These devices
historically have been served time via IRIG-B distributed time systems. The
substations will typically have a gps receiver for time and 1pps to drive
the IRIG generators. the backhaul networks are usually private circuit
based networks. In past years many of these were on SNA or some other
similar network. As these substations are upgraded they are being
implemented with local LAN's and will have time distribution systems based
on 1588 or ntp. This allows the removal of the IRIG systems. The backhaul
networks can then be migrated to packet based with whatever access makes
sense for each location. The time distribution systems are local to the
substations.
In test and measurement the LXI forum, LAN extensions for Instrumentation,
has mandated the use of 1588 for compliance. Again this is a local time
distribution paradigm with a local time source.
Many of the "time" based event correlation systems use a local source of
time, typically gps, for time stamps. This is then sent in non-real time to
the monitoring systems for overall system correlation processing. I agree
with your thought that most of these are not applicable to the TICTOC work.
Hopefully this info is helpful.
Pat
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