rickman wrote:
Daniel60 wrote on 12/6/2017 1:10 AM:
rickman wrote:
Daniel60 wrote on 12/5/2017 8:13 AM:
James Wilkinson Sword wrote:
On Sat, 18 Mar 2017 02:37:53 -0000, rickman wrote:

On 3/17/2017 10:28 PM, James Wilkinson Sword wrote:
On Sat, 18 Mar 2017 02:01:09 -0000, rickman
wrote:

On 3/17/2017 8:02 PM, James Wilkinson Sword wrote:
https://en.wikipedia.org/wiki/Nation..._2008_incident






Can someone explain why a power station should disconnect due to
detecting a small frequency drop?* Would this not make things
worse?

When I read that article, it said that this was no longer the
rule.* In
fact, the problem was caused by some smaller generation facilities
tripping off the grid when the current rule was to *not* trip at
that
point.* They were running old software.

I assume that not entirely unlike blowing a fuse, the general
rule is to
separate portions of the grid when things are going wonky.* I
can only
imagine that there could be parts of the grid damaged if the
flow of
power is not well regulated.

Agreed.* But if a power station detects the grid is at a slightly
low
frequency, why on earth would it be a good idea to cease generating?
The low frequency was presumably caused by a lack of input,
making the
power stations throughout the country labour a little and slow down.
Taking more power stations off the grid will exacerbate the problem.

Did you read what I wrote?* That is not the rule.

Yes, you said they seperate if the frequency is wrong.* Which is not a
good idea is it?

Coming in very, very, late to this discussion, but .....

It would seem to me that if the freqs that two generators were
operating at
were slightly different, then the instantaneous voltages being
produced by
the two generators would also be different, so one generator would be
supplying power to the "real" load *and* to the slower generator!

Keep in mind that the power lost in transmission is not zero.* A
sufficiently small difference in phase (rather than frequency which
would
result in phase creeping) would simply result in a smaller or larger
loss
in the transmission.* Given the difference in phase of voltage on the
load
this would result in current leading or lagging the generated voltage
and
result in a torque that would speed the lagging generator and slow the
leading generator since the back EMF is created by the current.

If one generator was running at 50Hz and the other was running at, say,
49.95Hz, then every1,000 cycles or so, the two waveforms would be
exactly in
phase ..... for an infinitesimally (??Sp) small time!!

If the two generators were both running at 50Hz but one lagged the
other by
some degrees (your second case, and not the one I originally considered)
could possibly be as you mentioned.

The point is that neither of these two cases are realistic because the
frequency is never perfectly stable.* That's the point, the whole grid
is a living, breathing entity and every part responds to the rest in a
way that tends to lock it together.* Talking about two generators being
some small amount different in frequency for any length of time won't
last, they will be pushed together.

Thanks for the memories!!

As I was sitting here, catching up on these posts, I recalled, back
about 40 years ago (in another life ;-) ), I worked at an Australian
Army H.F. Transmitter site where, each Tuesday, we would test out our
on-site, (3) 300KVA Blackstone generators by bring up one of them,
syncing it to the mains supply, disconnecting the mains and then, a
couple of hours later, bring up another gennie, sync it to the first
one, then drop the first one off-line, and then a couple of hours later,
sync this gennie back to the mains.

All good fun!!

Daniel