James Wilkinson Sword wrote on 12/6/2017 12:09 PM:
On Wed, 06 Dec 2017 11:27:40 -0000, rickman <gnuarm_at_gmail.com> wrote:
Daniel60 wrote on 12/6/2017 1:10 AM:
Daniel60 wrote on 12/5/2017 8:13 AM:
James Wilkinson Sword wrote:
On Sat, 18 Mar 2017 02:37:53 -0000, rickman <gnuarm_at_gmail.com> wrote:
On 3/17/2017 10:28 PM, James Wilkinson Sword wrote:
On Sat, 18 Mar 2017 02:01:09 -0000, rickman <gnuarm_at_gmail.com> wrote:
On 3/17/2017 8:02 PM, James Wilkinson Sword wrote:
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
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
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
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.
Indeed, and presumably also if they're a little out of phase permanently.
Although presumably there's a limit. If I brought up my generator 180
degrees out of phase with the grid, something bad would happen - melted
coils? I think what happens with power stations is they use the grid to
spin up the generator before introducing it's own fuel.
I have read they just spin it up by the power source and adjust the
speed/frequency and phase to match the grid as much as possible before
connecting it to the grid.
The real issue is how does it all remain stable with so many points each
trying to do its own thing but responding to the grid? I think of it as a
flock of birds. No one bird controls how the flock moves, but they will
part and dodge to avoid a hawk diving in to take one because in essence,
they are all connected in a grid.
Any bird flying slightly too fast will adjust itself as it comes too close to the next. Any generator spinning slightly too fast will have a bigger current drawn to push the others, so it will slow and the others will speed up.
If I said you had a beautiful body, would you hold it against me? -- Monty Python, Episode 25