On 08/20/2003 03:37 PM, Rick Tarara wrote:
>
> Power is off. Two generating plants, each with a max output of 1000
> Watts--generators at 100 Volts. One transmission line at 1000 volts.
> A load (still switched on) of 1600 Watts--say two factories each
> wanting 800 Watts at 100 volts.
Interesting scenario.
> OK--how do you turn the power back on?
You'd better hope that there is a switch in
the circuit diagram between the two factories, so
that they can be brought up separately. If not,
this is a deadlock scenario: if the power goes
out it will never come back on.
You'd also better hope that there is enough
uninterruptible station-service power at the
substation where said switch is, so you can
open that switch while the grid is down.
> What, if any, role do the transformers play in this scenario?
1) Transformers obviously play a role in connecting
power to/from the high-voltage tie-line.
2) To answer a question that wasn't exactly asked,
*saturable* transformers play an important role
in regulating the voltage that customers see.
> How does the phase get synchronized?
In the scenario posed here, probably one generator
will motor the other until they are in phase.
Probably. Maybe.
In a slightly different scenario, AFAICT there's
no reason to expect that phase will ever get
synchronized.
To make sense of this, you have to imagine the
tie-line as having lots of inductance, *not*
being a dead short at AC. Let's assume the
two generators are at nearly the same frequency,
but not exactly. So they will drift in and
out of phase. During times when they are out
of phase, you have an inductor with a big
voltage on one end and a big opposite voltage
on the other end. There will be huge amounts
of VAr, i.e. lots of energy stored reactively
in the inductance.
In a more-realistic scenario, you can imagine
an L/R ladder network, with resistances (R)
i.e. the customer load on the rungs of the
ladder, and inductances (L) along the struts
of the ladder. This means the weird reactive
flows won't be conspicuous at either end of
the ladder. (Remember, L/R ladders look like
the diffusion equation.) But customers near
the middle of the ladder are going to see
some ugly stuff, I imagine.
[Still not claiming to be an expert. Struggling
to figure stuff out.]