I guess I can take all this to mean: No Tolerance;-)
Randy Gross
<7trwb.485456$pl3.173036@pd7tw3no>...
:
:
:
in
: message : > In article <n6gwb.481036$pl3.82486@pd7tw3no>,
[email protected]
: > mentioned...
: > >
: > >
: > >
: > > : > > > On Sun, 23 Nov 2003 14:04:59 +0000 (UTC), "Randy Gross"
: > > >
: > > -----------------
: > > Frequency variations in themselves do not cause a stability problem
if
: all
: > > generators change frequency together. The problem occurs when
: differences in
: > > frequency between machines occur and a sustained difference of any
: value
: > > between machines will cause problems. Normally if a machine tends to
: > > overspeed there will be torques produced to speed up other machines
and
: slow
: > > the fast unit. This sort of jockeying around goes on all the time but
: the
: > > average is held to to 60Hz while the instantaneous frequency of the
: system
: > > generally will be within 0.05 Hz. How close the frequency can be
held
: > > depends on the system, the number of units, and the control used. A
: single
: > > generator will show far more variation than an large grid.
: > > Other problems can occur with large frequency drifts. some of these
may
: > > include the loss of such things as critical feedwater pumps,
resulting
: in
: > > the shutdown of a generator, leading to further shutdowns, etc.
: >
: > One should not talk about frequency, but about relative phase angle,
: > leading or lagging, between generators.
: -----------
: From a stability analysis viewpoint you are correct. However, note that
I
: said "sustained" difference of any value is a problem (as I didn't want
to
: get into stability analysis per se). By the time there is such a
frequency
: difference between machines, it is too far too late to do anything but
break
: out the candles. Transient speed (and associated frequency) variations
are
: going on all the time- in analysis one simply looks at the speed
differences
: and these are best handled in terms of relative phase angles.
: From a non-stability point, the system frequency will always be changing
: due to load changes and the responses of the various prime movers. In
: extreme situations the frequency change can be enough to cause problems
as
: indicated. In other cases changes in the power balance between sections
of
: the system can cause line tripping and islanding of the systems where the
: islands may lose generation due to over or underspeed.
: Thank you
: --
: Don Kelly
:
[email protected]
: remove the urine to answer
:
:
: