Rich Grise said:
I've heard that they have fairly sophisticated control electronics
that sync-up the turbines before they put them on line. How in heck
you control the speed of a multi-megawatt turbine-driven generator
is kinda beyond me. A valve in the
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The idea is that the frequency of the whole system floats up and down. If a
machine speeds up with respect to another, then there will be power transfer
between machines to bring them back to the same frequency. In cases where
this power transfer is insufficient, then the system will become
unstable -blackout time as the system breakers operate on power surges and
some areas shut down because of excess load and others overspeed and trip
out because of insufficient load. Not considered a good thing.
As for the control of a multi-megawatt machine- governors are used - new
ones are electronic and old ones are entirely mechanical. For a steam
machine, a steam valve is controlled (typically about 0.5sec from full
closed to full open) but fuel control follows for longer term control. For a
hydro unit, hydraulic pistons adjust the water control gates. In the case of
high head units, this is done slowly (30 sec to 2 minutes) to avoid water
hammer surges (or special surge towers are used). An exception is the case
in the Kemano plant in BC where Pelton wheels are used to drive 160MW units.
The head is about 2000 ft so gate/valve opening is very slow. In this case
as the load may change in 100MW jumps (aluminum pot lines are on or off, no
in-between), there is a deflector which can be put into or removed from the
water jet to quickly allow load pick up or dropping.
As for synchronisation- there are special control units to do this but it
can be done by a human operator simply watching a synchroscope and voltmeter
(a set of lights if no synchroscope), tweaking the speed and voltage then
closing a switch at the right time. A good operator can often do it faster
than the electro-mechanical control. The process is essentially the same as
would be done with 1 to 5KW units in a lab.