Induction vs. Synchronous Generators
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this. One reason is power factor correction.
We will explain this in depth later, but
suffice to say at this juncture, induction
generation works out to be most favorable
when the generated load is small compared to
your total plant load. Another reason is
that the single stage turbine with an
inexpensive, self-contained lubrication
system is limited in its power producing
capabilities. At higher powers more
expensive multi-stage turbines and
pressurized lubrication systems are
required. The major advantage of the single
stage steam turbine induction generator
package is its simplicity: no gear, no
pressure lube, simple controls, and simple
connection to electric grid. Note:
connection to grid is required for
excitation. All these factors result in a
relatively low cost package, which when
applied in a simple topping application,
results in extremely fast payback on
investment.
A synchronous
generator runs at a constant speed and draws
its excitation from a power source, external to,
or independent of, the load or transmission
network it is supplying. A synchronous
generator has an exciter that enables the
synchronous generator to produce its own
"reactive" power and to also regulate its
voltage. Synchronous generators can operate
in parallel with the utility, or in
"stand-alone" or "island" mode. Synchronous
generators in the <15 mw power range are
only available as 4-pole (1800 RPM) units,
are almost always geared, and require large
pressure lube systems. Most synchronous
packages over 1.0 mw are driven by
multistage steam turbines and typically
involve more sophisticated controls and
monitoring equipment. Although more complex
and costly, larger synchronous generators
can have a lower cost per kw due to their
economy of scale.