Synchronous generator variable speed and constant excitation

AI Thread Summary
An electrically excited synchronous generator operating at variable speed with constant excitation current behaves similarly to a permanent magnet generator, as both maintain a proportional relationship between output voltage and RPM. The generator's frequency is directly linked to its RPM, and a fixed field current mimics the effects of permanent magnets. The discussion raises questions about the feasibility of using this setup in applications like wind turbines, typically utilizing induction machines or permanent magnet synchronous generators (PMSG). Determining the optimal excitation current involves producing the rated voltage at the rated speed, often supported by feedback mechanisms to stabilize voltage output. This approach suggests potential advantages in specific applications where constant excitation is beneficial.
Vanguard
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TL;DR Summary
will an electrically excited synchronous generator act as permanent magnet generator if provided with the similar excitation current at any speed?
The question is regarding an electrically excited synchronous generator.
Consider that this generator is not connected to the grid and thus not locked with the grid frequency.
This generator is spinning at variable speed and gets constant and similar excitation current
meaning that the excitation current does not change with the speed.
Will this in fact mean that this generator is acting as a permanent magnet generator?
 
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Vanguard said:
Summary:: will an electrically excited synchronous generator act as permanent magnet generator if provided with the similar excitation current at any speed?

The question is regarding an electrically excited synchronous generator.
Consider that this generator is not connected to the grid and thus not locked with the grid frequency.
This generator is spinning at variable speed and gets constant and similar excitation current
meaning that the excitation current does not change with the speed.
Will this in fact mean that this generator is acting as a permanent magnet generator?
Welcome to PF.
The synchronous generator frequency is always proportional to the RPM.
The output voltage is proportional to the product of RPM and field strength.

If you replace the field with permanent magnets, then the voltage and the frequency will still be proportional to the RPM. So a fixed field current is the same as a permanent magnet field.
 
thank you.
I'm wondering if this kind of application makes sense over a PMSG.
would it be possible to use this kind of installation with a regenerative converter like in wind turbines
that usually use an induction machine or a PMSG.
Also, how would you determine what is the optimal excitation current?
intuitively, I would use the current that produces the rated voltage at rated speed (e.g 11kV@1500RPM)
 
Often, there is a feedback loop that compares terminal voltage with a set point, and manipulates excitation to hold that voltage constant.
 

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