Generator excitation
Generator excitation
(OP)
Im a beginer here, i just wonder why a generator should always have a DC excitation?
If in transformers dc cannot be transformed (unless its pulsating dc) why is it used in excitation for generators as well. Is it because the magnetic field is moving magnetic one due to it rotates as the prime mover rotates it?
hope someone can share ideas, thanks.
If in transformers dc cannot be transformed (unless its pulsating dc) why is it used in excitation for generators as well. Is it because the magnetic field is moving magnetic one due to it rotates as the prime mover rotates it?
hope someone can share ideas, thanks.






RE: Generator excitation
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Generator excitation
Induction generators are excited by the AC line voltage.
respectfully
RE: Generator excitation
RE: Generator excitation
The dc voltage is used to generate the magnetic field in the rotor. This voltage can then be used to under or over excite the field to produce a lagging or leading power factor.
RE: Generator excitation
The load determines the power factor. The excitation determines what share of the total KVARs of the load is supplied by a generator. Changes in excitation also tend to change the system voltage in about the same ratio as the ratio of the generator capacity to the total system capacity.
With a stand alone generator, the excitation controls the voltage and has no effect on the power factor.
Induction generators are a special case that are probably best ignored for now.
respectfully
RE: Generator excitation
But my question really is cant we not use AC as excitation meaning we remove the rectifier diodes before going to the rotor to excite the generator? Our generator is brushless too. synchronous.
RE: Generator excitation
This principal was once used to produce drives for speeds above synchronous speed.
Practically, the efficiency of applying AC to the field of a generator would be faily low. A machine built and optimized for frequency conversion would have acceptable efficiency.
Try browsing through some old electric machinery and drive books. The books that are too old to have been scanned and posted on the net.
respectfully
RE: Generator excitation
The rotor needs to be a magnet with a N and S pole (excitations lets you vary the streght of this magnet)
As the magnet's Poles rotate inside the wire coils of the stator makes the AC for each pass of a N-S pole. for a 2 poles making 60 revoulutions a sec makes 60 htx, wher a 4 pole only needs to turn 30 rps
If AC was used then the N-S magnet poles would be switching.
If the rotor was not turning, you have a transformer with the staor as the secondary (output),
If the primary side of the transformer starts to rotate....you get a something...?
RE: Generator excitation
Thanks guys!!
RE: Generator excitation
I have been to a generator class put on by these guys, and feel it's about the best one I ever went to.
http://
This etraining class is new, but is right in line with the course book from his instructor lead classes.
RE: Generator excitation