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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
In order to get the most power out of a power source I believe one needs to match the load to the impedance of the source. How do I measure the impedance of a 3 phase generator? Do I measure the resistance of one of the phases and divide by sqrt(3) or something like this?
Registered Member #347
Joined: Sat Mar 25 2006, 08:26AM
Location: Vancouver, Canada
Posts: 106
For a delta load, take the resistance between two phases and multiply by 1.5, and that's the resistance each leg of your delta load should be.
You don't want to extract maximum power from a generator continuously, it will overheat, and would be less than 50% efficient. Generators and motors are run well below their maximum power for higher efficiency. Are you planning to run near maximum power for any significant period of time?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The impedance of a synchronous alternator is complex, made of resistance and something called the "synchronous reactance" (google for more info)
The reactance is usually large compared to the resistance, so it's what sets the power limit: and therefore the generator is more than 50% efficient even at maximum power output, because reactance dissipates no power. Trying to load it beyond the maximum just results in it losing sync.
The situation is somewhat different in a PM synchronous alternator charging batteries through a rectifier, in that there's nothing to fall out of sync with, but even so, if the generator is well designed, I expect the reactance will limit the power.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
The 3 phase will be connected in Star. Its use will vary with the wind. It is part of a wind generator. Actually, if any of you are interested, I have kept a photo diary of my project at
The output from the PM alternator will be rectified. So, if it is Star should I multiply by 1.7 instead?
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
tesla500 wrote ...
For a delta load, take the resistance between two phases and multiply by 1.5, and that's the resistance each leg of your delta load should be.
You don't want to extract maximum power from a generator continuously, it will overheat, and would be less than 50% efficient. Generators and motors are run well below their maximum power for higher efficiency. Are you planning to run near maximum power for any significant period of time?
David
This may not really be what your all talking about but FWIW most utility scale generators are designed to run at or near max output almost indefinately. There is also a chart called a generator 'D curve' wich gives some light to maximum ratings based on things like power factor. I cant find a good example online but pulling out some of my notes here based on the D curve with a lagging PF of .85 or less the generator is limited by field heating, with leading PF of .95 or less it is limited by armature core end heating, and inbetween up to unity PF is limited by armature heating. To match the load I beleive is handled mostly by the excitation circuits to adjust var output to match the load.
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extracting the most power from a 3 phase generator
