generator excitation versus load
generator excitation versus load
(OP)
Is it possible to determine the full load excitation requirement for a low voltage synchronous generator bsaed on the no load readings?
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generator excitation versus load
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generator excitation versus loadgenerator excitation versus load(OP)
Is it possible to determine the full load excitation requirement for a low voltage synchronous generator bsaed on the no load readings?
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RE: generator excitation versus load
But the Automatic Voltage Regulator usually takes care of that.
If you are trouble shooting, don't be surprised if the no-load to full-load ratio is close to 2:1 or more.
Bill
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"Why not the best?"
Jimmy Carter
RE: generator excitation versus load
This is based on units built by CAT, KATO, EM, Ideal, AVK, Newage, Marathon and Baldor.
This is also based on loads with low THD, high load harmonics can have a big effect in some cases.
Mike L.
RE: generator excitation versus load
In my case, I am looking at three cummins/marathon 400kw slip ring generators. The no load excitation current readings are, in fact, right at 50% of the full load nameplate value. I am considering the current readng instead of voltage because the tests were performed cold (right after start-up) and the nameplate voltage values are for the hot resistance of the rotor.
Is the excitation proportional (linear) to load from no load to full load?? If 50% excitation is no load and 100% excitation is full load, will 75% excitation equal half load? And, for a specific number, will 67% excitation equal 34% load?? ( there is a reason that I picked this specific number)
My thinking is that the voltage is proportional to excitation but, I would like some confirmation (or some correction if I am wrong).
RE: generator excitation versus load
Maybe someone else can shed some light, sorry.
Mike L.
RE: generator excitation versus load
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: generator excitation versus load
There are some diagrams and equations in the following link which might help, especially around slide 8 on field current limit:
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RE: generator excitation versus load
Actually that would be quite an unusual condition - rotor heating is normally a limiting factor only at low lagging power factors. Under the conditions you noted it is typically the stator heating limit which dominates.
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If we learn from our mistakes I'm getting a great education!
RE: generator excitation versus load
RE: generator excitation versus load
The locus of rated excitation current shown on most capability charts is quite often inside the true maximum excitation limit imposed by saturation and rotor thermal limits - using that line moves the intersection with the stator limit considerably.
Somewhere I've got a marvellous old document from the CEGB which is one of the most detailed works I've seen on capability diagrams. I'll see if I can find it if you're interested.
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If we learn from our mistakes I'm getting a great education!
RE: generator excitation versus load
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: generator excitation versus load
RE: generator excitation versus load
RE: generator excitation versus load
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: generator excitation versus load
rhatcher:
The full-load excitation current is mainly dependent on the power factor and the generator synchronous reactance. A large hydro generator with 0.9 p.f. and a synchronous reactance of 1.0 p.u. with a no-load excitation current of 100% has a full-load excitation current of about 160 to 170%. I assume that small generator sets have synchronous reactances in the region of about 1.5 p.u. and higher. The air gap ampere-turns portion of the no-load characteristic then is smaller in comparison with the armature reaction ampere turns. A 2:1 excitation current ratio therefore is quite realistic.
How high is the synchronous reactance of the low voltage set in question? And why don't you measure the excitation currents over various load conditions? Should be easy.
Wolf
www.hydropower-consult.com
RE: generator excitation versus load
rmw