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Anonymous Poster #1

On Load Voltage Drop in Alternator

01/18/2012 10:45 PM

In 40 KVA ,16 pole permanent magnet Alternator voltage drops fron 450V AC No load to 390 Volts full load.stator resistance( 18 mOhm) , insulation resistance ( 100 Mohm) are correct. I am not able to find reason. Pl. suggest what should be checked.
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perry
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Join Date: Dec 2006
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#1

Re: On Load Voltage Drop in Alternator

01/19/2012 12:06 AM

#1; check the gov, speed up the engine perry
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Sudhir Kulkarni
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#2
In reply to #1

Re: On Load Voltage Drop in Alternator

01/19/2012 3:01 AM

Engine speed is almost constant.
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PWSlack
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#3

Re: On Load Voltage Drop in Alternator

01/19/2012 3:52 AM

Check that "full load" does not mean "overload".

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Sudhir Kulkarni
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#4
In reply to #3

Re: On Load Voltage Drop in Alternator

01/19/2012 3:57 AM

Loading is 90% of rated.
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PWSlack
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#5

Re: On Load Voltage Drop in Alternator

01/19/2012 5:38 AM

Check the operation and maintenance manual.

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leveles
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#6

Re: On Load Voltage Drop in Alternator

01/20/2012 12:50 AM

Permanent magnet tend to lose flux with time - aging. Provides right voltage at 5-20% less load.

Permanent magnet flux tend to drop as its temperature rises. Cooling down restores. Same as above.

If stator iron core (silicon steel lamination, not entirely soft magnetically) picks up static magnetisation, its useful flux declines. You may be able to demagnetize it, but it will reoccur. Same as above.

In all 3 cases everything works right till 60, 70, 80% output. Then a gradual decline. It may have functioned right as new. But aging effects were conveniently ignored. Use it as-is. As aging effects normally stabilize after a while. Trying to force the output only accelerates aging.

If you happened to have electronic post regulator, refer to the manual. Beyond a narrow range it is not normally designed to cover up aging decline in the generator proper.
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Sudhir Kulkarni
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#7
In reply to #6

Re: On Load Voltage Drop in Alternator

01/20/2012 6:38 AM

Good tips I will check them
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Andy Germany
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#8

Re: On Load Voltage Drop in Alternator

01/20/2012 6:26 PM

Does it have an AVR, I will be surprised if you say yes and it is also true. I personally have never seen an alternator with magnets and an AVR....(I am not saying NEVER!! Been too long on CR4 to say that!)

Assuming you answer NO, then a voltage drop is normally expected.

The drop is related to the designed gap between the rotor and stator. It could be made that the voltage remained constant for any load, but usually a "droop" is built in so as to not feed a dead short (or try to!!) with full voltage.......theoretically it could be made so that increased load increased voltage as well.....not that I have personally seen one so designed, but it could be......

In the RN, we did not have Alternators with magnets, but a wound rotor fed from a small DC generator on the same shaft. The DC generator fields were voltage "adjusted" by the AVR to vary its output and therefore the voltage output of the Alternator.....pretty conventional.....we used a 45% droop between no and full load......

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Haajee
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#9

Re: On Load Voltage Drop in Alternator

01/21/2012 10:29 AM

It is normal on full load.

Marking and measurements are not well defined.

See the German firms like Siemens marks Φ to Φ 380V where as we consider it 440V in general.
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nagasdolphin
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#10

Re: On Load Voltage Drop in Alternator

01/22/2012 7:09 AM

what is the rpm? and how you are rotating by engine or ?????
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toink
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Join Date: May 2012
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#11

Re: On Load Voltage Drop in Alternator

05/16/2012 2:28 AM

pls check the the exciter diod if diffective by using the multimeter , if this diod busted both led have continuety it means busted need to replace , then check the AVR as well

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Andy Germany (1); Haajee (1); leveles (1); nagasdolphin (1); perry (1); PWSlack (2); Sudhir Kulkarni (3); toink (1)

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