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sumairali
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Join Date: Feb 2014
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Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 9:22 AM

Hi all, Our 12MW alternator become magnetized and we have to replace the rotor, kindly help me to find the root cause of that problem....waiting for your reply...
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PWSlack
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#1

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 10:38 AM

A telephone call to the equipment mannufacturer would enable this information to arrive far quicker.

All hail synchonous communication systems!

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RAMConsult
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#2

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 11:13 AM

What does "...got magnetized..." mean, and who made that determination? After all, the rotor is one big electromagnet.

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sumairali
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#3
In reply to #2

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 12:18 PM

Our alternator make some humming sound so we take ot the rotor and disconnect all supplies from it aand during inspection our tools get attracted by rotor...
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RAMConsult
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#4

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 12:57 PM

...and now you think it's faulty??? The root-cause is that it's a big stack of steel laminations surrounded by many turns of wire that once carried large amounts of DC. Electromagnets often exhibit residual magnetism when the power is removed, that's what you're observing.

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sumairali
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#5
In reply to #4

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 1:44 PM

After 8 days its magnetism persist?? No its dont...
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RAMConsult
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#6
In reply to #5

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 2:55 PM

Why not? The amount of residual magnetism is a function of where on the B-H curve you were when the circuit was disconnected. It's also related to the rate-of-change of the magnetic field at the exact moment of de-energization.

If that's not satisfactory, then explain what you mean by "burnt".

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Wal
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#10
In reply to #5

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/02/2014 3:13 AM

days, months,years....it's normal aka residual magnetism.

It's the RM that gets self exciting alternators to start their excitation loop.

If you really want to demagnetise it and render it non self exciting then de-gauze the thing with an AC field. It won't self excite again until you shove some DC current through it to remagnetise it but ..... what's the point to this?

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jack of all trades
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#7

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 3:45 PM

kindly help me to find the root cause of that problem

...Sorry, how do we do that with so little information provided?

Replace it if you don't know what you are doing, I am not going to start throwing around blind guesses for a 12MW alternator. There, problem solved and no one gets hurt.

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TonyS
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#8

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/01/2014 7:33 PM

In a previous topic you had two 3MVA sets, has one been on a body building course?

You hadn't a clue what you were doing then, you obviously still haven't a clue.

I've got to the stage I don't believe a word you say.

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cheeseslicer
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#9

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/02/2014 1:55 AM

How did you go Sumairali? Is it fixed yet?

What was found to be wrong?
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abasins
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#11

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/02/2014 5:07 AM

FYI,Types of Faults in an Alternatorhttp://www.electrotechnik.net/2014/03/types-of-faults-in-alternator.html

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pcchatur
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#12

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/02/2014 5:52 AM

When you say that rotor got magnetized, I understand that it got magnetized beyond the residual magnetic level and in axial direction. Normal residual magnetism is in radial direction and not in axial direction. If so, then the cause is inter-turn fault in the rotor winding. Whenever rotor continuous to operate with shorted (a good percentage of total turn per pole) turns, an axial magnetic field is created which "magnetizes" the rotor in axial direction (with poles at each end of the shaft). Under such conditions one has to re-wind the rotor. However, it needs to be de-magnetized. For which there are number of methods. You need not replace the rotor. You only need to re-wind the same.

We faced similar problem and the same was noticed when the rotor was put on lathe machine for taking a cut in the shaft area. The chips were not falling down. Instead they were getting attracted to the rotor shaft. Then it was found that the shaft got magnetized.
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Wal
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#13
In reply to #12

Re: Our 12MW ABB Alternator Rotor Got Faulty

05/02/2014 6:37 AM

If so....

then quite possibly.

OP where were your tools sticking?

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abasins (1); cheeseslicer (1); jack of all trades (1); pcchatur (1); PWSlack (1); RAMConsult (3); sumairali (2); TonyS (1); Wal (2)

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