Generator rotor winding gets cut after few days of operation 1

[manuvarier]

The rotor winding of one of our genset in our DP vessel twice failed because of the rotor winding gets cut after few days of operation. Both times, the winding gets cut at different location of the winding.The genset rotor was overhauled, rewinded, baked , rotor balanced, refitted and tested 2 mths back . A major maintenance was carried out then. Since then, after few odays of operation the genset was out of order because at one location the rotor winding was cut and there was no continiuty. The wires were reconnected by soildering and tested , all seemed ok. We continued running the genset after temporary repair for few days , the genset brokes down again because of the rotor winding got cut at a different location..
Please suggest , what could be the major cause of this faults recurring , what is the best solution to avoid such break downs.

 

[electricpete]

Just curious: Can you describe the location where the open circuit was found? Picture?

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(2B)+(2B)' ?

 

[waross]

Change crews.
I have seen this before.
A lobster boat used divers. The normal trip was 14 days. The divers would not dive more than 14 days at time.
The owner bought traps so that divers would not be needed. The boat could then be sent out for 30 days or 60 days at a time. After about 15 days, damage occurred to the refrigeration controls and the boat returned to port. The second trip after about 15 days similar damage happened and the boat had to return home.
Moral:
You can't send a boat out for 30 days with a 14 day crew.
Some-one doesn't want your boat to sail.
Be very careful. Life is cheap. Accidents happen. Seamen don't like to be upset.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[redlinej]

Can you describe the cut a way.i saw rotor give the problem before. because of improper balancing after being rewinded .

 

[manuvarier]

Hello electricpete - first location of the cut wire was the 2 wire that comes out of the rotor to connect the diode circuit on the excitation. The second location is the rotor winding near to the middle of one of the poles.

 

[Skogsgurra]

Bill
Liked your down-to-earth (or down-to-bottom) comment.
You have lots of experience.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

You'd certainly think the two open circuit events were related and there's not a lot of mechanisms for open circuit developing in different parts of the machine (huge vibration, bizarre cutting foreign material, ridiculously sloppy rewind come to mind, but none seem very likely unless there are other observations to support them)

From that standpoint, the odds are that Bill is right about sabotage. But you'll probably want to gather relevant facts to steer your decision. Even if you come to that conclusion, you'll need those supporting facts before presenting any conclusions that might be viewed as accusatory.

This cut "near the middle" of one of the poles... was that be visible from outside of the pole or required unwinding the pole to see the break?
Close up pictures or descriptions of the break and surroundings would be helpful:
What types of damage visible at break... mechanical, heat, arc? (recognizing heat/arc may erase original cause). Same question for adjacent turns?
Any reason you used the term "cut" as opposed to "open"?
Was the cut/break at a location of obvious mechanical stress concentration or just the middle of straight run of wire?
Anything unusual during inspection?


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(2B)+(2B)' ?

 

[waross]

Thanks Gunnar. I respect your even greater experience. I regret that we may never meet to share some coffee and some stories.
Yours
Bill

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[TheBlacksmith]

Cut or broken/chaffed? Sloppy rewind, loose wedging and support could allow movement due to magnetic forces. Although this may be more common in the stator, especially with a poorly supported end basket.

 

[powerjunx]

it seems operational problem and extreme vibration. so much uses of your thrusters?

plz post picture...it's worth a million word!


"..the more, the merrier" Genghis Khan