×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

generator rotor shaft current
2

generator rotor shaft current

generator rotor shaft current

(OP)
hello,
     What is the permissible value of generator shaft current? I read somewhere else that the permissible value of shaft current shall be less than 1 ampere.
      I am expecting your valuable comments.
Regards,
appunni
      

RE: generator rotor shaft current

Hydro-electric? Steam? DG?

Hydro-electric usually has shaft current monitor that can be set in the 100 - 1000 mA range. So that seems to be acceptable values in such macines. Don't know about the others.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: generator rotor shaft current

A shaft current alarm is indicating that arcing is present between shaft and bearing surfaces, in special cases also in couplings and gears. Arcing does not only destroy the bearing surfaces by creating craters but also deteriorates the lubricant over time and is damaging the shaft as well. Shaft currents therefore have to be avoided at all costs, especially for machines with ball bearings.

Shaft voltages of up to 50 volts are quite common in hydrogenerators. The oil film between shaft and bearing cannot be regarded as a safe barrier between these components. It therefore is imperative to insulate one of the generator bearings. A generator should be taken off line as soon as the shaft current monitor indicates an insulation breakdown. The low resistance of the shaft current circuit can be responsible for currents of 100 amps and more, far beyond the figures a shaft current monitor can be set.

I've never heard of a permissible limit figure for shaft currents.

Wolf
www.hydropower-consult.com
 

RE: generator rotor shaft current

(OP)
Thanks for valuable replies. Mr. Gunnar says about 100mA to 1A while Mr.Wolf says about 100A.
I hope more explanations will be there about this matter.
regards,
appunni
    

RE: generator rotor shaft current

I would be concerned to see 1A on a large turbo-alternator running on white metalled bearings. Even a few hundred mA isn't good, mainly because whatever is allowing that low current to flow will only get worse if not corrected.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: generator rotor shaft current

Where did I say that up to 100 amps are PERMISSIBLE?

ScottyUK is right with his comment. Even the arcing of a few hundred milliamps does degrade the bearing oil and is affecting the bearing and shaft surfaces, it only takes more time until the bearing in question fails. This can result in an outage of weeks if not months in case the shaft is damaged. The outage of a 100 megawatt generator, for instance, can lead to a daily loss of revenue of up to 100,000 US$ and more. The correction of a faulty bearing insulation can possibly be done in one day.

Wolf
www.hydropower-consult.com   

RE: generator rotor shaft current

(OP)
Thanks for explanations.
regards,
appunni

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources