×
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

Arcing on gen engine block fault

Arcing on gen engine block fault

Arcing on gen engine block fault

(OP)
Got a pretty decent fault today. Thought ild share.

Background and fault:
Conducting a inspection of a 175kVA gen set. Gen is reasonably old. It has come back from a site where is was run underloaded and not serviced regularly. Has a number of oil leaks and we are considering writing it off. Once we fixed a start fault we heard some ticking. We localised it down to a small arc from the base of the crankshaft pully to the engine block. Arc happens at 2 to 4 second intervals. Quite a strong arc since we could see it clearly even with sunlight. We noticed our RCD had a fluctuating display of .5mA to 1.2mA.

Initial fault finding.
Initially thought that the battery alternator may be screwed so we disconnected it and ran gen off the battery. No change

Thought than maybe the gen alternator may have a fault so tested winding continuity, insulation resistance and earth continuity. No change.

Thought than since the gen is filthy, that the belts may be somehow causing a static charge to develop. Cleaned the gen and arcing disappeared however RCD still indicates a fluctuating earth current.

Still not convinced we had actually fixed the fault, we tested the RCD current transformer. Continuity checked out. Point to note the arrow on the tranny pointed away from the star point on the gen. Turned it around yet no change.

Considered testing the RCD however didnt have any spares and it passed a the RCD test.

RE: Arcing on gen engine block fault

Disconnect the field leads and try again. It may be a failing field coil in the alternator. Even better, temporarily short the rotating diodes.

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

RE: Arcing on gen engine block fault

(OP)
Cheers waross. Im unsure what where your going with that fault process. If i disconnect the the main field windings the ill have no voltage and most likely no RCD fault.

Getting to the diode pack on the rotor isnt a easy task and im unsure what output or result ild get.

Point to note, I loaded the gen today and once it got past 180A/phase (Full load is around 240A) the RCD current increased steadly over a few minutes from 10mA to 25mA which tripped the RCD.

RE: Arcing on gen engine block fault

No voltage will discriminate between a static issue and a failing rotor. If the arcing is still there with the diodes shorted you have a static issue. If zero volts clears the fault, you may have a rotor fault.
Alternately, check for voltage on the non-drive end of the alternator shaft. You may also ground the non-drive end and measure the current. If this is a static issue a grounding device on the non-drive end may solve the problem.
If the engine bearings are badly worn you may have an air gap issue on the drive end of the rotor.

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

RE: Arcing on gen engine block fault

(OP)
Ended up been the shielding to the toliroid. The cable which connected to the toliroid had a earth shielding which had broken down. This was causing a fault current to be induced into the cabling. As for the arcing...who knows? Its not there anymore

RE: Arcing on gen engine block fault

"toliroid"? What is that?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Arcing on gen engine block fault

(OP)
Ah my bad spelling. I meant Toroid. Also known as a current transformer.

RE: Arcing on gen engine block fault

Thanks. That makes much more sense. Couldn't even guess what you meant.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

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