×
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

Spurious differential trips of power transformer on energization

Spurious differential trips of power transformer on energization

Spurious differential trips of power transformer on energization

(OP)
Although very infrequent, I have experienced spurious tripping of power tranformers upon energization via their differential relays (restrained trip).  These are generator step-up transformers (80-90MVA, 1998-2000 vintage) at natural gas fired generation facilities.  The differential relays are generally only "looking at" the transformers themselves.  In each case, after appropriate checks and analysis, the transformers were successfully re-energized upon a second energization.  Some of the transformers have microprocessor relays affording oscillography, some don't.  I am aware that the energizing current can vary widely based on when the transformer is energized and de-energized (during voltage cycle).

Has anyone else experienced this?  After some investigation, I am thinking that the problem may be that the relay setting that inhibits tripping during energization (triggered by % 2nd harmonic current as compared to fundamental) may be set too high.  Unfortunately some of the differential relays in question have this value factory set to 18% with no adjustment.  Others are set at 15%.  From what I have heard, some of the newer tranformers have much smaller 2nd harmonic content on energization, than older transformers.  Any comments or suggestions would be greatly appreciated.

RE: Spurious differential trips of power transformer on energization

Inrush currents.

Do your relays use harmonic restrain or actually harmonic blocking? And have you checked your other harmonic currents? (4th harmonics or 5th harmonics (overexcitation))

Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon

Make the best use of Eng-Tips.com
Read the Site Policies at FAQ731-376

RE: Spurious differential trips of power transformer on energization

It does happen, but the harmonic restraint and/or blocking is intended to make this much less likely.

What type of relays are involved?  

On some relays, you can just flat block the differential function for a programmable time delay after the breaker is closed.  This obviously degrades the protection somewhat, but it would solve the problem.  5 or 6 cycles is generally adequate.

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