×
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

Starting a transformer

Starting a transformer

Starting a transformer

(OP)
Iwas told that in  certain case we have to inhibit the 2nd harmonic protection during a  transformer start.
Can you help me with that

RE: Starting a transformer

Harmonic restraint is a function of the differential relay.  Check the instruction bulletin for the relay settings and test procedures.

RE: Starting a transformer

We don't inhibit the second harmonic.  Some protective relays use this characteristic of inrush current to desensitize differential elements during the energization of the transformer.

You understand that a differential relay looks at the current going into the transformer and compares it with the current leaving the transformer, and operates when the two do not match within certain limits.  

When the transformer is first energized, current rushes in, which is why we cleverly call it "inrush current" but no corresponding current flows out.  

An uninhibited differential element would operate under such circumstance.  In order to prevent that from happening while still allowing the settings of the element to be sensitive enough, some relay manufacturers use the presence of harmonic energy in the inrush current to inhibit the element.

old field guy

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