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


Transformer Differential Protection

Transformer Differential Protection

Transformer Differential Protection

A customer has installed a solid state transformer differential relay to protect a small pad mount transformer.  All of the hardware is installed.  This is a non-critical application.  I have never set a transformer differential relay, so this might be an excellent opportunity to learn how to properly set one.  Can someone give me some guidance (or refer me to a good book) on how to set Percent differential and the corresponding slopes along with the energization inhibit features.

RE: Transformer Differential Protection

Generally, the manual for the relay will provide you with application examples.  You will need CT Ratios for primary, secondary.  Power Transformer MVA, Pri Volts, Sec Volts.  If there is an LTC, the range of taps.

Quite a few settings that seem to be popular are:

Pickup (87R)  ~ 0.3 x Tap
Slope 1 ~ 25%
Slope 2 ~ 40-50%
87U     ~ 8
2nd Harm ~20-25%

GE has a free online book called The Art and Science of Protective Relays, that is also a very good start.

RE: Transformer Differential Protection

I agree with smallgreek.  Art and Science is based on electromechanical relays, but the principles are the same and this would be a good supplement to the relay instruction manual.

Protecting a small padmount transformer with differential relays is unusual.  Mainly because it would be unusual to have CTs to use on both sides and a high side device that can be tripped by the relay (instead of fuses).

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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close