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


High Impedance Protection

High Impedance Protection

High Impedance Protection

In High Impedance protection, for external fault conditions, the secondary current from the CT's of the unfaulted phases circulate through the secondary of the saturated CT (of the faulted phase), as the unfaulted CT's see the saturated CT secondary as a low impedance than the relay combined with the stabilising resistor.However for internal faults, how does the secondary current from the CT's circulate through the relay, why don't it pass through the CT which has the low impedance among them?

RE: High Impedance Protection

CT's do work in reverse. If you pass current through the secondary of a CT, it will create current on the primary.

Take a little time and let that sink in.

RE: High Impedance Protection

For in-zone faults, all the CTs saturate as they try to drive current in parallel through the high impedance relay input. You don't need much current through the relay, just voltage above the trip setting. See IEEE C37.234.

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