×
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

Differential CT grounding

Differential CT grounding

Differential CT grounding

(OP)
Hi everybody!

It is recommended  that for a differential relay connection, the CT’s should be grounded at one end only and not at both ends. I will really appreciate if someone explains me in detail what problem is encountered if the CT’s are  grounded at both ends. Is the relay going to trip due to an external fault (short circuit as well as ground fault)?

Thanks in advance.

RE: Differential CT grounding

Suggestion: The reason why the ground should be made at only one point is to avoid improper relay operation and damage to the CT interconnections. If the grounds are made at two or more locations, circulating currents may be caused to flow in the differential circuit because of differences of potential between the grounding points, owing to the flow of large ground currents during ground faults.

RE: Differential CT grounding


See recommendations in ANSI/IEEE Std C57.13.3-1983 …Guide for the Grounding of Instrument Transformer Secondary Circuits and Cases  Figures 11-15 pertain to differential relaying applications.
  

RE: Differential CT grounding

(OP)
Thanks everybody. I got the answer. I am little confused though from the GE DGP relay connection diagram which shows that the CTs (either side of a generator) are to be grounded at both ends separately. These CTs are of course common for diff. and other protections. Am I missing something there?

RE: Differential CT grounding

Every set of CT secondaries should be earthed at one point.

The CT's on either side of the generator do not have a common connection point when using the DGP relay, so they are treated as separate circuits, and earthed separately.

Generator Differential schemes for older protection relays had the CT star points connected together and could be treated as one set of CT secondaries, so only one earthing connection is used.

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