×
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

Security factor metering current transformer.

Security factor metering current transformer.

Security factor metering current transformer.

(OP)
I recently had a problem where a 51N protection saw a sawtooth oscilography (see attached file) and the main distance protecctión 21 didnt measure well beeing in a diferent winding.
In the subestation there where three windings for each phase two for protection and one for meassurement. Each winding made a paralel from two torodial current tranformers since there where two cables entering the GIS. Therefor 6 toroidals for each phase 4 for protecction and two for meassurement or metering. There where two types of toroidals 5P30 and 0,5 SF5.

On a visual visit we found the following,

One of toroidals por the 51n winding was a 0,5 SF5. and was in paralel with the one from the other cable 5P30. Besides there could be some lack of isolation in the windings terminals.

What is the error in a metering winding above 120% of the nominal current? Could you use a metering tranformer for protection if the SF is above the Icc.

Is there any problem using metering transformer and protection transformer in paralel to get the addition of the currents if it does not reach the Security factor?

Any clues why you can see a sawtooth oscilography (document attached)?

Thanks in advance Antxon

RE: Security factor metering current transformer.

It's been a few years since I was responsible for metering accuracy but I seem to remember that revenue class CTs maintain acceptable accuracy up to 200% primary current.
Protection CTs may trade off low current accuracy for the ability to meter quite high current levels before saturating.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

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