×
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

current transformers

current transformers

current transformers

(OP)
hi,
the use of class x, p, t CT's for unit protection is what is normally recommended, were we can specify what knee point is wanted etc...
what are the implications when we use class 5P or 10P ct's for unit protection. will the ct's satuarate more easily? are these types normally used for unit protection?

thanks

RE: current transformers

The 5P and 10P class also includes 2 other parameters, accuracy limit factor and burden rating.

A full protection CT rating would be something like 5P20 - 15 VA. '5P' defines the accuracy class. The accuracy limiting factor of '20' means that the CT will maintain the composite error limits of the accuracy class (in this case 5%) up to 20 times rated current, when the CT is loaded up to 15 VA burden (that's relay impedance plus round-trip lead impedance from the CT to the relay and back).

Accuracy limiting factor is directly proportional to applied burden. Therefore, if the actual connected burden is half of the rated burden, the limiting factor will double.

To put in terms of knee-point voltage, like for a Class X CT, for the example above...assuming a 1A rated secondary, the above 5P20-15 VA, would have a knee-point voltage of around 300 V or more....that's 20 x 1A x 15 ohms = 300V.

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