×
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

How to calculate CT ratio

How to calculate CT ratio

How to calculate CT ratio

(OP)
Hi,

I am trying to find the CT ratios for my 33KV switchgear protection relays, as the equipment is very old i cannot find much information so far.

Is there a way to calculate what the turns ratios should be?

Any help would be much appreciated.

Regards,
Melvin.

RE: How to calculate CT ratio

Transformer Turns Ratio (TTR) test

RE: How to calculate CT ratio

35kV/120V >> 35000V / 5V = 292:1
Under some fault conditions the line to ground voltage may rise to the line to line voltage. All protection PTs should be rated for line to line voltage.
There may be exceptions for line metering PTs.
The primary voltage should be equal or greater than the highest expected line to line voltage.
The turns ratio is generally multiplied by 120 and the transformers are rated as (Primary voltage):120 Volts

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

RE: How to calculate CT ratio

To know the CT ratio in the absence of reliable nameplate data, your best option is to do a CT primary injection; injection of current of known magnitude into the primary side.

RE: How to calculate CT ratio

Waross, I think the question was about CTs.

I agree that testing may be your only option.

RE: How to calculate CT ratio

(OP)
Hi,

Thank you everyone for the help, its much appreciated.

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