×
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 transformer sizing for relaying protection

current transformer sizing for relaying protection

current transformer sizing for relaying protection

(OP)
Hi,

Can someone give a procedure to correctly size a current transformer to be use in protection ?. I guest it should be something like:

- pick ratio to be below of the nominal current of the system.
- pick accuracy limit factor to be above the maximum fault current.
- pick VA of transformer to match burden of the relay and cables

How you determine the knee point you should specify?
How you determine the correct secundary impedance you should specify?

Thanks.
Regards
Cristian

RE: current transformer sizing for relaying protection

assume IEEE standards:

A customer needs to install a system in which CT
rated current - now called IN - is 100A.
And he knows that when a short circuit,
electrical current reaches a level of 2000A (ICC). And that
the equivalent load of the relay to the wiring more
transformer is 100 VA.

For the CT protect the electrical system of this level of
short circuit, there is a need to design a
core protection that does not saturate up to 20 times the
rated current. Assuming that the client wishes
response has an error of less than 10%,
specification will say:
• core protection 10P20 - 100 VA (10B400) for
meet a load of 100 VA relay and not to saturate
a voltage between terminals 400 secondary
Volts (for IS = 5A).

kneeVoltage see annex

RE: current transformer sizing for relaying protection

(OP)
Ok, thanks, it is clear how to size a transformer of the P type under the iec60044. But what about the PX type?. You need to specify the rated primary, secondary, ratio, rated knee point,secondary resistance, resistive burden and dimensioning factor. Where you get all this information from? and how you deside if you should use a P type or a PX type?. Cheers,

RE: current transformer sizing for relaying protection

Hi.
You can find additional information about CT ( P, PX or TPS) in the next document ( see document presented by Marmite, no 194 ) next number 195,writed by Paola Fonti too.
Good Luck.

P.S.
 IEC60044-6 help you too.
You can try found a good Alstom document:
http://www.scribd.com/doc/48281340/B-CT-EN-AP-C11

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