×
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

Transformer Data

Transformer Data

Transformer Data

(OP)
What does it mean for a transformer to have a rating of 1500kva @ 55 deg c and another rating @ 1680Kva at 65 deg c.
I would have thought the cooler temp. would have the higher rating.
Thanks  

RE: Transformer Data

The simple reason the transformer has a higher kVA rating is that is allowed to run at a higher temperature, by taking more current the transformer will produce more heat losses I2t etc.
Provided the unit has a dual rating design it should be able to run at the higher load.  Cast resin units are popular with dual ratings and usally include cooling fans to achieve there maximum rated duty.
I suspect that if such units were run all the time at the top end ther life span would be reduced.  
The upper rating is more of an intermittent duty cycle.

RE: Transformer Data


One reference is IEEE Std C57.91-1995 Guide for Loading Mineral-Oil-Immersed Transformers
  

RE: Transformer Data

Comment on Sanditech (Electrical) Feb 6, 2004 marked ///\\\
The simple reason the transformer has a higher kVA rating is that is allowed to run at a higher temperature, by taking more current the transformer will produce more heat losses I2t etc.
///Please, would you clarify the heat losses I2t, which seem to be having unit Ampere^2 x time rather than Watts x time.\\\

RE: Transformer Data

Power loss to heat in the windings is I^2*R = watts.

Many liquid insulated transformers are rated 55/65C rise with two kVA ratings. Additional ratings are commonly available when cooling fans are applied on the radiators or oil pumps are used to improve circulation.

Solid dielectric transformers typically have a single rating unless provided with fan cooling. Temperature rise ratings are commonly 80, 115 or 150C.

RE: Transformer Data

Suggestion: The air cooled dry-type transformers also have temperature ratings.
Reference:
IEEE Std 141-1993 Red Book
Section: 10.4 Transformers

RE: Transformer Data

Comment on Hileg (Electrical) Feb 6, 2004 marked ///\\\
What does it mean for a transformer to have a rating of 1500kva @ 55 deg c and another rating @ 1680Kva at 65 deg c.
///Liquid-immersed transformers may be specified with a 55³C/65³C rise to permit 100% loading with 55°C rise and 112% loading at 65°C rise. In addition, 115°C rise, high-fire-point, liquid-immersed transformers are available from some manufacturers.\\\

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