×
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 Thermal Curve

Transformer Thermal Curve

Transformer Thermal Curve

(OP)
I have two Transformers whose thermal curves I want to include in a Protection Co-ordination study.  The Transformers are approximately 20 year old.
One is 300kVA and the other is 1500kVA.
Both are 3.3kV/415V and oil filled.
Where can I locate typical thermal curves which I can reproduce?

RE: Transformer Thermal Curve

I can't say I've ever seen an overload curve for a transformer, I would think that if if you want to push a transformer beyond it's rating you would rely heavily on the temperature protection on the transformer.  (Wired in to trip or alarm for immediate action)

If an overload is set at the transformers rating, no matter the delay you should be fine.  (Assuming your relay picks up at the setting and not 150% or so forth)

Short Circuit curves are readily available, but they generally start at 200% of FLA.

RE: Transformer Thermal Curve

Foti;

The thermal curves for the transformers can be plotted in accordance with ANSI/IEEE standards using the transformer test data if available. This method is preferable since it will give a more accurate damage curve for the transformer. The procedure is contained in standard IEEE Std. C57.109-1993. The following link describes the information contained within http://standards.ieee.org/reading/ieee/std_public/description/dtransformers/C57.109-1993_desc.html
Along with the thermal curves the procedure for plotting the mechanical portion of the transformer damage curves is also contained. Damage curves are plotted based on the transformer category type of which there are four categories for liquid immersed transformers.

The damage cruves can be plotted quite easily by hand once you have the transformer data.

RE: Transformer Thermal Curve

From the data, it looks like these are to IEC standards. I believe they have their own standard for overload and short circuit withstand of transformers.

RE: Transformer Thermal Curve

Suggestion: In older IEEE Standards (around 1975), the transformers had a damage dot instead of the damage curve. The dot in I-t chart indicated that the transformer current and time should not have been exceeded to have the transformer undamaged. Check with the transformer manufacturer tech support regarding this standard.

RE: Transformer Thermal Curve

(OP)
Thank you all for you helpfull responses.

It was the thermal damage curve that I had meant to refer to.

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