Transformer Thermal Curve 1

[foti]

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?

 

[gordonl]

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.

 

[umrpwr]

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.

 

[gordonl]

Here's a link to a good article on transformer thermal protection:

http://www.pes-psrc.org/Reports/K3_TR_Report.zip

 

[Modula2]

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.

 

[cuky2000]

Check figures 5-5 and 5-6 in the enclose publication.

http://www.usace.army.mil/publications/armytm/tm5-811-14/chap5.pdf

 

[jbartos]

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.

 

[foti]

Thank you all for you helpfull responses.

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