Temperature rise Vs Rated power of the transformer

[NickParker]

How to relate the temperature rise and the rated power of the transformer?

Transformers are normally designed for operation up to an altitude of 1000 meters. In case if the actual altitude at the place of installation is 1400 meter, it has to be derated according to IEC 60076-2

According to IEC 60076-2, if the installation site is more than 1,000 m above sea-level but the factory is not, then the allowable temperature rises during the test in the factory shall be reduced as follows: (a) For a naturally cooled transformer, the limit of top-liquid, average and hot-spot winding temperature rises shall be reduced by 1 K for every interval of 400 m by which the installation's altitude exceeds 1,000 m. (b) For a forced-cooled transformer, the reduction shall be 1 K for every 250 m exceeding 1,000 m. Any altitude correction shall be rounded to the nearest whole number of degrees kelvin.

The permitted temperature rise is 65 K. therefore, if the Altitude is 1400, it gets reduced by 1K as per IEC 60076-2. Say, if the rated power of the transformer is 10MVA; Since temperature is more-or-less proportional to the square of the current, the derated transformer rating is 10 x (64/65)^2 = 9.69 MVA (derated).

Is it correct?

 

[waross]

Or the permitted temperature rise is 64 K. Can you work with that?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[jghrist]

I'm not familiar with IEC 60076-2, but it seems to me that if the transformer has a temperature rise of 64K during the factory test with 10 MVA load, then you should be able to load it to 10 MVA at 1400 m without exceeding 65K rise.

 

[prc]

A more accurate way is to reduce the top oil temperature by 1 C by reducing the load. Oil temperature rise over ambient temp varies as loss is raised to 0.8. Loss varies approx as the square of the load.

 

[waross]

Are you expecting the ambient temperature to be consistently near or at 30 C?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[NickParker]

Are you expecting the ambient temperature to be consistently near or at 30 C?

Yes!

 

[waross]

hank you for respecting my question, Nick. I had to check.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!