Xfmr name plate ?

[sparky1976]

Guys,
Another silly question again from me,
I have A xfmr 11kV to 3,3kV Dyn1 on the name plate says
"Full load KVA"
7500/8400 OA
9375/10500 FA

Is it means 7500 KVA for W1 and 8400 kVA fro W2 with oil cooling only, and 9375 KVA for W1 and 10500 for W2 with oil cooling and force air/fans ?

Please advise

thanks
Pitat

 

[jnims]

It looks like your transformer has a dual temperature rating. Power transformers built to ANSI/IEEE standards may be design with an average winding rise over ambient of 55C or 65C. Sometimes transformers are show a dual rating 55/65C. What this tells you is that at the design conditions, 30C average over 24 hours without exceeding 40C, this transformer is capable of 7500 kVA (without fans) and will not exceed an average winding rise over ambient of 55C. Add fans and the capacity increases by about 33% to 9375 kVA with the same average winding rise. If the average winding rise is allowed to rise to 65C, the transformer's capability increases by 12% to 8400/10500 kVA (without fans/with fans)

Hope this helps

 

[SphincterBoy]

jnims, explain "rise over ambient"?

I have never fully understood this term.

Is it coil/winding temp. above outside air temp. or what?

 

[jwerthman]

jnims is correct except that the percentage increase from OA (self-cooled) to FA (forced-cooled) is 25% for this size of transformer. For ANSI-rated transformers, the 25% increase applies to transformers rated 2500 kVA to 10000 kVA OA. Transformers rated 12000 kVA and above increase by 33% for each stage of cooling. For example, a 12 MVA OA transformer with one stage of cooling would be rated 12/16 MVA OA/FA. If it has two stages of cooling, it would be rated 12/16/20 MVA OA/FA/FA. The increase from the 55 degree rating to 65 degree rating is 12% as pointed out by jnims. This applies regardless of transformer size. Most new transformers are rated for 65 degree rise and do not carry a 55 degree rating, but there are thousands of older transformers that were dual rated 55/65 degree rise.

For SphincterBoy, the 55 or 65 degree rise is average winding rise above ambient air temperature. Usual service conditions, as defined by ANSI C57.12.00, are 30 degree C average ambient over a 24 hour period with a maximum of 40 degree C ambient.

 

[sparky1976]

Yap,
I take another look at the name plate it says 55/65 C Rise,

Thanks guys.

 

[prc]

To Sph boy,
If it is a water cooled trf,the rise of 55 or 65 degree will be over the inlet water temp and not over the ambient air temp.The top winding and hot spot winding temp will be still more than this figure.The top wdg temp will be 5-13 C more than avg wdg temp (for FA cooled )and2-4 C more for OFA cooled trf.Hot spot temp will be 2-8 C more than top wdg temp.
In other parts of the world FA rating can be 150-200% of the OA rating.(up to 100 MVA rating)
The 65 C trf calls for thermally upgraded conductor covering insulation to meet the higher temp limit.In Europe and other parts of the world 55 C rise trfs are the std as per IEC.