Capacity of Transformer

Continuous average power is not the number with which you need to work. You need to look at a site drawing, take a survey of what is connected, based on its ratings, add all of that up appropriately and then factor in some margin for future additions.

You can not make valid conclusions from an average because you have no idea what percentage of a full load that average represents. Guess work is only correct 8.2% of the time. Oh, buy the way, I just guessed at that percentage.

What you have to ask yourself is, "Do you feel lucky?"

Respected sir,

Thank you very much for reply.

load status is as below.

full load cotinious = 225kw

feature full load continious =80kw

r Total= 305kw

p.f.=.8

Total load in kva= 381kva

(if % loadin 70%), capacity of xmer = 381/.7= 544 kva

say 500kva

This is the way i am calculating .

please guide in this regard

s.s. magdum

It looks like you have enough design capacity margin. The main difference between air cooled and oil cooled is the physical dimensions and rate of response to thermal loading. By that I mean that oil will conduct heat away much faster than air.

I believe that oil filled transformers will out perform air cooled in terms of life and protection of the windings. Recently, I learned that a common failure in a transformer winding is on the corner of the metal core. Too tight of a radius created a "hot spot" where the insulation would break down. If my information is correct, an oil filled transformer is a better choice for this problem. As for copper loss, it will be nearly the same for both. But how and where that heat is dissipated can be a problem. Either one will crank out some heat so you need to make sure you have enough ventilation.

An oil cooled transformer may have its own radiator for heat exchange. You might even be able to capture some of that heat to water lines that feed water heaters. I think you will have to check local codes for that possibility. Good Luck!

From your name, I guess you are from India. If so, you MUST go for ONLY a dry-type transformer for indoor installations, vide the Indian Electricity Rules, 1956. [Rule No. 64 (2) (e) (iv)]. A better chioce would be a packaged sub-station.

Thank you very much sir,

This is a in door instalation.

I am planning for pakaged sub station.

I am worried about cu lossess at hot

conditions whether they are more

than oilcooled xmer ?

please guide in this regard