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Old 29th January 2013, 06:13 PM   #1
costasx is offline costasx  United Kingdom
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Default Power transformer ratings and cross-sectional area.

I think there is an empirical formula that relates the power transformer's power ratings to it's cross-sectional area in cm^2, could someone please remind me that formula?

It's an empirical and approximative one, not exact.
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Old 29th January 2013, 06:28 PM   #2
oz7aff is offline oz7aff  Denmark
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There might be some thing of the subject here:

http://www.sandcastle.dk/artikler/Po...ansformers.pdf
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Old 29th January 2013, 06:35 PM   #3
costasx is offline costasx  United Kingdom
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Thank you oz7aff.
What is the book?
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Old 29th January 2013, 06:44 PM   #4
oz7aff is offline oz7aff  Denmark
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Coil Design and Construction Manual

Book. No. 160

B. B. Babani

I.S.B.N. 0 85934 050 3

First Published 1960

I think you can download the whole book here:

Coil Design & Construction Manual : B.B. Babani : Free Download & Streaming : Internet Archive
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Old 29th January 2013, 06:48 PM   #5
costasx is offline costasx  United Kingdom
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It's great, thank you.
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Old 30th January 2013, 09:12 PM   #6
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The core power handling capability is a function of the product of the core cross sectional area and the winding area. Google for something like core area product.
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Old 31st January 2013, 06:51 AM   #7
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by costasx View Post
I think there is an empirical formula that relates the power transformer's power ratings to it's cross-sectional area in cm^2, could someone please remind me that formula?

It's an empirical and approximative one, not exact.
The power in VA of a conventional 50Hz transformer can be crudely estimated by squaring the cross-section expressed in cm². Give or take 25%, depending on the quality of the iron, filling ratio, margins, etc
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Old 31st January 2013, 09:53 AM   #8
AndrewT is offline AndrewT  Scotland
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A = core area in sq in or a = core area in sq cm
VA = 31 * A^2 for flux @ 1T
VA = 0.75 * a^2 for flux @ 1T
If you choose a different flux, you just change the VA in direct proportion.
eg.
core 3cm * 4cm
a= 12 sq cm
Flux = 0.7T
VA ~ 0.7 * 0.75 * [3*4]^2 = 75VA
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Old 31st January 2013, 10:51 AM   #9
AndrewT is offline AndrewT  Scotland
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The numbers in my previous post are for 50Hz.
Slightly more VA is obtained with 60Hz.
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Old 3rd February 2013, 06:25 PM   #10
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Quote:
Originally Posted by AndrewT View Post
A = core area in sq in or a = core area in sq cm
VA = 31 * A^2 for flux @ 1T
VA = 0.75 * a^2 for flux @ 1T
If you choose a different flux, you just change the VA in direct proportion.
eg.
core 3cm * 4cm
a= 12 sq cm
Flux = 0.7T
VA ~ 0.7 * 0.75 * [3*4]^2 = 75VA
Andy,
I suppose you are meaning for so called wasteless cores.Are these formulas valid for c-cores or let's say double c-cores.I think that the size of window and the length of the core play a key role also,considering the constant flux.Are there any other formulas particularly aimed for c-cores regarding their different shapes?

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Yugovitz
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