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  #1  
Old 07-17-2009, 12:45 AM
Deano123 Deano123 is offline
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Default Calculate number of turns in transformer

I need to find the required number of turns on the primary and the secondary windings of a transformer.
Given it is single phase 110/25KV railway TX on a 50Hz system
the max flux density is 1.5Tesla when 1.13pu volts applied.
assuming a core area of 0.3m2.

How would I find this?? number of turns prim and sec
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  #2  
Old 07-17-2009, 03:29 AM
t_n_k t_n_k is offline
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Quote:
Originally Posted by Deano123 View Post
I need to find the required number of turns on the primary and the secondary windings of a transformer.
Given it is single phase 110/25KV railway TX on a 50Hz system
the max flux density is 1.5Tesla when 1.13pu volts applied.
assuming a core area of 0.3m2.

How would I find this?? number of turns prim and sec
Hi Deano123,

I get the following

Erms=222.14xNxAxBmax

Did you mean the primary is 110kV?

If it's 110kV (RMS) then for conditions at 1.13pu Vprim = 124.3kV

So Np=123.4x10^3/(222.14x0.3x1.5)=1243 turns

That's a big core CSA! [0.55mx0.55m]

For the 25kV secondary

Ns = 281 turns.

These are very sparse specs for such a big unit. You haven't specified whether there a limitations on magnetizing current, losses, efficiency and a whole lot of other stuff. Do you intend to build this?
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Old 07-17-2009, 03:33 AM
t_n_k t_n_k is offline
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Make that Ns=283 turns
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Old 07-24-2009, 02:22 AM
kkazem kkazem is offline
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Default Expert Answer

Hi Deano123,

Here is an answer from a top expert in the field, me! I have over 35+ years designing all kinds of transformers. I'm going to make it as simple as I can right now, as my time is very limited at the moment. This will require that you make a few conversions to use the CGS system, like 1.0 Tesla = 10,000 gauss.

Here is the formula for the first winding, based on the known input voltage. Normally the primary, so I'll use that term:

Np = number of primary turns.
Vp = known primary input voltage in volts. I'm assuming a sine wave input. If it's a square wave input, remove the factor of 1.11 from the denominator.
Bmax = maximum flux density in gauss.
Ac = effective core area in cm^2 (convert from m^2).
Fo = input frequency in Hz.

Np= (Vp X 10^8) / (4)*(1.11)*Fo*Ac*Bmax

In practice, you always round-up to the nearest integer turn. Then for the seconday turns, Ns = (Np*Vs)/Vp. This time, you can round up or down to the nearest integer turn, usually whichever is closest to the value you want.

In practice, the effective core area not only depends on the actual core area, but the type of core, like E-I laminations. Then it gets modified by the stacking factor; which depends on whether you interleave the laminations 1 by 1, 2 by 2, or butt-join them. It also depends on the lamination or tape-wound core tape thickness. The thinner the material, the closer to the actual measured core area.

That's probably more than you wanted to know. If you have more questions, please ask.

Good luck,
Kamran Kazem
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  #5  
Old 07-24-2009, 05:46 AM
bonjing bonjing is offline
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hi

what is the recommended frequency for 110v Ac and 220v ac
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  #6  
Old 07-24-2009, 07:27 AM
t_n_k t_n_k is offline
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Quote:
Originally Posted by bonjing View Post
hi

what is the recommended frequency for 110v Ac and 220v ac
Whether you use my formula or kkazems you'll get exactly the same answer.

Something is seriously wrong with your specification if you really mean 110V primary.

With a CSA of 0.3 m^2 at 50 Hz you'll need just 1.243 turns for the primary - even rounding up to 2 turns gives a ludicrous result. I think you need to re-check your spec. The CSA of 0.3m^2 is probably not what you intend.
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  #7  
Old 07-24-2009, 08:19 AM
bonjing bonjing is offline
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others they specify the frequency, 60Hz for 120volts ac and 50Hz for 220volts ac...

what is the truth about this?
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Old 07-24-2009, 08:26 AM
t_n_k t_n_k is offline
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Quote:
Originally Posted by bonjing View Post
others they specify the frequency, 60Hz for 120volts ac and 50Hz for 220volts ac...

what is the truth about this?

There is a comprehensive listing here on wikipedia

http://en.wikipedia.org/wiki/Mains_power_systems
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