Transformer Magnetic Field Calculation

[ed downey]

What is the formula for calculating the magnetic field strength at a 3 phase 480V to 120/208V 15kVA transformer.

I think the formula for a single conductor is B = 2* (i/r) {mG} {i is the current & r is the distance from the source in meters}

But i am not sure if this changes for a transformer.

I know the field strength will decrease by 1/r^3 but I am not sure what the starting field strength would be.

any help would be appreciated.

-Ed

 

[tom baker]

Re: Transformer Magnetic Field Calculation

If you are concerned with the EMF, then a guassmeter would tell you what it really is. The field would vary according to the load.

 

[ed downey]

Re: Transformer Magnetic Field Calculation

Tom, I agree only we have not installed the transformer yet so I was going to figure the transformer fully loaded (worst case) and then determine an approximate distance from the transformer that the EMF would be below about 4mG.
-Ed

 

[coulter]

Re: Transformer Magnetic Field Calculation

ed, tom -

Here is my current understanding on transformer magnetics: Xfmrs are designed to keep as much of the magnetic field as possible inside the iron core. Any of the mag field not inside of the core is a loss.

Following that thinking, any radiated mag field is inadvertent, subject to design tradeoffs for efficiency, materials costs,production costs. It would appear very difficult to calculate

I'm out of my area of expertise - as for xfmrs, I use and abuse - I don't design or build.

So, please educate me a little. I can't tell if my thinking is leading or lagging.

I've got a gauss meter somewhere. I bought it 10 years ago when my mother got worried about the xfmr outside of her window. If I can find it, I'll take a few measurements. Are we talking mVA, kVA, or VA?

carl
(My xfmr puns are always well maxed out)

 

[ed downey]

Re: Transformer Magnetic Field Calculation

I know the mG reading deteriorates at a 1/r^3 rate (with r = distance in meters) and by reading Karl Riley's book "Tracing EMFs in Building Wiring and Grounding" along with hearing tele/data guys squeel about EMF's in their IDF closets due to transformers it is some value outside the transformer.