Magnetic Flux Density: Quick Question

CSGAS · 17 Apr 2007 at 19:47

Hey guys and gals, need help with a transformer Question here...

Turns ratio (N) = 0.4
E = 500 V
f = 50 Hz
a = 60e-4 m^2

E = (4.44).f.N.(phi)

where phi = flux density (Wb)

So I get phi = 5.6306 (Wb)

B = (phi)/a

where B = magnetic flux density (T) and a is area (m^2)

The answer is B = 0.94 T but I keep getting B = 940.00 T which is quite a few powers off!

What is wrong?

Cheers
Chris

calnen · 17 Apr 2007 at 19:53

Probably just being dumb, but is the fact that its a turns ratio significant? Shouldnt it be something like the number of turns per unit length thats used, so where does a ratio come from?
If its not significant then dont mind me - having not done any EM for a couple of years I dont remember the equations you're using or anything.

Melm0 · 17 Apr 2007 at 19:55

Can you explain the E = (4.44).f.N.(phi) you used?

Cheers

CSGAS · 17 Apr 2007 at 20:41

calnen - its the Turns Ratio:

N1/N2 = N with N1 being no. of turns in the 1st coil and N2 the no. in the second. N1 = 400, N2 = 1000 ::: N = 0.4

Melm0 - E = (in this case) Supply Voltage, f = frequency of supply, Phi = magnetic flux created in the core.

Can anyone else help?

Amleto · 17 Apr 2007 at 20:42

Melm0 said:
Can you explain the E = (4.44).f.N.(phi) you used?

Cheers

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

It says there that N is the number of turns, not the ratio. Also E has to be RMS. it is not clear which 500V is.

CSGAS · 17 Apr 2007 at 20:47

Doh!

It all makes sense now

I apologise for being a idiot! I was wrong calnen! don't listen to me!

Not only does it make sense now, the calculations now work

Cheers!