How to study transformer??

[ahmed osama]

If i have a transformer 110v/12v and can deliver 2 A ,can i using such info. to know the L (inductance) of the 1'st and 2'nd coils of the transformer??

 

[misley]

:?
No, you can't. You have to know a lot of parameters as core material permeabiality etc...In praxis that is pretty impossible...

 

[ahmed osama]

:?
No, you can't. You have to know a lot of parameters as core material permeabiality etc...In praxis that is pretty impossible...

well i asked only for the L (inductance) of the coils..

well what about plug in the transformer to AC source and leaving the other coil open circuit then measure the current and i know the voltage of the ac source

so Z=V/i

and mag of Z=2PiF * L

pi=3.14....
F=freq.

so i got Z,F and so i will get L?????

 

[misley]

Well, complex impedance has a real and imaginary parts...Transformer is not ideal device and it has some losses at real part of impedance...You need to calculate those losses if you're planning to use your math...!

Z=R+jX
X=jωL

Be careful!!

 

[DarkJedi]

You can get the parameters of the transformer, u have to do some meassurements for this, like in short circuit and open curcuit test, u meassure voltaje, current and power.

it's not that easy to get, there is a lot of theory there, u have to get the whole equivalent circuit of the tranformer to find out the inductance of it.

Check "Electric Machines" of Chapman or any other electric machines book, there you will find your answear.

 

[ahmed osama]

Well, complex impedance has a real and imaginary parts...Transformer is not ideal device and it has some losses at real part of impedance...You need to calculate those losses if you're planning to use your math...!

Z=R+jX
X=jωL

Be careful!!

Well yea right i forget R

and my idea is a simple fast test only to know roughly the L value

 

[misley]

Z=R+jX
X=jωL

Oh, what a mistake make...

Correction: X=ωL, not jωL!!

 

[pico]

I think it's not so simple. Becuase of the mutual inductance.

 

[sajal1975]

hi,
here is a tutorial for transformer
www.elect-spec.com/variac_tutorial.htm

 

[bjeservice]

Dear Ahmed Osama
the way you mentioned is wrong to calculate impedance because in theoritical transformer you will see that Z is infinity as your way , because the back emf.
to get impdance you need to do short circuit test , so you pass full load current into secondary turns of transformer and measure the current and voltage in primary coil tjen z=v/i
regards

 

[VVV]

Yes, ahmed osama, you are absolutely right.

First, you measure the current through the primary, without any load in the secondary. Then you measure the DC resistance of the primary (with an ohmmeter). From that you calculate the actual primary inductance, or magnetizing inductance, as it is sometimes called.

Then you measure the secondary voltage, again without any load. Since the primary to secondary voltages are related by the relation Vp/Vs=Np/Ns, you can calculate the turns ratio of the transformer. You have to be careful, though, if you really want to be accurate. The voltage across the "primary" is actually the voltage across the L of the primary (remember, you have an R in series with it, though to a first approximation you can consider the entire mains voltage is across the L, neglecting the drop across the R).

(Np/Ns)≈Vp/Vs

Once you know the turns ratio you can easily calculate the secondary inductance, knowing that the ratio of the inductances is equal to the square of the turns ratio:

Lp/Ls=(Np/Ns)² so Ls=Lp(Ns/Np)²

Regards,
VVV

 

[Code Warrior]

Simply measure by inductance meter.