Re: [TCML] Disassebling a huge transformer

[Ed Phillips <evp@xxxxxxxxxxx>]

garry neeley wrote:

> How can I figure out the inductance besides using lcr meter? Bamacoiler


Use the "3 meter" technique..

First, get a handle on the reactance.. hook up a volt meter and ammeter 
and feed AC through the coil.  Start with low voltage so that the 
currents are reasonable.


Put the unknown in series with a known resistance, magnitude 
approximately equal to the reactance of the unknown. Apply voltage to 
the series combination.

Measure the voltage across the resistor and across the unknown, and the 
series combination.

Now, you can solve for the R and X of the unknown either with algebra or 
graphically.

That is, Vcombination = Irms * sqrt(Rtotal2 + X2)
You know Irms because it's Vknown/Rknown
Rtotal = Rknown + Rx

Jim"

   Haven't seen anything on this method in years - used to give it as a 
lab exam excercise when I was a grad student teaching EE lab at 
Caltech.  It was actually too advanced for some of those mechanical and 
civil entineering students.

   Note that any measurements such as these are valid only at the 
particular coil voltage [and hence core flux] and may not apply for 
other voltages.  Magnetic cores aren't very linear and this particular 
gadget may or may not have any air gap.

Ed

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