How to measure leakage inductance - Page 2

AndrewT · 19th March 2006, 12:10 PM

Hi Eva,
thank you.

powerbecker · 19th March 2006, 07:39 PM

Eva:
..Thus, when measuring from the primary with the secondary shorted, you have to substract the primary DC resistance plus 13.6 ohms from the primary measured impedance in order to get the actual inductive reactance....

and don´t forget to subtract it geometrically, otherwise :

...error will ruin your experiment..

Regards
Heinz!

Zerokool2k5 · 28th August 2008, 07:41 AM

Percy or anyone who can respond,
When u measured the primary impedance, 350ohm, is that just the primary inductor's impedance or does it include the DC resistance as well (Zinductor + Rdc)? also, I take it that there is no impedance reflection from the secondary since the secondary is a open circuit.

Primary:-
Open Secondary = 350ohm (.93H)

thnx

megajocke · 28th August 2008, 09:03 AM

"
Thus, when measuring from the primary with the secondary shorted, you have to substract the primary DC resistance plus 13.6 ohms from the primary measured impedance in order to get the actual inductive reactance."

More correct would be:

X = sqrt(Z^2 - R^2)

Where X is reactance, Z impedance and R resistance. For example a 10 ohm resistor in series with a capacitor having 10 ohms of reactance at the specific frequency will have an impedance of 14 ohms.

Zerokool2k5 · 28th August 2008, 08:04 PM

Maybe I should have made the question more clearer.
When u measure the primary impedance with the secondary OPENED, are u actually measuring the primary INDUCTOR'S impedance or are u measuring (Zprimary_inductor+Rdc), assuming the that there is no reflecting impedance from the secondary since the secondary is a open circuit?

megajocke,
When u shorted the secondary, don't forget to account for the reflecting impedance from the secondary seen by the primary.

thnx

Conrad Hoffman · 28th August 2008, 09:21 PM

Here's a Word doc that should be of use. Whenever I find some handy formula, I toss it in. The first section on transformers should be pretty clear.

megajocke · 29th August 2008, 12:38 AM

Of course, when measuring with the other winding shorted you will see the own resistance, the leakage inductance and the reflected resistance of the other winding all in series.

But my point is that the magnitude of the impedance does not equal the sum of the magnitudes of reactance and resistance. Z = R + X is true though if you do the calculations with complex numbers [X = jwL where j = sqrt(-1) and w = 2*pi*f]

With the other winding open the winding resistance will be neglible compared to the inductive reactance of the magnetizing inductance though.

Zerokool2k5 · 29th August 2008, 09:57 PM

Hi,
Thanks u, megajocke and Hoffman, for your help. Hoffman, ur doc certainly helps alot....

thnx

19th March 2006, 12:10 PM	#11
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi Eva, thank you. __________________ regards Andrew T.

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19th March 2006, 07:39 PM	#12
powerbecker diyAudio Member Join Date: Dec 2004 Location: Berlin	Eva: ..Thus, when measuring from the primary with the secondary shorted, you have to substract the primary DC resistance plus 13.6 ohms from the primary measured impedance in order to get the actual inductive reactance.... and don´t forget to subtract it geometrically, otherwise : ...error will ruin your experiment.. Regards Heinz!

28th August 2008, 07:41 AM	#13
Zerokool2k5 diyAudio Member Join Date: Aug 2008	Percy or anyone who can respond, When u measured the primary impedance, 350ohm, is that just the primary inductor's impedance or does it include the DC resistance as well (Zinductor + Rdc)? also, I take it that there is no impedance reflection from the secondary since the secondary is a open circuit. Primary:- Open Secondary = 350ohm (.93H) thnx

28th August 2008, 09:03 AM	#14
megajocke diyAudio Member Join Date: Jan 2003 Location: Solna	" Thus, when measuring from the primary with the secondary shorted, you have to substract the primary DC resistance plus 13.6 ohms from the primary measured impedance in order to get the actual inductive reactance." More correct would be: X = sqrt(Z^2 - R^2) Where X is reactance, Z impedance and R resistance. For example a 10 ohm resistor in series with a capacitor having 10 ohms of reactance at the specific frequency will have an impedance of 14 ohms.

28th August 2008, 08:04 PM	#15
Zerokool2k5 diyAudio Member Join Date: Aug 2008	Maybe I should have made the question more clearer. When u measure the primary impedance with the secondary OPENED, are u actually measuring the primary INDUCTOR'S impedance or are u measuring (Zprimary_inductor+Rdc), assuming the that there is no reflecting impedance from the secondary since the secondary is a open circuit? megajocke, When u shorted the secondary, don't forget to account for the reflecting impedance from the secondary seen by the primary. thnx

29th August 2008, 12:38 AM	#17
megajocke diyAudio Member Join Date: Jan 2003 Location: Solna	Of course, when measuring with the other winding shorted you will see the own resistance, the leakage inductance and the reflected resistance of the other winding all in series. But my point is that the magnitude of the impedance does not equal the sum of the magnitudes of reactance and resistance. Z = R + X is true though if you do the calculations with complex numbers [X = jwL where j = sqrt(-1) and w = 2pif] With the other winding open the winding resistance will be neglible compared to the inductive reactance of the magnetizing inductance though.

29th August 2008, 09:57 PM	#18
Zerokool2k5 diyAudio Member Join Date: Aug 2008	Hi, Thanks u, megajocke and Hoffman, for your help. Hoffman, ur doc certainly helps alot.... thnx

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