Inductance measurement with variac

i have a few questions about inductance measurements. Since I do not have a signal generator I used my variac. I am measuring inductance of windings of my permanent magnet generator. I placed a 2 ohm resistor in series with two of the output lines of the generator.
1. Is it absolutely necessary to use a signal generator.
2. The generator is wye connected and I am measuring voltage across windings at the output. Would this be considered two inductors in series since it is wye connected. Is it necessary that I measure voltage across the two individual windings.
3. There are 3 magnets on the rotor. Does this influence the inductance measurement. Should I have removed it or left it in since that is how it would be in the circuit.

I don't know a lot of motor theory but I'm aware it's a complicated field and requires a lot of expertise.

3. There are 3 magnets on the rotor. Does this influence the inductance measurement.

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Nearby metal affects inductance of a coil.

When the metal is magnetic, it affects inductance.

When the magnets are moving relative to the coil, it affects inductance.

When the motor is driving a mechanical load, it affects something in the sense it slows the motor and causes it to draw greater current. That's about as much as I can say.

It would be fun to experiment and find out what happens in each configuration. Unfortunately it is not easy for us to move parts inside a commercial motor at our whim. And it is hard for us to fabricate our own motor, to close tolerances, and balanced.

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Edited to add:
Back-EMF is another force generated in a moving motor. Perhaps it does not necessarily change inductance of the coils, but it creates a voltage which throws off readings.

Appreciate the reply. this was my first attempt at inductance measurement and I'm not very confident in doing the formulas or the method I'm using. Using the Per lundahl method I came up 80 mh. These are the measurements I took.
Resistance of the windings: 5 ohms
Voltage supply from variac: 48 vac 60 hertz
Voltage across 2 ohm resistor: 3.08 vac
Voltage across windings: 46.9 vac

1. Is it absolutely necessary to use a signal generator.

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Yes, it's better to do a sine frequency sweep. This will reveal the shape of the LR rolloff curve. Then you can locate where is the range where you can make sure the LR time constant is actively affecting behavior.

Even though your tests with 60 Hz might be okay, it yields just one plot on a graph. You'll get more of a grasp on inductor behavior if you vary the frequency. I suppose this means you need a signal generator and oscilloscope.

I don't know what's the purpose of the induction measurement. If you want to derive parameters of the generator model, particularly the synchronous reactance Xs, your measurement method isn't bad.

You'll probably observe that the inductance is to some extent current dependent and also may vary when rotating the generator shaft.

If the DC coil resistance is about 5 Ohm, it will be better to have the series resistor the same value for max accuracy. For reliable result, you will need a meter with 4 digit or more display.

48V AC is perhaps too high; you should use a voltage so that the total current (same current flows via the resistor and the inductor; they are to be put in series) is around 1A (higher current will give greater voltage drops but unnecessary heating; you have only the voltage to be measured).

When you use the equation, you must remember that your L is actually a L-R (apart from the extra R) combo.

I cannot guess how you got 80 mH. Please tell me.

I cannot guess how you got 80 mH.

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Quite obvious.

Z = V/I = √(R² + X²)

L = X/ω = 1/ω √(Z² - R²)

FvM said:

Z = V/I = √(R² + X²)

L = X/ω = 1/ω √(Z² - R²)

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I guess I am becoming dumber and dumber.

I=3.08/2=1.54 ---> calculated from the 2 Ohm test resistor;

Z=V/I=46.9/1.54=30.4545 ---> same current for the coil.

X^2=Z^2-R^2=30.4545^2-5^2=907.27; hence X=30.04

omega=2*pi*f=2*50*3.14159=314.159; hence L=30.04/314.159=96 mH

What I am doing wrong?

60 Hz has been specified.

FvM said:

60 Hz has been specified.

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Thanks a lot!!

I= 3.08/2 = 1.54
Z= 46.9/1.54 = 30.4545
L = 30.4545/ 376.92 = 0.08079 = 80 mh
The method I used was the only I found online that specifically used a variac. That's why I wasn't real confident in my results.
In C-mitra formula there seems to be a another step that is not in the method I used. The part where he arrives at 30.04. What is this calculation for.
I appreciate that you put the formula plus plugged in the numbers. I do not know all the formulas yet but with the numbers plugged in I can figure out how to do the math. I scratched my head for a while trying to figure out that ^2 means squared. At least I think so. I worked the problem several times but I keep coming up with 902.47. What am I doing wrong.

Reread the earlier post. The 30.04 is the L-R that you had already stated.