How Do You Test the Industance of Transformer?

Yes I used an L C R meter .

Ah..now I come to think of it I've also done it by a bridge method and some maths! Balancing the impedance against a decade resistance box or some such.
It was years ago...something to do with measuring the impedance of telephone equipment for BABT approval.

Del

Re: above... it was driven using an AC source of course.... at various frequencies..
I don't want you guys thinking I dont know the difference between inductance and resistance

ah, I hvnt thought about this.

I thnk everyone who come here will know this difference.

Do you find when you use different bridge or RLC gauge, you will get different values, especially for a higher voltage transformer?

I expect it will vary with frequency...
I assume you are talking about mains frquency transformers...my experience is just low power audio frequency stuff.

Del

In fact my aim is to high frequency or pulse transf. not the main transf.

Im not transf manufacture. I used to winding the main transf by experience.

I know audio transformer is difficult to wind. if you would get a wide band.

I would measure the inductance of a transformer at its operating frequency with any other windings left open circuit.

No it shouldn't change between different inductance bridges....

BUT it may!!! the Q of the inductance can make different types of bridges read differently - some bridges will state that the error in reading increases quite alarmingly as the Q factor decreases -For a power transformer the Q could be quite low at 50 or 60 Hz

So yes different bridge types may well give different values of inductance - Especially if one bridge biases it with a dc current or drives it into saturation.

For a power transformer, out of the bridges I have available, I would use my Marconi inductance analyser which is used purely for power transformers, to detect shorted turns etc... with a built in oscilloscope to observe the B-H curve....

John.

Thank you John,

its good answer. I vote for you。

flux chain /i = L or delta B/ delta i =L

is its principle of test.

I remember you ask a question about leak industance calculation. Its out of my depth. I think the best bet is still testing in practice.

Marconi instrument is good. I hvnt got .

Ours is made in china, but not as good as that. but it can be used in practice.

I've done it with a capacitor to make a tuned circuit and measured the frequency. But the fly in the ointment is that the inductance will always depend on the B-H curve and, so, is variable. You have to get the frequency and voltage exactly right.

from principle its done, but in fact different connect method of the tuned circuit will get different value, serial and parallel are different for its Q value as point out by John above. and if you gt BH curve, you at least make sure it will not saturate in it working.

however, there is a long distance between theory and practice.

You're right CN. I was too terse again. I always used series LC and I monitored the secondary to see that the voltage and frequency were close to what I wanted. Oh, and I sat across from the filters guy so I had an almost unlimited supply of high quality capacitors - that helped.

HI cnpower,

When measuring inductance, use the lowest voltage setting you can without getting a noisy reading. Inductance varies with applied voltage, because the current flow affects the magnetic flux in the core. You don't want to saturate the core, or the reading will be low. It won't take much to saturate a small pulse transformer. For those use 100kHz or above if you can.

Regards,

S

use small current to prevent from satuation. right.

However, flux is not linear with magnetic field. thats why different cutrrent can get different flux and responsive L. or in other words, mu (u) value is different.

"use small current to prevent from saturation. right."

Correct