Hi, i need to measure the inductance of a 70kVA linear reactor. What are the most cost effective (e.g. cheap) options? I already measured it with a bench LCR meter, but i do not trust the results; it read 5mH.
Try applying a DC voltage, say from a bench power supply, and noting how the current rises with time.
L = E * T / I
Some of the big utility transformers take, I think I heard, minutes to ramp up.
John
"John Larkin"
** Is the manic, the depressive or the autistic John Larkin talking here ?Or maybe just a pedantic bloody fool who cannot spot a novice's typo ?
...... Phil
First of all, you might calculate what inductance is expected (to know if 5 mHy is reasonable). What is the voltage or current rating and operating frequency for this inductor?
By Xl=2*pi*F*L, 5 mHy would have a reactance of 1.885 ohms for 60 Hz.
So, it would be a 70kVA load if 363 volts were applied across it.
But if it has a large laminated core, it may not show its full, large signal inductance with a very small voltage across it, as you have with an LCR meter. The meter is probably also not be measuring the inductor at 60 Hz. Of course, if it was truly a linear inductor none of that would matter, but it probably isn't really.
I think a better way to measure it would be to apply a low voltage across it with a step down transformer, measure the voltage across it, and the current through it, and calculate the inductance that would produce that ratio of voltage to current, which is the Xl.
At your service!
Where's the error?
I do know that big utility transformers are tested this way. Their inductances can be in the kilohenries, and losses and distributed capacitance are way too high for conventional LC bridges to measure anything sensible.
John
"John ASD & BP Larkin"
** Is the manic, the depressive or the autistic John Larkin talking here ?Or maybe just a pedantic bloody fool who cannot spot a novice's typo ?
The " k " might just be.
...... Phil
Might not; I assume he meant what he said, and that assumption doesn't prove autism.
In the power biz, that's just a medium-size inductor. But even hundreds-of-VA power transformers and inductors usually report silly numbers with an electronic-type LC meter or bridge. I recall an appnote somewhere that said it can take a half hour to measure the L of a big utility xfmr... might be interesting to google some rainy afternoon.
John
(in manic phase, which I am 95% of the time. Even my VW transmission throwing a tooth can't get me down, but that's a whole nother story.)
"John ASD & BP Larkin"
** Yet another example of it in action though........ Phil
"How incredibly boring."
- Alan B
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