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Reactor inductance measurement

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.
 
J

John Larkin

Jan 1, 1970
0
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
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin"
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.


** 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
 
J

John Popelish

Jan 1, 1970
0
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.

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.
 
J

John Larkin

Jan 1, 1970
0
"John Larkin"


** Is the manic, the depressive or the autistic John Larkin talking here ?

At your service!
Or maybe just a pedantic bloody fool who cannot spot a novice's typo ?

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
 
P

Phil Allison

Jan 1, 1970
0
"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 ?

Where's the error?

The " k " might just be.




....... Phil
 
J

John Larkin

Jan 1, 1970
0
"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.

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.)
 
P

Phil Allison

Jan 1, 1970
0
"John ASD & BP Larkin"
Might not; I assume he meant what he said, and that assumption doesn't
prove autism.



** Yet another example of it in action though.





........ Phil
 
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