anorlunda said:
@jim hardy can you help with this question?
Difficult because he says he's already measured it, so I'm confused as to what is the question.
Wye connected, he says... Where did he connect his inductance meter probes?
Line to Neutral he'll measure the inductance of a single phase
Line to Line he'll measure twice the inductance of a single phase,
electricalguy said:
Using an inductance meter phase A of the stator when not running has a measured inductance of 108.5uh on the high end and 84.3uh on the low end depending on rotor position, with a resistance of 0.2 ohm.
What's inductance? Flux per amp-turn. So of course it varies with rotor position because reluctance of the flux path changes with air gap. And it sounds as if his airgap changes with rotor position by ratio of his high/low readings.. All three of his sets have ratio about 1.3 suggesting that's how much airgap varies. Is it a salient pole machine ? or the effect of slots reducing area of iron at airgap surface of rotor? ?
electricalguy said:
I will give you some of the specs of the alternator. The rotor has 12 poles, with an inductance of 12.90mh,
12.9mh (from a spec sheet ?) is a lot different than 80-107 measured .
I suspect if he'll pull the rotor out that's about what he'd measure.
Now
electricalguy said:
The motor specs are a 1/3hp induction motor with 115volt supply, 6.4 amp supply at 1725 rpm.
six pole pairs at 2429RPM gives frequency of of 2429 X 6 = 14574 cycles per minute = 242.9 hz.
So he's got a belt drive frequency changer.
I wonder it it's perhaps a car alternator driven by a washing machine motor ? . Sounds like really interesting project. Matbe he'llpost a picture
So once again - if OP would tell us what it is he's tryng to accomplish he'll get responses from both the practical AND the academic sides of the PF aisle .
electricalguy said:
I am having difficulty calculating the inductance of each phase of the stator winding when it is at full operation.
Why would its inductance change with load ?
B-H curve does flatten a little
but if you're not near saturation you can consider permeability constant.
Accounting for BH curvature in my day we did graphically
Take control of armature current and make a plot of open circuit voltage versus armature current
Move armature current in increasing increments all same direction - if you overshoot a point don't back down to the intended current just plot that point where you landed and move on to next point.
When voltage curve flattens start back down.
Now you have the BH curve, with field hysteresis , for your alternator and you can see how close to the knee is your normal operating point.
If you're after Leakage reactance try this
short circuit the field so as to cancel flux that goes through the rotor or better yet, remove the rotor and just.. test the stator...
force maybe an amp of AC through one phase , measure voltage
From voltage drop Ohm's Law gives you Z
You know R, and X= √(Z
2 - R
2) for first approximation.
We'd enjoy seeing a picture of your experiment.