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50 Henry inductor for 2000v

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GammaRay

Mon Sept 07 2015, 04:41PM

Registered Member #5323 Joined: Fri Jun 15 2012, 02:14PM
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Current will be around 5 amps. But the windings will need to withstand up to 2000vdc.

Hazmatt_(The Underdog)

Mon Sept 07 2015, 06:26PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
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You probably don't realize that 5 amp handling at 50 H inductance is basically the primary side of a pole pig.

That is going to be a very large inductor, probably 20 AWG wire, and weigh 100 lbs or so.

See what I mean?

Ash Small

Mon Sept 07 2015, 11:10PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
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Posts: 4245

Or several smaller ones in series.........

Signification

Wed Sept 09 2015, 12:41AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Just of interest:
I saw the neat MIT demo for the class RL circuits which I think used something like a 30H inductor. The lecture explained the equations of charging AND discharging the huge resistor-inductor RL circuit.

The following lab illustrated, using a car battery, how long it took to get a small incandescent light bulb to full brightness through the inductor-slowed current (based on the previously derived equations). Eventually it hit me that the demo did not illustrate the SLOW decay of the lamp intensity when shut off. Which was HALF the of the equation (since the switch opened the circuit). This bugged me for quite a while. I finally drew out a circuit add-on (the modification was surprisingly simple!) that would show both, slow rise and slow fall of current with a simple bit of rewiring--It did require blowing a simple 1/4 amp fast fuse when the switch was opened, but that's OK. I would have loved to see it work anyway.

I -may- have tried this with the large secondary NST inductance + R, but don't seem to have any memory of success or even trying...does anybody know why this wouldn't work? Guess I'll try sometime soon.

radiotech

Wed Sept 09 2015, 01:47AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Look into the inductance found on the primary of PTs .

I have a 2500 Volt PT here, and the primary inductance is 35 Hy.

I just measured it.

If you are experimenting with a 50 Hy coill on a 2000 volt circuit, you need to
what the B.I.L. (basic impulse level ) is.

Signification

Wed Sept 09 2015, 06:32AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
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Posts: 367

I think I have an 8400 V PT (I will have to check the label--it may be 84:1 ??). I had no idea the "L" was so high in these things, I will look into it

The NST (15kVAC@60mA) is one I rebuilt and repotted--it is now rated 17.5kVAC @ 70mA. I an assuming the highest safe voltage level would be about 15kV but I think MUCH lower would be better--variac. And I am assuming the bulbs can be incandescent <<70mA and work fine if arcing is not overlooked. I don't remember the inductance but it is high--with a few 10's of distributed kilo-ohm resistance.

...don't know about B.I.L--wasn't mentioned in the RL lecture---will look into it.
I may do this thing after-all. I don't think I will need a higher current, in fact, probably much more than 12V batt due to Ohm's law and the secondary "R".
---------------------
OK, I am beginning to recall things...I just did a calculation and something looks 'hinkey'. If L=20H and R=10k, then L/R is only 2ms. What gives? I think in the demo it was L=30H and (internal R) = 4 Ohms yielding L/R=7.5 sec...something easy to 'observe'. In fact, come to think of it, this may be the glitch I ran into in trying this---WAY to much 'R' It looks like high voltage 'R' may be a hard voltage incandescent to find. It also looks like the internal resistance of an NST will be problematically high. The demo'ed inductors had TINY (relativity speaking) resistance, come to think of it.
This may just turn into a VERY interesting project, despite being a demo. just so it shows the RL delay in play BOTH ways!!
ps
Now I am thinking (as I write) huge inductor + supercap fot LC time constants??? That would be in MINUTES! I may re-read this in the morning and find it ridiculous--been up 20hrs.

radiotech

Wed Sept 09 2015, 07:18AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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A 50 Hy choke, 60 Hz at 5 Amps would have 94,250 volts across the terminals.

Quite a demo !

Signification

Wed Sept 09 2015, 06:20PM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

How do you get that high voltage--I have been trying to match it using V=Ldi/dt. I get 15,000V.

Would that not be, for 30H, 60mA, @ 60Hz, about 100V?
Using V=LIf.
I sure may be wrong, I was writing at first thought, that previous message.
===========================
edIT

OK, I see that if you take, not the RMS, but the INSTANTANEOUS / maximum di/dt you get V=LwA=50*5*(2*pi*60)=94250v

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