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Pole pigs, and saturatable reactors

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Kolas

Mon Oct 15 2007, 07:16PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

Hey guys. This post has mostly to do with saturatable reactors. But since the load is a pole pig (actually two) i thought I'd throw that in the title too.

First. The video.

Ok so the video starts with the reactor's DC winding at 0V. It's obvious that the current is successfully being limited. at the end of the video, the power is suspected to be about 24kW.
My configuration consists of two very large variable reactors, in series with a choke, and the two pole pigs. (I have enclose a picture of a reactor showing all 3 windings) I'm using the inside primary on the pigs, so I'm trying to put ~120v across each LV winding.

Right now the reactor's individual windings are in parallel. But one reactor doesn't offer enough current limiting. So my question is: can I put one reactor's individual windings in series to control 240V. I suspect the reactors are meant for 208V.

I only want to use one reactor to control both transformers.
Any help would be appreciated, thanks.

Steve Ward

Mon Oct 15 2007, 09:34PM

Registered Member #146 Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055

Seems like you should have no problem seriesing the windings. If your phase them incorrectly, then you will cancel out almost all of the inductance, but the other way will give you about 4X the inductance (of one winding alone). So it should be pretty obvious when you get it right :P.

One thing i never understood about saturable reactors is that they use a DC input to bias the core. This would give asymmetrical inductance as when the input is in one direction the core fluxes add (and saturate the core easily) but the other direction the fluxes subtract, so you have to push more current through your ballasting winding to make it saturate. Perhaps there is more to it than this?

Kolas

Mon Oct 15 2007, 09:47PM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

With the reactors, it deosn't seem to matter which polarity the windings are powered. They are connected in series inside, so I kinda doubt it matters.

Well I tried putting the reactor windings in series, it works quite well except for one thing.
The DC winding now has in excess of 1000V across it (electrons will jump through air) And instead of limiting by how much DC Voltage is across it, it seems that it limits by how much of a load is put across that winding.
I shorted the DC winding and the controlled windings are almost a short. If I leave 0 load across the DC winding i get almost full quenching of current. Any ideas? am i now going to control with a variable resistor?

Marko

Mon Oct 15 2007, 11:22PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

One thing i never understood about saturable reactors is that they use a DC input to bias the core. This would give asymmetrical inductance as when the input is in one direction the core fluxes add (and saturate the core easily) but the other direction the fluxes subtract, so you have to push more current through your ballasting winding to make it saturate. Perhaps there is more to it than this?

That's why two cores are used with AC winding out of phase on each other, so output is symmetrical. At least as I figured out.

Now I'm not quite clear with the pic but are those two windings on separate C pairs under the big winding?

Kolas

Tue Oct 16 2007, 02:35AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

hey

I think i can safely say I had it wired incorrectly when I made my last post.

I'm depending on the schematic found at the bottom of this page.

The transformers I have seem to match this quite true to form. There are two cores: each are wound with large wire very close to the core and the cores are not touching. Around the outside of them is a DC winding; which seems to be insulated for amazingly high potential.

On a name plate the DC control winding(s) is speced at 25V 4.5A.

I've now rewired it (there are 4 ways it can be wired) and control voltage has to reach about 60V rms to fully saturate the reactor. (or more likely the pig) Is it possible that putting the reactor in series would require twice the voltage to saturate it? Or have i yet to configure it properly?

That's about all i got. later.

Steve Conner

Tue Oct 16 2007, 07:36AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yes, the two windings need to be wired out of phase. If you are getting high voltage induced in your control winding, you need to swap one of them over. The induced EMF in the control winding should cancel.

Steve, you are right that each core of the reactor will only saturate in one direction. That's why it's made with two cores wired back-to-back. Well, the textbook diagrams often show a fancy three or four limbed core, but the way Kolas's reactor is built with two separate cores makes it clearer. The two cores are separate magnetic circuits with their own high-current windings, and only the control winding is common between them.

Spedy

Tue Oct 16 2007, 08:51PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Err. What IS a reactor, exacltly? It looks to me like three coils wound like chain links. Would someone please explain? I'm clueless... Anyway, that's a pretty cool video. The arcs where awesome.

Dr. Dark Current

Wed Oct 17 2007, 01:02PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Spedy wrote ...

Err. What IS a reactor, exacltly? It looks to me like three coils wound like chain links. Would someone please explain? I'm clueless... Anyway, that's a pretty cool video. The arcs where awesome.

You put a small DC current on the control coil, this changes how much the core saturates, which in turn changes the amount of current that flows through the drive coils. It's like a magnetic amplifier.

Spedy

Wed Oct 17 2007, 05:16PM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

jmartis wrote ...

Ah. I'm guessing that the middle one is the control. That's pretty cool, I wonder who invented them...

J. Aaron Holmes

Fri Oct 19 2007, 06:18PM

Registered Member #477 Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546

Some years ago, I'd suggested to TCML the idea of using multiple seriesed MOTs to make saturable reactor ballasts for pigs and the like. Due to tolerances and differences in construction, I imagine you definitely *do* need to worry about induced voltages in the control windings, even when things are wired correctly. At the time, I created some neat-looking schematics showing how such things might be used to ballast pigs, including a double-hot configuration that would allow you to ground the neutral of your pole pig, which is something you aren't usually able to do with a single 240V reactor. I've never tried this myself, however a couple of folks did and reported ok results:

Cheers,
Aaron, N7OE

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