My new PT: 14.4kV Westinghouse / High Voltage / Forums

Forums

4hv.org :: Forums :: High Voltage

« Previous topic | Next topic »

My new PT: 14.4kV Westinghouse

previous 1 2 3 next

Move Thread

LAN_403

sparky

Thu Jul 26 2007, 07:46AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

Well, I got the 120V rated transformer interfacing a 240V 30A dryer outlet for the time being. i'm using another lower voltage PT in series on the primary side for extra windings so I can pass 240V without saturation. I'm using 200 ft worth of stranded 10AWG on a mid sized transformer core for inductive load ballsting. This provides some ballasting - seems to allow up to 36A average and the wire gets slightly warm... I might upgrade to a 40A range outlet...

Thu Jul 26 2007, 09:48AM

Registered Member #809 Joined: Wed May 30 2007, 08:59AM
Location: Melbourne, victoria
Posts: 114

cool!!! they are big arcs!!so your using your dryer outlet

i want one!! any more pics, vids?

J. Aaron Holmes

Thu Jul 26 2007, 03:58PM

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

sparky wrote ...

Well, I got the 120V rated transformer interfacing a 240V 30A dryer outlet for the time being. i'm using another lower voltage PT in series on the primary side for extra windings so I can pass 240V without saturation.

Nice arc! 8.5+kVA from a 1.75kVA tranny is definitely pushing things!

Putting transformer primaries in series to avoid overvoltage is fraught with peril. Your little PT probably won't pass more than 1A without the secondary shorted, so I assume that's what you've done. Realize then that the inductance of the primary becomes minescule. When you're not drawing an arc from the big PT, the total impedance of the ballast + little PT + big PT arrangement is then hugely dominated by the inductance of the big PT's primary, causing it to see ~240V. Have you measured it? Really, I expect the smaller PT is doing almost nothing to limit the voltage to the big PT, but rather is acting simply as part of the ballast, and that you'd accomplish the same thing by adding more turns to your ballast and getting rid of the smaller PT.

EDIT: And BTW, though I don't doubt a PT or pig can run at 2x rated voltage for some time (I have tried it), you may be seriously challenging your transformer's insulation, especially if you run a TC and subject it to 2x voltage plus the resonant rise, spikes, etc. that come out of a TC primary circuit. My friend destroyed a very large pole pig that way! Many people who have experience only with smaller transformers like to say that putting 240V into the 120V windings of a pig will lead to saturation, and that you won't get 2x the HV out. Which, as far as I can tell, is baloney with these big units.

Cheers,
Aaron, N7OE

sparky

Fri Jul 27 2007, 12:48AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

Actually yeah, I did do some measurements on the primary of my large PT. It reads 118.5 V --- voltage can be 121.2 V but well within standard operating range. I've never had more than this on the primary.

The smaller PT isn't shorted and is left without a load.
All the ballasting is coming from the green wire wrapped transformer core.... I think I might need more wire -- only 200ft worth so far... I'm averaging 35A load.

Here is a video clip... enjoy.
]1185497326_530_FT27570_dscn0834.avi[/file]

J. Aaron Holmes

Fri Jul 27 2007, 02:16AM

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

sparky wrote ...

Actually yeah, I did do some measurements on the primary of my large PT. It reads 118.5 V. The smaller PT isn't shorted and is left without load. All the ballasting is coming from the green wire wrapped transformer core.... I think I might need more wire -- only 200ft worth so far... I'm averaging 35A load.

Here is a video clip... enjoy.

Your small PT *isn't* shorted, and is passing 30+A!?!?!?!

Believe me; that ain't good! So your small PT must be seriously saturated or arcing internally. That is the only explanation. If neither of these conditions exist, then your PT would pass < 1A. I'm assuming, then, that you measured the 118.5V when you were *not* drawing an arc. If you drew an arc, the voltage across the big PT would plummet and the voltage across the small PT would soar to ~240V. This is probably causing your small PT to saturate, under which condition it might easily pass 30+A. Don't fry your new toys!

Even under no load, you are very fortunate if the voltage on your big PT is such a nice 1/2 of the 240V supplied.

Cheers,
Aaron, N7OE

sparky

Fri Jul 27 2007, 03:15AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

The voltage drops down to 90 V when arced - then again so do my neons too...

What do you suggest I do Aaron? What the best way to run this set up using a balanced system without investing in another PT?

J. Aaron Holmes

Fri Jul 27 2007, 04:02AM

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

sparky wrote ...

The voltage drops down to 90 V when arced - then again so do my neons too...

What do you suggest I do Aaron? What the best way to run this set up using a balanced system without investing in another PT?

It would be interesting to scope it. There is probably some serious non-sinusoidal action going on.

Well, as far as not investing in another PT, how about in a 30+A 120V socket? Might only cost you $20-30 in parts/wire. Do you have access to the breaker box? A dedicated "geek socket" like this is always best, IMO. This also helps a bit with RF polution in the rest of your house wiring (if you're building a TC), since otherwise any RF getting into the mains ground gets to take the "long way", which may send it past some high-$$ computer and stereo gear

.

Another possibility is that your dryer socket has a neutral lead. Does it? Some do, some don't.

Getting more PTs is certainly good!!

But I'm always a bit shy of anything that involves putting primaries in series where that connection is left to float. You're just asking for trouble, because who knows where that connection will float off to when the loads on the transformers are not balanced? If the outputs are placed in series or parallel, you're definitely better off, but... Instead of getting another PT, you might just look out for a 120/240V transformer. It doesn't have to be a transformer made for turning 240V into 120V. It could be a 480V transformer with 120/240V secondary, for example. In this latter case, you can just leave the e.g., 480V winding disconnected, and use the 120/240V secondary as an autotransformer. Or get a variac; same idea. But high-current 240V variacs can command a hefty price tag!

For my own HV geekery, I installed a four-prong 50A electric range socket next to my breaker box in the garage. That lets me have 50A 240V or 120V. The heads are a little expensive when new from the store, but that's what junky surplus stores are for; I got 5 used ones for $5 from Pacific Industrial in Seattle last year. That was before they moved, though, and now I'm told they're way less junky

Cheers,
Aaron, N7OE

Steve Conner

Fri Jul 27 2007, 08:56AM

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

The smaller PT will be acting like a saturable reactor. I expect it has much the same effect on the waveform as a triac lamp dimmer turned to about halfway. If I were you I'd ditch it and just put more turns on your ballast choke.

sparky

Fri Jul 27 2007, 01:43PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

UPDATE:

I do have a double pole single throw breaker and wire job - 4 wire to be exact. The demonstration area I have lined up for October only have a single 240V 60A 3 wire connection.... so I'm going to be investing in something in another transformer anyways...and run both in sets of primaries in series and secondaries in parallel. Maybe - just maybe I can put a breaker box in for 120V 60A and run it close to the transformer with RF protection gear and an on -off switch. That would be good.

My target is power is 5500 watts...

J. Aaron Holmes

Fri Jul 27 2007, 04:25PM

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

Steve Conner wrote ...

The smaller PT will be acting like a saturable reactor. I expect it has much the same effect on the waveform as a triac lamp dimmer turned to about halfway. If I were you I'd ditch it and just put more turns on your ballast choke.

But regardless of keeping the small PT or putting more turns on the ballast, a PT somewhere is going to be seeing 240V at various points, right? That doesn't seem especially nice. At least not if you're *also* going to be "mean" to the PT(s) by using it/them for a TC.

sparky wrote ...

I do have a double pole single throw breaker and wire job - 4 wire to be exact. The demonstration area I have lined up for October only have a single 240V 60A 3 wire connection.... so I'm going to be investing in something in another transformer anyways...and run both in sets of primaries in series and secondaries in parallel. Maybe - just maybe I can put a breaker box in for 120V 60A and run it close to the transformer with RF protection gear and an on -off switch. That would be good.

I see. The series/parallel thing should work ok. Also, you might just check with a local tool rental place and see if they rent out tool transformers. Or you could rent a generator.

Cheers,
Aaron, N7OE

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob