RE: On the Trail of a MegaVolt (fwd)

[<sroys@xxxxxxxxxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 11 Nov 2004 13:20:05 -0600
From: Carl Litton <Carl_Litton@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: RE: On the Trail of a MegaVolt (fwd)

Thanks, Jim.  Excellent information.  Agreed also that Ultra should
probably be Very.  Agreed also on the insulation issues.  

It will certainly be fun to try though!  

I've read your excellent article on the tertiary winding transformer
many times.

On what I am actually referencing, I put a temporary page up showing the
diagrams that came from the sites of others.  The first is the one I
described in detail:

http://www.dawntreader.net/hvgroup/motstacks.html


Thanks again, Jim.

Carl

-----Original Message-----
From: High Voltage list [mailto:hvlist@xxxxxxxxxx] 
Sent: Wednesday, November 10, 2004 8:14 PM
To: hvlist
Subject: Re: On the Trail of a MegaVolt (fwd)

Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 10 Nov 2004 16:01:51 -0800
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: hvlist <hvlist@xxxxxxxxxxxxxxxxx>
Subject: Re: On the Trail of a MegaVolt (fwd)

At 03:25 PM 11/10/2004 -0700, High Voltage list wrote:
>Date: Wed, 10 Nov 2004 09:58:44 -0600
>From: Carl Litton <Carl_Litton@xxxxxxxxxx>
>
>Subject: On the Trail of a MegaVolt
>Our local high voltage group is currently engaged in an ultra-high
>voltage project.  I believe that the controlled generation of a
Megavolt
>is possible at the amateur level - not streamers/sparks from a Tesla
>coil - but a real 1 million volts output from a specially constructed
>power supply that can be operated without overheating (or blacking out
>the neighborhood).

I don't know that 1 MV is really "ultra" high voltage.  It is, after
all, a 
voltage that is within the realm of standard power transmission lines 
(750kV is RMS voltage)

Voltage isn't really the issue, either.  It's fairly easy to get 1MV
from a 
Van deGraaff type machine, air insulated.  What you're really talking
about 
is serious power in an amateur system, with 1 MV output potential.  Say,

more than a few milliamps?  Implying tens of kW? (after all, X-ray power

supplies put out 100-150 kV at 100mA)


>To this end, we have acquired a large number of megavolt-rated
>transformers.  Rated output at the secondaries is between 0.1 and 0.15
>Megavolt.  We successfully created a control circuit allowing us to run
>a 0.15 Megavolt transformer to dead short or air gap without internal
>arcing or overheating in any part of the circuit for our 8' tall
Jacob's
>Ladder this Halloween.  In fact, we were finally able to power it
beyond
>its rated output without problems (~0.175 Megavolt):

So you were running many milliamps to run the ladder?


>Brief synopsis and pictures here:
>(http://www.dawntreader.net/hvgroup/megavolt.html)
>
>This preamble brings me to my question that I want to submit for review
>and comment by all the great science available on this list.  Has
anyone
>actually used any of the so-called 'stacking techniques' for MOT's that
>are all over the HiV pages on the net but without any real photos of
>such in actual operation?  These techniques purport to allow the
>'stacking' of notoriously friable MOT's such that 4 to 8 times their
>2100Volt rated output can be continuously produced without subjecting
>the windings to more than twice their rating.


This is mostly a matter of clever design.  First, you have a grounded 
centertap (like a Neon transformer), so the max voltage at any point, 
relative to ground, is 1/2 Vout.
Then, you just trust the insulation on the transformer to float the core
on 
the "outside" transformers.

You can also use isolation transformers. Some have proposed using a pair
of 
MOTs back to back for this. (I'd saw off the HV secondary, and just wind

your own coupling windings on the cores... who cares what voltage it's
at, 
as long as both transformers have the same number of turns).

What you refer to is the classic cascade technique?

There's the Greinacher cascade:
http://home.earthlink.net/~jimlux/hv/grein.htm
http://home.earthlink.net/~jimlux/hv/cascex.htm for a nice
implementation 
of this.

or, for an example using transformers with tertiary windings:
http://home.earthlink.net/~jimlux/hv/xfrmr1.htm



>One such advises the direct connection of the secondaries of 2 MOT's to
>produce "120 volts which 2100Volts above ground" at the primary of the
>second MOT???  I can't get my mind around this to believe it.  Then the
>technique advises that the primaries of 4 more MOT's may now be
>connected to this output in 'anti-parallel' manner.  What in the world
>is 'anti-parallel?'  Then the secondaries of the 4-pack may be series
>for a usable 8400 volts.  Further, it states a 'mirror image' stack can
>be built and added in series to give twice that voltage.


But, while a MOT can probably take 2kV from coil to core (since it
probably 
had to pass a 5kV HiPot test in mfr), it's not safe to say that a 100kV 
transformer can take 200 kV from winding to core.




>This would, of course, be wonderful if it were true.  Since most (~ 60%
>of them) of these megavolt transformers are not center tapped, an MVT
>stack is certainly conceivable following the same concept.


Your problems making 1MV AC will not be with transformers, per se, but
with 
other insulation and structural issues..