Re: Why people don't use MOTs in a TC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, July 17, 2002 7:19 PM
Subject: Re: Why people don't use MOTs in a TC


> Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<evp-at-pacbell-dot-net>
>
> Tesla list wrote:
>
> > >         Every time I read about MOT's in series I keep wondering about
> > primary
> > > to secondary breakdown.  Don't see how this can be avoided,
considering
> > > the construction.  Any other thoughts?
> >
> > Several techniques are of use:
> > 1) Sink it in oil... Assuming the sucker was good for 2.5 kV before,
it's
> > now good for 7.5 kV, or so.  What sort of hipot testing do they do from
> > primary to core?
> > 2) Various back to back cascades, using the MOT as an isolation
transformer
> > (heavy, but it will work...)
> > 3) A healthy dose of hoping..
> > >
> > > Ed
>
>
> [1.] This won't help the internal breakdown, as all the ones I've seen
> have encapsulated windings.  Hipot testing doesn't tell you much about
> long term breakdown, particularly if the potting has any voids in it
> where corona can form.  One way of checking that is to look for RF noise
> due to corona at the same time as the hi pot test is run.  When I worked
> at Hughes we had a group which built high-voltage capacitors for radar
> pulse-forming network.  If they saw (or heard) any evidence of corona
> they'd pitch the part.

The 2 MOTs I have are conventional looking unencapsulated ones.. HV winding
is wire and kraft paper.
The breakdown of concern is coil to core, rather than within the winding,
so, unless the whole thing is potted oil immersion would work.

>
> [2.] I've wondered about that, but it would take a lot of transformers
> in cascade if you're going to series vary many, and the ones at the
> input side have to carry all of the current for all subsequent ones.
> Has anyone really tried it?

I've done a couple cascades, subsequently dismantled, and as you point out,
it takes (literally) a ton of transformers.  This is definitely an approach
for someone who a) has no money and b)doesn't ever need to move the unit.
>
>