Re: Series vs. Parallel resistance

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 4/9/02 7:17:10 PM Pacific Daylight Time, tesla-at-pupman-dot-com
writes:


>
> Hi everyone,
>
> I'm starting work on a 20kva control cabinet for my distribution transformer,
> and I have a few questions about ballasting. I am planning on using two GE 30
> amp 580 volt cut-core variacs as inductors, but as I understand this can
> result
> in nasty 60hz resonance in the 240 volt circuit. I have access to a .25 ohm
> 160
> amp dynamic braking resistor that I am planning on putting in series with the
> variacs. Would this work ok? Would it be just as effective to put a few oven
> elements in parallel? Is this something that I just have to rig up and test
> to
> see what works best? 
>
> Also, Does anyone out there have any GE/Yokogawa switchboard volt meters for
> sale? 
>
>
> Thanks, 
> Jim




Jim,

I did encounter a 60 hz resonance problem when using a welder as ballast with
my 5 kva transformer.  I don't know how to tell in advance if a given set up
will cause this problem.  I do know that a safety gap placed across the rotary
gap will let you know if you have exceedingly high voltage in the primary.  I
originally used multiple oven elements in parallel as resistive ballast in
series with the welder.  The problem with them is the resistance is too high
(maybe 17 ohms each from memory) and it takes quite a stack of them to make a
one or two ohm resistor.  I ended up buying some large power resistors from a
surplus dealer, 1.5 ohms at 1,0000 watts.  My ballast set up now consists of a
5,000 watt luxtrol dimmer (variac) in series with a 1.5 ohm resistor.  The
resistors need a fan on them as they get very hot.

Ed Sonderman