Xfmers-110 to 220 (fwd)

To: "'Tesla List'" <tesla-at-pupman-dot-com>
Subject: Xfmers-110 to 220 (fwd)
From: Tesla List <tesla-at-stic-dot-net>
Date: Thu, 7 May 1998 23:45:35 -0500
Approved: tesla-at-stic-dot-net

----------
From:  Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent:  Thursday, May 07, 1998 12:48 PM
To:  Tesla List
Subject:  Re: Xfmers-110 to 220 (fwd)

> ---------- Forwarded message ----------
> Date: Wed, 6 May 1998 12:50:01 EDT
> From: Boombast99 <Boombast99-at-aol-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Xfmers-110 to 220
> 
> In a few weeks I'll be making a trip to a country that uses 220v as the
> standard line voltage.......I have a large supply of 15kv NST with the
> primaries rated at 110v.I plan on bringing some friends a medium size
> TC........would I be able to use 2 -15kv NST and run the primaries in
series
> using the 220v line voltage and of course hooking up the secondaries in
series
> to the tank circuit of the TC? Any problems here?.

It will work, I assume you will hook the secondaries in parallel, per the
usual configuration, otherwise you'll have the much discussed problems with
the centertap ground on th NST.  The NST's (and their loads) need to be
identical, or the line voltage won't evenly divide. Meter the actual
voltage across the primary to check it after you hook it up. 

Example of a situation where it won't work: Two 110V lightbulbs in series
across the 220 volt line. One is a 100 watt and the other is a 20 watt.
What happens? The voltage across the 100 watt bulb is about 30 volts, the
voltage across the 20 watter is 190 volts, leading to a very, very short
life for the 20 watt bulb.  The moral is, measure the primary voltages
after you have it hooked up.


........Also their A/C
> voltage is 50hz,but I don't think that will matter except a little
different
> tuning from 60hz?

At 50 Hz, the leakage reactance of the NST (which is what limits the output
current) will be 5/6 what it is at 60 Hz, so your NST will put out more 20%
more current. This will increase the resistive heating of the transformer
by 44% (which is pretty significant).

Also, the iron losses in the transformer will be increased by 20% (this is
why old aircraft stuff runs at 400 Hz, low losses with a small core). 
However, I would expect the iron losses in a NST to be around 10% of the
total load, so now they'll only be about 12%, an increase of 10 watts or
so, which shouldn't make much difference.

So, watch the temperature of your NST, or make sure the primary current
isn't appreciably higher than you run with on 60 Hz.  Also, if you are
running power factor correction caps on your NST's (or they are internally
corrected), your correction won't be "correct" any more. The caps would
need to be reduced by 5/6.


 I want to take every thing with me and won't have time to
> search for local 220v NST.
>  Thanks, Dan
>