Re: Rebuilding an OBIT (transformer efficiencies)

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

Original poster: "Kevin Ottalini by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ottalini-at-mindspring-dot-com>

Hi Jochen, Richie, Finn and All:
	I just wanted to remind everyone that the core size and
power carrying capability is severely related to the frequency
of operation ... 60Hz is grossly inefficient.

I have a 20kv 8KW transformer that I am bringing up that only
weighs 11lbs.  The core itself is only 4.5 lbs. The critical
factor:  it runs at 20KHz.

See three pics of the assembled and disassembled unit here:

  ftp://ftp.mindspring-dot-com/users/ottalini/highvoltage/XFMR

This transformer is air-cooled only (muffin fan), no oil
and runs continuous duty.  The input is 220v at 20KHz from
a solid-state converter box (220V, 60Hz to 220V, 20KHz).

Relative to 20KHz, 60Hz practically looks like a DC source
to a transformer ... lots of time with current flowing in only
one direction.  On the average, (assuming 50% duty cycle)
the flows are all balanced regardless of the frequency, but
transformer cores love change and hate DC (unless you're
using them as chokes!).

(In a way, this is sort of like a small inductive TC
secondary).

Kevin

----------
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Rebuilding an OBIT
> Date: Thursday, December 14, 2000 6:09 AM
> 
> Original poster: "Finn Hammer" <f-hammer-at-post5.tele.dk>
> > Original poster: "Jochen Kronjaeger"
<Kronjaeg-at-Stud-Mailer.Uni-Marburg.DE>
> > >
> > > TRANSFORMERS DO NOT SATURATE DUE TO TOO MUCH CURRENT BEING DRAWN !
> > Then how come that you need bigger cores for higer power?
> 
> Jochen, Richie, all!
> Interesting question, which has kept me pondering for years.
> 
> I think the answer is this: you don`t _need_ a bigger core for higher
> power, but ultimately it helps.
<snip>
> So the recommended power troughput of a given core size is a compromize
> btwn. copper losses and iron losses.
> 
> Somehow it is my feeling that the core is only needed to make the
> transformer able to stand idle, open circuit secondary, without drawing
> excessive current. If the windings were properly interleaved, and the
> leakage inductance was extremely low, it would possibly be able to run
> at full load without the core.
>