RE: [TCML] transformer theory questions

["Brian" <brianv@xxxxxxxx>]

Hi Guys,

If you decide to weld the core just make sure you do not over clamp or under
clamp the core, if you over clamp then you will get a bow shape to the core
and that will lead to gaps in the core laminations which will increase the
losses, if you under clamp then you may end up with laminations with gaps
between them and those will get welded in place and increase the losses,
just make sure you snug it up good weld near the top and bottom corners on
the outside of the core or top of the core it makes no difference, just keep
as close to the edge as you can same with the center leg you can weld either
side of it on the top and bottom if you want.

 Microwave transformers are really low end transformers where regulation is
not important that is why you may see them welded in just about any spot on
the core and also the lowest grade of magnet steel.  Core losses can
contribute to poor regulation and heat and higher excitation current, though
most of the heat generated by the core happens when the transformer is
unloaded that is when the core is fully excited, under a load the core is
not fully excited and the heat is a combination of several different things
happening between the core and the windings I^2R losses, small gaps(you can
never get rid of them entirely) However power transformers will be most
efficient when:
1. The primary winding copper loss equals the secondary copper loss
2. The iron loss is equal to the total copper losses

This is the target I shoot for when designing power transformers I have done
many of them from small control transformers to larger KVA units for
distribution substations. I do not know if any if this information is useful
to you but I thought I would put it out there just in case

--BrianV

-----Original Message-----
From: Lau, Gary [mailto:Gary.Lau@xxxxxx] 
Sent: Monday, September 21, 2009 10:48 AM
To: Tesla Coil Mailing List
Subject: RE: [TCML] transformer theory questions

Hi David,

I had thought about the possibility of eddy current losses, but I also
recall seeing some cores having a weld tying all of the laminations
together, clearly shorting the laminations.  It may be that to get eddy
currents, the laminations may need to be shorted in two different places?  I
don't recall if the welded cores I've seen had a single bead or not, and
it's unclear if a hack saw hack job would also short in multiple places.
But "don't do it" is surely the safest course of action!

Regards, Gary Lau
MA,  USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of David Rieben
> Sent: Monday, September 21, 2009 11:09 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] transformer theory questions
> 
> 
> Hi Thomas, Gary, all,
> 
> I would also suspect some unwanted eddy current losses/heating of the core
> to result from
> "cutting across the laminations", too, as this would almost certainly
short
> some of the
> laminations together, electrically.
> 
> 
> >> What happens if you cut into the frame of a transformer, cutting the
> >> across
> >> the iron lamination?
> 
>  > I wouldn't do that.  I expect that the consequences are largely
> mechanical - like you won't be able to get it back together again after
the
> laminations are mangled.
> 
> \
> > Many thanks
> >
> > Thomas
> 
> > Regards, Gary Lau
> > MA, USA
> 
> David Rieben
> 
> _______________________________________________
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