From: John Woodgate
Subject: Re: welding a transformer core
Date: Sat, 21 Dec 2002 20:37:33 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sat, 21 Dec 2002 21:19:05 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Gibbo
wrote (in <firstname.lastname@example.org>) about 'welding
a transformer core', on Sat, 21 Dec 2002:
>You understand that increased secondary current means increased primary
>current. This primary current passes through the leakage inductance and the
>series resistance. These both rob the primary proper of volts, this, of course,
>reduces flux. Reduced flux = reduced core losses.
>This is *highly* simplified !
It's by no means TOO simplified, except that, in addition to the series
resistor representing primary winding resistance and the series inductor
representing primary leakage inductance, there should be a resistor in
parallel with the primary of the ideal transformer, representing the
iron loss (hysteresis loss). The value of this resistor is frequency-
dependent, but that usually doesn't matter for mains transformers.
There should also be a resistor in series with the secondary winding,
representing its resistance, or this can be transferred to the primary
by multiplying by the square of the turns ratio.
Then there is a capacitor from primary to core, one from secondary to
core and one from primary to secondary; these can often be neglected.
This model is a really good representation of a mains transformer, up to
1 kVA or even higher.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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