Xfrmr theory, was Re: I could cry......

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Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>

Guys,
     neither your's nor John Freau's reply seem to make any sense to me.
>From a physisist's conservation of energy point of view (perhaps incorrect,
but I'ld like to understand why) I see energy comming in as electricity,
being transformed into magnetic field energy, being transformed back into
electric energy in the output winding. The maximum magnetic field that can
be generated in the core (the saturation limit?) represents a limit on how
much energy can be transfered through this mechanism.

The statement below that "[core area] in principle has nothing to do with
the power handling capability of the transformer" flys in the face of
common sense (which is not always correct, so explain if not so) and it
flys in the face of the engineering data that says to select a core
cross section based on Volt*Amps of the coil.

-Peter Lawrence.



>Resent-Date: Tue, 17 Apr 2001 18:49:04 -0600
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>Subject: Re: I could cry......
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>Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" 
<evp-at-pacbell-dot-net>
>
>Tesla list wrote:
>> 
>> Original poster: "Peter Lawrence by way of Terry Fritz
><twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>
>> 
>> I am very puzzled by this claim. A 12-120 NST actually puts out about
>> 6-kv at 60-ma when in service in a neon sign, and I've disected some NSTs
>> and measured their iron core cross section area and that always seems to
>> agree with 6 x 60 => 360 watts for this example, not 1440 or 2880 watts.
>> 
>> I've never seen an NST whose core cross section would support its face-plate
>> rating kV x mA (as opposed to other kinds of power transformers).
>> 
>> It was my understanding (possibly incorrect...) that core cross section
>> determines maximum power transfer because the cross section limits the
>> magnetic field energy and therefore the secondary power output.
>> 
>> Can anyone clarify this issue?
>> 
>> -Peter Lawrence.
>
>	The 12 kV is the open-circuit voltage, and the 60 ma is the
>short-circuit current.  The cross-sectional area of the core sets the
>number of turns/volt required for a given flux density in the core; the
>bigger the cross section the fewer volts/turn.  In principle has nothing
>to do with the power handling capability of the transformer.  In
>practice, because of winding resistance, more wire is required to handle
>higher powers, requiring a bigger core on which to fit the windings,
>etc.
>
>	Note that the voltage of the transformer under load depends on the
>nature of the load.  With a resistive load your transformer should put
>out 6 kV at a load current of about 42 ma.  With a capacitive load the
>current can vary over wide limits; for the "matched value" recommended
>by some people the no-load voltage would rise until the insulation broke
>down or the core saturated.  A transformer with a capacitive load such
>as encountered in TC service can and probably will put out much more
>power than the product of the nameplate voltage and current.
>
>Ed
>
>
>