Re: Saturation in transformers.


"Patrick Turner" <info@xxxxxxxxxxxxxxxxxx> wrote in message
news:437308A3.C34A2311@xxxxxxxxxxxxxxxxxxxxx
>
>
> Ian Iveson wrote:
>
>> Patrick Turner wrote
>>
>> >> > Your explanation wouldn't be easy for anyone without serious
>> >> > knowledge
>> >> > to follow.
>>
>> >> Why not? I followed it OK. I think.
>>
>> >> Generally there are as many ways of explaining as there are
>> >> variables.
>>
>> >> > Fs = 22.6 x V x 10,000
>> >> > ------------------
>> >> > B x Np x Afe
>> >> >
>> >> > Where
>> >> > Fs = frequency of saturation,
>> >> > 22.6 is a constant for all equations,
>> >> > V = voltage in rms across the primary,
>> >> > Np = primary turns,
>> >> > B = maximum allowable magnetic field strength in Tesla in
>> >> > the
>> >> > core,
>> >> > Afe = cross sectional area of the central core leg, in
>> >> > square
>> >> > mm.
>> >> >
>> >> > The saturation is a voltage caused phenomena.
>> >>
>> >> No.
>> >>
>> >> Fundamentally, magnetic field depends on current. A voltage
>> >> without
>> >> a current will not cause a magnetic field. Saturation arises
>> >> from
>> >> a
>> >> magnetic field, therefore it is directly related to current,
>> >> not
>> >> voltage.
>> >>
>> >> By your own formula, you should be able to see that saturation
>> >> depends not just on voltage, but also on frequency. For an
>> >> inductor,
>> >> the upshot of voltage and frequency is current.
>> >
>> > If you read RDH4, you'd see where they say saturation is a
>> > voltage
>> > related phenomena,
>>
>> The laws of physics won't change if I read RDH. Of course current
>> is
>> related to voltage...look up Ohm's Law.
>
> If you are not into reading RDH, then i suggest many other books
> may
> provide a
> better source of info than I have tendered to the group so far.

I dare say. Perhaps you could read one over the weekend.

> But we are dealing with the non linear behaviour of transformer
> iron....

No kidding?

>> > and sure there is a magnetizing current in a tranny, whether
>> > loaded or
>> > not,
>> > and that current is due to voltage applied across an
>> > inductance.
>> > but once that voltage exceeds a threshold the steel saturates,
>>
>> Rubbish. Only true at a particular frequency. You must know
>> better
>> than this, so I take it you are squirming, as usual.
>
> Well look at the formula I quoted above from my website.
> Its the well known *transfromer equation* that relates the
> applied voltage, frequency, Bmax, number of turns and the core
> section
> area.
>
> I am not squirming after having desinged and wound dozens of very
> fine
> power and output transformers.

So you say, incessantly. Not one of your claimed customers has ever
endorsed any one of your claimed products, and I am not surprised.
You spend a lot of fools' money pretending to do what many
manufacturers of excellent reputation do for a fraction of the
price.

>>
>> > and the coil becomes a short circuit when the steels field
>> > cannot
>> > continue to
>> > oppose the current flow of the current from the applied
>> > voltage.
>>
>> No. Some time ago I pointed out an error in RDH. Perhaps you
>> ignored
>> me and failed to amend the diagram? The inductance does not
>> plummet
>> as depicted, but actually trails off more gradually as current
>> increases.
>
> If you examined the current wave form as V across a winding is
> increased,

Blah de blah...obfuscation again. Wriggle, squirm.

> you will find there is a sudden increase in the 3H after what is
> called
> the saturation
> phenomena.

Wriggle, squirm. The singular of phenomena is phenomenon, but better
to avoid the wriggling, squirming obfuscation and just call it
saturation. Once you arrive back on earth you may realise that it is
necessary to define an arbitrary point in the process you describe
at which you say the iron is saturated. It is not sudden like a
switch. Look it up, but not in RDH because the diagram is wrong. Or
perhaps it would help to look at the RDH diagram and try and see
*why* it is in error. As I have said several times, the best
definition I have seen is the point at which the current spike is
double the magnitude of the underlying current waveform. A more
useful definition could be a particular proportion of distortion.

> The iron appears to have magnetic store of energy to oppose the AC
> flow
> for *parts* of the cycle, ie, the top and bottom part of the wave,
> so we
> see
> large current *spikes* where the coil acts as if it has become a
> short
> circuit
> for part of the cycle.

No. Once again, it is not a short circuit, ever. It is never a short
circuit. Since you are the one claiming to do loads of real
measurements, perhaps you could say when you measured this short
circuit?

> But for other parts of the cycle around the zero crossing region
> the
> iron energy is providing
> some oposition to the flow of current in the wire.
>
> If you looked, you would know.

Before I knew, I did look. But looking is not knowing, as you
clearly demonstrate.

>> The situation is exacerbated by what you, with your crazy notion
>> of
>> feedback, would call positive current feedback: as current
>> increases, reactance falls, so current increases further,
>> etcetera.
>
> There is no crazy notion of FB.

Give you half a chance and you will invent one. Don't you see the
parallel with your hopeless notion of triode "internal feedback"?

> Electro magnetics isn't easy to understand.

It would help if you found out about algebra.

> But why does not a large current flow when you apply
> a voltage across a coil?

Er, it might, or might not, depending on the time, the resistance
and the reactance.

> The magnetic field the applied voltage sets up opposes the flow.

No. The current sets up the magnetic field. Otherwise you wouldn't
get the phase difference, clot.

The changing magnetic field produces an opposing voltage, which
opposes the applied voltage (not the current, which I suppose you
mean by "flow"). The residual voltage drives the current through the
winding resistance.

In the case of a transformer, the current in the secondary produces
a field opposing that produced by the primary. The residual field
is, more or less, the same as that produced by the primary alone
when the secondary is open circuit. Hence the transformer can be
modelled by a resistance in parallel with an inductor made up of
just the primary and the core.

Such a model is generally accepted, and can be useful even up to the
frequencies used for SMPS, where matters become more complicated
because of core losses and skin effect. For the kind of frequencies
and waveforms we are talking about, it is hardly a black art

>> But, so considered, the feedback is less than unity so the result
>> is
>> finite...whereas with a short it would be infinite. In fact an
>> equilibrium is reached for any given current, and reactance does
>> not
>> disappear as quickly as you think, or as RDH shows.
>
> I didn't say the L dissapears once a threshold has been reached;
> but it
> is as if
> there is a sudden large reduction fall in inductance at
> saturation.

You said ***"short circuit"***. That is the point you are defending.
A sudden fall, a large fall...neither of these is a short circuit. A
short circuit is somewhere close to zero ohms. The effect you are
trying to describe is not a short. The impedance falls quite
quickly, the current rises quite rapidly, reaching by my adopted
definition twice the instantaneous value which would flow if the
iron remained magnetically linear.


>> Of course there is also primary resistance, which remains
>> unaffected, so that is two reasons why the coil does *not* become
>> a
>> short.
>
> Well when the inductance ceases to oppose the flow during the wave
> cycles due to
> saturation, the applied voltage to the primary tends to be a short
> circuit current, ie,
> the mains applied voltage sees only the DCR of the primary.
> This situation *is* regarded as a short circuit.

Squirm, wriggle, obfuscate. Let's just unpick it this time shall we?
What is this "DCR" you have thrown in...like the "saturation
phenomena (sic)" we saw before. It is a characteristic of your
squirming obfuscation that you try to blind people with pathetic
grandiose attempts at jargon.

You mean resistance, don't you? By "DCR" you just mean resistance,
yes? Resistance at DC? Have I worked it out correctly?

As opposed to ACR perhaps? Do you perceive a difference between ACR
and DCR? Perhaps it would help if you were to realise that it is a
defining characteristic of resistance that it is the same for AC and
DC? Surely if you pretend to make good transformers, you must also
pretend to know the difference between resistance and reactance?

So really you just mean resistance. Why then did you call it DCR?
What is the purpose of this wriggling, squirming obfuscation?

Because you just said that a resistance is regarded as a short
circuit. By who, I wonder. You alone, in all the world, sadly.

Let's look at that again...

> the mains applied voltage sees only the DCR of the primary.
> This situation *is* regarded as a short circuit.

Did you really say that? Look, you even underscored the "is".
Crikey. Worth another look...

> the mains applied voltage sees only the DCR of the primary.
> This situation *is* regarded as a short circuit.

Should I bother any further with a conman who thinks that a
resistance is a short circuit?

And, what is more, it doesn't only see the resistance. It also sees,
for much of the time, the full inductance of the transformer and,
for that portion of the time when saturation occurs, it also sees a
considerable remaining contribution to the inductance by the core,
plus it sees the inductance of the windings as if there were no iron
there at all. In addition, the apparent resistance it sees in the
winding is modified by the core losses.

Not a short then, is it?

>> Further, you may notice that a saturated transformer gets hot. A
>> short dissipates no power (only current, no voltage drop), so
>> where
>> do you think the heat is coming from?
>
> Two things, core losses, and copper losses.

And how would they happen if the primary appears as a short? You
haven't seen my point at all as usual. Can't have losses without
power, can't have power without voltage, can't have voltage if it's
a short. No matter how much I suggest it, you still haven't looked
up Ohm's law.

>> > The very field in an inductor opposes the current flow...
>> >>
>> >> If you think of it as a load resistance in parallel with an
>> >> iron-cored inductor with a given core and number of windings,
>> >> it
>> >> is
>> >> the current through the inductor that produces the magnetic
>> >> field,
>> >> hence too much current leads to saturation.
>> >
>> > The too-much-current occurs after a voltage threshold hold has
>> > been
>> > reached.
>>
>> Only at a particular frequency (sigh...). Do you remember any
>> school
>> maths?
>
> See my formula.

The one you got from RDH? Don't need to, it was burned into my brain
aged about 13.

> Seems to me my maths are better than yours.

I can see how it seems like that to you.

>> Remember the common questions that ask you to reduce an
>> equation to its simplest form? Why was that an important skill to
>> learn? Because it allows you to see the essential relationship
>> without the complications of mathematical clutter and particular
>> circumstance.
>
> The transformer equation is the simplest way to relate the design
> parameters of a transformer.

Maybe so, depending on what you are designing for. But the thread is
not about how to design a transformer, but rather how to understand
how transformers saturate. But you won't have noticed that in your
rush to con another fool out of his money.

>> In this case you would substitute voltage and frequency for
>> current,
>> and end up with a very simple formula. That would improve your
>> basic
>> grasp of the relationship, which would be true for *all cases*.
>>
>> Armed with this fundamental understanding, you can quite easily
>> derive whatever practical formula you wish, depending on the
>> particular problem you are addressing. If you are interested in
>> frequency and voltage, then you can derive the formula you gave
>> from
>> RDH.
>
> I did derive my formula from what is in RDH4 and a few other old
> books
> that explain everything.

You derived your formula? You mean you copied it from one of the
zillion places it appears.

> Often their explanations are totally incomprehensible.
> Electro Magnetics was designed by the schitzoprenic brother of the
> God Of Triodes, and this dude made the use of iron, wire, and
> volts
> to be as confusing as possible.

I can see your problem...

>>
>> Fundamental understanding is, in other words, transferable.
>> Without
>> it, particular knowledge is just empty fact. That's why you have
>> to
>> keep reading the book...you lack the conceptual framework to
>> construct your own thoughts.
>>
>> If you know the core, and how many turns on the windings, and how
>> much current through each, you are home and dry. The only reason
>> you
>> need to drag voltage and frequency in is in order to calculate
>> the
>> current.
>>
>> You won't see what I mean, and neither will Phil. Oh well.
>
> I do wind much better transformers than I can buy from anyone.

So you keep saying, but no-one who has bought one agrees. How would
you know anyway? You don't test them properly. You don't even know
Ohm's law.

> My conceptual understanding levels are good enough.

For conning fools out of their money, perhaps.

>
> Phil knows more about it than you do, and he can explain it when
> he
> isn't
> acting like a complete fukken idiot.

Then check the last statement of his last post to me, where he
finally admits to some approximation to the truth about current.

My estimation is that he actually knows less than you, if that is
any comfort. But he has had enough failed education to fake a
different level of smartness.

cheers, Ian


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