[time-nuts] Transformer inrush current and transformer simulation

Gerhard Hoffmann dk4xp at arcor.de
Wed Jun 8 03:54:23 EDT 2016

Am 08.06.2016 um 02:31 schrieb Mike Monett:
> I was not interested in examining the frequency response, saturation
> effect or core losses. These are only important after the  core goes
> into saturation.
> I was  only interested in the result of switching at the peak  or at
> the zero  crossing. This is clearly defined at the beginning  of the
> document.
> ...
> The saturation  and  core  losses   are  outside  the  scope  of the
> investigation. The  investigation was only to examine the  effect of
> switching at  the  peak or at the zero  crossing.  This  was clearly
> stated at the beginning of the paper.
> My analysis  correctly defined an unloaded transformer  as  the only
> case where  switching  at  the peak or the  zero  crossing  made any
> difference. This was the goal, and it was met.

Saturation is not outside the scope. It is the very heart of the problem.
You need to build up a voltage opposite to the grid voltage to keep the 
current small.
That requires an inductance and that requires a core that can be magnetized.
If the core is already magnetized to the limit from a previous session, 
it is as good
as simply not there at all. What remains is some meters of copper wire 
without an
appreciable L and that is not enough.

I'm haunted by that effect myself on a regular base in that I have a fat 
class A  Krell
audio amplifier and it pops the fuse of my living room once in about 5 
times of
switching it on.

> I also showed that very few solid state switches were available that
> switched at  the peak, that most vendors simply supply  devices that
> switch at  the  zero  crossing and state to get  a  model  that will
> accept the  surge currents, that switching at the  peak  could cause
> severe surge  currents with capacitive loads,
Nobody uses large transformers anymore, everybody has a diode bridge , 
and a DC/DC behind it. Then zero voltage switching makes sense.

>   and that  I  could not
> find any reference that stated switching at the peak would not cause
> core saturation.
I provided references that zero voltage switching leads to saturation, 
and so did others.
> Your comments   offer   no   additional   information  regarding the
> advisability of  switching  at the peak or  the  zero  crossing. The
> information you  do supply is irrelevant to the problem,  and mostly
> irrelevant to LTspice.
you are right. This is not a LTspice problem but your modelling problem.

 > Attila Kinali
>> It is upon moral qualities that a society is ultimately founded.
>> All the  prosperity and technological sophistication in  the world
>> is of no use without that foundation.
>> You need to consider getting new sigs. The two you post  have little
>> or nothing  to  do  with timenuts, and I'm  sure  everyone  has them
>> memorized by now.

OMG , I'm not Attila, but I may need a special time nuts .sig!

regards, Gerhard

Es ist schon alles gesagt worden, aber noch nicht von jedem. (Valentin)

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