[time-nuts] Maser 0.7 nsec jumps solved

Mike Monett timenuts at binsamp.e4ward.com
Wed May 25 12:59:20 EDT 2016


>Am 23.05.2016 um 05:15 schrieb Jim Palfreyman:
>> As far as a remedy goes we are going to try a solid state relay that only
>> switches on at 0V in the AC waveform. This should slow the inrush current,
>> and hopefully the magnetic impulse.
>
>In the context of transformers and motors, switching on at 0V is
>actually the worst point in time.
>
>< https://de.wikipedia.org/wiki/Einschalten_des_Transformators > (German)
>
><
>http://electrical-engineering-portal.com/practical-considerations-of-transformer-inrush-current
> >
>
>regards, Gerhard

LTspice shows  switching  at 0V is the best point in  time.  With no
flux in the magnetics, the inrush current is limited by  the circuit
resistance. The magnitude is given by Ohm's law: I = E / R.

Switching at 0V,

I = E / R
= 0 / R
= 0A

However, switching  at  the peak of the voltage can  give  very high
inrush currents. You can verify this with LTspice. The  schematic is
at

http://www.pst.netii.net/misc/48b961a6.gif

There are two circuits. They are identical except the second has the
applied voltage  shifted  by 90 degrees. The  inductors  have  1 Ohm
series resistance (not shown.)

The waveforms are at

http://www.pst.netii.net/misc/48b96217.gif

The currents are IL1 and IL2.

Switching at  0V, IL1 starts at zero. It rises to a  peak  of 900mA,
then falls  back  to  zero. The DC offset takes 3  or  4  seconds to
decay, then the current is stable at zero +/- 450mA.

Switching at the peak, IL2 is

I = E / R
= 169.7 / 1
= 169.7A

It takes over twice as long for the starting surge to decay. I could
still detect it past 8 seconds.

This analysis shows switching at 0V is the best option.

If you wish to do further analysis, the LTspice .ASC and  .PLT files
are at

http://www.pst.netii.net/misc/48b96262.zip

The wikipedia  article  states "To avoid magnetic  inrush,  only for
transformers with  an air gap in the core, the inductive  load needs
to be synchronously connected near a supply voltage peak."

https://en.wikipedia.org/wiki/Inrush_current

Clearly, from  the  above LTspice waveforms, switching  at  the peak
gives the  highest inrush surge that is possible to obtain.  It also
takes the longest time to decay.

MRM


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