Re: Pig current limiting

Tesla List wrote:
> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi>
> The tank supply I am designing uses a 3-phase pig transformer and a 6 diode
> bridge to charge a filter capacitor of 15 uF. After that there is a reactor
> that charges the primary capacitor usign resonant charging.
> Of course, every time the primary capacitor gets charged the filter (15 uF)
> capacitor voltage drops a little down: I need a device to limit the current
> used to re-charge the big capacitor.
> A suitable resistor will delay too much the recharge (and develop losses
> and heat!) and the capacitor will never reach full voltage.
> I was thinking to some limiting reactor on the 400VAC (primary) side.
> My questions:
> - if I use a simple autotransformer, it will limit the voltage but the
> current will be still orders of magnitude too high, right?
> - what about using a non-linear reactor, one that allows the current to
> rise until a value X and then will keep it about to that value. I mean like
> a MOT with secondary shorted? Who manufacture/sells these devices?


I would consider using what is called in power electronics a
"Notching Reactor".  It is basically a three phase wound inductor
on a common three phase core, used to attenuate "notching" effects
from SCR/Diode commutation in three phase bridges, power commutators.

These are used extensively on the line side of large Variable Speed
Drives (VSD) either variable frequency AC (inverters) or DC drives.
They can be made to very large sizes and can also include HF attenuation
filtering, which will be important on the large machine
you are building