TexasRF@aol.com wrote:
> Can someone explain what the shunts in these transformers are about? I can
> see what looks like a stack of four thin strips of metal placed below the
> secondary winding through the two core openings.
>
> I assume these make up two shunts. The purpose is not intuitive to me so
> hopefully there is a good explanation about how they work.
When current passes through the secondary, that produces a magnetic
field that bucks the field produced by the primary winding, causing
the primary current to rise in unison with the secondary current. But
if the secondary is overloaded, these shunts provide an alternate flux
path for the primary flux, to limit how much current the transformer
can draw from the line. They are equivalent to having an inductor in
series with the primary winding.
> I have removed the 2100vac secondary winding and replaced it with eight
> turns of thick insulation teflon covered wire to make up a 6.3vac filament
> winding. This winding needs to withstand about 10kv in the twt amplifier it
> will be
> used in. With no load connected to the winding it measures 6.84vac so a
> primary resistance will be added to trim the filament voltage.
>
> In checking the primary current, I see 4A flowing with no load. This was a
> surprise and I wonder if this is a result of the shunts?
No. The shunts slightly lower the primary current. This high
excitation current is a result of the transformer having so few turns
on the primary winding that the core begins to saturate near the end
of each half cycle. This is the way they push the power level up per
pound, to minimize the cost of the unit. If you can add some primary
turns, this current will drop, dramatically.
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