Re: Freau's efficiency theory=Success!

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Original poster: "R.E.Burnett by way of Terry Fritz <twftesla-at-qwest-dot-net>" <R.E.Burnett-at-newcastle.ac.uk>


Hi John, all,

> I thought that adding PFC would stop the NST's (over-current) suffering.  

I believe this is not the case.

A PFC capacitor connected across the primary of an NST draws a reactive
current from the supply which is 180 degrees out of phase with the
reactive part of the NST current.  The supply current is the sum of these
two currents.  So the inductive part of the NST current is cancelled by
the capacitive current drawn by the PFC.

This reduces the overall current drawn from the supply line,  but the 
windings of the NST still see the same total current with or without
PFC.  It is only the line current which is reduced by cancelling the
reactive contribution.  However, PFC is still worthwhile as reduced line
current makes life easier for the Variac, circuit breakers and wiring.

This is one of the reasons why I believe that larger systems should be
designed with high PF in mind from the outset.  A poor power factor in 
a large system burdens the transformer and ballast,  and requires a lot of
PFC capacitance to make a significant improvement in the power factor.

							Cheers,

							-Richie,