Re: power factor correction?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds by way of Terry Fritz <teslalist-at-qwest-dot-net>" <gerryreynolds-at-earthlink-dot-net>

Excellent question.  I hope I can answer it in a way most can understand.
Most people can relate to resistive loads where the current is simply V/R
and current is in phase with the voltage.  With a transformer (especially
with high leakage flux as with NSTs), the transformer presents an inductive
load to the mains (I will neglect the resistive component here).  Since the
voltage - current relationship is:

      V = L di/dt

(di, dt are calculus terms that you can think of as small changes of current
in small amounts of time - ie, the rate of current change)

The current is out of phase from the voltage (current lags voltage).  The
degree it lags is effectively represented by the POWER FACTOR (PF).  With
the inductive load on the mains, more volt-amps's are required to deliver a
certain power to the transformer's output than what could be needed with
POWER FACTOR CORRECTION (PFC).  Normally, Power in WATTS is expressed as:

     POWER (watts) = PF * Volts *Amps            (PF is between 0.0 and 1.0)

If the PF is .5 and you need 1KWatt off the mains, you will need to draw
2KVA's.  Now, with a Capacitive Load on the mains, the following is the
current - voltage relationship:

     I = C dv/dt

For this case the current leads the voltage.  By putting a Capacitor across
the transformer's input, one can correct for the lagging current (with
leading current) and make the load look more resistive (closer to a PF of
1.0).  This is a way of reducing the required AMPs from your line (and
hopefully not blow the breaker)


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, July 05, 2003 5:48 PM
Subject: power factor correction?


 > Original poster: "Adam Britt by way of Terry Fritz <teslalist-at-qwest-dot-net>"
<beans45601-at-sbcglobal-dot-net>
 >
 > What is Power factor correction and what do power factor correction caps
do?
 > thanks
 > Adam
 >
 >