Re: (ET) <no subject>

["Steven Naugler" <snaugler earthlink net>]

-----Original Message-----
From: David Howard <howie sssnet com>
To: elec-trak cosmos5 phy tufts edu <elec-trak cosmos5 phy tufts edu>
Date: Wednesday, January 13, 1999 8:38 PM
Subject: (ET) <no subject>


>
>>    In an AC circuit, having a low power factor does not theoretically
>>increase power wasted, it only increases the current needed to deliver
that
>>power.  Where you waste power when power factor is low is due to your I
>>squared R (resistive) losses.  If your current is needlessly higher, all
of
>>your voltage drops are higher and you have greater unwanted electric
>>resistance heating.
>
>
>Steve,
>
>not really true.  you forgot power also equals current x voltage,  and in
>the AC circuit the power that is lost during  the magnetic field creation
>and collapse 60 times a second.  this is real power loss not just heating
>losses. the energy that is takes though important to the motor operation
>does not activly turn the motor and therefore does no real work.
>
>I would love to see your power factor talk.
>
>Dave howard
>
  Dave

    Actually, yes really true.  An inductor, like a capacitor, is really an
energy storage device.  They are different in that an inductor stores 
energy
in the form of current, and a capacitor in the form of an electric charge.
A perfect capacitor can sit forever holding that charge without loss.  What
we forget is that a perfect inductor could hold a current indefinitely
without loss.  Real world inductors cannot do that because they are a wire
wrapped around a core, but a wire is just a form of resistor, and the 
energy
is shortly lost as an I squared R loss.  The DOE as part of its
superconducting researches is investigating superconducting coils that can
hold current indefinitely.  They hope to use them as off peak energy 
storage
devices.
    But I digress.  Let's say our example perfect inductor has an AC 
source.
When the current is positive, we build up the magntic field and store
energy.  When the current drops, the stored energy leaves until current is
zero and there is no longer any energy stored in the inductor.  The energy
has gone back to the original source.  As current reverses energy again
flows out and the inductor has a negative energy value.  This energy value
will fluctuate positively and negatively in a sinusoidal fashion.
    If you do the math and multiply current and voltage several thousand
time a second you would find that sometimes the product of voltage and
current is negative  (+I  times -V    and    -I  times +V) although most of
the time with a motor the product of voltage and current is positive.  With
a high power factor, the amount of time with a negative product of I times 
V
is very small.  My word processor cannot do or show integrals, but power is
actually the instantaneous product of (voltage times current times your
sample time) all integrated, then the product of that integration then
divided by the entire period of time you sampled over.  When your AC motor
is unloaded power factor drops.  You can still have very high currents, but
actual power delivery can approach zero.  If that superconducting inductor
that the DOE was developing had an AC power source hooked to it, you'd have
extremely huge currents but your power factor would be zero.
    I really need visual aids to describe the effects of inductance on 
power
and power factor.  The fact remains, however, that on an inductive circuit
not delivering work, the only losses are resistive losses.

Hope to argue again soon,

Steve Naugler