Hi everyone,

Russell McMahon wrote:

>  Power is product of voltage and current. If the current and voltage are >out
of phase (peak magnitudes do not occur at the same time) then the net >energy de
livered is less than maximum for the given voltage and current >peaks.
> Home installations are usually not power factor corrected and there >would be
minimal economic gain in doing so UNLESS you draw l;ess true >power in the proce
ss.
>

        In one of my readings, I came across an article about a circuit that
they claim was originally developed by NASA . In this article, they
stated that one way to keep power consumption down of electric motor
(induction type) driven equipments is to try to improve their
efficiency. Efficiency here means the ratio of the actual work performed
by the motor to the applied power in the form of electricity.

        The product of the voltage, current and the power factor represents the
true power actually consumed by the motor to do the work, while the
other power, i.e., the apparent power, is lost due to its conversion
into heat by the windings of the motor. The closer the power factor to
unity value, the more true power is delivered to the load and less is
lost.

        The mentioned circuit continuously monitors the power factor of the
motor and adjusts the voltage accordingly down to a level where the
power factor is nearly at unity level. This  is the highest power factor
yielding the best results. Note that the voltage is being decreased, it
is an accepted fact that when the voltage is decreased, the speed of the
motor will slow down. The change of the voltage is in a manner
proportional to the load, when the load is very light, the greatest
reduction in voltage can be expected and vice versa. Reducing the
voltage also reduces the speed  in a manner that the motor resembles
that of a full load (but not an overloaded one) motor thus achieving
higher power factor and lower power consumption.

Question, are the above explanation reasonable or the life of the motor
be shorten by using and trusting the device ? Also, am i really drawing
less power in the process ??

Regards,

        Alan



>       Russell McMahon
> _____________________________
>
> >From other worlds - www.easttimor.com
>                                 www.sudan.com
>
> What can one man* do?
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>
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>
> -----Original Message-----
> From: Morgan Olsson <morgans.rt@TELIA.COM>
> To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
> Date: Tuesday, 23 November 1999 06:06
> Subject: Re: [OT]Power Factor Correction
>
> >Terry A. Steen. Wrote:
> >
> >-snip-
> >
> >>The circuits are simple triac circuits that hold the device off for the
> >>first 0-45 degrees of current. Any power (the positive componant of V*I)
> >>that this current would have used is gone. MOST of the power used is taken
> >>from more than 25 degrees to 25 degrees after the crest. You ARE using
> less
> >>power.
> >
> >Just wondering...
> >Instead of softly pushig it, you kick it hard shorter time...  feels like
> the losses wuld increase as the I2R losses are much larger.
> >
> >I hav never seen any independant evalutaion of the idea neither in theory
> nor in practice.  Anybody?
> >
> >Instead, adding a transformer to lower the voltage suitable would be
> better... but also the transformer have losses... and adds more
> inductance...
> >
> >>BTW2: YES! Power companys like inductive loads and HATE capacative loads.
> >
> >NO!  I was once practising i a local power company.
> >There was an automatic central capacitor bank.
> >They have not installed any inductor banks simply because there is no risk
> at all that the total sumn of customer power would be capacitive.  Also, a
> large inductor battery would have more losses than a capacitor battery.
> >In elder days when capacitors this large was expensive to switch in/out,
> they used large synchronous AC motors, and by overfeeding the rotor
> magnetization they woud get a "negative" angle like a capacitor, variable by
> applied DC rotor current.
> >Also all those line voltage transformers are inductive enough...
> >The power company tries to get towards zero phase angle to get the lowest
> buy price for the electricity, as the losses in the lines from power plant
> then decreases.
> >Also of course they like us customers to have close to zero power to
> minimize I2R losses in thei distribution net and transformers, and also
> needing less big capacitor battery.  But they only measure and demand the
> angle from large customers.
> >
> >/Morgan
> >