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From: alab@ur-tut.UUCP (Daniel F. Luna)
Newsgroups: sci.electronics
Subject: Re: Power Factor Controller
Message-ID: <1287@ur-tut.UUCP>
Date: Fri, 8-May-87 05:30:11 EDT
Article-I.D.: ur-tut.1287
Posted: Fri May  8 05:30:11 1987
Date-Received: Sat, 9-May-87 18:47:17 EDT
References: <278@lpi.UUCP> <7988@utzoo.UUCP>
Reply-To: alab@tut.cc.rochester.edu.UUCP (Daniel F. Luna)
Organization: Univ. of Rochester Computing Center
Lines: 61

In article <7988@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>
>I'm not up on motors very much, but here goes...  As I understand it, the
>only situation power-factor controllers help with is motors that run for
>substantial periods at less than full power.  Things like refrigerators,
>which vary their output by cycling on and off rather than by running at
>lower output continuously, don't benefit at all.  My impression is that
>power-factor controllers are really of very limited use to consumers,
>since few motorized consumer products run at partial power for long.
  Power factor actually refers to "reactive power" on systems.  
Power factor is related to the phase difference between voltage and current
through (usually) inductive devices, like motors.  A capacitor will, if sized
and placed correctly, correct the power factor.  Power companies are unhappy
when the power factor falls below 1.  This leads to loss in transmission 
ability.  
   Power factor is usually not a problem for small users, like residences.
It is more a problem with industrial locations, where most of the power is
operating "reactive" loads, like motors and transformers.  (Transformers are
in florescent lights, too.)  Traditionally, power companies have capacitor
banks on poles along the distribution path to offset the power factors of
the reactive loads.  Many power utilities require that the customer fix his
power factor if it falls below a certain point, and I think that here it is
0.8 .  
   Things like incandescant lamps have power factor of 1.  Also toasters, 
electric stoves, etc.

   Your question brings to mind another device which was put on the market
a while back.  It does not control power factor, but "duty cycle".  It's
purpose was to cut "demand" costs in places by having air-conditioners, etc.
run only part of the time.  The problem I have with this is that it    
DRASTICALLY shortens the life of the compressor, because it does not let it
warm up correctly, keep its fluids separate, etc., and also because the starting
torque on the motor shortens the life of the motor each time it starts.  
Compressors like to "wind down"  before restarting, typically a lot longer than
these machines would allow.
   Demand is how the power company recovers costs for having all that equipment
running at once (and built, for that matter).  It again usually applies to only
industrial customers, but doesn't have to.  The idea is that they measure how
much power used for a 15 minute period.  The highest measurement for the month
is called the demand power. Rates of 6 DOLLARS per kwh are common for the 
demand power.  
   The power companies could provide all the power you needed from fewer 
generators if you didn't want it all at once (along with the rest of the 
world).  So, since they have to build, man, operate, maintain, etc. these
extra generators, they are compelled to recoup these costs.  It also serves
as a deterrent to wanton power consumption. -Hence the device above.

  (but i digress...)


   The idea of keeping the demand level down is OK, but using this brute-
force method simply shifts costs from the energy column to the repair column, and
multiplies it in the process.
'nuff said.

-- 
Daniel F. Luna 
PC-Person.
uucp: ...rochester!ur-tut!alab
arpa: ur-tut!alab@rochester
Standard Disclaimer here.   If it don't work, it ain't my fault.