Path: utzoo!utgpu!cunews!bnrgate!bigsur!bnr-rsc!jvincent@bnr.ca
From: jvincent@bnr.ca (John Vincent)
Newsgroups: sci.electronics
Subject: Re: Electric motor "power factor controllers"
Message-ID: <3861@bnr-rsc.UUCP>
Date: 4 Jan 91 13:36:11 GMT
References: <10932@rama.UUCP>
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In article <10932@rama.UUCP> jdc@rama.UUCP (James D. Cronin) writes:
>Every now and then I see ads for electric motor "power factor
>controllers."  They claim to reduce the amount of power used
>by electric motors.  Are they for real?  How do they work?
>I'm sure this should be more interesting than the ongoing
>"solar cell" flame wars :-)

It's been a while since I last took a motors/power course but I believe
the device you are referring to regulates the reactance of the
load presented by the motor.  In a "perfect" scenario the motor would be
a purely resisitive load under all conditions. This is not usually the 
case.  The load will usually have a capacitive (rarely) or inductive (typical)
component as well.  This will increase the power drawn by the motor.  
The job of the controller is to maintain the load as near to resistive as 
possible, usually by switching in capacitors to reduce the inductance.  
Power utilities do this all the time by the way. It is also bad for the motor
to present a capactive load so the load will usually be kept slightly inductive.
Power factor, if I remember correctly,  refers to the percentage of applied 
power which goes into the resistive (ie useful) part of the load. 
Resitive load -> power factor = 1.00 
Inductive load -> power factor < 1.00 therefore power is "wasted".

Please, no flames unless I'm totally confused.


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