daw1@rduxb.UUCP (WILLIAMS) (03/27/85)
POWER FACTOR CORRECTION 101
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power
....................
. A .
. .
. . reactive power
. .
apparent power . .
. .
. .
. .
.
Since a lot of industrial loads (and a lot of residential
loads, too) are inductive (i.e., motors), they have a lagging power
factor. That is, current lags voltage. So the power supplied is not simply
equal to the voltage times the current, but really equal to the voltage
times the current times the cosine of angle A shown in the
"power triangle" above.
What this means is that a larger apparent power is needed as
the load becomes more inductive (angle A increases). In order to cancel
some (or all) of the reactive power, capacitance is placed in parallel
with the inductive load. In practice, the capacitance is provided by a
bank of capacitors the utility places on a pole outside the factory.
Why would a utility spend their money on capacitors? Because
it benefits them! (For a given line voltage, a lower power factor means
a lower apparent power; this in turn means less current must be supplied
by them to run your motors.)
I think the residential meters just measure power; utility
companies probably have a way to handle power measurement at large
factories to take into account the power factor. Thus at home a bank of
capacitors will only help the utility!
Let me say in closing that I may be wrong. After a couple
of years working in semiconductors where 100 milliwatts is high-
power, my recall of power factor theory may be lagging too :-)
Doug Williams
AT&T Bell Labs
Reading, PA
rduxb!daw1 or rduxb!williams
PS: To drastically lower your electric bill, first remove the glass
cover on the gizmo on the side of your house. Then connect
jumper wire 1 from black wire X in the upper right corner.....
Just kidding!
rjk@mgweed.UUCP (Randy King) (04/07/85)
<><><> Actually, companies pay a penalty for a bad power factor. Reddy Kilowatt monitors it (through company meters). In addition to banks of capacitors, AC syncronous motors can be used to correct power factor. When used as blower motors or elevator motors, they can be strategically planned to compensate for the lagging PF. Randy King AT&T-CP@MG ihnp4!mgweed!rjk