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Power Factor & kWH?
wrote:
chocolatemalt wrote:
... If the power company is feeding you 1000W on a straight V*A basis,
and your motor is seeing just 700W of useful work on a PF*V*A basis,
there are 300W of energy that have "disappeared". I guess the question
is so simple that the answer is obvious: The energy is consumed within
the motor as non-useful heat.
No. If your motor used 700 W with a power factor of 1, 700/120 = 5.83 amps
would flow in your wiring. If the wiring resistance were 0.1 ohms, it would
dissipate 5.83^2x0.1 = 3.4 watts of heat, and you would pay for 703.4 watts.
With a 0.7 PF, 5.83/0.7 = 8.33 amps flow, so the wiring would dissipate
8.33^2x0.1 = 6.9 watts, and you pay for 706.9 watts. Your only penalty
is the difference, 6.9-3.4 = 3.5 watts. The power company is less happy
because they lose more power in their wiring, but they usually don't
complain, in the case of houses.
Nick
For business customers, the disparity in amps is registered
by the "demand meter". And the utility company adds a
multiplier to your bill based on that number. It's to cover
the larger wire and transformers required to deliver you
8.33 amps instead of 5.83 amps.
In Dallas, half the business bill is the demand surcharge.
Which means we pay much more for that "phantom" power than
the "real" power. Copper and real estate is expensive,
especially when NIMBY is applied.
-larry / dallas
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