Confusion with P.F and K.W?
But the thing is when p.f increases, K.W reading also increases as by the formula Power = 3 x V x I x P.F.
For Example: Suppose we have a 3ph, 100hp induction motor .
Case i )
At V= 245 Volts
I = 70 Amps
p.f =0.62
Case ii )
At V = 245 Volts
I = 70 Amps
p.f = 0.75
Question : When will the motor consumes less power.
If you calculate it by formula in Case2, the power consumption will be high.
Please Clarify my doubt.
Eventhough its a basic thing, leads to lot of confusion.
Answer:
I think you're confusing input power with output power. The formulas you list are for output power, so the pf being high means you get more power output.
An interesting link to a description of 3 different measurements of power in systems with reactance as well as resistance:
http://www.ibiblio.org/obp/electriccircu...
Assuming that the load on the motor is constant under the low power factor condition the motor will consume a very small amount more. the difference will be the heat generated by the additional amps through the motor winding resistance. The confusion is usually caused by not being specific enough about what is being compared. Power Factor is the ratio between Apparent Power (volt amps) and True Power (watts). Unless you have a separately excited wound rotor motor the Power Factor of a motor is determined by it's construction and can't realistically be changed. The closer it is to a Power Factor of 1.0 the better as far as cost to operate since less amps flow through the motor (and power meter) to produce the same amount of useful work.
Your examples are not quite right. 745.7 watts = 1 H.P.
Look at the formulas again:
Apparent Power = Volts x Amps (x sq root of 3 for 3 phase) This is what flows through the meter and what you pay for.
245v x 70a x 1.73 = 29669.5 VA (29.67KVA)
True Power =Volts x Amps x Power Factor (x sq root of 3 for 3 phase) This is the amount of useful work you get.
245v x 70a x 0.75pf x 1.73 = 22,252.125 Watts (22.25 KW)(29.84 H.P.)
245v x 70a x 0.62pf x 1.73 = 18,395.09 Watts (18.395 KW)(24.67 H.P.)
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