three phase induction motors

[Aaron321]

hey does anyone know the effiency and power factor of a typical three phase induction motor?

cheers,

[konthelion]

Well, it's always a good thing to start off with the definitions of efficiency, power, and power factor.

Let \eta be the efficiency, then \eta = \frac{P_{out}}{P_{in}}
Let P= power, then P=VI.

Therefore the average Power = VIcos(\theta)
By definition of power factor, it is the ratio of average power/VI.
Thus, the definition of power factor = \frac{VIcos(\theta)}{VI}=cos(\theta)

From here, use the Pythagorean theorem to solve for power factor of a three phase