The Power Factor "PF or pf" of an A.C. electric power system is defined as the ratio
of the real power flowing to the load to the apparent power, and is usually a
number between 0 and 1.0
(frequently expressed as a percentage, e.g. 0.8 PF = 80% PF)
Both NEMA and the IEC require that synchronous generator manufacturer's rate generators with a .8PF and display the prime kVA of the alternator on the data-plate.
EXAMPLE: 800kVA X .8PF = 640kW
of real power flowing vs. the apparent power of 800kVA which would be arrived at by multiplying voltage by amperage by the square root of three "1.732".
"Real power is the capacity of the circuit for performing work in a particular time.
Apparent power is the product of the current and voltage of the circuit."