Efficiency:

Efficiency of an AC generator is the ratio of the useful power output to the total power input. Since any mechanical procedure experiences a few losses, no AC generators could be 100 % efficient.  Efficiency of an AC generator could be calculated by using Equation (10-3).

Efficiency = Output /Input x 100                                             (10-3)

Example: The Given a 5 hp motor acting as the prime mover of a generator which has a load demand of 2 kW and what is the efficiency of the generator?

Solution:

In sequence to calculate efficiency, an input and output power have to be in the similar units.   As  describe  in  Thermodynamics,  a  horsepower  and  the  watt  are equivalent units of power.

Therefore, the equivalence of these units is expressed with a conversion factor as follows.

((550  ft - lbf /sec)/1hp) (1 kW/(737.6  ft- lbf /sec)) (1000  w/1 kW) =746  W/hp

 Input Power = 5 hp x 746 W/ hp = 3730 W

 Output Power  = 2 kW =   2000 W

Efficiency       =  Output /Input = 2000  W/3730 W = 0.54 x 100 =      54%