Efficiency of DC Generator & Condition for Maximum Efficiency


The power flow from input to output is known as power stages or power flow diagram.

Efficiency of DC Generator

Efficiency :

     It may be defined as the ratio of output in watt ( or KW ) to the input in watt ( or KW ).

Mechanical efficiency,


Electrical efficiency,


Overall efficiency, η 'or' commercial efficiency, or the efficiency of a generator is given as,



Condition for Maximum Efficiency :

Let,
  • Generator output = VI
  • Generator input = output + losses

=  VI + Ia2 Ra + Wc
 =  VI + I2 Ra   Wc
(assuming, Ia = I ; since Ish is very small compared to I)

Efficiency,

η  =  power output /  power input
(By dividing Nr. and Dr. by VI)

     To obtain the maximum efficiency the denominator should be minimum, therefore differentiating the denominator with respect to I and equate to zero.


Hence, the efficiency is maximum when,

VARIABLE LOSS  =  CONSTANT LOSS

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