The effect of change in fuel supply when generators are in parallel

 

Since the speeds of the two machines are tied together by their synchronous bond, the increase in fuel to the machine 1 does not make it run faster. 

Alternatively, it utilises the increased power input for carrying more load than machine 2.

This is possible because of angular advance of machine 1 with respect to machine 2. 

Here E1 advances E2 by an angle α. The resultant voltage Er sets up a current Isy which is almost in phase with E1. 

Hence, power per phase of machine 1 is increased by an amount =E1 Isy whereas that of machine 2 is decreased by the same amount. 

Since Isy has no reactive component, the increase in fuel supply does not disturb the division of KVAR but it increases KW of machine 1 and decreases that of machine 2.