Introduction to Electrical Power and Power Electronics

81AC Generator

Example 3.10

The no-load frequency of two ac generators is the same, 60.5 Hz. The FDR of

generator-1 is 0.0006 Hz/kW, and that of generator-2 is 0.0008 Hz/kW. If the two

generators are in parallel supplying a total load of 1500 kW, determine the load

shared by each generator and the operating frequency of the bus.

Solution:

Denoting kilowatt power P

1

and P

2

shared by generator-1 and generator-2, respec-

tively, we write the two generator frequency droop line equations as

f

1

= 60.5 – 0.0006 P

1

and f

2

= 60.5 – 0.0008 P

2

.

In parallel operation, f

1

= f

2

= f

bus

and P

1

+ P

2

= 1500 kW. Therefore, we write

f

bus

= 60.5 – 0.0006 P

1

= 60.5 – 0.0008 (1500 – P

1

), which gives P

1

= 857 kW and

P

2

= 1500 – 857 = 643 kW.

The bus frequency is then