Automatic Generation Control (AGC) (Con td..)

Any change of reference value will lead to a change in sharing among the generators. Thus by slowly changing the reference of speed governors we can over-ride the sharing which is imposed by the droop characteristics.

The question then arises: which generators should change their governor references and what the exact value of these changes ?

In a 2 - area system, if governors are present on some machines in both areas

and

a) power flow in certain ac line, which connects 2 areas is to be regulated.

and

b) Frequency has to be brought back to its nominal value after any load generation change

then

the references of atleast 2 governors (one in each area) in the system should be changed to achieve these objectives.

Note: It is not feasible to independently change more than one governor reference in one area, otherwise there is no unique value of reference change for different governors. Thus if more than one governors in an area are "on AGC", then their actions have to be in a pre-decided proportion and not independent of one another.

The AGC concept is illustrated by the following schematic in the next slide.