Consider Fig 6.4 with
In the case when ∆Pc1 = ∆Pc2 = 0, the speed changer setting is fixed irrespective of whether the load changer is in area 1 and area 2.
Let a sudden change occur at both the areas 1 and 2. In incremental steps ∆PD1 and ∆PD2.
Due to load change the frequencies drops by ∆ƒ1 and ∆ƒ2. If load increment in the two areas is equal and if the frequency drop is also equal i.e., if ∆ƒ1 = ∆ƒ2 = ∆ƒ (ss).
From the block diagram in Fig. 6.4 the incremental increase of generation is written as
Since ∆ƒss(S) is a steady state ...