In this forced oscillation case, the sources of oscillations are at generators 79 and 118.
System model:
Generators 79 and 118 are in GENROU model.
All other generators are in GENCLS model.
Parameter D for all generators equals 4, except for generators 79 and 118 whose D equals 0.
All loads are in constant MVA model.
Small signal analysis:
All natural modes have reasonably good damping.
External force:
Forced oscillations are injected into excitation systems as sinusoidal signals at generators 79 and 118 to cause resonances respectively with two system different modes at frequencies 0.65Hz and 0.43Hz.
Figure 1. Block diagram of the external force at generator 79
Figure 2. Block diagram of the external force at generator 118
Figure 3. WECC 179-bus power system