This model represents a simple islanded power system with primary and secondary frequency control open loop. Generator A has 30 MW nominal power, generator B has 10 MW.
The model starts at steady state, with both generators at full load supplying a 40 MW load connected at the A side of the transmission line.
At time = 2s, the load is decreased by 10%. The primary frequency controllers kick in and quickly stabilize the frequency, with an error of about 5% of 10% of 50 Hz, i.e. 0.25 Hz. Electro-mechanical oscillations are also triggered, but eventually die out thanks to the generator damping effect.
Subsequently, the secondary frequency controller brings back the system to 50 Hz in 300 s. Only generator A participates to the secondary frequency control action.