Equal-Area Criterion is employed to determine

Equal area criterion:

• It is used to determine the limit on the load which can be acquired by the system without crossing the stability limit.
• The principle of this method consists of the basis that when δ oscillates around the equilibrium point with constant amplitude, transient stability will be maintained.
• It is employed for the determination of the transient stability limit of the single-machine-infinite bus system.
• It is also used for determining the maximum limit on the load that the system can take without exceeding the stability limit.
• In a single machine infinite bus system, if the system is unstable after a fault is cleared, δ(t) increases indefinitely with time, till the machine loses synchronism. In contrast, in a stable system, δ(t) reaches a maximum and then starts reducing.