Question

Equal area criteria in power systems is used in the context of
1. Deciding maximum loading for a given excitation
2. Stability of a machine connected to infinite bus bar
3. Stability of power systems in which many machines are connected to infinite bus bar
4. Load distribution between a single machine and load drawn from infinite bus bar

Answer 1

Correct Answer - Option 2 : Stability of a machine connected to infinite bus bar

The bus whose voltage and frequency remains constant even after the variation in the load is known as the infinite bus. It has infinite inertia.

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.