Question

Direction: The following item consists of two statements, one labelled as ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answers to these items using the code given below:

Statement (I): Equal-area criterion can be used to determine the stability of single machine infinite bus system.

Statement (II): An infinite bus system has infinite inertia and constant voltage.

1. Both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I
2. ​Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I
3. Statement I is true but Statement II is false
4. ​Statement I is false but Statement II is true

Answer 1

Correct Answer - Option 2 : ​Both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I

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.

 

Therefore, both Statement I and Statement II are individually true but Statement II is not the correct explanation of Statement I.