Monday, 23 February 2026

📘 Power Systems – Question Bank (Page 7)

🔹 Section A: Conceptual Questions (Stability)

Q1. What is power system stability?

Ability of power system to return to normal operating condition after disturbance.

Q2. What are types of stability?

Q3. What is swing equation?

M d²δ/dt² = Pm − Pe

Q4. What is power angle equation?

Pe = (EV/X) sinδ

Q5. When does maximum power transfer occur?

At δ = 90°.

Q6. Maximum power transfer occurs at:
A) δ = 30°
B) δ = 60°
C) δ = 90°
D) δ = 180°

Answer: C) 90°

Q7. Equal Area Criterion is used for:
A) Steady state analysis
B) Transient stability
C) Load flow
D) Economic dispatch

Answer: B) Transient stability

Q8. If mechanical input exceeds electrical output:
A) Rotor decelerates
B) Rotor accelerates
C) No change
D) Voltage increases

Answer: B) Rotor accelerates

Q9. A generator has E = 1.2 pu, V = 1 pu, X = 0.6 pu. Find maximum power transfer.

Pmax = EV / X = (1.2 × 1) / 0.6 = 2 pu

Q10. If δ = 30°, find power transferred.

Pe = (EV/X) sinδ = 2 × sin30° = 2 × 0.5 = 1 pu

Q11. If δ increases beyond 90°, what happens?

System becomes unstable.

Q12. A machine has inertia constant H = 5 MJ/MVA. What does higher H indicate?

Higher inertia → Better stability.

Acceleration Area = Deceleration Area For stability: Area A1 = Area A2

Q13. If clearing time increases, stability:
A) Improves
B) Reduces
C) No change
D) Voltage increases

Answer: B) Reduces

Page 7 Completed – Stability (Swing Equation + Power Angle)